My '99 FRC had some worn driveshaft couplers I found when I changed the clutch. The BMW couplers were quite a bit softer than stock, and I didn't trust them to hold out under the conditions I put my car through.

So I got two LG solid couplers, a dial indicator and a washer shim kit from McMaster-Carr. I shimmed the couplers until run-out on both ends was unmeasurable when they were torqued down. It bolted up fine and spun freely.

10k miles, ~100 1/4 mile passes and many dozens of laps later the car is still running well, but occasionally it will get a very odd driveline vibration. Sometimes it starts after engine-braking, and other times after an up-shift. The vibration generally either stays the same or gets worse as long as the car is left in gear. If the clutch is pushed in, the vibration stops and stays that way even if the clutch is immediately engaged again. It really feels like the clutch disc is getting off-center from the flywheel.

I had put a new pilot bearing in it, and the TT bearings looked fine when I had it apart. I'm guessing the solid driveshaft changed the natural frequency of the driveline and allowed it to whip at certain RPMs, which destroyed one or more of the bearings. This allows the clutch disc to knocked off-center from the crankshaft.

If anyone else has any theories, please let me know, but I just wanted to warn others about following the same path that I did.

Edit: The cause of the vibration was pilot bearing failure. The TT bearings appear to be fine. I'm leaning towards damage during TT installation as the cause of the pilot bearing failure.

 

I am replacing my rear bushing with a solid one, but replaceing the front with a factory rubber one. This is because I am trying to get the best of both worlds: more strength, and no vibrations. I will get my car out of the shop soon, and I will let you know how this setup works.

 

I have solid bushings and no vibration that I can detect.

I'm guessing it's your flywheel.

 

Hmmm, how long have you had this setup? How did you remove the runout in the shaft (shims, machining)?

My flywheel is a Fidanza aluminum unit. The only way I can think of that it could cause vibration is if it was vibrating loose. I torqued it down to spec and used red loctite on all the bolts.

I've also removed the inspection cover and looked at the pressure plate to make sure its bolts weren't backing out or anything. Everything looked fine.

 

Not sure what kind of horsepower you're running, but I'm over 500 to the wheels and Randy at Doug Rippie told me to go with the stock (BMW) couplers. I've got 14,000 hard miles on them and they are OK so far. Here's a link to a thread that covers most of this.

http://forums.corvetteforum.com/c5-t...oday-pics.html

 

I've read that thread, and judging by how badly my previous set of bushings were when I took them out, I didn't think a new set of BMWs would last as long as my clutch. Looks like I'll be going back into the torque tube anyway (unless someone can convince me its my flywheel/clutch, in which case I'll pull the motor and get a few more other things done at the same time).

 

Does anyone else have experiences with running two solid couplers on a M6 car?

 

After pulling the motor (lost the #7 piston at Sebring), the culprit is found: the pilot bearing was destroyed. There still appears to be no (or at most one-half-thousandth) runout in the driveshaft itself. The front torque tube bearing also appears to be fine (or at least it doesn't make any noise, turns freely, and you can't significantly move the input shaft with your hand). I believe the TT bearings aren't tight enough fits to prevent some movement in the input shaft and clutch disc.

I'm chalking the failure up to damage during installation of the torque tube, or some sort of shaft harmonic causing the thing to whip at certain RPMs.

 

The solid mounts probably caused your pilot failure. Don't be surprised when the next one fails, followed by your tranny bearings. In fact, it wouldn't surprise me if the drive-shaft breaks. There has to be some give in the drive-line, you don't think your car is THAT rigid do you?

 

Most u-jointed driveshafts in other sports cars do not have any give engineered into them (e.g., Vipers with T-56s or TR6060s). Regardless of how well the shaft and transmission hold up, torsional stresses on the shaft shouldn't have any affect on bearings. They aren't stressed by engine torque.

The solid couplers would change the shaft's harmonics, which may cause whipping and bearing failure. However, I'd of expected the torque tube bearings to fail first if this was the case. I may have simply damaged the pilot bearing during installation of the torque tube.

 

I believe you are right that you may in fact have damaged the bearing during the installation.

What advantage do you believe you have over the stock driveshaft installation by installing solid couplings?

 

If I could have bought replacement GM couplers, I would have. It was either the BMW pieces or two solids, and the BMWs didn't look like they'd hold up to racing use very well.

 

Is there a shortage of the GM couplers? What type of racing are you doing?

 

Road racing, and I was not able to find any part number for the 10mm couplers. I was able to find an Opel part (# 90222781), but couldn't get it in the time frame I needed (and I'm not even sure its still being sold).

 

Grant, check your PM.

 

The BMW coupler IS the GM couple, GM doesn't make them, BMW Might not either, but they have them made. Mine had an actual BMW logo on it and I know it was original, I bought the car new. Call Randy at DRM and talk to him, they make Corvettes last through endurance races. He should be able to help you with your particular situation. One thing is for sure, you don't want solid couples on both ends of your TT. And in my opinion, (and GMs) you don't want them on either end.

 

Thats interesting, because the couplers out of my '99 were definitely not BMW pieces. They were much harder, less "rubbery" and did not deflect nearly as much. I inspected three or four different 10mm BMW couplers (aftermarket as well as OE), and found them all to be similar. None had the "Made in W. Germany" and "GM" stamps on them, either. Do you have one of the late-2000 cars with the 12mm bushings?

My plan was to save money by trying the solids, and if that didn't work out go to the LG CF shaft (which requires two solid couplers anyways). Unfortunately, I'm not entirely sure what caused the pilot bearing failure to know if I need to move to a CF shaft or not.

 

My car is a very early 2000. My cousins 99 had no discernible marks on them and I'm assuming they were original, it is a low mileage car.

 

Check bavauto.com, they were incredibly cheap, and original parts.

But Call Randy at DRM first, he might tell you something different and he knows more than I do for sure.

 

Alright, if I go into the TT again I'll give DRM a call. Since the TT's bearings are tight and it spins freely, I'm not inclined to do so just yet, though. Too much of a PITA.

This is what my couplers looked like:
http://forums.corvetteforum.com/c5-t...post1565817148