FlyingDog

I know very little about the guts of a slushbox, and I haven't looked at them in the WSM as Gregg suggested. This may be a little out there but here's a theory:

What if it's not the parts in the tranny that are expanding but the tranny case itself? Case expands and pulls all the guts backwards. Flexplate clamp then shifts due to the rearward pulling combined with heat/shaft-twist/vibration. When the car cools the case goes back to normal size but there is no longer a source of heat/twist/vibration to move the flexplate clamp, so the flexplate is pushed forward. Ken's cooler would've reduced heat, possibly reducing tranny case expansion.

Steve Cattaneo

Torque converter ballooning is real, and its affect is will know in the automotive industry. You haven’t seen it because you don’t know what to look for; you’re looking for a major failure. Front pump seal leaks and pump failure is the result of Newton's Third Law of Motion.


Torque converter ballooning and TC flange bearing wear movement as shown in Borland excellent animation, can easily push the engine crank against its thrust bearing, we are talking about a couple of thousands, not inches.

Nicole

I think this is finally beginning to make sense...

I assume that in order to replace the torque converter bearings, the transmission has to come out - correct? If I remember correctly, it's about 8 hours for the removal and replacement of the transmission, plus the labor for whatever else needs to be done. That can add up to a pretty significant bill many are not willing to pay. Does anybody have a rough estimate on the cost of replacing those bearings?

Bill Ball

Nicole:

Ideally the tranny should come out, but we removed the TC and replaced the bearing in Matt's 91 S4 without removing the tranny. As soon as my TT decides it's gone far enough and starts groaning and moaning I will be pulling it and the TC out with the tranny left in the car. The bearing is a small part of the job. Stan recommends front pump seal replacement too WYAIT.

PorKen

Nicole - Are you factoring the price at Bill's shop rate?

My only trouble with the TC ballooning is that the engine flexplate moves toward the engine. One crazy theory I had was that maybe since the TC flexplate is attached at it's periphery, if the TC englarges, the TC flexplate is bowed rearwards, towards the TC, which would pull on the driveshaft?

Steve Cattaneo

Nicole,
Can you do me a big favor; there is a euro, (VW, BMW. Audi and MB) ECU Turning Company in Germany that I want to be their NY Dealer. Their web site is writing in German, no English translation. Can you send them an E - Mail on my behalf

Drive to NY I will change them for you.

daveo90s4

Since the flexplate is pushed forwards, the central shaft must be being gradually pulled rearwards out of the clamp, right? Is rearward pull on the central shaft a force that would be caused by 'ballooning'?. If yes, then could be a candidate explanation, but not necessarily THE explanation. If no, then cannot be the explanation. Does this sound right to you folks who know about auto transmissions?

Nicole

So, if I understand this correctly, you can either remove the transmission OR the torque tube to do this job. When I got my car I had the transmission removed to replace the leaking torque converter seal (at 63k miles). I wish I would have known this then...

But it sounds like something that should be combined with a rebuild torque tube - no?

Don't say such things - I love to travel, and sometimes just need an excuse...

Schocki

Nicole,
You have to take the tranny out. Torque tube removal is only possible on 5-speed manual cars. There is not enough room...

majhopper

My own pet theory is that relieving TT pressure under certain circumstances can exacerbate the problem. ie - car on wheels vs car on lift.

I liked Constantines fix, but it almost seems too fixed. The Flex plate seems to be a Suck plate...

Bill Ball

Schocki: We did it on a 91 S4. The trick is sliding the tranny back and dropping the bellhousing. Then it takes some gymastics to get the upper rear TT bolts off and the TC cover off, but we managed. Figure about an hour more than a 5-speed TT.
https://rennlist.com/forums/showthre...highlight=tube
(pictures in post 23)

It's the same technique I used to replace the rear main seal on my 89 with tranny inplace.
http://www.billsworkshop.com/P928S4/seal/seal.htm

Bill Ball

What difference does the lift make?

majhopper

I don't know. But I do know that the WSMs call for removal of X-Member in many non-intuitive circumstances. We know the engine is not "balanced" cold, as per the .4mm advance on the pass side to compensate for unequal heat driven structural changes. Head on forces in an unbalnced system become lateral forces - and vice versa.

Black Sea RD

When we started looking into this whole affair, torque converter (TC) ballooning was looked into as a possible cause for the drive shaft causing a forward push against the front flexplate. What we found was the forward push does cause some wear on the TC housing bearings, not due to being pushed forward by a ballooning TC, but due to the tension of the forward push against the front flexplate and the subsequent backward push agianst the TC housing bearings.

I can understand the TC bearings wearing and causing some problems with the operation of the driveshaft. However, the bearing wear/TC ballooning does not seem to be the major cause of most of the incidences of forward thrust on the front flexplate. When one releases the forward pressure by un-clamping the front clamp and letting the flexplate glide back onto the driveshaft, the forward thrust comes back after a time, at about the same 3-4 mm load.

The theory this is being caused by a ballooning TC would mean the TC is still ballooning and still pushing the driveshaft forward at the same rate and the drive shaft will keep this up with each subsequent release until the driveshaft is moved way forward, the rear flexplate is hitting and machining itself into the TC housing, the transmission is not operating correctly and metal shavings are appearing from the TC housing opening.

Yes TCs are known to balloon and cause many problems. However, TC ballooning is not known to occur with the frequency that forward flexplate movement has been found in the auto 928.

As Borland has recommended, changing the TC housing bearings is a good idea when the trans is out of the car, as is replacing the TT bearings and the trans front pump seal.

Constantine

heinrich

I bet you don't have a 1995 Boxster