745T, Manual with Overdrive:

OD disengages intermittently - - frequently when hitting bumps, and/or under heavy throttle and/or under engine braking and/or under hard brake hit. (basically, any time there is significant force on the transmission case.)

It is 100% electrical, as the light on the dashboard, the O/D relay, and the O/S solenoid ALWAYS go on/off in unison - - the O/D physically disengages completely every time, as well.

The relay is fairly new.

I have simulated the problem with the key "on" but the engine "off", parked in 4th. With O/D engaged, I poke around with my thumb at the base of the stick (plunged deep into the rubber boot), and if I use enough force, O/D will disengage!

Fourth-Gear Lockout switch seems to be working just fine, as O/D will remain engaged until the stick is moved significantly (much more than I move it when doing the "thumb trick") - - so this is less suspect.

What I suspect (and am 99% convinced of) is that the wires routed through the stick have deteriorated, and are shorting. In fact, I feel I have essentially proven this - but I'm still wondering why the car never goes IN TO O/D when I'm driving in 4th!! If there was a short (acting in place of the momentary O/D switch), wouldn't it both ENGAGE AND DISENGAGE O/D intermittently? Is it possible that there is only enough stress/movement on the tranny case to cause the short when in 5th gear?

Please respond with your experiences/expertise! I'm probably going to inspect the wires tomorrow anyway, BUT I'd still like to hear an answer to why my short wouldn't cause intermittent ENGAGEMENT!

thanks a lot!!

-Cy
Volvo 745T