MGW-Fla

Hi Constantine,

So what exactly does all of that mean?? Are you saying that anyone attempting this who's car has an original flex plate should definately replace it & then torque to 66 ft.lbs, or that you should only torque to 66 ft. lbs IF you also replace the flex plate? Or are you ok if you do not replace the flex plate as long as you only torque to 62 ft. lbs.???

Also, please show & tell on your developed product you debuted at SITM, doesn't it resolve this issue? And can you explain who is "we"?? Thought you alone were the genius with all the R&D expertise on this subject, is there others you are working with or can you say? Sorry if that is common knowledge, I know you have been working on this a long time now.

One last question, is this situation only for the '87 S4s and newer? I thought I was supposed to be ok with my 85 auto, do I have that correct or should I add that to it's annual checkup too?

Please pardon my technical ignorance & all the questions... I'm trying to learn here & have copied & pasted most of this & the other threads referenced with the pics into Word Perfect to save & print to put in my 928 library for future reference. Great info by everyone, thanks for the continued 928 education.

Vilhuer

Any and all '85-95 MY automatic can suffer from this problem. Likely reason why its more common in '87+ cars is that engine hp and/or tq is beyond threshold which causes problems. Its possible in '78-84 MY automatics if shims are not set properly or they are left out. Even manual cars could have TBF too if clutch is set up all wrong or pressure plate is extremely strong. No real cases have been reported AFAIK.

Only sure fix is to somehow make flex plate to torque tube connection stay exactly where it is. There are three ways of doing this which have been used by several people. '83('84 ROW)-87 torque tube together with factory shims, Constantine's clamp and red Loctite. All have their good and bad points. I think its proven that all three ways work almost always. What doesn't work is just using 10% higher torque value. It might help a little if flex plate was new and tight but its only temporary help unless parts are renewed every so many years.

I would follow factory instructions to which end of movement range to set crank before clamp it tightened. I would think engineers had taken into account TT center shaft lenght changes when they wrote those instructions. From memory without checking its towards rear where it need to be set.

SharkSkin

Great write-up, Bill! I agree with Jim -- this ought to be copied to the DIY section.

Bill Ball

Constantine: I don't see how you pooped on anything. If the 66 ft lbs is a Porsche recommendation, great. I have no problem with that, although I've never seen a bulletin. I don't quite understand what the extra 4 ft lbs accomplishes.

The recommendation of a new flexplate is puzzling. HOW OFTEN should you install a new flexplate? Mine has never been stressed beyond 3mm of preload and looks like new, as you can see. Also, I will tell you, it flexes rather nicely. I mistakenly put the prybar on the flexplate and moved it a large fraction of an inch rather easily. My dial guage reading jumped way beyond the TBF spec limit and scared the **** out of me until I realized I had not moved the crank. Now, I have seen fractured flexplates, if that is the concern, but only in cars where the bolts were not torqued properly.

As to the red Loctite, I'd rather not, but that's just me. If it works for someone, great.

I just want to say that this modest endplay measurement guide is purposefully simple for two reasons. First, because my approach to most things is "keep it simple" because I think that works best most of the time. Secondly, I want others to feel like they can do this even with minimal experience and basic tools, because I think that is true for this job. Why else would I show a picture of the bellypan and the bellhousing cover to start off with? However, there are some fine points to this that could bear discussion, such as where to leave the crank at the end of the job before you torque down the clamp bolt.

Bill Ball

The instructions cover a bunch of dimensions, in a rather complicated way, that set the flexplate relative to the flywheel. I interpreted it is a 0.3mm gap, but I can't recall the crank positioning in those instructions. I need to go out for a while, but I will pull up the pages later and we can have fun with them. I will admit to having struggled with understanding them, and made my own conclusions with some uncertainty, so if anyone can ge to the bottomline with them, it would be appreciated. Regardless, so far it seems I have done no harm with my simplified approach.

AO

Ummm.... I'd suggest leaving it in the engine!

Actually, this was the question floating around in my head just before reading youre post Bill. I would think that if your endplay is getting up there near the hig end of spec you'd want to set it toward the aft since the migration seems to be forward. But what do I know... I've got a 5-speed.

Bill Ball

Andrew: In 5-speeds, most of the thrust bearing wear is from the clutch action and it is on the front of the bearing (crank pulled to the rear). On Dennis's engine, the front face wear was substantial. However, I'm not sure that has any relevance to where the crank is positioned.

AO

Bill-
In that crafty mind of yours, can you think of a way to measure crank endplay on a 5-speed without removing the clutch? Obviously it's easier removed, but maybe by releasing the coupling sleeve? Would that allow you to isolate the crank enough?

SharkSkin

Andrew, if you can find a place to mount the dial indicator on the front of the engine, you should be able to check crank endplay entirely from the front of the engine -- maybe even from the top. The stub shaft should slide enough in the pilot bearing for you to perform the check.

Black Sea RD

Hi Mel,

That information was given by conversation only with Porsche AG, it is not in any manual or bulletin. One can surmise that Porsche AG new about this driveshaft pullout problem and devised this newer approach to help combat it. What this means for the rest of us is that the front flexplate in our cars will lose their clamping ability after some time. Then the front flexplate should be replaced with a *new one* and then use the higher torque value for the pinch bolt. Again, you will not find this method anywhere and I doubt another call to Porcshe AG will get the same response.

The new clamp we designed is a much better clamp, holds the driveshaft much more firmly and can be reused without loss of it's clamping ability. As far as "we" and being a "genius," I worked with others to find the problem and a solution and although I finally designed the final product and commissioned more for other 928ers, I do not want to make it seem it was all me. Bad form that.

As we have said before, every 928 auto should be checked for this problem. There is a strong belief by us that some of the TBf problems are caused by mechanics that are ignorant of how important it is not to have any front pressure on the front flexplate. The only way to be sure is to check the front flexplate as Mr. Ball has graciuosly outlined for us.

Great seeing you and Pam at SITM,
Constantine

Bill Ball

Constantine: Oh, it's the clamp, not the flexplate itself that goes bad. Sorry, I am so literal. The clamp and plate are only sold as a balanced unit, so, now I understand the recommendation to replace it at some point.

Bill Ball

I don't see a problem with measuring it at the flywheel edge or off the pressure plate. It should move as a unit since they are bolted together. Dave mentions doing the measurements at the front of the motor, but I don't know if there is play in the manual tranny driveline, as there are no flexplates. So, I'm not sure if you need to loosen the TT clamp. Sorry to be so ignorant of 5-speeds, but I have only done a couple of clutch replacements and one 5-speed TT and didn't study the driveline.

SharkSkin

The part that will slide fore/aft, allowing you to make this measurement, is the tip of the stub shaft in the pilot bearing(red rectangle in pic).

Bill Ball

Dave, that is what I'm not so certain of. The stub shaft is clamped hard to the TT shaft. I would suppose there is a 1/2mm of play in the driveline, and that the stub shaft is not hard against the flywheel, but I have never looked at it. As the clutch arm is freely movable, I know the clutch pack is free to move, as long as the flywheel is, and I would assume Porshce would provide for that in the driveline. All the TT clamps are positioned on the shaft by bolt locating grooves.

SharkSkin

Well Bill, if that part I highlighted *doesn't* slide, then the tip of the stub shaft must be galled/seized to the inner race of the pilot bearing -- and the bearing should be replaced.

This is really the only place in the driveline that has any "give" as temps and lengths change. There is nothing between there and the input shaft on the transaxle that can change length except by loosening a splined connection.

The stub shaft should be a running slip-fit with the inner race of the bearing. It should be easy enough to move the crank back and forth with a prybar against the small amount of friction at this point. If the crank is not floating at this interface then that is a separate problem that must be addressed, probably at least a new pilot bearing plus clean up the tip of the stub shaft.

Andrew, did your stub shaft fit tightly on the inner race of the pilot bearing, or did it more or less just slip into place?