1989 760 Turbo overdrive issues

I have a 1989 760 turbo with 195,000 miles. Automatic transmission.

Overdrive functioning has been sporadic at best, functioning most reliably
when outside temperature is in the 80s (F) or so. I've replaced both the
solenoid and the relay (with new parts), with no change in overdrive
behavior. Now that the weather is turning cool, it doesn't work at all --
even after a long drive.

What's the next thing to check?

Thanks,
--Dale

 

Does the solenoid get power?

 

I assume that it does, because the OD works fine at some times.

 

Check it though, intermittant problems are often electrical.

 

Could be the return valve spring thats gone, it lives under the plate that
unbolts from the bottom of the O/D unit. check here for a brilliant
description of the unit, its the same one.
http://www.buckeyetriumphs.org/technical/JOD/JOD1/JOD1.htm

 

But this is an automatic tranny, the OD is located inside the tranny near
the front end of it.

 

Really? Sorry, I assumed it would be bolted on the end like the M46.
Apologies for bad info. I must take a closer look at my new aquisition. It's
got an auto box with over drive, but I must confess I haven't been over the
car yet. H Reg with 75,000 dealer serviced miles on it. Runs like a dream
compared to my C Reg with 320,000 abused miles on it. Must take a look at
the Haynes manual automatic box section to learn it.
Thanks for the heads up James.