Yes, port 1 is the correct one for feeding the B clutch. The second running seal on the stator shaft (the one near the end of the shaft, furthest from the torque converter) seals the B-clutch from the A-clutch so the chances are that air is getting by this seal when you’re testing it.

https://i260.photobucket.com/albums/...ps4eeb576d.jpg

The running seals get hydraulic pressure under them when they’re rotating, to provide a good seal. I can see that you’ve put Assemblee Goo, or similar, on the seals to try to get them to seal more effectively for your static test with air.

The whole transmission has to be fully assembled before you test the clutch hydraulics using the channels on the underside of the maincase. It’s usually the final test on a rebuild before the valve body assembly is fitted and the sump pan goes on. 5 bar should be fine for testing with air.

Phil

Yes, I would connect both and do exactly as you say. Clear the fault codes and then see if they return.

Both the fiber seals on the stator shaft are brand new. If I understand you correctly, air should not be able to get past? Could this cause the trans to go into fail-safe and throw a P0751 code?


Since I'll need to reassemble the whole trans before testing the clutch hydraulics, is there anything else I should check before I do this?


I have not checked the sealing sleeves (as was mentioned in previous post) but I'd be happy to if you think it's a good idea.


Thanks!

Awesome! I'll check that out tonight.



I vaguely remember getting a wire stuck between the bell housing and the flex plate the first time I reinstalled the transmission. I wonder if that was the 16 pin wire and I ended up damaging it :(

Hi Phil,


I'm beginning to feel as though there is really an issue still within the A/B clutch assembly.


I used to get inconsistent results when I performed the static air test. Sometimes the B clutch would actuate from port "1", other-times nothing would happen and it would just leak air pressure. Same thing would occur when checking the A clutch from port "2". I found that one of the fiber rings were damaged on the pump shaft. After replacing them both, I did a quick retest and assumed the problem was fixed.


Here's a short vid of the test where you can see the clutch responding but also hear the air leak: https://photos.google.com/share/AF1Q...U0WWRmMHBVS2FR


This evening I did that air test again and I could barely get the clutch to actuate, even at 50 psi. You could see that it was trying to move but it was failing to pressurize enough to respond.



I had pulled the A/B clutches apart before, expecting to see a visibly torn o-ring but everything was in one piece. Now I'm wondering if the o-rings were just too flattened from age to seal correctly.


Below is a pic I had taken of the A clutch (sorry about the quality). It almost looks like it is deformed at the top right-hand side.


Attachment 77690


What are your thoughts on this idea? Do you think, theoretically, that failing seals within these clutch drums be causing my symptoms?



I also took the pump housing apart just to be sure. I only found one o-ring around the perimeter but it too was in one piece. Is there anything else within the pump that could leak?



Below are pics of the disassembled pump housing:



Attachment 77691
Attachment 77688
Attachment 77689

Maybe this is a clue? If this is the case, can these seals even be tested with air under static conditions? :dunno:

TriX5,


I had a chance to do a visual inspection of the 16 pin cable going to the TCM and there was no visible damage. I didn't have a chance to test for new codes though I think I may have stumbled upon my issue.


I think the seals are bad in the A/B clutch drums which is causing a critical pressure leak. I thought the seals were good to go because I was looking for visible damage but as you can see in my post above about the A clutch seals the they appear deformed from age.


I think you recommended me changing them all the way back on page 1 :D

Hammer - Yes, O-rings deform when pressure is applied. However, over time they become much stiffer and less able to take the shape needed at point in the duty cycle. They take on a squarish shape if you would look at them in section. In the X5 transmission the fluid runs quite hot as it goes through a heat-exchanger at the bottom of the radiator. In my view this means the O-rings age even quicker than air-cooled transmission applications. (Transmission cooler is a misnomer in the case of this application, I feel it heats more than it cools...)

Hence my belief that once one bothers with the effort of removing and opening an AT, the minimum is to change all the seals and rings.

I am impressed with your efforts on trouble shooting this! Once you are sure the trans is mechanically sound any remaining issue should be electrical.

I think you’re getting overly concerned about the air pressure testing. Static seals like O-rings respond well to an air pressure test. Dynamic seals don’t. If you’re rebuilding the transmission you need the overhaul kit which includes all the gaskets, seals and plugs.

https://i260.photobucket.com/albums/...psvubhi5vs.jpg

https://i260.photobucket.com/albums/...psjqttadc3.jpg

Some of the phosphor bronze bushes in the transmission also act as seals for the clutches so it’s important to check them for wear. Ideally you don’t want a radial clearance greater than 25μm.

https://i260.photobucket.com/albums/...pssuiagsir.jpg

If you replace the seals and check the bushes, the clutches will be fine. I feel this is distracting you from the P0751 problem, which is an electrical/electronic issue.

Phil

Sorry, I wasn't trying to circumvent the diagnostic process. I've read that P0751 could mean both electrical or mechanical faults, some claiming that even low trans fluid could cause this code to pop up.



I'm just trying to eliminate every possibility so I don't end up having to pull this trans again.



Being on such a tight budget, I did not use a rebuild kit and only replaced the one split o-ring between the A/B clutches. All the other clutch seals are original to the car (other than the split fiber rings). At this point, should I bother replacing these seals?


Given that the code is implying an electrical fault and I've done the bench tests with no evident failures, do you think the solenoid itself is bad? What other electronic diagnostic tests can be done?


Again, I truly appreciate you helping walk me through this problem!