The three-speed automatic transmission in a DeLorean was supplied by Renault and the shifting is controlled by a computer governor assembly. The original governor unit is rather ‘old school’ by today’s standards, with analog circuits that were rather weak for the harsh environment underneath the car, so they tend to go bad.
Symptoms of a failing automatic transmission computer governor include shifting very late from 1st gear when cold or when the transmission is warm and you are slowing down, it will cut in and out of gears or will give you erratic shifting. The worst case is failure of the governor causing the transmission to start out from stop in second or third gear. This puts stress on the internal parts often leading to complete mechanical failure of the transmission - easily 10 times the cost of replacing the governor. It is extremely important to get the governor repaired as soon as these symptoms are noted.
There are two other devices that impact the shifting of the automatic, it is important to check them as well.
Full Throttle Kickdown Microswitch This switch will cause the transmission to drop down one gear when the throttle is "floored" (depends on speed and gear). If this switch fails open, flooring the throttle will NOT cause the transmission to downshift. If this switch fails closed (stuck), the transmission will upshift (1 to 2, 2 to 3) very late.
Throttle Position Cable This cable runs from the throttle spool to the governor. If disconnected, stuck, or adjusted improperly the transmission will shift early under load, or late under light throttle (depends on the failure). On the governor you can see the cable attached to a rotary lever. While observing the rotary lever, have an assistant floor the throttle. Make sure that the rotary lever goes through its full travel, as limited by the stop pin that comes through the lever.
DMC has developed considerably more stable microprocessor-controlled, electronic replacement unit for the internal portion of the governor. We’ve modified the shift points to make them more aggressive and more suitable for the DeLorean and it’s a relatively simple item to replace - removal of the transmission is not required.
The repair process involves removing the complete governor assembly from the car and sending it to your local DeLorean Motor Company dealer. They will install the upgraded electronics and ship the assembly back to you, often the same day received. Refer to the Workshop Manual Page G:06:03 for detailed instructions on removing and replacing the governor assembly. We strongly recommend that you service the transmission (replace fluid with Dexron III spec fluid and the filter PN 103702) at the same time. Be sure to order the two O-rings for the electrical connectors. They are Part Numbers 103698 and 103732.
NOTE: The most important caution when replacing the governor is to zip-tie the wiring back up to the frame of the car away from the exhaust system. Make notes/photos before you remove it. If the wiring rests on the crossover pipe it will melt and cause the governor to fail again (not to mention the mess it makes of the wiring).
Be wary of units advertised as "plug and play" but actually require extensive surgery to your existing governor assembly unit. These modifications destroy the "core value" of this no longer available part.
Revised DAS 8/4/2016 added details and references