Joseph/TX |
10-03-2010 12:18 PM |
Based on a similar problem I had recently, I'm going with driveshaft angle. As JerryC101 mentioned, there is a service bulletin regarding this problem ( I found it on ALLDATA). My '91 745T had developed a nasty highway vibration, which I found to be the center bearing rather than U joints, as I first suspected. The book said that the bearing needs to be pressed out with a hydraulic press - a shop job. Since I couldn't afford to take the car off the road -even for a day- at the time, I just grabbed a complete 2 piece driveshaft from the wreck yard for $35. This cured my highway vibration, but I now had a hard shudder whenever I started from a dead stop unless I just featherfooted it - more throttle, more shudder. I remember reading something about this in an old IPD catalog. It is supposed to be a common problem in cars that have been lowered, cars that are heavily loaded, or cars with sagging suspension due to age. They suggested "shimming" as a remedy and also said that in worst case the driveshaft would have to be shortened. It wasn't clear exactly what had to be shimmed, but in the course of further research I stumbled across the service bulletin.
Basically, there are four bolts supporting the center bearing/carrier assembly. Per the bulletin, I obtained longer bolts (about 1/2") of the same thread pitch (got mine from a fastener shop that had every nut and bolt known to man) and 4-5 flat washers per bolt. I removed the 4 bolts holding the center bearing assembly and replaced them with the longer ones, with 4 washers between the car body and the bearing assembly, thus lowering it and changing the angle of the driveshaft in the middle to more of a "V" shape rather than a straight line. I apologize if this is not a good description; I don't have a digital camera yet. However, if you actually get under the car and look, this will probably make more sense. Anyhow, depending on how you place the washers you can bring the driveshaft either up or down in the center. The bulletin said you may have to play around with the number of washers to get it right, although I initially used 4 and noticed an immediate difference; 5 was the magic number. Good luck with it!
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