I just bought a '91 745T (158k miles) and am wondering if the overdrive works. The reason I wonder is that when I am driving, and I turn the switch on the shifter on and off, no RPM change takes place, the engine does not make the slightest change in sound, nor is there any movement as there usually is when the transmission shifts. OR, if I start out on the highway with the shifter on (yellow light is on) and then turn it off, there is absolutely no discernable change.

The yellow arrow on the dash goes on and off, and I can hear the relay clicking when I turn it on or off. Am I missing something? I have pored through the FAQ's and it sounds like one possible issue might be the overdrive solenoid, but I am hoping I am just missing something obvious. Thanks for the help. WHERE IS the solenoid, and how much does it cost to replace?

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Darius in Albany NY '86 744 GLE, 91 745T

How many gears do you have?

Three: OD stuck off, RPM and noise too high at speed. Fix this.

Four: OD stuck "allowed", no big deal unless you are towing or something and want to defeat overdrive. Many drivers never use OD defeat anyway.

In our case it was stuck off. The solenoid had to be removed, energized to open the passages, and cleaned out with a blast of compressed air.

I have read about a trick to work around a failed OD solenoid - remove it and grind a passage beteeen the two orifices on its mounting surface, clean it all out, and re-install. You will have OD stuck "allowed", essentially a four-speed automatic with a pretty tall fourth. It will downshift into third what you tromp it, and you can adjust the downshift cable to your taste.

The solonoid is mounted on the driver side of the tranny and has a single wire going to it. You should feel and her it click if you look under there and have someone press the button with key on, no need to run engine. If the solonoid does not click then resolder the fuel pump relay as described in FAQ. Just because the relay clicks that does not mean it is good. It can have resistance at the solder joints and fail to pass full current and voltage to the solonoid.

If still no go make sure you are getting 12V to the solonoid. When you know you are getting 12V to the solonoid and it does not click then it's time to replace it.

If solonoid clicks and still no OD post back.
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David Hunter