PorKen

To summarize, the single split clamp (924 part#, jeez) is crap.


I want one of those 968 couplers for my S3 5-speed.
I reckon it would help with the low rpm/high torque 'rattle' (like a PKalm set).


Think if they'd put a double split clamp on the 928 flexplate, instead of the silly 28mm shaft...

(They put all the good stuff on 968s...like sprung/hyd. damped belt tensioners. )


94442124101 (superceded to 94442124102)


PKalm


PKlamp

928er

I think that part of the problem is that the bolts are re-used. The bolts a re a wear item and no matter what your opinion of the solution is, a new bolt on every use will minimize the slop in the movement...

PorKen

New bolt won't help. Even with 10% overtorque.
The problem is the design of the (single split) clamp (designed for a 4-cylinder Audi engine...NTTAWWT).

It has been well demonstrated, for a number of years, that increasing the clamping pressure will stop flexplate migration.

Not an opinion. Proven, fact.

928er

I agree that a new bolt isn't the complete solution. However, re-using the bolt and adding an additional clamp is not the best solution.... if you are adding an additional clamp... then at least use a new bolt in addition.

Tails

Still a very interesting subject and good to see the opinions and arguments are still being put forward.

I will not add anything to the flexplate migrating argument, as I have written sufficient on this subject over the years, as I'm just trying to maintain my vehicle with what I have got under the principle of "if it 'aint broke don't fix it".

I checked my forward flex plate yesterday and it still maintains it position on the drive shaft spine after 6 year since I applied locktite and the flex plate is flat.

I will again check the tension on the aft flex plate set bolt and interesting to note that "BB" has instituted a planned maintenance procedure for the tensioning and replacement of the aft clamp set bolt. I will institute this procedure. I have checked the tension of my aft clamp set bolt, but I'm not a "lead foot" drive.

Interesting subject "Tribology" with regards to oil film, friction, boundary lubrication and bearing failure especially on parallel rotating thrust surfaces?

A G M Michell developed a multiple tilting segment thrust bearing 100 years ago, which is mainly used in the marine industry, that ensure an "oil film wedge" between the thrust pads and the bearing collar is maintained. A single Michell thrust bearing is used on marine diesel engine developing over 70,000 kw.

It is therefore, in my opinion, essential that the correct viscosity lubricating oil, as recommended by Porsche, is used and as indicated by "BB". I cannot understand why very low viscosity synthetic oil are used by some owners in their cars.

Tails 1990 928S4 Auto

JET951

Hi Constantine , I was in a rush when I did my last reply( post no 54) & what I should of added was that the tension on the quill shaft after its managed to work its way forward is naturally a combination of the TT bearings inner sleeves grip ( which I know is not massive ) but it there , but the grip of the male & female splines at the rear of TT coupling area , so in other words the rear splines ( male & female ) together are still under considerable grip pressure , its just the forces that eventually move the TT quill shaft forward are greater than the nearly ( by comparison ) weak rear ward force of easy to deflect engine flex plate ( can be moved by a human thumb) , then we add to the equation of the flank ( non threaded ) part of the index bolt of the rear TT coupling that is now jammed / grinding up / into the TT splines , all these are griping forces and the poor old flex plate can not fight back ( its all fairly simple stuff really ).

Remember this is what Cosmo Kramer ( post no 1 ) saw, with the front coupling well held in place , but the engine flex plate deflected by the amount he mentioned, its because the TT quill shaft has migrated forward , they all do it eventually , because they only have one bolt in the rear coupling and its this coupling that looses the required grip tension needed of a ratio of about 2:1 , meaning the front coupling only looses the required grip tension less often ( all in standard form ).

I found that rear coupling index bolt( at work) we took out of a 928S4 that shows the "Teeth" marks on its flank , its a ripper because these "Teeth " marks can only happen by this bolt being shoved hard up against/ into the male splines of the TT quill shaft , we see it a lot on these , be it Auto 84 onwards or manual all year types.

See photo below ( it says it all )

Regards
Bruce Buchanan
Buchanan Automotive
---------------------------------------------------------

Dave928S

Here's a close up of the one I showed before.

Mine was taken out without prying the shaft back to relieve the pressure on the bolt shank, which accounts for the damage to the thread that you see.

Bruce must have pried the shaft back before removing the bolt, to make it easy to get out.

Edit - addition: Cosmo Kramers in post #29 looks like mine, with the same spline marks, and thread damage from being wound out without prying the shaft back. I also just reread one of Bills posts and he mentions that he has unexplained less spline showing at the front (he was wondering about TC ballooning), which sounds like the same forward migration of the shaft.

The theory that Bruce put forward regarding the shaft forward movement certainly fits with what he and I have experienced. The flex plate in an auto, and the sliding stub shaft in a manual, present no restriction to forward movement of the shaft, and neither do the bearings and carriers in the TT ... and importantly they don't push it back to where it came from to any degree. The rear coupler, even with a stretched bolt, still has some clamping force, and therefore frictional resistance to movement after being pulled forward with wind up, and has nothing pushing it back with the same force (only a weak flex plate) ... and so moves forward like an inch worm in the rear clamp.

Bill Ball

My rear clamp and bolt are just fine. My TT is original and and has no spline damage anywhere, but over the years the spline exposure at the front clamp decreased, but seems to have stabilized. Also, I very recently swapped out the torque converter. No change.