We just bought a '89 Trooper with the 2.6L four cyl, with an auto transmission.

We seem to have some sort of issue with the overdrive on the auto transmission. Every once in a while it will shift down into the overdrive, but most of the time it will just stay in 3rd (in regular D). Every now and then it will seem to work, and you can push the switch on the shifter, and it will go back and forth, but most of the time it will stay in 3rd.

We bought it with a bad head gasket and had it repaired right away. I think the car sat for about a year before we got it.

The question is: is the overdrive some kind of servo switched thing, or is it a vacuum line that might be cracked or loose?

Thanks for any help.