Catfood

So I'm pretty sure my 928s torque converter is on its way out. Help me ensure this is the right diagnosis before I tear into it.

My 928 has 191K on the clock and I have no record of transmission intervention.

I took a long trip about 200 miles and on my way back the throttle and response started to have a bit of distance between them. When I leave a stoplight I have sluggish response and the car will then have thrust, but when it tries to shift the tach will rise and is weak until I feel the car grab the next gear and then it will accelerate.

When I go to pass people it will take forever to get power and then go like a rocket as usual, but when I head towards a turn and lay off the gas and tap the brakes to set the suspension and then get back into the power it hunts for a bit as the tac rises and I wait then it finds a gear and I can go.

It does this under low acceleration and full throttle, but is consistent. I can rev the motor and start acceleration and it seems responsive but as soon as the next gear is concerned I sit and wait as traffic passes me by until it finds 2nd.

Im sure this is the torque converter, my question is what do I do to ensure to fix the problem when I get it under the car lift?

Thanks guys,

Catfood

928porschepatrick

Did you do a stall speed test.

Catfood

What does a stall speed test include?

928porschepatrick

The WSM at page 38-103 tells you the procedure.

Podguy

There are other things to look at. The first thing to do if you have not done it is to change the fluid and filter. When you take the filter out pull it apart and see how much junk is in the filter. If it is corrupted then the transmission is not getting enough fluid pressure. When you change the oil be sure to drain the torque converter too.

Second check for leaks. If you see oil on the bottom of the torque converter housing then the next place I would look at is the o-Ring on the front pump. If it is leaking the front pump will lose pressure and your transmission will act the way you describe. You can change the o-ring and front seal with only minor intervention into the transmission. It does not take much of a pressure loss to have some weird behavior. The Mercedes transmission is a lot more touchy than american trash that will get you home even with fluid pouring out of the transmission.

And I should mention this - what is your fluid level like. It has to be with in spec or things get strange.

928porschepatrick

if you trans is slipping upshift it could be an incorrect modulating pressure
or if you car is slipping during 2-3 upshift and then grabs hold it could be the K1clutch assume your car starts in 2nd gear

Bill Ball

Although some of the symptoms could be the TC, slipping during shifts does not sound like the TC, but more like the tranny clutch bands or other factors as Patrick mentioned. When you say no tranny intervention, I hope you don't mean it has not had regular fluid and filter changes. Those are an every 30K mile maintenance item. My tranny gets tempermental if I don't do that religiously. And like Dan said, these trannies are very sensitive to fluid level. So, attend to that first.

If you are sure it is the TC and want to replace that or have it rebuilt, you have to remove the tranny. The steps are covered in the WSM, but it basically dropping the rear suspension and crossmember, then the tranny. It can be done on high jackstands.

Mrmerlin

check the fluid level first ,
then smell it for a burned smell.
I will bet it needs to be topped up and changed
( changing the fluid will cure the low fluid as well)
make sure to drain the TC and swap in a new filter
Use Valvoline Max Life Dextron V,
red bottle you will need to have 10 QTS on hand,
though use only 9 the rest is for topping up can also be used in the power steering

WallyP

"Use Valvoline Max Life Dexron V"

Two comments:

First, Stan has a typo. He meant Dexron VI, since there was never a Dexron V.

Second, GM says that they tightened the specs for approval of Dexron VI enough that any fluid meeting the spec is actually equivalent. The SuperTech fluid at Walmart is quite a bit cheaper...

BTW - all earlier Dexron licenses have expired or been canceled by GM. There is no longer any enforcement at all for conformance to the earlier Dexron standards. On the other hand, GM is rigorously enforcing conformance for the Dexron VI.

Mrmerlin

Thanks Wally your correct, its VI.
Max Life seems to work well in the 928
http://www.valvoline.com/products/brands/maxlife/

Catfood

This seems like a good set of steps to take. The fluid level on the transmission is fine it was the first thing I checked. Im thinking it must be a seal, as I changed the transmission and fluid about 15,000 miles ago. At least its not as expensive of a problem as I was thinking. Time to go

Thanks guys.