Z

When I first loosened the front pinch bolt on my '88 S4 A/T, there was definite movement. The crank end play was .007", so things were still okay with the thrust bearing. I then did the Loctite procedure, using a new pinch bolt and tightening it to 110% of the torque spec, as someone had said Porsche suggested. The shaft was marked so that any future movement could be easily seen. After 2+ years there had been absolutetly no movement. The car definitely wasn't babied in that time, and had a good bit of full throttle "testing" on both the street and dyno in that time period.

Last winter I removed the transmission to replace that seal behind the torque converter that leaks fairly commonly. There was no sign of any pressure on the flexplate, like what Tom mentioned above. The torque converter bearings weren't making any noise or anything, but apparently had some wear because they were looser than new ones. Nothing that really seemed significant, but they weren't like new anymore either. I replaced the two torque converter bearings.

Since the transmission was out, I rebuilt the torque tube then too. It had never made any noise, but it was one of those "while you're in there" kind of things. I've got to say I would have never believed how well the Loctite worked at holding the splines in the front coupling. The shaft really, really, really did not want to come out of that coupling. Let's just say that the procedure to get it out wasn't anything that you're ever going to see in any Porsche shop manual. The front torque tube bearing was in very good condition when examined. The rear one wasn't bad, but like the torque converter bearings, it wasn't like new either. It spun freely, and didn't make any noise, but also had a little more looseness than a brand new bearing.

Apparently the torque converter bearings wearing is fairly common on the A/T 928. Once those bearings get loose, it should mean move movement back there, which would explain why that seal starts to leak, and also why the rear torque tube bearing wears faster than the front one. I was once told by someone who rebuilds the torque tubes that the rear torque tube bearing is typically the one that's worn when peoples torque tubes need replacing. The condition of mine seemed to confirm that. All of that combined leads me to believe that something back there with the torque converter, or right by it, is going on. Don't ask me what though.

There was someone that was supposed to be working on a slip type front coupling with a machine shop. Someone named Constantine maybe? It's been quite a while, and I haven't heard anything about it anymore, so I don't know what ever happened with that.

Were any changes made to the setup on the GTS? If extra torque was somehow related, I'd think that the problem would show up more often with those than with the S4. I know there aren't as many GTSs as there are S4ss, and they're probably more likely to have lower miles on them as well, but has anyone heard of the problem seeming to occur more with the GTS? I've heard of thrust bearing failure and also broken drive shafts on normally aspirated, stock displacement S4s. There are some A/T S4s with superchargers that have been around for a few years, and have 20K-30K or more miles with the superchargers on. I've never heard of any real problem with any of those as far as thrust bearing failures, or any drive shaft breakage. One of those A/T supercharged cars was getting close to 500rwhp the last I heard about it, and another a good bit more than that. I don't know what if anything has been replaced on that car in its past, but it was stock with I think around 140K miles on it when the supercharger was installed. As far as the thrust bearing, torque tube, drive shaft, and transmission, everything that was in the car when the guy bought it is still in there now, and doing fine so far. There are supposed to be some stroker motor A/T cars out there as well. I've never heard any mention of one of those having a problem with any of this either. It would be nice if some sort of pattern would start to develop, but as far as I know, there really hasn't yet.

John Struthers

Steve,
There are several -at least two- custom driveshaft outfits here in Midland TX.
From what I understand they do off-road and Hi-Po driveshaft/drivetrain applications fabrication to augment rebuilds and custom drive link/shaft/trains for the Oil/Gas well drilling around here. Local customers are Halliburton, Pioneer Energy ect... .
I've seen Hotshot trucks and trailers leaving here to as far away as Alaska.
So apparently their products are in demand due to timeliness and quality.
I'm working 12 hour days and in this weather will, no doubt, soon be sick.
We have a current 3 week job completion project before I see a break but will try to schedule a day off with the slave masters to make inquries.
I will need whatever drawing, pages from manuals and hopefully a physical example of what we have and pehaps a sketch and written requirement of what we need, to include shaft bearing location, spline engagement length, overall length, ( can we shave a thousandth, or hundredth off on length?) and allowable tolerances -not to tight, not to loose, just right!-. Though I 'believe' these guy's will have experience and knowledge in heavy duty, extreme use driveline/shaft developement and fabrication far beyond our comprehension.
FWIW
While I think this is a step in the right direction, it may, in the end be more cost effective to cannabalize or use parts of the Vette's for application up to the mid 400HP range and probably far easier to adapt and balance than out right fabrication of new parts...time will tell.
I can "probably", not sure yet, foot the bill for the initial product.
I know what you are saying about time. But will try to work it in.
There appears to be a difference between the Converter drive flange's in the 928 INTL Catalog: For Auto's.
78' - 82'
83' - 86'
87' - 95'
While the clamping piece remains the same for all models. So, obviously, if I end up footing the bill expect the proto-type to be for a 78' - 82' MY.
Also need to know what the difference between a:
Clamping Piece (used) - U922-421-255-00 and a:
Clamping Sleeve (used) - U922-421-051-01 -78'- 95' MY
Clamping Sleeve (used) - U239-421-239-01
If I can't get returnable donor examples I'll have to purchase the 78' - 82' MY parts and call it a day.
That's about $300.00 - $375.00 in USED parts alone including a new TC bearing, but not including a TT which I imagine they'll need for measurements.

Erik - Denmark

[QUOTE]Originally posted by Steve Cattaneo
[B]HI
1. On the last 5 928 transmission that I rebuild all had bad, worn TC bearings. The rear bearing next to the TC had the most damage. The inner race had a lot of lateral movement. The snap ring only supports the outer race of the bearing.
2. Contrary to your belief the rear flex plate flange can move forward in the bell housing pushing on the shaft. When I have more time I will post pictures.
3. What facts do you have to support your shaft flex theory? BTW manual transmissions engine do suffer from TB failure. Not as often as automatics.
4.I think the fix to this problem is to replace the front pinch bolt style flange with a free floating York style flange. This would allow the torque tube drive shaft to float in the front. So when the toque tube shaft migrates forward there would be no forward load on the crank shaft.

Hello Steve,
Thanks for your constructive answer, to witch I have the following comments/answers

1. If that the fact, yes, then the TC ballooning can be the reason - But before it starts moving the TC-shaft forwards the rear flex-plate will be bended backwards - I.e. that will be possible to check this by inspecting the condition of the rear flex plate (And this is visible)

2. Yes, but first it will bend backwards as mentioned in '1'

3. I am not sure what you mean, but I think you mean the possibility for the manual shaft to move - If correct see my answer '4'

4. Yes that could be a good solution, and maybe that possible to use parts from the manual clutch, where the clutch-shaft (item 4) can slide free in the clutch dishes (item 8 and 10) - see
http://forums.rennlist.com/upload/clutch_1.jpg
This clutch shaft is attached at the end of the Trans-shaft with a spline clamp like the automatic clamp - See:
http://forums.rennlist.com/upload/clutch_2_copy1.jpg
Maybe this shaft and hub can be installed, I think that was was Constantine in Florida (as Tony and Z mentioned) was working with - I know that Earl Gilstrom has contact to Constantine, so maybe he can help

Your questions: Yes that is all possible, only we have to find a proper mechanical engineer with up-dated knowledge (That's too many years since I got my degree as mechanical engineer, so we have to find a younger one) - But if parts from the manual model can be used that will be much easier and cheaper, and this parts are Porsche designed for the purpose

Z,
Thanks for you good write-up - You said:

Quote:
Apparently the torque converter bearings wearing is fairly common on the A/T 928. Once those bearings get loose, it should mean move movement back there, which would explain why that seal starts to leak
My questions:

1. When you said the converter bearing, I expect you mean the two converter shaft bearings - Correct?

2. Where do you have that typically leak?

PS: I made many things on my 928, but have never touched the converter
Regards from Erik in Denmark

heinrich

STEVE:

1) I am in, I own a 5spd but am bound to own an auto, and I'll throw my $$ that way DEFINITELY
2) Your analysis of the problem may or may not be correct, but I have OFTEN thought we should have a free-floater or a U-joint, and
3) A free-floater WILL DEFINITELY stop these failures, whether they originate from the TC, or something else, or the front, or the shaft itself.

DO IT, I am in. Please.

"I think the fix to this problem is to replace the front pinch bolt style flange with a free floating York style flange"

Lizard928

Has anyone thought of modifying the TT so that it is impossible for the shaft to migrate forward,
say add a ring around it so that it cannot slide through the bearings, then also make it so the bearings cannot slide forward, the only thing of this is you might have to change the style of bearing used in the TT

Z

The ones I meant are the two bearings in the front converter housing. They're #4 and #7 in the picture on page 37-126 of the shop manual.

It's the seal behind the torque converter, that's pressed into the front of the primary pump casing. The seal is #16 on page 38-150 of the shop manual. When it leaks, transmission fluid leaks out of that small grill at the bottom of the transmission case, under where the torque converter is located. It seems like an awful lot of automatic transmission 928s leak there. When I got the new seal for mine, I found that seal has been updated several times, and there have been at least three different Porsche part numbers for that seal. That leads me to belive that there must have been some reason for them to keep changing it like that.

Greg86andahalf

Steve,

count me in. I know first-hand how good your work is.


Greg

Erik - Denmark

Z,
Thanks for the info,
Regarding the bearings:
- The condition of the rear bearing could support Steve's ballooning theory so far that it is under a axial load from the converter, but as I understood you, the bearing did not have several mm's slope, only 'loose' as you said, I understood that so, that the bearing was still intact without visible axial slope - Correct?

But then you said something I do not understand: quote: ...........Apparently the torque converter bearings wearing is fairly common on the A/T 928. Once those bearings get loose, it should mean move movement back there, which would explain why that seal starts to leak, and also why the rear torque tube bearing wears faster than the front one.........................

You said 'move back' - If that's the case, then it is opposite to Steve's theory

Regarding seal:
Good to have that info, if one day I get a leak! ..................

Regards from Erik in Denmark

Earl Gillstrom

Tom,

Checked Gary Knox's '88 and there has been no movement. Still has .008 CS end play.
Gary's car was the first car to have the "Loctite Fix". The car has been driven ~30,000 miles and many many DE track days and no movement.

I hate to say this, but, I don't think that it would be wise to drive your car (especially with the SC). Something happened back there and should be checked.

Note to all with autos: Knowing Tom's experience, check your crankshaft end play.
It is easy to do with the bell housing cover dropped, but on most cars, you have to drop the exhaust.
I have not tried this, but why not see if you can check the play from the front. If you can't get the crank to move, then check from below.
I do know that the end play is impossible to check if the flex plate is pushed forward. I have been unable to move the crank until the pinch bolt is released on all of the cars that got the Loctite fix.

Garth S

Earl,
Could you please elaborate upon the last statement, "...been unable to move the crank until the pinch bolt is released on all of the cars that got the loktite fix". Preceeding that was the (valid) suggestion of assessing CS end play from the front---to do that, I'm assuming you mean with the pinch bolt still locked down and the flex plate in a 'neutral' position (certainally not thrust ahead into the crank face).
If one could get adequate movement in the latter case to determine CS end play, surely it would apply regardless of application of loktite(290).
Tom's case/observation is compelling and of greatest priority: my query concerns those who have released the 'acquired' front flex plate pre-load, applied the '290' fix,and have witnessed neither further movement along the splines nor flex plate pre-loading(towards the crank).My presumption is that with the flex plate locked to the splines in an unstressed, neutral position, there should be adequate 'flex' in the flex plate to allow the crank to experience it's nominal ~ 0.003"-0.012" float ???
As an additional point, Tom mentioned having had considerable difficulty in releasing the loktite. Did you have similar experiences in those cars where you had released loktited splines? - or was Tom's case perhaps made more difficult if there was the beginning of axial shear at the splines?(SC level horsepower)
regards

Z

None of the bearings involved were really bad yet. The rear torque tube bearing was looser than the front one. I think I know what you mean when you say "slope". Basically that the inner portion of the bearing could be moved at an angle to some degree compared to the outer portion of the bearing. Both torque tube bearings did allow for at least some movement that way, with the rear bearing allowing for more of that type of movement. I don't kow about the two bearings in the torque converter cover though.

It may not have been the best choice of words on my part. I meant that once the torque converter bearings get loose, it should mean more movement back in that area, not movement backwards there. Basically I meant that looser bearings there would allow for more axial and angular movement.

That was kind of interesting with the newer versions and part numbers for the seals. Back when I did the replacement, Porsche was showing the newest part number version in their parts listing. When ordered from them though, they sent out the previous version part number seal. Thinking that it might be a good idea to try to get the latest version, I had the parts guy try to order one of those newer versions again, with the newest part number. Once again the older version showed up.

shaaark89

garth,
i don't think anyone else has released the loctited splines except myself and z. i've done it on two cars. one when replacing a trans and the other my black car which is not supercharged yet.
z did it when replacing his converter seal. in all cases it was extremely difficult to release it.

Earl Gillstrom

Garth,

I have heard of a few guys that have had to release the loctite and all said it was very difficult and took a lot of heat. I have never had to release one.

With everything "normal", the flex plate has a lot of flex, so it is easy to check CS end play.

With the hub forward before releasing the pinch bolt (before Loctite fix) it is impossible to check CS end play. At least I was afraid to pry that hard with a large tire iron.

When we did the first few loctite fixes, we were afraid that the Loctite would not work on the oily shaft. Now it looks like a less adheasive Loctite might be better. As far as I know, 290 is the only penetrating grade.

Garth S

Earl & Tom,
Thanks for restating what I thought you had either said or meant. Aside from the concern which we all share for Tom('s car) as the unknowns are pondered, there seems to be a positive spin on some of the more general issues:
- if anything, the loctite 290 fix not only works, it works too well. This is good news provided there is no looming secondary issue as Tom has observed, and when one applies the "fix", everything is tension free and dimensionally correct.
The signifigance of this is reflected in the following observation (humour me, with only one data point/ car to 'see' here in the boonies): Prior to releasing the front pinch bolt this summer on an '88 that had no indication of ever having been touched at ~31K miles, there was a distinctive visible mark on each spline 3.0mm behind the pinch collar - ie., the orriginal factory position. The pinch bolt had in excess of 50 ft-lbs prior to release, and wnen released, the flex plate preload caused a retreat of 3.05mm. In essence, the orriginal factory position was (self)restored, and loctited there.
This allows you to think all will be well for many years, with precautionary monitoring.
With the large surface area (of splines), as you infer,a lesser strength loctite would likely be adequate [regular, blue 272]. The benifit of 290 is the low viscosity, allowing it to flow into the splines and - act like 'super glue'.

Earl Gillstrom

Garth,

Your findings of 3.05 mm (.120") release distance is what I found on the first 4 cars that I did. Later, I stopped measuring, but one car had the flex plate jammed against the flywheel. I wish that I had measured that one.

Tom and Garth,

Loctite application: Maybe one drop of 290 in one slot would hold the splines from moving and facilitate release when necessary?

I was looking thru Gregs site and stumbled on this. It is on a 5 speed, but had the symptoms of your problem. I know that you loctited the rear pinch bolt, but could the rear clamp have migrated? Here is an excerpt of the post.

http://www.nichols.nu/tips.htm

Drive Train
Clutch Damage: Torque Tube Moved Forward

The rear coupler bolt apparently loosened, and allowed the driveshaft to "work" inside the splines. Over time it eroded the splines and somehow caused the shaft to inch forward. This is hard to figure as the press fit of the shaft into the bearings would (I thought) have prevented any fore/aft movement.

As it inched forward, the bolt wore a flat spot (sort of) back along the splines. This flat spot was the only thing preventing the shaft from rotating completely in the rear coupling. Once the bolt was removed, the
shaft could be spun quite readily!

Marty
86.5 Indischrot 5-speed