GMC Western States

 Tech Center Number 8 - June 1994


Some of you that have never adjusted your rear brakes may need to remove the 'knock-out plugs" that are contained in the lower section of the brake backing plates. The 'knock-out plugs" are removed by driving {punch) them into the drum area. Removal of the drums are necessary to remove the 'knock-out plugs". This will provide a slot for inserting a screw driver into the brake adjustment mechanism.



If you grease your own (or have it greased), have you ever wondered what's the proper technique for greasing the steering column shift assembly (the grease zerk between the two U-joints which is above the steering gear box)? Since grease never comes out the top slide surface. The grease seems to disappear or goes out the bottom near the lower U-joint. Here's a tip for proper greasing of the steering column. First of all, the column should be filed with grease to allow free operation and to keep out water. Water will run into the cavity and causes all kinds of problems if it stays inside. Filling the cavity with grease can be accomplished via grease gun and a properly placed finger. That's right! Place your finger at the bottom of the cavity (small hole in center) which is just above the lower U-joint. Press your finger over the hole while greasing the shaft zerk and eventually the grease will flow out of the top of the cavity. Now it's full and water can not enter! While you are at it, don't forget to grease the zerk in the center of the lower universal joint.



Several coaches have been observed that have been modified by placing a fuel filter between the Fuel Pump and Carburetor. The steel fuel line has been cut and a Rubber Fuel Line with an in-line Fuel Filter has been added on top of the Engine. Hose clamps have been used to secure the rubber fuel line. Several times I have placed my hands on the fuel line near the connections and noted wet fuel on my finger. The steel fuel line was placed on top of the Engine for a very good reason, to minimize fuel leakage on top of the engine (a definite fire hazard}. So, I advise everyone to inspect the fuel line and verify that no one has tampered with the steel fuel line between the fuel pump and carburetor. A recommended location for the addition of a fuel filter (if desired) is under the coach, between the frame (drivers side), just in front of the fuel transfer valve {between transfer valve and Engine). Maximum protection is provided in this location which already contains rubber fuel lines and makes fuel filter installation a snap. Don't help create a fire hazard !!!



If you haven't replaced your steering damper (looks like a shock absorber) lately, you may want to remove it and check for fitness. Most are worn-out and we don't know it! A good steering damper helps stabilize your steering while traveling down the road. We need all the help we can get. Replacement units are available from GM or from several after-market sources.



If you have a leak down problem which is predominately on one side, the following tip may be of interest for your Power Level and Electro Level I systems. Crossing of the air lines to the valves will isolate the problem to the air bag/lines if no change in leak down occurs. If the leak down goes with the lines (cross configuration), then the problem is within the valve area. Once you know where to look, finding the leak is much easier {air bag/line area or valve area). Operate in manual mode only with lines crossed and replace to original position before operating the coach. This is a trouble shooting aid only and is for a temporary connection.



The top bushing in the distributor can wear out. Prolonging life involves properly lubricating the internal parts. Most handbooks recommend GM Distributor Grease, but few vendors know what it is.
The bushing is an oilite bushing and should not have worn out at 94K miles unless someone had washed it with solvent. This bushing should be only cleaned with engine oil. Also the six spaces under the plastic seal should not be cleaned with solvent since the sintered iron outside shell is porous also. Clean with engine oil and fill with the grease below.
General Electric GL 622 should be used in the star wheel, in the pole piece and plate center, in the space around the upper bushing and inside the upper bushing. This is silicone dielectric grease, a poor lubricant, but the only grease that will withstand the ozone generated within the spark gaps.
If new oilite bushings are obtained somewhere, they should not be lapped. If the fit is too tight, reaming with a very sharp reamer is acceptable.
The handbook assembly instructions don't explain the gear alignment. The end of the distributor cap mount that has square corners should be aligned with the drive pin hole that is in line between two teeth. If aligned the other way, the distributor will be turned half a tooth when timed normally.
Everyone with an old distributor should check the upper bushing for wear by trying to move the rotor from side to side. Some are so bad that the star wheel wears off its tips and those of the pole piece about .020 in. This can cause occasional backfiring through the carburetor.
If the mechanical spark advance or the pole piece vacuum advance motion are not completely free to rotate, the distributor should be disassembled for the re-lubrication per the manual.



Everyone knows what a rainbow looks like, but do you know how it relates to RV problems ??? Read on.
Water drops in the sunshine refract visible light into its various colors so that we see the range of "visible', radiation. Above violet, frequency-wise, is ultra-violet (UVA and UVB on your sun-block bottle). Below red is, as the name implies again, the infrared radiation band, radiant heat.
Radiant heat travels very much like light does. It passes through clear glass and through a stream of rushing-by air with very little loss. So what, you are thinking. Your exhaust system is the hottest part on your RV and emits radiant heat all of the time, about 2,500 degree F, that it also radiates visible red light. No matter how much convection cooling air is rushing past your manifolds they will send radiant heat into all surrounding items. If you install headers, the instructions will advise that you insulate certain critical components with reflective insulation. Headers are larger than manifolds and can be closer to these items than manifolds. Still, the same principle applies to manifolds.
One critical area apparently overlooked by the GMC designers is the brake line to the right front brake. It runs just behind both of the exhaust pipes below the manifolds. One solution is to put reflective shields about 10" wide between this line and each exhaust pipe. Brake fluid doesn't circulate continuously like most other fluids do, and since Dot 3 brake fluid boils at around 284 degree F (old) to 400 degree F (new), this is the most likely spot, other then overheated brakes, to cause temporary brake loss. The shields also protect the plywood "firewall" behind the brake line.
There are areas all along the exhaust system that suffer from radiant heat. Check above the mufflers, you might find the original very thin aluminum corroded and the insulation behind it warped and crumbled. Replace the insulation with 1-inch aluminum-clad building insulation and the whole aluminum panel with shiny stainless steel (all 3 bays is best).
The starboard side of both fuel tanks has a hot exhaust radiating heat into a baffle. The baffle gets hot and radiates heat into the fuel tanks. Another source of radiant heat into fuel tanks is the highway, especially blacktop. As noted above, the rush of air under the coach does not block this radiant heat. Besides, the hot air from the engine contributes convection heating to the tanks.
Radiant heat is also a consideration in where you park. Parking on the bright side of a shiny metal or light colored RV will allow it to reflect radiant heat into your rig when the sun is shining. A light-colored wall will do the same. Walls, parking lots or rocks that heat up during the day will continue to radiate heat after sundown.



Two serviceable items, external to our FWD Transmission, which can cause erratic shifting are as follows:
1) Vacuum Modulator - the common failure is a ruptured diaphragm.
2) Governor - the common failure is a dirty or stuck piston or a worn weight assembly which effects the entry and exhaust valve opening.
Both of these items are easily removable for a periodic functional test and cleaning. Condition of the Vacuum Modulator Diaphragm can be checked by pulling a vacuum (hand pump with gauge) and verifying that a vacuum seal exists. Also, inserting a pipe cleaner into the vacuum connector pipe to check for the presence of transmission fluid is a valid test. If transmission fluid is found or a vacuum leak is detected, the Vacuum Modulator should be replaced.
Governor condition can be inspected after a thorough cleaning in solvent. Air dry and blow out all passages. The valve piston and valve sleeve must be free of nicks, burrs and scoring (free valve piston operation). Disassembly and removal of the valve piston may be necessary to verify condition (tap out the gear pin, remove gear and valve piston).
An additional test is to verify the entry and exhaust valve opening sizes (0.020" rain). A metal cover surrounds the governor weight assembly on the GMC. Two screwdrivers or similar objects can be used to move the weights completely inward for the exhaust valve opening measurment. These tests can reveal a governor in near-worn-out condition which can create shifting problems.


 Tech Info