I could have told you that you're losing pressure... But nothing is safer than measuring
The problem is that you still have oil in the pan when pressure dissappears = pump should be getting oil. There's really nothing that can fail in the pump so we'll have to look elsewhere.
What causes pressure to drop after half a minute? To me it really sounds like it runs out of oil but I guess we'll have to rule that out and think of other causes.
If the filter comes lose you will need an additional 2-3 cm of oil in the pan to ensure the pump gets what it wants. I now think you have enough oil even if the filter would be lose but I'm not 100% sure.
Oil level is not changing even if the pump is running. Sounds impossible to me but who knows... We know the pump is working running as we have line pressure and the car is moving.
EDIT: Maybe the filter screen really is clogged...
Drained the oil, and it is a tad darker than new.
When i took down the pan, large lumbs of a soft nonmetallic material is in the bottom, and the filter is partially clogged.
The material in the pan was collected on a piece of filterpaper and washed down with brakecleaner.
This reveals a green/greyish fibrous material, which i assume is coming from one or more of the friction discs inside.
This is apparently what has been going on:
The transmission released volumes of this fibrous material from somewhere and the fibres quickly clogged the oil filter.
Because the material is "sticking together" it flakes off the filter when the vehicle was resting, dropping the material back into the oil pan. When i then restart the car it takes a few seconds to suck it back up into the filter and reclogging it again.
So....what to do now. The gearbox had only 6000km + my 200km on its back, so i sort of hate to leave it here.
Im getting concerned that the Castrol DEXRON III multivehicle oil might have played a big role here? Or else it was just the age that killed whatever is missing inside somewhere.
EDIT;
Think about it....The previous car had this box in for 6000km, was left out of service, but started and moved around now and then for some 7years or so, then i fitted the box, and maybe the biggest mistake i made was to give if some new oil....? I have a hard time accepting it, though. When i dropped the pan, the pan was clean, and the oil in nicer condition than now. Hmm...
Either TIME, or OIL caused the fibrous material to come. What else was changed that would have caused this sudden change?
Checked my books and you've been running way too much oil from the beginning. 7,5l is the magical number of which 2,5l in the TC,and the 7,5l assumes the whole system is completley dry. So 5 litres would have been the right amount in a completely dry box. When you later did the cold / engine shut test there apparently was not enough oil.
Is it possible that the box has been slipping for you the whole time, filling the pan with gunk?
Otherwise I can't really tell you why the gunk is coming lose but here is what I would do:
1. Clean up the pan and filter and install.
2. Fill the box with the right amount of oil.
3. Flush it.
3. Enjoy your working box for some 100 kms.
4. Repeat. Use a new filter this time.
EDIT: Is there any chance you were in gear when topping up the oil the first time?
Cleaned the pan, let as much oil as could drip out, emptied and cleaned the filter with ultrasonic cleaner(marvelous machine), reinstalled everything, filled it up with new oil, it has taken approx 3,5liter and is now right between min and max with engine idling in P, after all gears has been shifted through.
Remarkably, all gears are working flawlessly, despite the gunk is missing from somewhere.
Pressure in Neutral idle, 5bar, 8,5 in reverse, 5 in D/2/1. Pressure increases to 9,5 when i pull the kickdown wire in idle D.
The million dollar question is why it generated the gunk, and that i dont have a good answer for.
I dont think it has been slipping, but on the other hand, what else could it be? The shifts were really firm, and gave a good impression of a sound box. Could it be that the gearbox was dragging on other gears ?
Currently there are no signs of something dragging or slipping, on the other hand, i must be missing a substantial amount of friction material somewhere now.
The first fill was done according to the service manual, so i actually dont think i was way high in the initial fill, but it looked like it on the oil stick once the filter became blocked. I think the fluctuating level was just the pump dumping air into the oil.
The car was running beautifully, and the incident happend after just 5-7km of driving. All other drives was done with warm car, this was actually the first time the car was driven in near zero temp. The particles in the pan were rather "crude" and fibrous, looking like something was torn off, more than slow wear.
Ok, maybe the TC will lose some oil during standing. Haynes says 3,9 l after pan removal so that sounds quite right.
I earlier reacted to the color of the fibres, green? Do you have a picture?
I thought the frictions are always red/brown. Here is a pic from my last overhaul:
Forgot a rag in the box?
If the pump would be dumping air in the oil, where would that air come from?
EDIT: Googled around a bit and found a guy with pretty much the same problem. Suddenly gunked the filter and lost all gears. Gunk away, work again. Only problem he found was a bit to much oil. Maybe it will cause dragging.
First picture is the view in the oil pan. None of this was magnetic.
Here we are looking up the screen. The gunk is falling off the screen, and is resting on the bottom of the filter frame.
Looking into the rest of the oil drained in the bucket after settling/draining it also has a considerable amount of gunk.Turning the bucket here makes it visible in the corner.
First filtering of the first 0,7liter i lowered the volume with initially. The fibres are visible.
After filtering what was on the bottom of the pan, still wet:
And finally after washing it down with brake cleaner. This is where the colour becomes evident.
I did twist my brain a few times if i should have forgotten anything, inside, but even if i did, then how would it be granulated like this?.
In case everything goes down the drain, i will be looking at dissecting this box to know what was wearing. Do you know of a good source for repair/overhaul kits for the AW71L?
I don't think that look like friction fibres but I may be wrong.
I paid my (not so) local automagicshop (JN-Trading / Finland) 210€ for all frictions, steels and gaskets. Alto brand, original quality (they said). Alto makes high-perf clutches as well.
It was sprayed down in brake cleaner and dryed with compressed air.
Its going to be interesting what this actually is.... Thinking about getting it analysed for composition.
I have microscope capacity in the shop, so maybe i will look into it later.
Quick and dirty flame test reveals the colour of the green material found in the tray flames up bright green, suggesting the majority of the ingrediense in the powder/fibres is copper.
Secondly it does not burn away even when redhot, so it is definetely not plastic.
Here is a picture of the AW pan content after an overdrive burn-up. The big chunks in the rear of the pan are melted and hardened friction material. Also note the black strains in the oil. That's friction material. Note that this gearbox was fully driveable, except for the overdrive.
Cleaned up the box, flushed it, everything was fine. Starting to drive it around in normal driving. The box lost drive almost the same place it happend last, after equal kilometers.
So;
6000km in donor car.
200km with no issued.
6-7km from cold one morning, then clogged.
Flushed and cleaned everything out. work flawlessley for 6-7km, then clogged up again.
Partly stripped it down.
Several of the discs are still having the part number printet on the frictions, so not much wear, exept on one of the assemblies where all 5 frictions are missing 0,5mm, and the steels are blued/cracked.
Obviously it has been dragging under power, but not really noticably.
This is the only place i have found an issue. GB seems too good to discard, but what caused it the first place?
Risc by replacing steels and frictions on that assembly is that it will come back again. Can it be the oil feed to that clutch is not providing enough clamping force?
Let's refresh my memory, is it the brake mostly to the rear end of the box? That one should be engaged in 1st an reverse. Maybe too little play due to some crap in the piston assembly. Sounds like a quite light dragging as the clutch / brake did not burn up. I'm having a hard time believing that the clamping pressure would be reduced at only one piston assembly. If you're a hardcore badass you could probably drill a hole in the right spot and measure :p
Overhauling the box (including valve body) is pretty straight-forward, although a bit timeconsuming. If you're interested in buying only needed plates, I may have some new and some old but working plates.
Line pressure was on specs according to the AW71 manual for the 240(greenbook). Could not find one for the 940, assumed it was pretty much the same.
Now, im not too strong yet on the oil path in this box(first time inside an autogear), but i have traced the piston flow back through the ports, ok, back through the shaftseal, seals look as new, followed the path back to the housing, also ok, nd thereon it gets into the valveassembly, and here im getting concerned. Many has told me that the valveassembly is irrepairable, and that if there is a fault, then i will never find it. Now, thats a challenge....
I havent yet checked if the piston clamping the clutch package is physically frozen, will check this tonight, including the piston seal.
