Hi!
I have a 1992 740 automatic, and my overdrive wont work. The arrow on the dash wont go away. As far as I know, there is no damage to the wire going to the solenoid, and the fuse and relay look fine (and I have changed them before as well). In the past, it would come on and off randomly, but now it never comes on. My idea is to run power straight to the solenoid from an unused switch I have on my dash (with a fuse of course). I am wondering if this will mess up my transmission. Does the overdrive solenoid always have power? Or does it only get power when the rpms are high enough? I have seen overdrive bypass kits which are just a metal plate, which leads me to believe that having constant power to the solenoid would be fine, but I am worried to do it. My goal in doing this would just be to see if the solenoid works or not, and to see if it is an issue in the wiring (so probably not a permanent fix). Any information or suggestion is helpful. Thank you and have a nice evening.
-Jor

 

(all this applies only to the automatic overdrive in AW70/71/72 transmissions)

the OD solenoid has power when the ignition is on and the light is off. the actual shifting into 4th/OD happens according to hydraulic pressure valves inside the transmission. When the OD light is ON, then the relay is UNpowered, and the transmission will never shift to 4th/OD.

if the light is stuck on, there's two possible scenarios.

1) the OD relay is bad. Visual inspection will not tell you much of anything. the relay has to be tested with a volt meter, and testing its various signals, with it plugged into the circuit.
2) the OD button on the shifter or its wiring is bad. this too can be tested with a meter, the two wires to the button should be normally open, and close when you push the button.

you can remove the OD solenoid and replace it with a metal plate that has a slot milled into it that interconnects the two passages on the side of the transmission, this has hte same effect as OD always enabled, the trans will shift to OD when it feels like it. IPDusa and others sell these plates. or you can cut your own slot on the OD solenoid face to interconnect the two passages, and leave the relay unplugged. if you do this, remove the OD relay, I believe that will permanently extinguish the light.

 

OK - do you want to be able to downshift from 4th to 3rd?

Most people given the cost of that repair do not.

As others have suggested - Take the solenoid off the side of the transmission - with a dremel (or suitable ) tool and grind a slot between the two oil passages in the solenoid, to allow oil to flow. Cut the wire - you won't ever need it again. Leave the small oring off, replace or reuse the large solenoid oring. That will make 4th gear work when the trans tells it too - and it's free!

Remove the relay to make the light stay off and - your 4 speed transmission is working again and you have spent very little.

 

Thank you! This was very helpful.

 

I have performed this operation on my 740, but my light still comes on occasionally.

 

If the relay is unplugged, *AND* the wire to the solenoid is taped off so it can't short to ground, then I can not see any way that light could come on.

 

I'll have to check the wire, the solenoid is gone. Thanks for the idea.

 

there's a RELAY as well as the solenoid, and I *think* if that relay is pulled, the light is disconnected.

 

Thanks Pierce!

 

Did you ever just change the OD relay? In most cases a new relay solves the issue of not having OD, light on, etc.