I've been reading about the preload but the posts are so many years old I just want to make sure a couple things before I check it. I've got an 82 auto, which apparently doesn't get as bad but I should still check correct? Is it fairly normal maintenance to simply loosen the pinch bolts, front and rear, check threads and then reinstall or is there a step missing? Thanks

Jon

 

Not an issue with an 82. However to make the check will do no harm but not needed.

 

The 82 model has a different connector that requires shims to align correctly. Those things do not work loose or let the shaft slip through the clamp. I think the later style clamp was introduced around 1984 or 1985 and then the fun started.

 

Thanks all, that was the information I needed. But if it helps those with later models, is it still beneficial to just loosen the pinch bolts then retorque once the preload is off?

 

Not at all a bad practice to check for any pre-load on the front flex plate in any model year 928 automatic.

Also depending on service history, the shims, washer and bearing that should be mounted on the front of your drive shaft may or may not be present. A visual confirmation would be needed to confirm if those pieces, that were used to set the flex plate to fly wheel distance and discontinued in 1984, are still there or not.

While doing the checks at both front and rear, it wouldn't be a bad idea to replace the pinch bolts with fresh ones and torque them to the higher 65-66 ft. lb. value. Interestingly this newer torque value came from a conversation between Porsche AG and the field techs working on Fred R.s 928 after a TBF incident. Interesting story behind this new torque value which is now a very common practice by many "in the know" in the 928 community.

Cheers.

 

Constantine,
Did you mean to say that the shims and circlip were discontinued after the 1984 model? Or were you being absolutely literal since the manufacture date for some 84 928s was in 1983? My 84 Euro has the shims and circlip.

 

Hi John,

The Porsche WSMs call out the discontinued use of these items from MY1984 and forward. However, all 25m automatic drive shafts have the space and groove at their front to mount these items.

Some POs or their mechanics have backdated to using them in their 928 as a way to stop the drive shaft movement at the front flex plate with the 25mm drive shafts. 25mm automatic drive shafts have been found into MY 1988 928s from the factory. Other later MY 928 automatics have had their TTs changed out with 25mm drive shaft installed.

Still others who may have had the items installed in their 928 from the factory may have not re-installed them after a TT R&R according to the direction in the 928 WSMs.

So this is why it would be best to visually check to see if the items are present. And if they are present, to check that they were mounted correctly according to the WSMs.

Cheers.

 

Very Interesting!!

Since I installed your bearings onto a 25mm drive shaft and that TT into my GTS, then I could conceivably install the shims and circlip necessary and never have to worry about Thrust bearing failure again?

That just seems too easy.

 

What ever happened to just a good ol fashioned slip yoke that would allow the TT to have slight in and out motion as needed?

 

The splines would wear out if it did that unfortunately.

 

Yes, as long as the WSM procedure is followed to the letter to guard against TBF using these parts.

Since the TT is already installed, another way is to use the RiTech clamp being sold by Roger. A bit easier to install than the old parts and easily adjustable going forward.

Still others have had reported success with the PorKen helper clamp, also sold By Roger.

So you have a few different options.

 

In other words, like the 928 5-speed clutch setup which can be morphed into the 928 automatic drive line. However it would necessitate new drive shafts and a new flywheel disc to accommodate the sliding capture of the new drive shafts.

A discussed above, there are other options to stop TBF from occurring that are less costly than re-designing the 928 automatic drive line.

The first step is for the 928 automatic owners to educate themselves about this problem and check their drive line regularly.

Cheers.

 

Thanks for the clarification, Constantine!