I have a 740 GLE -87 and the OD works ok when engine is cold, but after a few minutes I have to drive faster and faster (110-120 km/h)to keep OD in "working position". When it's real cold, like yesterday here in northern sweden (-20 C) it works pretty good.
O-ring problem? and if, which one?
/Bosse.

You do not mention auto or standard, I am assuming auto.
What is the OD light doing? Does it go on and off with OD button?
The first step on almost any OD problem is to resolder or replace the OD relay. Complete details are in the 700/900 FAQ section.
I doubt the O rings would cause a problem, never heard of that. Many problems can be temperature sensitive but that is not necessarily an aid to diagnosing the problem.
--
David Hunter

If this is a maunal transmission with a Lycock Overdrive, three areas to inspect AFTER making sure the transmission is full of transmission fluid. Well, while you are under there, check number two as well.

1. If your dash light goes out when the OD does not work, replace the 4th gear switch on the transmission.

2. Clean and tighten the contacts on the solenoid on the overdrive unit.

3. Two actuating piston O-rings need replacement. The overdrive has to come off the transmission. The tranny can stay in the auto. See the 700-900 FAQ's under the Features section at the top of Brickboard pages.

If your actuating piston O-rings are factory original, you may also need to change the actuating pistons as well.

The actuating piston O-rings in some of the late production 87's had Teflon O-rings. It takes about 660C (350F) to soften the Teflon O-rings sufficiently to stretch them without damage to install them. Without the heating, the repairs done by shops not using the heated O-rings failed well before the "normal" expected lifespan of the O-rings.

To solve this, the actuating pistons were replaced with an older style which allowed the use of rubber O-rings not subject to the heat requirements needed for installation.

Duane