I have an 86 Coup with 26,000 orig miles. MY over drive only kicks in on occasion and with the price of gas lately , ouch ..... and suggestions as to why it only works when it wants to ???

Well i have a 86 corvette and my 4+3 tansmission dont work. Corvette had alot of problems with this 4+3 tansmission and i think it is junk.

My dad's 85 had the same problem and he took it to the shop and the only thing they foound wrong was the tranny fluid was too high and they drained some of it. Now it works 95% of the time he said.

Hope that helps.

My 4+3 stopped working also. After looking up some repairs, it looks like we have to check the overdrive solenoid plugged directly into the overdirve unit. Check the wiring and connection. Next you have to disassemble the switch inside the shifter knob and check all the connections. You (we) may have to replace the switch in the knob assembly. There may be a way to check voltage with a meter or something. (?)
Hope this is helpfull. If anyone has success, please let me know.