Supplemental Vacuum Pump

Courtesy of Eugene Fisher

Large motor homes have a problem - when the motor stops the vacuum source is gone. The driver has one pump of the brake pedal and then no brakes. This is not just a GMC problem. They tell many stories of wild rides both forward and in reverse with no brakes. The result is either coasting to a stop or really bad accidents. Many solutions to this problem exist, from large pressure tanks and Powermaster units to supplemental vacuum pumps. The pump described here come from several models of GM cars made from 1982 to 1992.

It is a good idea to test the pumps at the wrecking yard to be sure they run and pump and then check them at home to make sure they hold the vacuum and operate at the correct pressure. Jim Davis tells us that you can find these pumps on the following cars in wrecking yards:

Buick

82 Skyhawk-J
82- 85 Skylark-X

Cadillac

82 Cimmaron

Chevrolet

84-86 Celebrity-A
82 Caprice-B
82 Cavalier-J
82-85 Citation-X

Oldsmobile

86 Cierra-A
82 Firenza-J
82-84 Omega-X

Pontiac

85-86 6000
82 J2000
82-84 Phoenix-X

The pump is also available new from GM. The part number is 22034995 and a price of about $300.

You'll find these pumps on the driver's side front fender well. There's a small (carbon) filter that is on the line just before the pump. Insist on getting the filter with it, and the electrical plug that goes to the pump(and the rubber mounting plate). You may have to go out in the yard with the knuckle dragger to show him what you're talking about. From left to right on the lugs, the first lug is 12 volt constant. The second one from the left is ignition switch or toggle switch. The fourth one is ground.

Connection A (Red wire) battery positive, 12 volts+ through a fuse.
Connection B (Black with white stripe) ignition positive, 12 volts+
Connection C (plugged) not used (not used in factory system either)
Connection D (Black wire) ground, 12 volts-

The pump is powered via the A connection, but will only run if it receives power from the ignition switch on the B connection.

It appears from the literature that some owners tee the pump into the vacuum line to the brake booster. This would require a check valve in the brake booster hose ahead of the pressure switch to keep the engine from drawing down the pump vacuum if the motor stops.

The better method is to use the booster pump as it was in the original application and installed between the motor and the brake booster. The pump has a pressure switch so it will not turn on unless the pressure gets below about 5 pounds. I find that idling around in town the pump often comes on, which makes me happy since I also need the brakes in town. Some owners install a switch to disable the pump until they need it. This makes me nervous since I am sure when I need this emergency backup I will have enough to do without remembering to turn on the pump. A side benefit of the pump is that if your brake booster has developed a leak, the pump will run all of the time to make you aware of a problem before an emergency occurs.

The pictures show three different mountings. I have seen about five different mountings. The first mounting is on the floor board near the windshield wiper motor.
This mounting requires a homemade bracket to mount the pump in the position shown. This picture does not show the carbon filter going to the motor but this is necessary to keep residues from the engine and vice versa. Notice the Right angle hose that exits the pump. The adaptor comes with the pump and attaches hose to the brake vacuum booster. This connection is hard to see in the other mounting pictures.

The second mounting is in front of the driver side wheel well liner.
The picture is looking up, in front of the driver front wheel, with the wheel well liner on the right. They told me a lot of room was available to mount the pump in front of the liner using wood screws. I did not have a lot of room on mine and had a hard time finding enough room to attach the pump to the wood.

This is a great location since no brackets are required and the hose removed from the brake booster will reach the pump and a short new hose from the pump easily reaches the brake booster. Replacing the original hose to the brake booster is very easy if required. Note the small black filter in the input hose to the pump.

The third mounting is in a different location using a homemade bracket.

I really feel secure with this pump installed since there were no modifications to the brake system no bleeding of the brake lines or modification of the original equipment. The system is fail safe since if either vacuum source fails the other still works.

It must work since my motor has not stalled on a hill since I installed this system (grin). Gene

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