transmission doesn't engage

[85MSteinway]

Just brought my L6 out from under the cover to enjoy this year. Everything works fine for a few minutes. all gears engage. After a short time it starts slipping and then acts like its in nuetral. All gears including reverse. 3-2-1 selector knob doesn't make a difference. turning off the car and waiting a couple minutes before restarting will put the car in drive for a few minutes before symptoms return.

Transmission fluid might have been a little low, its hard to get a reading on that stick. I added until it was clearly at the max warm level. That didn't make a difference. The only other thing is my Brake Lining light flashes, more like there is a short than a warning. Which might be the case since I had to snip the rear sensor wire when I did a brake upgrade in the fall. Its possible my handy work is faulty and its all just a coincidence, but figured I'd add that bit of info since its a new issue.

Anyone have some advice and where I should start loooking? Thanks

Jay

[plip1953]

Please bear in mind that I know very little about auto boxes, but always enjoy trying to help problem solve, and thereby learn new stuff from that.

Having previously experienced a slipping box (not in an E24), it was simply a case of adding fluid and then all good again. You've already done that and it's made no difference, but is it just conceivably that the old fluid had deteriorated to such an extent, and especially so when hot, that it's effectively lost it's ability to function. More a thought rather than said with any conviction!

The other thought concerns your likening it to being in neutral, although you suggest that the transition from having drive to no drive is relatively gradual rather than sudden. My assumption had always been that selection of park,reverse, neutral and drive were achieved purely mechanically, but perhaps that is completely wrong? But if that is actually the case then I don't see how neutral might become "self-selected" unless the lever also moved?

The brake warning light aspect is interesting, and I could maybe see how it might in some way interfere with the switchable modes function (although does you car have that?), but struggle to see how else it could affect gear selection/drive.

Almost certainly none of the above will have been of any help, but I'm certainly intrigued to see what the experts might have to say.

[85MSteinway]

In regards to "neutral" it isn't dropping to neutral, just that is the way it behaves. it slips, almost like a worn and heated clutch would, until there is no engagement at all. And then it acts as though it were in neutral. Ie: pressing the accelerator just revs the motor even if it were in drive etc. turning off the engine for a just a moment and restarting will get things working again for a short time (1 minute)

Today I'm going to drain the sump. I've never been inside, but my 5 series manual says there is a filter inside. perhaps I just need to give it a cleaning and replace all the fluids instead of just adding a dose. I will follow up with my results.

[plip1953]

In regards to "neutral" it isn't dropping to neutral, just that is the way it behaves. it slips, almost like a worn and heated clutch would, until there is no engagement at all. And then it acts as though it were in neutral. Ie: pressing the accelerator just revs the motor even if it were in drive etc. turning off the engine for a just a moment and restarting will get things working again for a short time (1 minute)

Today I'm going to drain the sump. I've never been inside, but my 5 series manual says there is a filter inside. perhaps I just need to give it a cleaning and replace all the fluids instead of just adding a dose. I will follow up with my results.

That makes good sense. It did occur to me whether the filter might blocked? Some years ago I asked my local garage to change my gearbox oil and filter (which I'm pretty certain has never been done in over 30 years ie since new), but they were concerned that some of the sump bolts might shear, and abandoned the task. So as a side issue I'd be interested to know how you get on with the sump removal.

[85MSteinway]

ok well, sheared bolts sound terrible. Maybe I'll just do a 100% fluid change first before moving on to sump removal.

Jay

[85MSteinway]

changing fluids didn't change anything. exact same behavior. tomorrow I will remove sump to inspect magnets/filter.

Jay

[85MSteinway]

Ended up having my local shop take a look. they put in a new filter and sealed it back up. All is well again. In fact I'd say it performs much better than it has since I"ve owned it. They said it had a good deal of metal shavings in it.

Jay