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Wondering if it's possible for a faulty vacuum kick-down modulator to put the transmission into a no-man's land between neutral and engaged, where no selection can take place.
Or maybe a leak in the vacuum line, causing the modulator to be partially operated, giving the same result..
Since you've turned your transmission inside out and found everything to be ok, IMHO, given the failure event was so gentle, I would have been surprised to have found any major breakages.
Just a thought.
UpFixenDerPorsche.
PS: also curious about no reversing lights but think that's a separate issue.
Last edited by UpFixenDerPorsche; 06-02-2021 at 12:22 PM.
The modulator applies a controlled amount of vacuum as defined by the adjustment selected. The amount can vary from very little to quite deep vacuum. If there is no vacuum the shifts will be rapid but firm if there is vacuum they will be slow but smooth. More to the point if there is no vacuum as in the line gets disconnected or blocked the shifts on part load become very hammer like as in they feel as though they may harm the tranny type harshness. Some kind of "false neutral" does not seem possible.
On the other hand if the actuation system pressures are not where they should be it is not too difficult to visualise that the planetary gear setup might just end up in some kind of "no mans land" not able to resolve the gear arrangement that is required given such is controlled by pressure.
Wondering if it's possible for a faulty vacuum kick-down modulator to put the transmission into a no-man's land between neutral and engaged, where no selection can take place.
Or maybe a leak in the vacuum line, causing the modulator to be partially operated, giving the same result..
Since you've turned your transmission inside out and found everything to be ok, IMHO, given the failure event was so gentle, I would have been surprised to have found any major breakages.
Just a thought.
UpFixenDerPorsche.
PS: also curious about no reversing lights but think that's a separate issue.
Hi John,
We have checked the vacuum line from transmission to engine. It is good.
We have also simulated a vacuum with a pump plugged on the modulator. It was good since it did not solve our issue.
I am looking at pictures of my valve body taken on february, 21th. See post #134 in page 9.
Do you see something strange ?
I see only 17 *****, and no ball in holes 4, 13 and 14. And 2 ***** at the wrong place.
I check with with the following diagram (WSM page 38 - 130a, 87 models onward).
Certainly, if the valve body is not assembled correctly, you would expect there to be problems with the transmission.
I only see pictures of the valve body halves apart, with ***** and pieces mostly on the separator plate.
I don't see any pictures of the valve body cleaned up and ready to screw together.
The pieces tend to go everywhere, with the tiny springs required difficult to keep track of.
Did you completely disassemble all of the pistons and springs from the two halves?
I assumed you had and were following some sort of document to tell you where the pieces all go.
I wouldn't dig into this matter yet. You don't want to open a can of worms or open to many 'construction sites" at once. Working pressure needs to be within spec. to give the tranny a chance to work.
I stumbled across this 722.3 valve body rebuilt pdf on the net. On page 5, # 26 shows the working pressure control valve. I don't know how far you guys dug into the valve body and if all plungers and valves were taken out for inspection plus cleaning.
If working pressure is still too low, this would be a good place to start. I once had an Audi that lost engine oil pressure completely from one second to the other. Later we found a very small piece of metal in the oil pressure control valve, it was locked into the open position. After removal, everything was fine again.
After all that was done so far, try to go step by step.
Did you completely disassemble all of the pistons and springs from the two halves?
I assumed you had and were following some sort of document to tell you where the pieces all go.
Hi Greg,
Yes, we completely disassemble all of the pistons and springs from the two valves.
We followed WSM, old rennlist threads and ATSG documents.
I think it could be good to check and to clean again the valve body.
You can clearly see in this picture that while the transmission was fully disassembled the modulator was not removed. Under it there is a piston that it moves. Please remove and inspect this.
Also, while the transmission was disassembled and every seal replaced this makes the air checking of the circuits even more important as it is very easy to damage a seal when reinstalling no matter how careful you are. After the transmission is assembled and before it is installed you should always air check the circuits in case you miss something!
Lizard,
I have checked with the team. The modulator has been removed and cleaned by air before this picture 😉
BTW. I did a brain storming I am sure that the pan has been shocked by my (ex) "friend" when the transmission was hot. When I wanted to drive it two days later, the transmission was cold. Maybe something was dilated at the time of the shock, and it broke when it was cold.
About working pressure and valve body, we will work on it on next week. Very busy this week ...
About the 18 ***** and springs, is it the same diagram between S4 vs GTS ? I have shift-valve body ref. 722 250 430 7.
Last edited by Fabien92; 06-09-2021 at 12:04 AM.
Reason: picture
06-02-2021, 11:37 AM
I am sure that the pan has been shocked by my (ex) "friend" when the transmission was hot. When I wanted to drive it two days later, the transmission was cold. Maybe something was dilated at the time of the shock, and it broke when it was cold.
