PORK CHOP ISSUES (6/29/05)
Another reason to have it at the spec ride height is that if it is
too low (or too high) the axles from the final drive to the wheels will
be at an angle to where they should be and you will get more wear on
the cv joints as well as more noise and possible vibration from the
axles.Emery
****************
Those inner joints are what are called "tripot" cv units that
have 3 needle bearing rollers which slide in precision machined
grooves. They are very low friction designs but have a very low
tolerance for angle changes. The spec ride height is already close to
the limit of joint angle during acceleration. If you are high, you will
get a very distinct 3 per rev waddle--even with new joints.
Now that you have me thinking about this, another issue is the toe
change curve with trim height. If you raise or lower the coach from
spec, the wheels will experience a greater degree of toe change with
ride motion, which can cause some strange feeling steering motions.
I found some info on the "pork chops".
to measure the angle, lay the pork chop in its installed
orientation with the tail to the right. Draw a horizontal line
from under the tip of the pail through the center of the hexagonal
hole. Draw a perpendicular line through the center of the
hexagonal hole. Finally, draw another line from the first hex
point to the left of the perpendicular hole through the center of the
hexagonal hole. The angle between that line and the perpendicular
line is the measured angle.Bob De Kuryff
*********************
The three angles that GMC used on the motorhome were 23 degrees (part
number 413683), 25.5 degrees (part number 418352) and 28 degrees (part
number 416373).
Since all pork chops were made from the same steel casting, there was
no part number molded on them. The supplier put the part number
on a paper label that is long gone from most of them. However,
GMC used color coding on the side from six to nine o'clock. The
28 degree one had a daub of yellow paint in this area; the 25.5
degree one had a daub of white paint; and the 23 degree had no color
coding.
If you can find the color coding then you don't have to go through the
above measuring process. If there is no color you either have a
23 degree one or the paint daubs have work or weathered off.
My suggestion would be to call Cinnabar. Wes Coughlan would
probably be able to quickly tell you everything you want to know about
them. His tech assistance number is: 231-258-4117 Monday through
Friday 9am to 5 pm Eastern time zone. Emery
***********************
Any metal object, like a torsion bar, can be flexed (in this case
twisted) a certain amount without permanent deformation. When
that "elastic range" is exceeded, the part is permanently affected:
it takes a "set". The elastic range of any part is
determined by a number of factors, including the metal's constituent
elements and how it's melted, poured, cooled, formed, shaped, heat
treated, etc., etc. Among the things that can be done to a
torsion bar is to subject it to a "counter-rotation" and "lock in" that
stress by heat treatment; that is, it can be pre-stressed.
The purpose of pre-stressing is to extend the effective elastic range
of the bar by taking advantage of the fact that the bar can be twisted
in either direction the same amount -- pre-stressing in the opposite
direction to the expected load makes the bidirectional range
unidirectional and twice as great. That's why the torsion bars
have load direction arrows.
If
the torsion bar is un-pre-stressed, when the weight of the coach is
applied to the torsion bar, the bar twists and approaches its elastic
limit. Additional loads, from added load, bump impacts, etc., can cause
that elastic limit to be exceeded and the bar to take a set. When
the bar is pre-stressed, the weight of the coach returns the torsion
bar to its original "neutral" position, relieving the pre-stress.
Now, additional loads, road bumps, etc., have the full normal
uni-directional elastic range for use without causing damage.
That's the theory, as I understand it. But as so often, the
theory doesn't always work perfectly. For many reasons, that
pre-stress can be lost. Whether from material quality flaws, improper
forming, processing, or overloading, the pre-stress may be partially
lost -- the bar will take a set, which means the bar is no longer
capable of supporting the design load. Bluntly, it's damaged and
defective. That brings us to my ultimate question: Is it
really advisable to install a different pork chop fitting in an attempt
to compensate for a defective torsion bar. Certainly, short-term
results may be satisfactory, but is that likely to continue? I
argue not. Once the elastic limit has been exceeded, the metal is
never the same again; it will not heal. In the case of a
pre-stressed part, the situation is perhaps even worse than in the
classic case because the metallurgical matrix has been strained so far.
It's my opinion that a torsion bar which cannot be adjusted to attain
normal ride height (using correct procedures) should be replaced or
repaired. What say ye?
Ken Henderson
*************************
UPDATE- We have reviewed all the various information provided and found
the "Left" Torsion Bar twisted about 4 Degrees thus reflecting a
fatiguing
condition. Right Torsion Bar is good. Ken Henderson's
dissertation was right on the mark! Replacement left Torsion Bar
is on order. Using the method of
measuring the angle Emery provided, a template was fashioned and I in
fact have 23 Degree "Pork Chops". We can also measure any others
that I may acquire. It was suggested we reassemble with new
Torsion Bar in place and then have coach weighed for individual wheel
weight, which is our plan.
The marking numbers stamped on the narrow side of the Pork Chop, i.e.
14, 15, 17, 19, reflect the foundary/Batch number. The Chops are
all the same until
the 6-sided hole is punched in at the desired angle, i.e. 23,25.28
Degrees.
George Hagans
************************
REPLACE TORSION BAR
Just finished torsion bar job. Was attempting to set front ride
height and found the right side low and the left high, adjusted the
right side up and left down. end result the left side adjuster all the
way down and the right almost all the way up, and the coach ride height
still high on left and low on the right? Now I am not understanding
this at all! So typical of me I removed both torsion bars, found the
torsion bar on the right side was marked with a "L", I had two Left
torsion bars! Not Good!
Talked with Jim Bounds, Max at Bushkirk-Rush and folks at
Cinnabar. What I found is; Some say the Torsion bar should be installed
with the letter end to the rear, mine were installed with the letter to
the front (A-arm). Others say it does not matter which way they are
installed.
What I did; Ordered a used "R" torsion bar from Jim Bounds ( He
was very busy and needed to remove it from a doner coach, got it in a
very timely fashion, Thanks Jim!). Not knowing which end go's where, I
ask jim to mark the torsion bar he was about to send me as to which end
went into the A-arm, Which he did. The letter end was forward into the
A-arm!!
I installed the right bar letter forward, and the left with the
letter to the rear! re-adjusted the ride heigth, Can now adjust both
sides to correct setting.
My thoughts are it does not matter which way they are installed,
but very important to make sure there is a left and right torsion bar
installed on the correct side. Dale.
------------------------