GMC Western States

 Tech Center Number 26 - September 1999

Inner CV Joint Bolts
By Chuck Garton

I have road in various GMC publications about coaches losing all six inner CV joint bolts and being stranded along the roadside waiting for service.
I bought a 67 Toronado new and have lived with these bolts for over thirty years. The maintenance manual states that these bolts be replaced whenever removed and never be roused. After reading this, whenever I was at an Oldsmobile or Cadillac dealer, I would check at the parts counter and find out that these bolts were never stocked.
Now, I keep a new set on hand, and when I use them I order a new set from Cinnabar. I also keep a set of used ones in the motorhome in case I lose some while traveling. However this is treating a symptom and not curing the real problem.
When I purchased my 1974 Sequoia 26' in November of 1977, I had had no experience in maintaining a motorhome. One day in 1979, I was under the coach doing something, when I noticed that all six bolts on the passenger side CV joint were loose about one turn. The book said the torque was 65 foot pounds, so I torqued them to specifications.
After a 500 mile trip, I was again under the coach and the same six bolts were loose about one turn. This time I installed new bolts and lock washers and torque them to specification. My next trip was also 500 miles and after that trip the six bolts were again loose.
Being real sharp and on top of things, it only took 2,000 to 3,000 miles (tightening the bolts every 500 miles) and a passenger side front wheel bearing failure to figure out the real problem!
After the bearing replacement, and going by the maintenance schedule of replacing the front wheel bearings every 25,000 miles, I have never had one inner CV joint bolt come loose.

Editor's Note: This is a reminder that the front bearings MUST be serviced every 25,000 miles.


Transmission Vent Alert
By Bill Harvey

The November 1998 issue of the Tech Center Number 23 had an article 'Transmission Venting Simplified'. This article suggested the use of a 1/2" ID radiator elbow, Car Quest P/N 21784 along with some 1/2" copper tubing and a pill bottle to make a vent trap system. This was a very simple approach to a potential fire/safety problem - namely how to divert any expulsion of transmission fluid away from the engine and hot exhaust manifold. It did not require removing the trany in order to access the vent on top as some earlier vent protection schemes had done.
However, as is often the case, simple may not be fool proof. Recently when starting and moving our coach a short distance, I noted trany fluid dripping from both the front and rear of the trany pan. After pulling the coach back over the grease pit for examination and tightening all the pan bolts, I determined that the source of the leak was not the pan. Next step was to check the top of the trany. There was fluid in the trough on the left side which could then run down the side of the trany.
Further examination revealed that the synthetic rubber elbow used on the trany vent was pulled off. An attempt to push the elbow back into place over the vent resulted in frustration. The previously semirigid rubber was now quite soft and "gooshy" to borrow a phrase from my granddaughters. Whether this condition resulted from exposure to trany fluid or engine heat, I can't say. However, if anyone is using this venting protection scheme, it is seriously recommended that they check the condition of this elbow. With the OEM vent cap removed with this vent protection scheme, there is nothing to slow down the venting of trany fluid, for whatever reason, from running where it shouldn't.
The elbow can be forced back over the vent and clamped in place with the hose clamp. However as soft as the rubber had become, it may be necessary to replace the elbow later, In the meantime care should be taken when removing the pill bottle trap for inspection of trany fluid so as not to dislodge the elbow on the vent.


Steering Damping
By Bill Harvey

Does your coach steering seem a "little loose"? After several steering box adjustments followed by a rebuild, my steering still wasn't as tight as I felt it should be. In other words I had to "herd" the beast down the read with constant attention so that it didn't wander off in the ruts or fail to hold on the straight and narrow.
Here again a simple solution existed for a bothersome problem. It seems that the fitting which clamps the end of the Bilstein Steering Shock Absorber to the tie rod had come loose. A 24" bar clamp was required to center the fitting on the tie rod so that it could be clamped properly in place.
The centering procedure requires that the shock be compressed fully and the position noted with the steering straight ahead. Then allow the shock to expand fully and note this position. Then simply compress the shock to the mid point between these two positions and clamp it tightly in place.
This makes a world of difference. Wish I had done it miles and miles ago.


A new Failure Encountered And Something Learned
By Bill Harvey

The Problem
Being an inherently lazy Casual Mechanic, I have long subscribed to the dictum 'if it ain't broke, don't fix it". The corollary to this is that if it works, it isn't necessary to understand how it works. Obviously this entire philosophy doesn't play very well with a 24 year old GMC with 150,000 miles on it.
The latest example of the fallacy in this thinking became very apparent while we were on our semiannual swing to the east. While we were crossing the tip of West Virginia between Ohio and Maryland, the engine started backfiring in the carburetor. As we progressed easterly it became apparent that the problem was occurring whenever we attempted to accelerate or even maintain speed when going up hill. You can't imagine the fun of trying to pull away from a light at a busy intersection while burping and belching.
As with any intermittent problem it was impossible to diagnose, although we tried like heck. First, we investigated the carburetor including float valve, accelerator pump and even the secondaries.
Since it seemed to be related to a drop in manifold vacuum at the carburetor, we checked for vacuum leaks and even replaced a couple of hoses. It was noted that backfiring in the carburetor has a tendency to blow certain hoses off their fittings if they are loose. Replacing and tightening these hoses was probably a good idea, but it didn't solve the problem.
We noted one other circumstance that we tried to relate to the problem. This was that the backfiring occurred more frequently after the engine got hot. We were getting warmer to solving the problem - no pun intended.
After belching and burping for over 500 miles and several days of intermittent driving, late in the afternoon the engine just plain stopped and wouldn't start again. Now we had a failure that could be diagnosed. Intermittent failures are the worst kind and essentially impossible for the Casual Mechanic to diagnose.
However, even the Casual Mechanic has a fighting chance when something won1 run. A quick check verified that fuel was getting to the carburetor so the problem had to lie with the ignition. No spark! Ergo, the problem must lie with the source of the spark - the HEI Coil. Fortunately we had a spare coil. Actually it was the original coil that I had replaced a couple of years ago when we were having carburetor problems.
After burning my hand on the hotter-than-H coil, I removed it and sticking in the original, we were off down the road. No more problems for the remainder of the trip. I had managed to check continuity on the failed coil while it was still hot. The primary winding was open. A check after the coil cooled down indicated continuity again.
Now we had an answer to part of the problem. Backfiring had been occurring only after the engine had warmed up. That indicated that the coil opening was subject to heat. But why did the backfiring occur under load? Is there some something occurring that caused more heat to be generated in the HEI coil under load?

The Education
Despite being inherently lazy, I have a great curiosity and a semi-logical mind creating a great desire to understand "what's happening". To accomplish this understanding, it was necessary to review the operation of the HEI as it differs from standard point ignition.
Both systems utilize an engine driven rotor to switch the spark to the plugs. However the HEI generates and switches the coil output both mechanically and electronically rather than strictly mechanically as do the breaker points. This is done with a magnetic rotor with eight lugs or points on it. As these line up with, but don't touch, the corresponding lugs on the stator, the magnetic field provides for the flow of voltage from the electronic control module to the primary winding of the coil. Then as the rotor/stator alignment shifts, breaking the magnetic field causes a collapse in voltage in the primary coil. This collapse generates an output pulse of 35,000 volts from the secondary. This is fed through the distributor to the appropriate spark plug.
The alignment of the rotor with the stator can be altered either mechanically with the vacuum advance or electronically through the control module. (The MSD system uses external electronics to further adjust spark advance.)
It is generally accepted that a 'hotter' spark is required when the engine is under load. (Don~ ask me why, but that is what the True Mechanics tell me.) If this is the case, it is reasonable to conclude that more heat will be generated in the coil as the result of the additional current required to produce the hotter spark. This is one theory that would explain the backfiring under load.
Another theory is that the slight shift in timing caused by loss of vacuum advance would cause the current in the coil to flow longer producing more heat.
In either situation the additional heat could weaken an already weak coil causing a breakdown at the wrong time. But why did the misfire cause backfiring in the carburetor? This was almost too much for the Casual Mechanic. However, maybe I have reasoned it out as follows.
It appears that when the primary coil opened prematurely, the spark generated may have occurred before the intake valve had completely closed causing the backfire in the carburetor.
While engine miss did not appear to occur with this failure, this is also a symptom of coil failure. One way to detect a coil problem is to tune the AM radio between stations and listen for spark noise.
Finally, remember when replacing a coil to be sure to get the coil wires in the right slots. The color coding may differ from the old coil so check the accompanying instructions.
After all this has been reasoned out, it appears somewhat logical. However, as we were belching and burping through towns and up hills, all we knew was that something wasn't working right, and we couldn't figure out what or why. Maybe next time we have a problem, we will have figured it out ahead of time. HAH!

Editor's Note: Chuck Garton mentioned that the coil is the most failure prone part of the HEI system. In fact, for the HEI equipped engines that he has owned, he has carried a spare distributor complete with cap and new coil installed.


Parts and services for the GMC

The following represents a list of places where the Western Staters can go for help. This is particularly useful in time of breakdown on the road when far away from home. Not all these places are for emergency repairs. Some are just for parts, supplies and equipment. This list is in no way exhaustive. ff you know of any other places you would like to add to the list or you have an update, please send us the information.

There is no endorsement of any of these places by Western States.


Glendale(Phoenix), AZ (602)934-5295


San Diego, CA (619)452-8999
After market suspension and steering upgrades, transmissions, engine and accessories.

(650)948-8664 - Technical Assistance
(800)720-2227 - Parts (from MI)

Gardena, CA (800)462-7635, (310)515-4974
Custom dash panels with instruments.

Sierra Madre, CA (818)355-7753
Frank Sullivan Digi Panels and Doug Thorley Headers.

Industry, CA (818)961-0790

GEORGE DIMICK Coronado, CA (619)435-3300
Front wheel bearings.

Ontario, CA
(909)983-7872, (909)982-7747 (shop)
Complete service and engine rebuilding.

San Raphael, CA (415)456-1904
Full mechanical services.

Orange, CA (714)633-4731 Duane Simmons

Santa Ana, CA (949)261-5898
Custom GMC parts: Welcome step, transmission
cover, ladder, and more.

Fulierton, CA (714)879-6140
Custom exterior painting (Imeron).

El Cajon, CA (619)442-9100
Interior and exterior renovation and supplies
by Sy Gregorich

West Pittsburgh, CA (510)458-5800
Complete service of the GMC.


Longmont, CO (303)530-4995
Custom engine, transmission, water pump.


Okeechobee, FL (941)763-1121
Full parts and service, hard to find parts.

Orlando, FL (407)859-9000
Parts, service and renovation.

Jacksonville, FL (904)381-6209


Buford, GA (770)271-7502
GMC parts and service since 1973.


Sandusky, MI (800)715-1133
Sales, service, parts and restoration.

Sandusky, MI
(800)720-2227 (parts - GM licensed)
(650)948-8664 (technical assistance from CA)
(810)648-2444 (service, sales and renovation)


Northfield, MN (507)663-7266


Saint Louis, MO (800)654-0374
GMC Parts Man


Albuquerque, NM (505)821-0543
Complete service of GMC's since 1973.


Novelty, OH (440)423-0809
After market suspension and steeling upgrades,
transmissions, engine and accessories.


Beaver Creek, OR (503)632-6953


Genesse, PA (814)228-3338

Quakertown PA (215)536-1246
Total GMC service center.


Houston TX, (713)872-7200

Fredericksburg, TX (210)997-3690
Front wheel bearings and hubs.


 Tech Info