PorKen

It's been a month since (the install), and there's been no detectable movement. Normally, it has moved 3-4mm within a week or two of release on my '86. Even after I bumped up the bolt torque to 60ft/lb.

Steve Cattaneo surmised a while back that torque converter ballooning might be the cause of TBF. Others have said that worn converter bearings would allow this. One reason for TC ballooning is restricted cooler lines, which the 928 has!

Trading the banjo fittings, 20+ feet of hose/tube, and two coolers for straight through fittings, 6 feet of hose and a low restriction cooler has seemed to have stopped flexplate creep on my car. I'll keep checking it over the next few months.

I still don't know how the flexplate moves forward, though. Someone theorized vibration creep?

Also, the weather has gotten into the 80's, and I haven't seen over 180°F pan temps, yet. It's usually around 160°.

GregBBRD

The converters are enclosed in their own housing. They could balloon until they pushed the transmission oil pump through the back of the transmission and they would not effect the torque tube or the front flex plate....the cast aluminum housing that the converter is enclosed in would crack and break if the converter pushed more than a couple of millimeters. Take a look at the workshop manual and see how all of these pieces are assembled and you will see what I'm talking about. The aluminum housings are never damaged, nor have I ever seen a converter that had any signs of ballooning. This is not the cause of the problem.

Since Porsche clearly recognized the problem on the early cars and made a positive stop for the flexplate, the problem has to be either "creep" or from the twisting of the torque tube shaft from torque. Since the GTS vehicles suffered more from this problem than the earlier models, we have always assumed that the problem had a direct relationship to torque. Guess the supercharger guys might be able to answer this.

I can't even begin to imagine what transmission temperature would have to do with this problem....perhaps you could share your insight/thoughts on this.

greg brown

PorKen

None of the previous theories have really struck a chord with me, TC ballooning (± worn bearings), fast shaft twist shortening, vibration creep.

I never considered the heat load as contributing factor...but it could contribute to expansion of the converter housing, and/or the torque tube? I suppose the converter could transfer some of it's heat into the driveshaft, which would make it more maleable?

I've seen no movement, without Loctite or any other special treatment, besides the cooler running temps. I haven't babied the car. If anything, I've driven it harder, as the increased lockup of the converter with the cooler oil temp makes the drive much more responsive, both in acceleration, and engine braking. I have been rev'ing it higher that I used to, too. My car was recently dynoed at almost 300ft/lb RWTQ.

One other factoid, I had left off the lower cover during this time, so I could more quickly check the flexplate movement.

GregBBRD

Again, somehow Porsche knew this was going to happen on the early cars. I would think that if it was something that could have been cured by adding a cooler or building a stronger something, they would have done it, instead of building the stop on the end of the torque tube shaft, like they did.

I'm guessing it is a pure mechanical thing that could not be prevented...like torque shaft flex. Glad you are so happy with your cooler.

greg brown

PorKen

If the Engineers knew it was a going to be a problem, why would they discontinue the use of the retaining circlip, then delete the circlip groove, at the same time that engine torque was increased? Because it was too difficult to set up in the field, or did they say: "fugedaboutit"?

They did increase the diameter of the center section of the shaft, but this didn't stop the flexplate problem (it may have created a stress riser where it is necked down, though). So I'm guessing they were either barking up the wrong tree, or they didn't go big enough.

RngTrtl

Porken, I have been wondering about the same thing. I release mine about every 1000 miles or so with the same 3-4mm of movement that you have. I am going to be installing a tranny oil temp gauge into the pan in a month or so and am thinking of doing that same the you have done with the tranny cooler upgrade. I will keep yall posted, hopefully with similar results that you have found.

Bill Ball

Keep evaluating it, Ken. It is so variable, a couple of checks are not enough. We just checked George Suennen's flexplate a few days ago after a period of at least a year. Maybe 1mm movement as opposed to the usual 3-4, and he drives the **** out of his 438 HP 90 S4.

IcemanG17

Very interesting......I'll keep following this.....if I continue to track my 88 & if it ever gains some serious HP-Tq than I will look into a better cooler.....

It does make sense that torque winds up the tube then releases it causing the problem....interesting that GTS's have it worse...but an extra 50ftlbs will make a difference!

jetrainor

I know of an easier solution however it may not still be available.....i purchased and installed one of Constantine's flexplate clamps when i put my new engine in after TB failure.....4000 kms later, much of it spirited......not a millimeter of movement on the spined shaft and no pressure on the flex plate...a wonderfully engineered but simple solution for automatics. Just my 2cents worth

87 euro auto

Bill Ball

Constantine's clamp or, at TT time, use of an early style TT with the circlip retainer, do the trick.

Black Sea RD

Glad to hear it's working for you and you are enjoying your shark again! Thanks for the good news and kind words!

Constantine

Black Sea RD

Not to start a long debate about this subject matter, but our research supports the statements made above by Gregg B. which are spot on.

Also the Porsche AG driveline engineer I exchanged emials with said the reason the drive shaft was enlarged from 25mm to 28mm was to cope with the added torque of S4 and later models.

Constantine

heinrich

I am in agreement with Greg and Constantine.

borland

You can locktite the splines or Constantine clamp it, but your worn out deep groove torque converter bearings will still look like this....



Replace them every 75K miles and be worry free. The reduction in drive line noise is reason enough for me.

PorKen

If you don't go with a rear cooler, I would suggest at least converting the banjo fittings on each side of the trans to straight through.

IIRC, I have a circlip groove on my driveshaft, I could add it. But it hasn't moved, and I didn't do anything but reduce the transmission oil temp, and made it easier to pump.