bigs

Anyone know if the increased HP and torque from forced induction would result in a greater risk of thrust bearing failure? Would you need to check the flex plate more often?

Imo000

I don't think it would but some theories are based on the torque tube streching under load so maybe a more frequent check would be a good idea.

Jim bailey - 928 International

Since we do not know for sure why it happens but do know it does not seem to be much of an issue until you get to the S-4 models (which use the same torque tube as the 83-86 cars) it probably makes a lot of sense to check for preload especially if you exercise that increased power on a regular basis. Basically all the theories ....convertor ballooning , convertor bearing /spacer wear, driveshaft twisting would imply that more power could increase the incidence of failure.

heinrich

I'd say you're straining the crank more, but not the timing belt. The belt and its components suffer more abuse only when there is increased inertia in the HEADS. Since no forced induction causes this, I think you are adding zero stress to the belt.

heinrich

Oops OK the other TBF ... well yes i am with Jim, you're wringing the crank and wringing the entire driveline with more force. So greater TBF likelihood.

bigs

Related question -

Since no one knows for sure why it happens, is checking and adjusting the flex plate travel the only necessary precautionary step to prevent it?

heinrich

It is the only sure fix available today Bigs.

Jim_H

Totally disagree. The SC engine revs much quicker which has to put more stress on the belt. I'm not saying to the point of failure, of course, but there is definitely more stress on the belt.

mspiegle

I tend to agree with that. If the acceleration of the belt increased, then the force must also increase.... right?

Edit: Wouldn't free-revving your engine be 3x as harmful to the belt then? (thx heinrich)

bigs

TBF meaning thrust bearing failure, not timing belt failure. Sorry for the misunderstanding.

Bill Ball

Even though I am not in the super-high HP club, my 5 lb booster stresses the drivetrain pretty good and quite often. The image in my sig is pretty much how I drive to work these days.

I check the flexplate and crank endplay often on my 89 and just had occasion to check it again a few days ago. The flexplate ALWAYS moved 3 mm each time I released it, no matter how long it had been. It was a constant. More interestingly, the position of the clamp on the end of the TT has gradually migrated down the shaft so that less and less of the the splines would show after each release. When I bought the car 5 years ago, there must have been close to an inch of spline showing. Now that is down to maybe 1/8th of an inch. On the check a few days ago, it moved very little - maybe 1 mm. I do have what I believe is torque converter bearing whine. SOMETHING is migrating or ballooning. The good news is that crank endplay is fine. The bearing whine is quite minimal and has not changed since I first noticed it about a year and 10K miles ago.

heinrich

Bill that has got to be one of the best real-world time tests so far. Very troubling.

bigs

Whoa! Don't those disappearing splines make you more than a little nervous?! Seems like something's gotta be pushing forward!

Jim bailey - 928 International

Bill somehow I just have to laugh when I see your burnout video...... especially when You comment on driveline issues ! I think you need to drop that trans install a slip and figure out what is moving.

Bill Ball

Yeah, Heinrich. Bur I can't see that the SC has had any adverse effect, and I was surprised to see almost no movement on the last check. This is after a 4 or 5 of months of lighting up the tires fairly regularly and driving the car at the limit in the desert.