FRONT END

Rare Parts are in Stockton, CA and only sell to businesses I believe. Some of the above #'s are no longer available but may work for a cross reference.

I think 66 thru 78 Toros and 67 thru 78 Eldos CV joints are the same.Milt Wade-Las Vegas
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On separate occasions I removed the axles from both sides without pulling the hubs or knuckles. After loosening the axle nut at the hubs along with the 6 twelve-point bolts holding the axles to the final drive output shaft flanges (wheel still on and on the ground) jack up the front end and remove
the wheels and twelve-point bolts. By pushing the axles up and to the side you can pull the them out of the hub and drop them down underneath the engine / final drive. I remember that on the right side it helped to take off the shock absorber and raise the lower control arm and knuckle few inches using a bottle jack so that the angle improved to let the axle come out. I then took the axles to a CV rebuilding shop and let them do the dirty work. Good luck with yours.Phil Stewart
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Last weekend I serviced the inner & outer CV joints on my GMC. The outers were questionable so I used a pair from an Eldorado I recently stripped. Remember the thread about "the clicking noise?" It was the CV joints. (Thanks again to Jim Bounds for the tip on this.) I power flushed the outers using clean solvent & compressed air and laquer thinner as a final rinse, they looked too good to disassemble so I settled for repacking and installed the new boots. No photos on the outers.
I removed the axles according to advice rec'd on the net. Pretty fast & easy compared to most suspension work. R&R took about 6 hours, the disassembly, cleaning & reassembly about 4 or so. It would probably be quicker for someone who has done it before but I haven't.
Just for my own experiment with grease, I used Mobil 1 on all joints except the passenger side inner. Time will be the judge on this experiment as I used the stuff that came with the boot kits on it.

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Just a reminder that you do not have to take either ball joint apart to remove the axels.

For drivers side jack the lower A frame high enough to pull the axel from the hub and than turn the steering to the right and pull the axel out from behind the hub. For passenger side remove the oil filter, position the steering wheel straight ahead, jack up the A frame enough to slide axel out of hub by moving inner end to rear where filter was and pull axel out through the filter area. I never remove the ball joints unless I have to because of the chance of damaging the seals.

Steve you may have exceptionally clean solvent but I would never clean the CV joints without taking them apart. One particle under a ball can ruin it in a short time. How can you inspect the balls and races with the joint together? If you have gone this far take them all apart and carefully service them in ccordance with the manual.

Just my opinion of course but these are precision matched sets and must be kept very clean and will greased to avoid failure. Tom
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I don't think you will find it too hard to tackle a CV joint job, as long as you follow the book and do things carefully. A few further thoughts however.

The bolts at the Final Drive may be pretty tight, so you might want to loosen them slightly before getting the wheels off the ground. When you clean the CV joint, don't use any kind of cleaning fluid on them but
rather a clean lint free cloth. The balls can be popped out if necessary, but be sure you get them back into their same positions as it is easy to get them all mixed up!It takes a bit off time and care to wipe all that grease and mess out of the joints.

If you use the plastic blue boots on reassembly, they are rather stiff and hard, at the clamping points so it is hard to stop them from leaking grease. I used this kind but had to redo the clamping and finally with
double wrapping clamps and reefing them up to just below the breaking point, they now don't leak. (don't use the pinching kind of clamp-I don't think they can pinch tight enough). If I do it again I will use
GM ones instead as I believe they are of a softer and different material which allows the clamp to bite into it better. My old GM ones were 20 years old and still good, but I replaced them just because I was doing
the joints.
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BOOTS, CLAMPS,--DOUBLE WRAPPING

Replace the CV boot with out removing the axle

Jack up the front of the coach, block it, remove wheel (optional), remove the tie rod from the knuckle(optional, but it will give you more room & flexibility), cut the old boot off, with a snap ring pliers, EXPAND snap ring in the outer CV joint and slide axle towards the inner plunge joint, clean as needed, install new boot on axle, slide axle into outer CV joint, snap ring will expand as axle is pushed into CV joint, MAKE SURE SNAP RING IS SEATED, install grease and position CV boot, burp the air out of the boot and clamp it, try to keep the surface for the outer clamp surface as dry as possible. This is about an 1-1/2 hour job per side, good luck. Bob Drewes in SESD

I got them from NAPA --
Boot Clamp (large) PUJ-3416 -- Torque to 65 in-lb.

Boot Clamp (small) PUJ-3415 Manny (no longer available)
*****************
Here are some more part numbers and sources -- Ken

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On reassembly, you might want to consider reversing the shafts from left to right as they are identical and in this way the splines at both ends will be getting their wear points on the opposite side of the spline, most likely not a major issue but and idea for longevity.

I believe the bolts at the final drive are a grade 8, and Wes C. recommends that one replace them with new ones, which likely is not a bad idea as these need to be reeffed (torqued) up very tight so they
don't come loose. For the size of bolt they are torqued very tight!

When I did mine I did it as a preventive maintance plan at 68,000 miles and 19 years on the original boots and they still looked good, but with that age I didn't know how much longer they would go. I now carry them
as spares but when I redo them next time I think I'll go back to new OEM's. Claude in Victoria.

However ---- Last year I replaced the final drive fluid and gasket, and I got the gasket from

NAPA / VICTOR: "Part number P 28883 Axle Hsg. Cover".
( Fel-Pro # RDS 55034 cover
#rds30094 final/trasn Gary Kosier)

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The final drive cover gasket that comes as two pieces stapled together, is to be installed
as though they were one gasket. Leave them stapled together and install making sure the vent
groove in the gasket is on the same side of the final drive as the small vent hole at the top left
side of the final drive cover.Charles Wersal
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The final drive cover gasket that comes as two pieces stapled together, is to be installed as though they were one gasket. Leave them stapled together and install making sure the vent groove in the gasket is on the same side of the final drive as the small vent hole at the top left side of the final drive cover.Charles
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It was labelled "made by Victor Reinz (Dana)". It was a ONE PIECE gasket, and it had the slot for the vent hole. The material was a bit thicker than that used on the 2-piece gaskets. I looked at it and compared it to the old 2-piece gasket,

I only used this for the trip to Clifty Falls last April, and had no problems with fluid leaking. The complete final drive was replaced after that because of a failed pinion gear bearing (bearing fell apart when we removed the retainer plate). I discovered then that this gear was going bad when we bought the GMC, as that loud whine disappeared after that. Now I know what a GMC is supposed to sound like. :>)

My point - this gasket does not necessarily have to be a 2-piece part. I can't really figure out the function of that uncut section over the vent passage, unless it was to make this passage smaller (?).
Just my opinion.Erv Troyer

FINAL RATIO	RPM @	RPM @	RPM @	RPM @	RPM @	RPM @	TEETH	TEETH
	50 MPH	55 MPH	60 MPH	65 MPH	70 MPH	75 MPH	PINION	RING
TORO 2.73	1690	1859	2027	2196	2365	2534	15	41
ORIGINAL 3.07	1900	2090	2280	2470	2660	2850	14	43
3.42	2125	2350	2550	2760	2980	3150	12	41
CASPRO 3.50							57 CHAIN	65
3.50	2166	2394	2600	2812	3032	3248
3.55	2200	2420	2640	2860	3080	3300	11	39
DUNN 3.63	2247	2471	2695	2919	3144	3368	55 CHAIN	65
3.66	2274	2500	2730	2955	3183	3412
3.70	2300	2530	2760	2990	3220	3450	10	37

Your site was very helpful. You might add the division formula that R Black posted on calculating the ratio
."Count the teeth on the two sprockets and divide the little number into the larger."
I had 41 teeth on the ring gear and 15 teeth on the pinion gear. 41 divided by 15 = 2.73

Also the note that Milton Wade posted that the "If I remember correctly the amount of teeth on both the pinion and ring gear are on the edge of the ring gear." I found 41-15 on the side of my ring gear and I counted 41on the ring gear\Charles Wersal
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The Caspro 3.42 setup does not use the chain drive gear from a TH325 and the stock TH425 driven gear. But it does appear that some rebuilders are using this, infact the gears might not be the same thickness.
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I have a Dunn trans in mine which I took the cover off to look at it before I installed it.Caspro has a 57 tooth sprocket at the torque converter and the Dunn has a 55 tooth sprocket.They both have a 65 tooth sprocket on the front of the trans.A few years ago someone had the formula of how to figure out what the ratio is in the GMCMM magazine,anyway the Dunn ratio came out to 3.63-1 and the Caspro was 3.50-1.HTH Milt
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NEW POWER DRIVE RATIO---Caspro Company
It's not very often that a revolutionary new component is introduced for the GMC
motorhome. Caspro, who offers other unique GMC components has introduced a new transmission gear kit, that effectively changes the OEM final drive ratio from 3.07 to 3.50 and for those members who installed the 3.21 final drive the change goes to 3.66. The 3.07 gear ratio was originally designed for the 1968-78 Oldsmobile Toronado that was less than half the weight and wind resistance of the GMC motorhome. Furthermore, the Toronado had 15 inch wheels while the motorhome has 16 1/2 inch wheels and larger diameter tires. Consequently, the motorhome engine is always struggling to do its job, because it cannot turn at high enough revolutions to generate its rated power and suffers under the inadequate torque multiplication of the overall drive gearing.

This change allows the engine to operate more nearly at its most efficient torque speed rpm (2550 rpm). In the driving speed range of 55-70 mph there are three very significant gains that are achieved. First the engine is permitted to turn at a slightly higher RPM, which enables it to generate approximately 35 more horsepower at the same road speed. Second, the mechanical torque multiplication to the wheels is increased by 14% for an average total increase of 72 lb. ft. of torque. Third, the torque converter load, under normal conditions, is reduced which minimizes heat, thus extending the life of the transmission. It is important to understand that this mechanical (drive-ratio) torque increase occurs in the power train after the engine horsepower increase, and therefore the delivered benefits are additive. The above benefits are for the 455 stock engine, the 403 engine will be in direct proportion to the ratio of engine sizes that is 89%. At 65 mph with the 3.21 final drive, there is a 60 HP increase over the stock engine and the stock 3.07 final drive.

This modification requires removal of the transmission and returning your old turbine shaft. The new drive-sprocket and drive shaft assembly kit also includes a new chain and sealant, along with new ball bearing, snap ring and seal that are assembled to the exchange shaft. The complete kit will cost $875.00 plus a refundable $250.00 core charge (your old turbine shaft must be returned for the refund) plus shipping. The kit will be available by the end of March, 93. Contact:
Chuck Stoddard
Caspro Company
P.O. Box 390
Novelty, Ohio 44072
216-423-0809

Installed at your own home garage, the costs are:
$1195 final drive (3.42); final drive core charge $150; final drive crate
$50; speedometer adaptor $75 and shipping of about $60 UPS. Ship the old
unit back for about $60 and get your core charge and crate refund of $200.

3.55 drive unit $1190
3.70 drive unit $1390
Speedometer adaptor $70
Core deposit $300
plus shipping

Regarding axle ratios, I personally feel there is nothing to lose in going to as low a ratio as is possible. Certainly anything up to a 3.90 or so would not be too much, camper special pickup trucks routinely use 4.11 and 4.56 ratios after all.

GM recommended a ratio of 3.42 in the early 1970's on most full size car lines with 454-455 engines in the trailer towing packages. This was considered adequate to tow a 7000 lb travel trailer with, say, a Caprice or LeSabre. 1973 up Three Quarter and One Ton pickups with Camper Special Equipment had a mandatory 3.73 ratio as a minimum requirement.

For best economy for travelling under a heavy load it is desirable to gear a vehicle for operation at or up to ~400 rpm below the net torque peak at the usual road speed. This assumes the engine makes adequate torque to carry the load at that rpm. I generally would shoot for a 60 mph cruising speed, and appropriate gearing for that. Driving a large vehicle over 60 starts to really use a lot of power and fuel, and setting them up for say 75 mph cruise is kind of pointless, theres not much scope for good economy at that speed anyhow.

Aerodynamic drag is the largest issue from a cruising perspective. According to a chart I have in a GMC Dealer Data Book heres the Air Resistance Demand Horsepower figures between 30 and 70 MPH for a relatively square nosed vehicle of 60 sq/ft frontal area.

30 7.8
35 12.3
40 18.4
45 26.2
47 29.9
49 33.8
50 36.0
52 40.4
54 45.3
56 50.5
58 56.1
60 62.1
65 79.0
70 98.7

As you can see, horsepower just for wind drag is very significant. Driving 56 mph takes about half the output to overcome the wind that 70 mph does. Rolling Drag losses go up proportional to road speed/weight, and not exponentially as wind drag. Twice as fast or twice the weight = twice the drag for weight and rolling resistance for the most part. Takes about 20HP to overcome rolling resistance of a GMC at 60-65 MPH. At 30 MPH it would be more like 10HP.

Another thing to consider is there is approximately 145-160 net HP availible in the first place from which you can deduct the drag;-)

I would definitely think the factory installed 3.07 is too tall for the application. The GMC would be 'driveable' right down to a 2.41 in all likelihood, but with disasterous economy and performance implications. One real gas eater is operating an engine below 7" Hg or thereabouts vacuum readings- your power enrichment system is activated and mixture strengths are increased quite drastically and this pulls fuel economy way down. If a higher numerically ratio set of gears permits you to cruise and handle minor grades and headwinds without a susbstantial loss of manifold vacuum, you will get better economy. Liberal use of second gear can help also. Keep vacuum over 8" as much as possible.

Just for reference, the tires on a GMC rolls about 675 revolutions per mile. Multiplying 675 times the axle ratio gives the engine RPM at 60 MPH. 675 x 3.07 = 2072.25 rpm @ 60 MPH.

Dividing 2072/60 = 34.5 rpm per MPH. At 100 MPH the GMC would only do 3450 rpm at this rate- thats a pretty tall ratio! Of course there is slight slip at the torque converter, so the actual figure is slightly higher as indicated on the tachometer.

The torque peak of the 455 is about 2800 RPM as I recall, this means a range between 2400-2800 RPM would be the ideal for cruise economy. 2800/675 = 4.14, which would be about the lowest ratio you'd want, and 2400/675 = 3.55 which would likely be the ideal, at 60 mph average cruise speed in any event. A 3.42 is not far off that, and with slight converter slippage would be pretty darn close to ideal.

I've seen the Caspro Power Drive Chain system and the aforementioned box for switch pitch control made by the Toro List member and they are both excellent units and I will be using both myself. The switch pitch converter is desirable if you have an opportunity to obtain one, not vital, but a definite refinement.

Anyhow, basically to sum, the benefits of a high numerically ratio axle are substantial for the typical owner, and although even a 2.73/3.07 etc. will work and drive acceptibly with adequate performance, the penalties for economy and performance would probably substantially pay the costs of an upgraded axle ratio in a short time. Go for the 3.21 3.42 3.54 3.73 if you can get them!

>Here are my questions. With a 3.07 at what engine rpm am I running at
>22 mph in first gear?

2200
>
>Now my next set of questions. Same speeds in the same gear with a
>3.42?

These figures are approximate- if you just swapped axles and did not make other changes, if those are the speeds your GMC currently upshifts, it will continue to do them at pretty much the same RPM, but a slightly lower road speed.

First gear is about a 2.5 ratio and second is about 1.5. If you multiply top gear RPM by these figures you can determine the RPM in the lower gears.

The GMC motorhome jumps in and out of ruts in the road because the front wheels do not run in the same track as the rear wheels. This is an original design constraint of the GMC. Slack or looseness in the front suspension, steering and rear suspension aggravates this condition. Tires can also affect this condition.

Extended wheels / Spacers
I also am only able to navigate my driveway on dry pavement. I put spacers on the front wheels a couple years ago and then could not get up even on dry pavement. It upset the geometry enough to cause the front tires to alternately spin and at the same time bounce the front end of the coach to the right. Almost wound up in my neighbors yard over about a 30 foot cliff. Someone suggested backing up, which I mastered but always had a lump in my stomach each time. Finally gave up and took off the spacers. Now I am back to square one. Enjoy the link.

http://www.gmcmhphotos.com/photos/showgallery.php?cat=3773

Bob Sobrito
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Dave Mumert
Just for information, the distance from the center of the bearing to the wheel mounting face of the hub is 4.28", the offset for Alcoa wheels is 4.567". So the center of the wheel is about .29" inboard of the center of the bearing pair.
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It is clear that GMC had the technology to change the offset of the GMC / Toronado front wheel drive but chose not to. Here is a picture of the offsets talked about by DaveM , above:
http://www.gmcmhphotos.com/photos/showphoto.php?photo=19160&cat=3619
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I held back getting into the spacers opting to watch and see how it went. In standing on the sidelines though I have been maintaining many coaches with them and on occasion have installed them. As was reported, I also saw no degridation in the reliability of the front bearing assembly and though it would be easy to have sided with the engineers that said the pressure would destroy the integrity of the assembly it was good I did not say that because it does not seem to play out.

I will say though that most people opted for spacers because they felt they had some driving problem they thought the spacers would cure. I have to say this should not be the reason to get them. If you have driving issues, you really need to go back to basics and solve the problem first. Bone stock, the GMC will track doen the road as good as any car runnign whatever speed you like with 2 fingers on the wheel. If yors does not then there is a problem with the system that needs more than the "bandaide" effect you would have in putting on spacers. Yes, spacers may mask a problem making it more palitable but the problem would still be there. Solve your issues first then if you feel froggy and wanna do it then get spacers and see if you can add on perfection. JimB

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Don't blame the spacer for not being able to go up the hill.Your front end is worn to the point that your toe in is great enough to cause enough sliding.Repair it and you'll not have to tell people that the spacers don't work. JimK

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I have a wandering problem with mine I am trying to resolve as well. I have Lenzi knuckles and hubs,Lenzi relay lever, idler arm, offset bushings, wheel spacers,new BF Goodrich rag walls, new ball joints and just did a string alignment and I am still not satisfied with the handling. BobW
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Extended wheels can correct the tracking. Machining a hub-centered adapter for these wheels is needed because extended wheels available are not hub-centered but hang from the stud bolts. The load of the GMC wears these bolt holes and causes other problems. The extended wheels have been calculated to increase the loading on the hubs and bearings( already at maximum ) by 450% ! An interesting article in the GMC Motorhome News (September 1998) by Chuck Aulgur, Mechanical engineer, describes the technical aspects of this mounting. The results spacers do not significantly reduce the life of the front bearings, Hubs, etc. Users of these wheels say this eliminates the rut running.

Thanks Scott for taking the time for pictures and dimensions. The numbers are not exact but close enough for me to draw my conclusion.

The tread centerline is running just inboard of the inboard bearing but I can't believe how close together the two bearings are! They are so close together they may as well be called one big damn bearing! If I were to follow through and have the offset match the bearing center, then the wheel could be moved out about 1 to 1.25 inch. This may help waggle some but I feel it isn't enough to bother. OK, so I'm the dufuss. Whether this small change would help bearing loads or not, I cannot say. At this point I am more inclined to believe the offset is correct for this front end geometry. Man, I can't believe that bearing spacing. Don't be a hot rod in the corners is all I can say.

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Dave, (and now Brent), I think that you have it basically correct here. I have no expertise in the theoretical pro's and con's of this issue but I do have a bit of experience. There are at least a half dozen people who have run a fair number of miles on the wide rims. Mike Mayo in Colorado has (I think) around 20,000 miles on his coach (I tried to call him to confirm the mileage but he was out). Jim Robertson in Los Osos has over 10,000 miles (his coach was the one recently noted in a posting for sale with the Cadillac 500 engine - there was a picture of it with the wheels). My belief is that the front bearings can indeed handle the stresses. This assumes that people keep their bearings well greased and change them out at 25,000
miles. Whether they weaken the ability of the front end to handle a severe bump at high speed . . . who knows?

I had the wheels and hub/spacers on the coach for a relatively short time to test the setup. I think that there is no doubt that they help the rut stability problem. However, they do indeed change the geometry of the front end. Torque steer is definitely an issue. They clearly accentuated a left to left-right-left (or is it right-left-right) front drive wiggle upon starting out. I talked about with this with Mike Mayo, and he felt that this was the only significant negative to the wide wheels. I found the ride to be harsher and I felt the bumps more extremely. This may have been my coach or it may be the offset. Likely it is something that can be adjusted out of the coach with some creative alignment work. I took them off the coach because I will be doing a lot of work on the front end and wanted to be sure that any problems are not related to the wide rims. My intention is to try them again once everything is overhauled - bearings, hubs etc. My suggestion for the perfect set up is to widen the frame at the front, which is in agreement with Brent's most recent posting. This would mean not only changing the frame, but getting custom sway bars, axles etc. It would probably work superbly though. If anyone would like to seriously experiment with my rims on their coach, then please get in touch.Vic Marks
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Four bagger modifications change the side to side roll stability of the GMC but do almost nothing for the tracking problem. The four baggers in essence remove the bogie action on the GMC and convert them into four independent wheels.gene

THE GMC MANUAL X-7725 PAGE #A-22 IS WRONG FOR BALL JOINT TORQUE
I torqued the upper ball joint stud nut according to the GMC Manual X-7725, page #A-22 and stripped the threads. It list 100-125 Ft. Lbs. for the upper and 40-60 Ft. Lbs. for the lower. Are these numbers reversed. After a closer look I realized that the lower ball joint stud is larger than than the top. Makes no sense to me that the torque spec for the lower ball joint stud would be less for a larger stud. Gary Bovee

THE GMC MANUAL X-7525 PAGE #3A-22 IS CORRECT FOR BALL JOINT TORQUE.
. In my manual,(7525) on page 3A-22 it shows that the upper is 40-60 ft pounds and the lower is 100-125 ft pounds. emery

Bought them at my local Miracle miles parts store.
NAPA or Auto Zone-------the latter I think.

The Moog number for the offset upper bushing is K-7104. The number for
the regular bushing is K-7006.
The other Jim 78GB 500Cad

Ball Joint Replacement
Do NOT drill all the way through the A-arm
when replacing riveted ball joints. Actually, if you're following the
"Book", it doesn't say to drill all the way through. Good auto shop practice
is (wearing safety glasses):
1. Center punch the rivet.
2.   Drill a small pilot hole (I use double-ended 1/8" bits, cheap) about
1/4"-3/8" into the rivet. Object here is to get said hole as CENTERED as you
can. This is quick.
3.   Now, get out a drill bit which is slightly LARGER than the rivet
diameter, and slowly enlarge the 1/8" hole you just made. When you get down
around the level of the A-arm, stop frequently and examine the hole. When you
contact the A-arm, it will show as a line or crack part way around the hole
you're making. If you're real lucky, the hole will be perfectly concentric
with the rivet hole, and the rivet head will come off on your drill bit.
Usually....
4.   When the hole contacts the A-arm, stop drilling, get out a large sharp
cold chisel and BFH (big f... hammer). Remove the rest of the rivet head.
The closer to centered your drill holes are, the easier this will be.
5.   Finally, drive out the headless rivet with a punch or drift.

This is the "right" way to remove riveted ball joints on a GMC or any other car, and causes minimal scarring of the A-arm, and no distortion of the rivet hole.HTH.Rick

Do yourself a big favor and use 3/8 hardware and when you're finished, spot weld the bolts. It isn't
any harder to grind a spot weld off that it was to grind off the original rivits if you ever have to replace them. Easier in fact. Also, while you have the ball joint accessable, thread the castle nut on, grip it
with a socket and pump that thing full of synthetic grease while rotating the joint through all of it's travel. Do this several times. It's the best insurance you'll ever get that the thing has been properly
pre-lubed. It also gives you an opportunity to check the zerk flow.Steve

If your lower ball joints are held to the control arms with bolts, your lower control arm is at risk. The holes for these bolts might be egg shaped from loose bolts or improperly drilled out rivets. This puts a lot of stress on the ball joint hole at the end of the lower control arm and eventually failure of the control arm. I have heard of rivets becoming loose but it seems most of the failures have come after maintenance has replaced the lower ball joint.

WHAT TO DO
1) Check the bolts on the upper and lower ball joints at every lube and bearing check.
2) Check the tip of the lower control arm with a sharp scribe or at least a finger nail looking for cracks.

The crack in the control arm shown in the picture could have easily been found this way. This control arm was from an active GMC and had not yet failed. The GMCMM article Jan99, points out that this procedure will not find hairline cracks. You would need to tear down the suspension and carefully check the area around the hole.

3) If the bolts will not stay tight, the ball joint should be replaced and possibly drilled out for larger tight bolts. ( I am not sure green goop (locktight #----------) will help, but it cannot hurt)

Standard A-Frame
This picture shows the standard reinforcement that GMC provided on the A-frames. After-market suppliers can provide even more reinforcements. Bill

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The question keeps coming up on the net as to why the front wheels are not in line with the back? IT WAS COST. In order to save money GM used off the shelf control arms they already had, only to cut costs. They soon had a lot of trouble the 73-74 had seven small patches were then welded on the weak
spots. from the 75s on they made a little better plates thru the 78s, however GM again fell short and only reinforced the three sides of the hex and its the top three sides that brake out. I have photo of most of the control arms 73 Thu 78 years showing the patches and the break outs. I found out the hard way, I for the first time ever had a local garage work on my motorhome [bad move ]for they installed the new torsion bars in backwards. At high speed about 150 miles later both bars strip out the control arms at the same time. Yes, there is a front and rear to the torsion bars I called GM in Detroit and they nor any dealers I called could tell me how they went in! I called Cinnabar,Wes at that time said he did not know. Well, for what it's worth there is a left and right and the ends are stamped with a R or L next to a little arrow, that end goes to the front. Should you ever need to replacement you can use Toronado or Eldorado lower control arms but be sure to have them reinforced and the ball joint bolts welded by someone that knows how. Jim Anstett Loveland Colorado
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Control Arm Sources

Cinnabar
They have rebuilt control arms for $459 with new ball joints and bushings. If your old control arms can be rebuilt they will give you $200 for the core return. These must be GMC original reinforced control arms.

Buskirk
I just got off the phone to Buskirk and talked to his chief Mechanic Max. they do have the HD arms but they come in a kit including the new torsion bars. They have to be installed at Buskirks. max does not think they are suitable for anything but the stretch coaches.Thomas

He says that if they find any cracks they have them repaired at a good welding shop. You do not need new ones.

There is a poorly kept secret ( only the 300 who go to rallies know, because the talks are never published;>) that the bearings on the GMC can go well over 100,000 miles without any problems.
the most traumatic thing you can do to the front end of your GMC is to grease the bearings by removing the hub and Knuckle to check and remove the bearings, and we are supposed to do this every 25,000 miles.
Every front end,boot, taper, knuckle, socket, drive line bolt and bearing are stressed to the max and the front end alignment is almost always compromised. Yet, this is the traditional GMC/Thoma method for bearing maintenance.

Our forefathers knew that removing the bearings was a problem and in 1974 published and used a technique to grease the bearings in-place.
Alex Birch and contributed by Kosier.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=5987
Walter Wallace
http://gmcmotorhome.info/wallace1.html

What they did not have was a unified way to grease the Zerk and would often blow out the inside seal with too much grease.

Dave Lenzi has come up with a unified approach to using the Zerk to grease the bearings in-place, and WiperMan,(KenH) has published a description on how to use the Zerk.
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4641

In 2008, I broached the question " could we drill our knuckles, in-place, to add THE ZERK without removing the knuckle. Mr. Druber (gutsy guy) answered back that he had done his own knuckles and figured it would be possible to do this modification ,in-place

********************************
I believe the knuckles can be drilled for the zerk quite easily without removingthe knuckles.

Last fall (2007), I serviced the bearings and installed zerks to grease nexttime per Dave's recommendations. It is easy to see (or measure) where the spacer islocated in the knuckle when it is out of the knuckle. I took a center punch andpunched the knuckle right in the center of where the spacer is when it is installed. I then got a 6" long 1/8" drill bit from Grainger's and drilled a hole from the inside

out, that is, from the bearing side out, then installed a press in zerk. To finish the job, I ground a groove around the periphery of the spacer, and across the OD anddown the sides with a Dremel grinder to provide a grease path from the newly drilled hole to the bearings. This was with Dave's blessing via a telephone conversation we had before doing it. This was done with the knuckles off, but there is no reason whyit couldn't be done with the knuckles mounted on the coach with everything removed. RayS

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So I contacted my friend,Bob Hardeman, a local GMC machinist, to develop an appliance that we could use to drill our knuckles (in-place or removed) so we could add THE ZERK ourselves.

Here are the first pictures of this on-going development.
http://www.gmcmhphotos.com/photos/showphoto.php?photo=28898

Cinnibar and Gateway sell 'matched' sets of Timken wheel bearings. These include a spacer ring that installs between the two cones whose thickness dictates the assembled axial clearance of .0095". The bearings will have this hand etched on the spacer. They cost about $80 per set including inner and outer seals. (CAUTION: Do not mix these bearing parts with any
others as this will change the clearances.)

Why is that important you ask? Good question. The outside of the hub should measure from 2.0015" to 2.0020". The inside diameter of the bearing that I have, measures 1.970". If I were to press that bearing on a hub with maximum outside dimension of 2.0020" there would be a.032" interference fit. Thats pretty tight and would reduce the axial clearance of the bearing by some amount. How much? I don't really know, however the cinnabar engineers have run tests on the various bearings with maximum and minimum dimensions for both the hub, knuckle and bearing and decided that in the worst case of each, an axial clearance of .0095" is the minimum
clearance that can be safely used.

Cinnabars part number - 12351677
Gateway's part number -
Others to use in a pinch: (same bearings but not clearanced for our
application) Use at your own risk!!
Bower/BCA--------------------------- A-23
CR -------------------------------------- BR-23
J.C. Whitney------------------------- 38-0649-P
New Departure---------------------- S-77
Timken--------------------------------- 23 Specify .0095 axial clearance
NAPA---------------------------------- Set-23
Federal-------------------------------- A-23

SEAL PROBLEM (4/10)
For those of you that were at the last GMCMI rally in Montgomery, and attended Dave Lenzi's session on front wheel bearings, you may recall that he and others had noticed a change in the way they manufacture that inner seal (the one that seals against the CV joint). The inner portion of the steel portion of the seal, instead of being just straight, in some cases has been manufactured with a slight curl-up lip. This lip is just high enough that, when set properly can make contact with the bearing cage. This contact makes for steel shavings that can get into the inner bearing and cause failure. That is why the grease on my left side bearings looked darker than the right...it has some steel shavings mixed in with it. Fortunately, the contact was quite minor and did not create enough to cause a failure, or even any noticeable damage to the bearings or races.

I talked with Dave some about this. It seems that National is *one* of the only brands making the correct seal for our GMC. It is National Seal #5123. This seal does NOT have the turned up lip that can cause us problems. Things have changed since I did these bearings 6 yrs ago, including the way we install the seal. Had I installed the seal (a Chicago Rawhide seal with the lip) using todays method of referencing off of the knuckle, the seal would have been deep enough that it would have made significant contact with the bearing...perhaps leading to catastrophic failure.

My point, if you are not sure of the seals that you installed last time, maybe you better check them. I have posted pics of the two seals...my old seal with the "lip" and the new seal National #5123 on the GMC photo site. It may be hard to make out. It is hard to see, but the difference can be "felt". Larry

http://www.gmcmhphotos.com/photos/showgallery.php?cat=5446
--
Here is some more information from Dave Lenzi about the seal problem. provided by CharlesW
http://www.gmcmhphotos.com/photos/showphoto.php?photo=33538&title=pict0258&cat=5450

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GMCMI parts list shows:
Inner is NAPA 47471.
Outer is NAPA 47470.
Paul Bartz
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Information on the seals only.
Front inboard---National# 5123, C/R# 25515
Front outboard---National# 5109, C/R# 24888, Victor# 47470 Denny Allen

Inner seal is Federal 5123, national 5123, NAPA 47471, or Delco 290-19.
Outer seal is Federal 5109, National 5109, NAPA 47470, or Delco 290-17 Tom Warner

REBUILT KNUCKLES
Price $125.00 each with your old knuckle as a trade in.
Ken re-sleeves the knuckle with drill stem pipe. Lawrence

ROTORS
What I bought from JCW was a rotor for an eldorado. I had the center bored to the GMC size. Then turned an arbor to a snug fit in the centerhole,put the two rotors face-to-face on the arbor and used the GMC rotor as a drill jig. Voila, instant GMC front brake rotor. Works for the rear discs, too.Gary Kosier

Dave Lenzi is doing so many new things for the GMC and I hope he is getting a lot of business and credit for his innovation. Here is one of the small things he talked about ( almost a side light). He talked about how most of us are setting the seal to the CV joint -- in the wrong way.

I have posted his handouts and maybe more importantly , my interpretation of what he said about this subject.
http://www.gmcmhphotos.com/photos/data/3221/Dave_Lenzi_s_seal_tool.pdf

This is not a video as it says, it is a pdf format so that you can blow it up to see some of the detail.
All of the credit for this goes to Dave Lenzi, and I hope I have not made any huge mistakes ;>)

The OEM bolts can be held in place with small rubber O rings so that they are easier to get started when assembling the knuckle and hub.

There used to be three suppliers for bearing puller tools for the GMC front bearings. All of these use comparable Split Rings that clamp over the bearings. Now there are none

The first two pullers use the OTC927 puller to attach to the Split Ring. This is the same operation that is described in the GMC Service Manual. This procedure has not changed in the past 20 years. It is possible to use an impact wrench with this puller if you use an 8 point socket ( or the following procedure) to drive the square end of the OTC puller. Since there is no thrust washer or center hole in the plug in the center of the bearings, the OTC is supposed to be driven with a large wrench on the thrust nut in the middle of the puller as shown in the picture below. However, no one does this since it is too slow and hard, everyone drives the square. To install the bearings an impact wrench cannot be used as the wrench must fit over the threaded rod.

One hint that some may find helpful is to use a nut for threaded rod to
connect 2 sockets together to hook to the square drive on the end of the
puller. Just drop a 1/2 inch drive socket onto the puller hex end up, drop
the long threaded rod nut into the socket and then use another socket to
turn it all. When you put the two sockets and long nut together you
effectively have a 1/2 inch square drive to 1/2 inch square drive.Dave Mumert

pull / install hub from the knuckle
alignment plug to keep bearings straight during install
seal install tool
bearing removal / install

Gil's puller appliance with the Warner split colar and an inpact wrench would have worker much better than the OTC.

Press on the Bearings
We started using the OTC to press on the bearings as per the GMC and Cinnabar instructions. Again the bearings were so tight it was very hard to use the open end wrench on the OTC puller and we were unable to use an electric ratchet because the pushing nut is only available from the side. Also, there was no guide to keep the two bearings and spacer aligned up while we were using all of this force to press on the bearings. Finally this old Fart got tired of all of this work and put on the Thoma puller with the alignment plug, and pressing cup , and used the electric impact wrench to spin on the bearings.

I can see why Thoma designed his puller to use an impact wrench and Warner's new design uses hydraulic jacks for this job. You might change your bearings one time using the OTC puller, but you would not want to do it every day. This is really hard work.. The impact wrench and the
alignment plugs and fixtures make all of the difference

Inside Seal
No where did it show or tell how to insert the inside seal through the hub. The manual says it is possible with a tool no longer available, or you could make something. We did not replace the inside seal which is not too good. I am going to ask an old veteran how they do this without removing the knuckle.

Clearly the inner seal is a problem. We will have to go back sometime and fix this. With out removing the knuckle, it is very difficult to replace this seal and make it seat correctly. I am going to buy an electric impact wrench to carry with me. This is really hard work. We still need to get the final design on the PVC bearing packer. I like it better than the inexpensive two cone versions or doing it by hand. Stay tuned, there is more to come.

Next time I will read Rich and Betty's step by step instructions better and I will have a tool and parts list.gene

1 3/8 inch allen wrench for the brake caliper
2 one inch and square wrench for the OTC puller
3 Two pri-bars to remove the hub
4 wrench for the seal retainer
5 wire clothes hanger to hang the caliper
6 bearing grease packer
7 Ball joint tool
8 3/8-16 tap
9 two large cotter keys
10 3/4 box end wrench
11 1 1/16 socket for ball joint
12 side cutters and needle nose for cotter key
13 9/16 end wrench
14 1 1/2 socket ( we had this)
15 torque wrench (we had this)
16 grease gun
17 pitman arm puller
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The price is right for the Warner's puller for the backyard mechanic (me). But the ergonomics sux bigtime.

You'll need at least a 3' x 3' minimum HARD surface to hammer on the removal construct once the OTC puller is attached. It ain't fun and you have to use the OTC puller crossbar as a lever when you're hammering. In my case, it was 3 hammer blows for a 60 degree turn on the screw before repositioning the wrench.

Even if you succeed in removing the bearing set out in the boonies, IMHO, you'd be hard pressed to be able to install bearings in the field using the (first 15) Warner puller without introducing contaminants on the new or repacked bearings on install. The "pushing" pilot's collar should've been thicker and coarse knurled, for instance, enabling you to stop it from turning with the screw with your Mobil One covered fingers rather than using a tool. Hey I was a journeyman toolmaker in my previous life.

On the Warner (first 15) puller bearing install, here you are with Mobil 1 synth all over your hands trying to reassemble everything and you have to grab the pilot while you extract the pusher screw... you get the picture...
I sure hope carb cleaner is not carcinogenic since that's what I used to clean my hands... but if it is it's too late now, sigh.

It took me a week (well I take a lot of breaks) to do the front bearings. Blisters took a long time to heal and my left hand finally regained some feeling after a day or two afterwards (the one holding the wrench that I was beating on with the hammer)

Final review, yes it does the job. The $$ is very reasonable compared to what is out there in the GMC world. But it is not easy and you have to have a rigid, relatively clean, hard surface to work on it. Not a roadside repair.

If Tom, or anyone else, can get a machine shop to machine some 1/2 inch to 1/2 inch female adapters out of SAE 8620 chisel steel properly heat treated it would be a GREAT accessory IMHO. But in small lots the cost will probably be prohibitive, unless you have a friend in the biz.

If you cut off the female drive sides of two impact sockets and weld them together using suitable rod it would work too IMHO.(not Gene)
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I just changed my bearings and had no trouble. My hands were too covered with grease to take pictures. We are going to have a bearing party 'real soon now' and I will be taking many pictures with a cam-corder and a digital camera.

I pulled my hubs off the knuckles with a slide hammer ($69.00 Canadian mini dollars) then removed the knuckle.

The biggest job was jacking up the coach and finding enough blocks to get all the wheels off the ground (I was doing a complete brake rebuild at the same time).

The actual job of pulling the bearings off the hub was quite anti-climatic. One hint that some may find helpful is to use a nut for threaded rod to connect 2 sockets together to hook to the square drive on the end of the puller. Just drop a 1/2 inch drive socket onto the puller hex end up, drop the long threaded rod nut into the socket and then use another socket to turn it all. When you put the two sockets and long nut together you effectively have a 1/2 inch square drive to 1/2 inch square drive.
Dave Mumert

It is not necessary or desireable to remove the knuckle from the coach to service the wheel bearings, and I really do not understand how this practice got started. It is sometimes extremely difficult to remove the lower ball joint from the knuckle with out the proper removal tool, and it is possible to damage the ball joint if you are not careful in removing it. The easiest method and the one I use is to follow the method in the GMC manual by removing the hub with the slide hammer. You can see this method on Billy Masseys site at: http://bdub.net/twarner.html
warner
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I just got done putting the whole shebang back together here, so everything is still fresh in my mind (what's left of it, anyways, LOL)
* Break 1 1/2" axle nut and lug nuts loose before jacking the coach up & removing wheel & tire.
* Block rear wheel before jacking front corner up
* Support the coach at where the front frame is bolted to the side frame rail.
* Use upended bucket or a milk crate for setting the caliper on once you get it off.
* Careful with removing those old rusty cotter keys - soak liberally in
penetrant &      good luck (I still had to break off the lower ball joint
key and drill it out, not fun)
~~~~~~~~~~~
* Remove caliper and place it on upended bucket behind the control arms near the frame. The threads for the caliper guide pins (3/8 socket head) are on the inside knuckle "ears" should you care to shoot penetrant there. I ended up heating the thread area with a propane torch even with penetrant and big vise grips in order to remove mine)
* Back off axle nut so just a few threads are engaged.
* Remove tie rod joint & lower ball joint with appropriate tool. I used a puller with    a 2 1/2" throat and a 1 1/2" opening. Rotate tie rod end up out of the way. Do not lose the lower ball joint seal, which will fall off.
* Back off upper ball joint castellated nut but *do not remove* yet.
* Break the joint loose via crowbar pressure between the upper control arm and knuckle while striking the knuckle at the ball joint seat area with a big hammer.
* Knuckle will drop down to loosened castellated nut.
* Remove the nut and brake hose support bracket.
* Remove axle nut and the knuckle & hub assy is out
The rest of the procedure is shown on the web, as you've noted. Once you've removed the cover plate between the hub and knuckle (3 bolts) you can pop the knuckle off using a couple of crowbars if it doesn't want to come off.
You may want to get some new 3/8-16 x 3/4" grade 5 bolts for the above cover as the heads are usually buggered up from wrench slippage. Hacksaw screwdriver slots on the ends as shown on the web. Also new caliper guide pins ($3.59 ea @ Autozone) may be required.
Now would be a good time to replace the CV boot if it shows any signs of deterioration.    Ask yourself if you want to go through all this again to replace it (I replaced mine). The boot kit will come with grease and bands for around $10. I used Mobil One grease instead.
** Remember to make sure the outer (towards the rotor) grease seal is seated after dropping the knuckle onto the new bearing set **
Re-assembly is straightforward although having an extra pair of hands sure helps *a lot* in lining up the stub axle and lower ball joint without nicking the inner bearing seal. Once lower ball joint nut is started enough to hold, shove the assy onto the stub axle far enough to start the axle nut & take a break. Wash rotor with brake cleaner.
***Bend the upper ball joint cotter key ends so that they will remain above the end of the joint, precluding any possible contact with the CV boot.***
The 3/16 x 1 1/2" axle nut cotter key requires a bit of finagling to install. File a radius on the ends and curve it gently until you get it well started. Then you can pry it in the rest of the way using a large screwdriver.
That's all I can think off - HTH~ Ritch & Betty
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Mission: Get to know my 75 Palm Beach better by servicing her front bearings. Since she had 67,000 miles on her when I bought her, and no indication via paperwork that the recommended servicing was ever done. Why go to the expense of buying a $500 bearing puller kit and get my hands dirty when I could go to someone else and let him learn how to do it? Well, I wanted to "do it myself" and learn something about this wonderful machine. You should have the Maintenance manuals. Also, the June 96 issue of GMC Motorhome News had a step by step instruction. I am not going into discussion of axial clearances, or knuckle tolerances. My knuckles had 75k on them. They looked good to me. I don't want to argue about bearing sources, bought mine from Cinnabar. I don't own a micrometer, but wished I had one to hold the pages of my manual in the wind. I write this to give confidence to someone who wishes to try it himself. I had ken Thoma's bearing tools and video. Many clubs own these, but I am far from my club mates. Without complications, you should get the job done in about 3 hours per side.

Tools and stuff required: bearing set with two seals for each wheel, bearing removal tools by Ken Thoma or equal, 1 1/2" socket, large breaker bar for aforementioned socket, needle nose pliers to remove cotter pins, new replacement cotter pins, 3/8" allen wrench to remove brake caliper, short piece of wire to secure the caliper after removal, 3/4" box/open end wrench for removal of tie rod end nut and upper ball joint nut, 9/16" box/open end to remove the retaining plate bolts, 1 1/16" socket for removal of lower ball joint nut, hacksaw, vise, narrow blade screw driver, 3/8-16 tap, jack stand, bottle jack, grease for reassembly, crow bar or other prying tool, pitman arm puller to "pop" lower ball joint free, torque wrench to reinstall axle nut (220 ft/lbs size), grease gun to regrease to tie rod ends, and ball joints.

If you don't have this stuff, get it and then read on. I spent literally hours running around town to get a bigger tool to remove the axle nuts. This is very tiring. My axle nuts were exposed to the weather, other than the hub cap. They were frozen on. A 1/2" drive breaker bar broke with my weight on the end of a 2' cheater pipe. I got a longer breaker bar. It broke. I bought a 3/4" drive breaker bar, and, of course, a new 1 1/2" socket to go with it. (Now I had two new 1 1/2" sockets, a size not formerly in my tool box.) Now, we are ready to go.

1. Jack up one side at the frame rail, but don't lift wheel until lug nuts are loose and axle nut is loose. If you are lucky enough to have a dust cover hiding your axle nut, you will have to remove it. Jack some more and remove wheel.

2. Remove brake caliper (2 3/8" allen machine screws) and tie it to frame with wire.

3. Detach tie rod from knuckle, then loosen upper and lower ball joint nuts. Using pitman arm puller (about $8 at car parts store) to pop loose the lower ball joint, use pry bar to pop loose the upper ball joint, carefully hold onto the hub/knuckle assembly and remove the ball joint nuts. The assembly may want to fall to the pavement. Pull it loose from the spline shaft and head for the bench.

4. Put the whole thing on the bench with the rotor and wheel studs facing down. Pry out the seal in the end of the knuckle (use a screwdriver). Remove the three bolts securing the retainer plate. This is fun (not!). Use a short 9/16" box-open end. When you have them in your hand, go to the vise, and one at a time, clamp a bolt into the vise, and carefully saw (with hacksaw) a slot into the end of each nut. Clean up the threads in the knuckle with a 3/8-16 tap. All of this will make it much easier to reinstall the retainer plate.

6. Push the bottom hub seal down as far as it will go to make way for the bearing removal tool. Remove the bearings with the appropriate puller. Put the bearings on the bench the way they came out. Clean up the hub, remove the seal that was laying there, and remove the retaining plate and wipe it out. Take the old seals and put them with the old bearings, in the same order as they were on the hub shaft. This helps know which seals go where, and how they were oriented.

7. Pack your bearings (I used Mobil 1). Put the retaining plate in place, and put a new seal down around the shaft. Reinstall new bearings, then reinstall the knuckle. It's fairly easy to get the retaining plate fastened with your newly modified bolts. When you get them aimed up at the hole, hold the bolt head with your finger under the head, applying force "up" while you take your narrow screw driver and from the top, insert the screw driver into you "slots", screw the bolts in by turning counterclockwise (remember they are backwards from your vantage point). Once you have them tight with the screwdriver, then get the wrench out and tighten some more. The plate should mate flat with the bottom of the knuckle. Pop in a new seal at the "top" of the knuckle.

8. Take the whole assembly to the coach. The hardest part for me, in the whole procedure, was getting the lower ball joint into it's hole, the drive axle spline engaged in the hub, and the upper ball joint forced down into it's hole. All while you are holding the weight of this thing. This whole thing is heavy! Try this. Squat down facing the wheel cavity. Hold the weight of the hub/knuckle at the end of your knees. Stick the axle shaft into the hub, and at the same time, gather the lower ball joint threaded end and insert it in the lower part of the knuckle. If you can get some threads out of the bottom, with your third hand, get the nut started. Now you can rest some of the weight on the bottom. When you get the spline all the way in, you should be able to force the upper ball joint down into it's hole. You need enough threads exposed to install the brake line clamp plate then the nut.

9. Tighten up the ball joint nuts, install the tie rod end. Reinstall the brake caliper. Make sure the brake hose did not get "moved" within the clamp while you have been wrestling with the whole mess. This could cause the brake line to pull apart when you turned the steering wheel. Install the axle nut, torque to 220 ft/lbs or whatever your sources tell you. (I have heard and read anything from 160-230). This procedure draws everything inside the hub together with the CV joint. Re-cotter pin everything, regrease the ball joints and tie rod end. Reinstall wheel. Test drive. Look underneath. If it looks good, give yourself a pat on the back.

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Torque the Front axle nuts
By the book: X-7525A; Page 3A-8, INStALLATION, line 4
Install drive axle washer and nut. Torque nut to 140 ft. lbs. If necessary to align cotter pin slot, tighten nut and install NEW cotter pin and crimp. Torque not to exceed 280 ft. lbs. NOTE: Do not back off nut to install cotter pin.Mark A
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Front Suspension and Final Drive

1-ton Hubs and Knuckles (Version II)