GMC Western States

 Tech Center Number 17 - March 1997


On the last day of the Huckleberry Roundup at Mt. Hood, almost as an afterthought, your Technical VP circulated a short questionnaire to help determine the content of future technical seminars. Thirty-one responses were received. Do-it-yourself maintenance ranked first interest followed by new products and parts availability and then mechanical change-over and conversions. Since the questionnaire wasn't available to everyone, please drop a note to the Technical VP, Frank Condos, or the Secretary, Bill Harvey, and let us know what you would like to see covered at future roundup seminars and in the TECH CENTER.


Many of us have suffered from wandering coach syndrome. Even after we have followed most of the recommendations, replaced tie rod ends and steering lever bushings and adjusted the steering gear box, we discover that the problem is wear and slack in the lower steering shaft (short shaft).

A completely rebuilt unit is available from Caspro, or the slip joint, shaft and lower U-joint assembly can be obtained from Cinnabar. Both of these are fairly expensive, so your Tech VP has undertaken a DIY refurbishment that as of publication is still a "workin-progress", needing a long term durability road test. However, this looks promising enough to be discussed here. A follow-up is
planned for the Prescott Roundup.

For the initial check, determine if the upper and lower clamps are simply loose. If so tighten them. [See Mountainaires Safety Reminders under Best of the Rest.] The next step is remove the upper and lower clamp bolts and remove the shaft assembly. Examine the internal splines on the shaft. It is more likely that these will be worn than the external splines on the steering column shaft or the gear box. A loose clamp may allow the these splines to wear so that the shaft will be loose even when the clamp is tight. If the internal splines are worn, a replacement is necessary and this refurbishment will not work.

Beginning at the upper end, the upper CV joint is exposed by removing the cap screw locks (They will probably break) and cap screws. Remove the cotter pin and shaft nut and slide the shaft from the CV joint. Remove the remnants of the boot {If the boot is whole, you probably don't need to continue with the rebuild since it is obvious that the shaft has been reconditioned quite recently), slip the shaft from the lower yoke and remove the dust cap and seal. Clean and inspect all parts. At the lower end, the yoke and cross U-joint is replaceable using a Precision Universal Kit #338. Remove the C-clips inside the yoke and press or drive the bearing cups and cross through toward the opposite side. If you don't have access to press, a vise will work.

Inspection of the shaft will indicate wear patterns on the blue plastic coating. Wear through the coating to expose the base metal is probably the major source of play. The coating is thermal plastic about 10 mils thick and was probably hot dipped. (It is not Teflon, since it will soften at too low a temperature). I have successfully recoated the shaft with a bisphenol-a epoxy resin and hardener commonly used to coat table tops. This material flows thick. A single coat is about 5 mils thick. After hardening, it can be sanded, yet it is tough and will not chip. It does bond with the blue thermal plastic. If the blue plastic is worn through, I recommend stripping it and coating the entire shaft with two coats of resin. Let the shaft hang vertically to set for about 72 hours at room temperature. Sand using a sanding block and wet/dry paper to achieve a snug fit in the yoke. Remember the only vertical movement is the slight body to frame movement through 20 year old body mounts.

Play in the CV joint can be removed by replacing six ball bearings. Correctly sized balls are available from any good bearing house. Take your CV joint along for match. The CV boot is available as a GM part or try an after-market CV axle boot for smaller GM cars or a VW. Grease and reassemble. If the clamp bolts indicate any wear or thread damage, replace with the correct GM bolt or a Grade 5 or better bolt. Use self-locking nuts. {Thanks to Ted Smith of Topeka, Kansas, for his input.)


You may have read or heard about the test program that Consumer Reports covered in the July 1996 issue. This test involved 4.5 million miles of New York taxi service. Taxis were driven roughly 60,000 miles. The engines were then disassembled and wear measured. Some of the significant findings included:

1. No single oil stood out. All 18 multi-viscosity, API Service SH and two synthetics performed well.
2. No meaningful differences in wear were noted between oil changes at 3,000 and 6,000 miles.
3. There was no discernible reduction in wear with Slick 50 or STP Oil Treatment.
4. While synthetics appeared to perform no better in the taxi test, they remain worth considering for extreme driving conditions of high temperatures, heavy loads, or extreme cold.
These test may not settle any arguments, but they do provide the first objective data, outside of a few technical journals, on current offs.


The November 1996 issue of Consumer Reports discussed claims that reformulated gasoline reduced mileage. In summary, the testes showed a 2-3% reduction in mileage from conventional unleaded gas and no measurable difference between RFG and RFG II as required in California. These tests were run on current vehicles with closed loop engine management systems which can compensate for enleanment. Our carbureted GMC engines are meter based and calibrated for gasoline available when they were originally designed and manufactured. Tests with RFG indicate the possibility that our engines will run 15-20% lean. This excessively lean burning contributes to power loss resulting in poor mileage as well as shorter valve life and cracked manifolds. [See a similar observation under Best of the Rest Heritaqe Cruisers.]
Help is on the way. Joe Mondello has been working on a re-calibrated jet and metering rod combination and has promised that information will be available for the Prescott Territorial Ramble. Cinnabar Engineering is in the midst of developing a re-calibration which will provide stochiometric air/fuel ratio over the entire power range. Cinnabar's plans include a carburetor rebuild/exchange program.


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