5L40-E Hard Shift 4->5, dark oil, BMW code 37

[Esgra]

Hello all! I am new to the forum, but I have been using it for at least 8 years as a guidance to repairs on my '05 X5.

About a year ago my transmission hard shifting from 4th to 5th speed. It has caused a couple failsafe modes, and it seems to be isolated to hard acceleration, especially when the engine is still relatively cold. It also makes a "squeal" when this happens, which quickly resolves (about 5 sec). I thought it could be something innocuous, so I changed the fluid and filter as a starter. I used ACDelco synthetic Dextron V ATF (it is a GM transmission). After changing the oil, the symptoms did not alleviate, so I double checked that I added enough oil.

When changing the oil, there was some metal stuck to the pan, but it was a small amount (sort of a slurry). However, when I checked the oil (probably a month later), I noticed it was very dark.

About 3 months ago, I drove the car and noticed a spontaneous downshift from 3rd to 2nd, but I could not repeat it. I was also able to record a BMW code 37 on INPA (Gear Monitoring 5).

Anyone have any idea what the issue could be? Right now, I do not drive much as I have the car in a storage locker. I imagine I am looking at a transmission overhaul. If so, does anyone know what I need to overhaul (just the valve body, or the whole works), and where I can find parts?

I am willing to rebuild it when I find time, and I will write-up my work as well.

[80stech]

If the oil is dark/burnt there is probably a clutch pack slipping.

[RRPhil]

A dodgy 4-5 shift could be down to an accumulator issue (possibly a broken spring)




or maybe the shift solenoid



However, burnt oil clearly isn’t good and could relate to a fault with the overdrive clutch.



This clutch is also used in Manual 3rd gear to provide engine braking. Can you feel overrun braking in 3rd gear when selected manually?

Phil

[Effduration]

junkyards are full of X5's, and I don't think a used transmission will ever be cheaper...
I suggest you buy a used transmission of the same type.

You may end up rebuilding yours, but I would probably just swap in a replacement.

a quick check on car-part.com shows several near me for $350-$600...

[RRPhil]

If you do replace it, you want a YZ model (24007525323).



If you fancy having a go yourself, 13 years ago I did a bit of a write-up, here: https://xoutpost.com/837639-post1.html

The biggest issue is the heavy-duty circlip!



Phil

[Esgra]

RRPhil, thank you for the reply. I haven't been driving it lately, but I did notice a "slip" on third. I was coasting and the engine sort of picked up RPM briefly. It almost felt like a manual clutch disengaging. It could have been absence of the overrun braking. I will have to drive it around to see. Yes, the oil was very dark despite just recently changing it. It could have been the remnant fluid, but it was, in my judgement, way too dark - almost black.

I could find a used transmission, but a lot of X5's from that era are in the same high mileage range as mine (190k). Honestly, even though it has been a great car, I am thinking of supplanting it with something else as it may become a reliability issue in the future.

If I take on a rebuild/replacement, what else should I do to the car to extend its usable lifespan? My goal would be to make 300k miles. I have replaced the oil pan and valve cover gaskets, alternator, HVAC fan, power steering rack and pinion, CCV ventilation, various leaking hoses, break lines, almost all suspension bushings and ball joints, struts, and some other minor repairs and upgrades. Would a VANOS rebuild be in my near future?

[X5chemist]

Has the trans oil thermostat ever been replaced? They have a tendency to break. A non cooling transmission will not last long.

[Esgra]

Not yet. I’ll add a new thermostat to the list. Does the cooler itself tend to go bad? I have a suspicion of a coolant leak somewhere but have not been able to track it down. I did not see any oil in the coolant reservoir, and the transmission oil looked fine (other than black) when I changed it and topped it off. It could also be the expansion tank but I’ll have to look around for any leaks. I have a code for a bad aux coolant pump so I’ll be changing that soon as well.

[X5chemist]

Mine had a coolant leak at the cooler. A new mounting plate and seals fixed it. The thermostat was in pieces when I took it out. Yes, the cooler can go bad. Easy to replace too.