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Internally, there isn't very much that 2nd, 3rd, and 4th gear have in common to make them all slip.
There's a section on "Troubleshooting the Automatic Transmission" in the workshop manual (starting on page 38-111.)
The very first entry is "Condition: Transmission slips in all selector lever positions".
I'd probably start there....
Hi Greg,
yes, we will start by the first entry in 38-111. Check of modulation pressure and bowden cable. On next week. 😉
Hi Gazfish,
You’re right. My failure was easy to solve before to rebuild all the transmission. But it’s done, and easy to say at the end. All used parts have been changed, it’s always a good thing. In the team I am the newbie 😂. My two friends are very good mechanics 😉 But it was the first time on a 722.3. They have rebuild the transmission on their wasted time, for nothing. I am not sure that a professional takes time to understand the problem. He takes a spare transmission.
We are on a lost covid free island in South pacific 😂 not easy to find the good mechanic and the good spare parts in local.
My friends did a very good job, and I learned à lot about my 928 😊
We will solve this last problem, with all your help 😉
Greg and others here are a lot more experienced than me and can chime in, but my guess would still be B2 slipping when the fluid is cold for some reason. Sticking piston, wrong pin length, low pressure, or some other issue preventing it from clamping properly. The fact that the higher gears are ok means it’s not the torque converter. As mentioned a few times here, knowing the pressures is key before you dive in again.
I don't know what your problem is, from here, but It's super easy to "fold" the edge of the sealing lip on the B2 piston seal, when inserting the B2 piston.
(This has happened to me.)
And it is impossible to see if part of the lip is folded, with the entire B2 piston installed.
I use an old B2 piston that I have cut the large piston part off to help me not have this problem.....all that is left is the part that normally goes through the seal.
When I install the new seal, I temporarily insert that cut off part through the new seal for about 30 minutes. This enlarges the seal closer to the correct size.
Because the "big" part of the piston is gone, it is simple to see if the seal folds.
After doing this, I have not had any issues with the seal lip folding under when I install the B2 piston.
Pretty simple to pull the B2 piston and check the seal, with the transmission installed....
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Pretty simple to pull the B2 piston and check the seal, with the transmission installed....
Thank you Greg !!
we will check both B2 piston and modulation pressure. 😉
BTW. What is the vacuum value in the hose from the engine to the transmission (to the pressure control valve) ? We would like to check if the hose is not cutted off.
No vacuum at the 5 way splitter is not good at all. What about the brake booster is it working? AC vent flaps are all working?
Check if you have vacuum at the front presseure damper line first, it uses the same dynamic vacuum source. Your car must shift very hard without any vacuum at the modulator!
If there is no vacuum in the feed line to the 5 way connector, there must be a disconnected line under the intake.
Check if you have vacuum at the front presseure damper line first, it uses the same dynamic vacuum source. Your car must shift very hard without any vacuum at the modulator!
If there is no vacuum in the feed line to the 5 way connector, there must be a disconnected line under the intake.
Hi Schocki 😉
Thank you very much. I will check that today.
And what about my modulation pressure at 4.6 bars from 0 to 140 km/h. WSM talks about 4.4 bars at 140 km/h or 50 km/h, but nothing about all the range speed.
Modulation pressure is measured with the vacuum line at the modulator disconnected.
The test is designed reach a desired pressure at a fixed speed.
How does you car shift?
07-30-2021, 07:01 PM
