Questions and Answers

Jeep Wrangler Transmission Swap Q. My question is as follows: I purchased a 1987 Jeep Wrangler and the previous owner replaced the 5 speed with a automatic transmission from a 1991 Jeep Cherokee. It now wants to take off in third when in drive, second when in second range and first when in low range and will not shift unless you do it manually. What could they have done wrong and how do I correct it?

The transmission came from a wreck and was assured that it worked fine before they put it in the Wrangler and had the drive shaft shortened.

Thank you in advance for any and all information,
Jim

A. What did they do wrong? I don't know. It could be anything. The most likely possibility is the 1991 Jeep Cherokee is an electronic transmission and the 1987 Jeep Wrangler is not.

If the AT Control Unit was not installed on the 1987 along with the associated sensors, Throttle Position Sensor for example, it will just not work.

In addition, the Single Board Engine Control Module (SBEC) in the 1991 Jeep Cherokee are different for automatic and manual transmissions. And both are different then the 1987 Jeep Wrangler, if it uses a SBEC. It could have a Micro Computer Unit (MCU) which is totally different.

Wait, I do know what they did wrong. They tried to put an automatic transmission into a vehicle that was never designed for it. The way to correct it is to take the automatic transmission out and put the 5 speed manual transmission back in.