2001 BMW 530i 5hp19 WEAK reverse

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So about a month ago during a snow storm I seem to have lost reverse in my 209,000 mile 530i. This transmission is known for shearing apart its revrse drum, but I'm not sure that's the case here: when it's COLD, reverse functions at idle for a few feet. If it warms up, or if you hit the gas, there's nothing. But if it's cold, it will idle back into a parking space.

If the drum were broken, would it do this? Or is the solenoid/clutch just shot?

The car is sitting in my garage and I'm thinking about dropping the pan and changing the fluid and filter once the temps warm a bit (I'd prefer at least 20F outside) just to see what happens.

I bought the car last spring with the hopes of using it as my winter beater, but I've found that not having reverse makes driving a lot less convenient.

BTW all forward gears work as intended. It hunts for gears as good as it did, but drives just fine, going forward.

Thoughts?
 
First check is fluid level...

Cold fluid is a lot more viscous, so a worn band/clutch might function with thicker fluid, then go away when warm...but I've seen odd behaviour with low fluid level...how difficult is that to check on this car?
 
I replaced the reverse drum in my 5HP19 (2000 323i) a couple years ago. It is possible that your drum is cracked, but not completely broken. The crack would allow enough pressure to operate the clutch pack when cold, but as the fluid warms up the pressure would become less as more fluid would leak out of the crack.

If it turns out that it does have a cracked drum, the front lower valve body needs to be inspected. The main pressure valve is housed in the front lower valve body and it wears a step into the casting over time. The step that wears into the valve bore prevents the main pressure valve from operating correctly. The resulting high pressure breaks the drum.
 
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