I have a 1991 740 with only 127,000 miles. Yesterday when I started it, the arrow overdrive indicator light on the dash lit up and stayed on. I touched the overdrive button several time but it would not go off. I also restarted the car several times thinking this would help. It did not. When I drove on the highway, the car would not shift into overdrive. It rpm’s would rev, but it would not shift. On the last few weeks, I noticed that the car was shifting hard. Not as smoothly as in the past and the gas mileage has dropped of significantly.

What help and or suggestions can you offer on how to start to fix this?

Thanks for your help

Try the overdrive fuse and relay. This solved the problem on my 240, with identical mechanical specs. used cost about $25. I don't know where it is located on the 740; probably behind the ash tray and fuse block. Which specific relay I have no idea. On the 240 it is reached by removing the glove box and reaching with the left hand toward the radio housing. Instant cure.
Check fuse first, then replace relay.
If that doesn't work, the problem is probably the overdrive solenoid on the transmission housing. More expensive repair, but nine times out of 20, the relay cures the problem.

Thanks rstarkie, Uncle Olaf, and lucid for the starting points.
The arrow stays on no matter what I try to do. The overdrive remains locked out as well.
I will start with looking at the fuse and then attempt to locate the relay. I’ll let you know the results

I'd say start by checking Fuse #12 (the Arrow light gets +12V from another source).

Here's what's involved in OD control...

1) Fuse 11 (200) or 12 (700/900) supplies voltage to items #2, #3, and #4.

2) The Shifter button/switch turns the OD relay off and on

3) The OD relay controls the OD solenoid and the Upshift ("OD off") Arrow light (separate wires). When the Arrow light is ON, the OD relay and solenoid are OFF.

4) The OD solenoid allows OD engagement when ON, (this is the "default" OD relay/solenoid state at start-up)

If your shifter switch makes the Arrow light go on and off, then the OD relay is working (although it could still be failing to control the solenoid voltage due to burnt contact points).

If Arrow light doesn't go on and off, start with the Fuse. If fuse is OK, suspect OD relay, shifter switch, or wiring to the relay.

If Fuse 12 is blown, suspect the wiring from relay, going out and under the car to the solenoid.


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Hey Ellis,


I think Starkie nailed it. Most likely your overdrive relay. If you're handy with a soldering iron, its a cheap fix. Check out the FAQ, its great.


Regards, Jon

First place to look is the overdrive relay.

Lots of good reading in the 700/900 FAQ's accessed by the drop down menu in the upper right hand corner of the page.

http://www.brickboard.com/FAQ/700-900/TransmissionAuto.htm#OverdriveRelay

Randy