Recently purchased a C-4,"first vette", on the way home had problems getting the overdrive to engage. entering the freeway on a downhill ramp, it kicked in. The overdrive light came on the dash as well, I drove home about 110 miles with no problems. I have never been able to engage it since? I have by-passed the ECM, so the gear selection should not be an issue. I have replaced the switch and solenoid. I checked the connections on the trans,seem ok. What about opperating temp? this time of year its hard to get it to 180, the day it engaged it was warmer around 195 or so. Can anyone shed some light on this??? The only other thing that I can see thats iffy is the solenoid connections, and Ive noticed that the solenoid engages when the car is started, is that normal? :wtf: :confused: Oh I have replaced the filter and fluid, the fluid I changed looked new already.

Hello.
You did not say what year your car is. on the 84/85 there is a throttle pressure cable going from the 4+3 up to the throttle body. And it was removed from the 4+3 in late 86 i believe. They each work a little different. My point being, What year do you have.
David

Its an 86, Finally after all the above I figured it out! Hard wired the trans OD solenoid....Did the trick, shifts great now...Thanks:cheers: