Hey all,
I have a 91 silver 740 automatic tranny that has had problems with overdrive not working until its warmed up. Now its not kicking into OD at all. Is it dying? I have 225,000 on the car. Any suggestions on what to do?

definatly get a new O/D relay Also dosen't hurt to clean or replace the tranny filter good luck!!

There is a green wire (at least it was green on my 87) that runs from the shifter OD button to the transmission. Due to being exposed to the elements, a lot of times it sheds its insulation and shorts out against the aluminum transmission case. When this happens it can fry your OD solenoid. I was lucky mine just had grounded out my OD, the solenoid was undamaged. Check to make sure this wire still has its insulation intact.

The OD relay is often the problem. It may be fixable- or you might need a new one. Part number is 3523804. On your fuseblock, it's the right front corner relay and the tallest one in the block. It's the farthest one from the driver's seat on a US-model car. Remove the coin tray and cig lighter piece, but pulling off the cig lighter trim and remove two screws in the left-hand edge under it. The coin tray turns and pulls out then.
Do yourself a favor and mark the side of the relay facing you- that will help when reinstalling. It just pulls out of its socket. See the 700 FAQ- Relay Locations for a picture.
It can be opened up an re-soldered internally or simply replaced with a new one. It's the simplest fix and beats the heck out of replacing an OD solenoid.
A fluid change is always a good idea- every 30-50K miles is recommended. No need to change the filter though- just open the top radiator cooler line and flush 6 or more quarts through it. neat and easy. See the FAQ. Don't even need ot get under the car, and you won't spill a drop if you're careful.
--
Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

Look at my post this same day, 1/16/04, on 240 automatic transmission overdrive problems. It may be helpful; I don't know. I never had a 740. Sometimes you can troubleshoot better if you have a good notion of the "theory" under which a system operates. Perhaps - just maybe, okay? - your "overdrive" solenoid could be failing when it has been "on" for a while and heats up - I have seen this happen before on Laycock overdrives, and soon the solenoid fails altogether.
Best wishes.
RDS

Lots of guys here have fixed their OD problems with something as simple as changing the fluid.

I would check the kickdown cable too. It might be getting loose. And put new fluids in the trans and the differential.