Don Carter

After our monthly PCA gathering this morning, Steve stopped by with his red 90 that came from DFW a year or two ago to check a few things out on the lift. We checked his flex plate and found he had some movement. We found the rear pinch bolt not torqued properly and it looked like the shaft had migrated towards the rear a bit. After re-torquing the rear, relieving the flex plate pressure I tried to retorque the front flex bolt. I couldn't get the torque wrench to click at 62 ft lbs, it just kept turning and turning. I eventually realized the bolt head was stainless, and remembered that the bolt isn't supposed to be stainless. Luckily I had a new pinch bolt on the shelf. See below the stretched stainless bolt. Looks like it was very close to breaking which would have led to a long afternoon of drilling and such. We wrapped things up by installing a spare PKlamp I had on hand so he should be good to go.



This is what it looked like before relieving the pressure. On my 86.5, I don't think this much of the splines are visible. Any opinions on if the the shaft is too far back? The end of the shaft extends inside the clamp to about and inch and a half.



Less splines were visible after relieving the pressure.



This car also has an unusual X pipe, maybe an early prototype?



Unfortunately, the rear joint from the high flow cats needs work.

Mrmerlin

Warning the front drive shaft doesn't look correct. its too far back,
might the TT have been rebuilt and the wrong shaft was used ?

Did you verify that the rear of the shaft was lined up with the bolt cutout at the trans axle?

Note for the rear bolt, its a good idea to remove the bolt to inspect the location of the drive shaft,
simply re torquing the rear bolt is not the best idea,
as if you did not remove the bolt then you dint add any blue loctite to the threads.

From Bill ***** tutorial this is what the drive shaft should look like

link.

http://www.google.com/url?sa=t&rct=j...52434380,d.aWc

MainePorsche

That's quite a bit of spline up front. Almost 2 inches or about 50 mm by eye. I have 7.4 mm spline marked on mine.

Mrmerlin

the clamp at the cat has been superseded,

the new band clamp has a step in it so it will more easily conform to the cat outlet diameter

soontobered84

That looks like a magnaflow X. Available at most any muffler shop.

Don Carter

Stan,

There's no way to know if the rear pinch bolt is properly tight if you take it out first, so I torqued it first. I didn't remove it to check the notch because we were not prepared for major surgery and I didn't have a plan in mind for trying to move the shaft if it wasn't aligned with the bolt. I figured better to have it tight than lose. I told Steve we'd need to do more research and it was likely that the shaft was too far back and further work may be needed.

I'm familiar with the newer clamps and recommended them to Steve.

Mrmerlin

actually you will know if the rear bolt is tight as it will be rather difficult to remove.

anyway they are usually loose, so a simple turn and you will see how easily the spins out .

to investigate this shaft position remove the front and rear pinch bolts .

Inspect where the rear shaft cutout is in the trans input collar from the picture it has to move quite a bit.

Hopefully the shaft was just improperly installed and the shaft once positioned correctly will be of the correct length.

Since the shaft has to come forwards about 1 1/2 inches you can use the front flex plate to move it.
So mark the flex to the flywheel then remove the 6 outer bolts,
then slide the flex onto the shaft and tighten the pinch bolt tighter than snug is good.

You can use a block of wood and a pry bar to move the shaft forward.
try to pry as close to the center of the clamp as possible dont pry on the flexplate.

NOTE the less side loading of the shaft the better,
so you don't induce a bend into the drive shaft

123quattro

Yep. About $75 on Ebay. They work well.

Bill Ball

Here's what I think is going on at the rear. I drew this a long time ago when a similar situation was noted at the front...

How this happened is a good guess. Normally the shaft is held tightly in the TT bearing center bushings. Changing dimension A from the prescribed 2mm usually takes some pounding unless the carriers or bushings are very worn. Somebody really screwed this up and I would also evaluate lateral play in the shaft from most likely worn bearings, bushing and/or broken carriers. The shaft should not have any play and should not slide very easily once you release the rear clamp. The bearing can also come out of the carrier in which case the shaft would flop around. Probably not the case as you would have ridiculous vibration.

FredR

Don,

The pinch bolt is well goosed-if someone put a stainless bolt in there it will not have any where near the tensile strength of a similar sized HT CS bolt-which considering it is on a joint that cannot cannot grip correctly in the first place is Kamikaze for a 928 auto- are you sure the flex plate is not grossly distorted- I have seen a local one many years ago that was so badly contorted you would not believe it so possibly you have experienced double jeopoardy-slippage at both ends that has saved the motor- let's hope so. Presumably you have checked the crank end float?

Something looks way wrong in there whether there are likely to be secondary consequences depends on exactly what has happened.

If I was to hazard a guess I would think the shaft has migrated relative to the torque tube bearings but doubt such would happen in service. I do not know the 86.5 model but presumably dimensionally- it should be similar configuration to the S4/GTS.

Starting point has to be alignment at the torque converter end as Stan suggests- what your photos shows suggests it just cannot be right or the thrust bearing would long since be toast. That or your front flex plate would have to be so badly bowed such that you just could not miss it.

My front flex plate looks more like the photo from Bill's procedure. If I was to guess what happened I would think some PO's mechanic has had the TT tube out and perhaps dumped the end on the floor for support not realising how easy it is for the tube to migrate relative to the carrier sleeve. We know the front clamp can migrate and we know the rear one can also but both at once? Well I guess it is possible but do not remember reading about such happening previously.

If the torque convertor bearings are known to have been replaced in recent memory then I can understand the retiscence to remove the gearbox but if you do remove it, do the job properly and WYAIT the TC bearings, the TT bearing [Contantine super bearings], check the flex plates and everthing up securely with a recognised procedure that is "guaranteed to work"

Good luck

Fred

Black Sea RD

The drive shaft had moved rearward in the torque tube (TT) and the rear pinch bolt was forced into the coupler ahead of the rear drive shaft groove, just where the rear splines start in Bill's picture.

This happens with some frequency by those who do not use the WSM during a TT R&R. Usually when the TT is being placed into the car and the drive shaft gets pushed through the bearing units rearward. Then the rear pinch bolt groove doesn't line up when everything is together and the mechanic just forces the rear pinch bolt into place to get it done.

This needs to be corrected soon before the drive shaft fails.

HTH,

tmpusfugit

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