I have a very low mileage 1982 Trans Am that has the THM Metric 200 3-speed automatic transmission. In the last six months, I have noticed a problem in the way the transmission downshifts from third gear. Basically, when the car slows down from third gear, it behaves like a manual transmission when the clutch is not released (i.e., rpms decrease below normal range and engine almost stalls). Eventually the downshift occurs (abruptly). I recently have forced the downshift by moving the gear shifter to 2 at the appropriate speed. When I do this, the problem does not occur during the downshift from second to first gear.

I know that it is time to replace the transmission fluid and filter, but I am trying to troubleshoot the shift problem before I take it to a transmission shop. Is this indicative of the torque converter clutch not releasing (i.e., remaining locked) and, if so, how is that problem best corrected? Or, is the problem something else? Thanks very much,

 

unplug the torque converter wiring and see if that helps... if that trans even has a plug- it might be all hydraulic..

 

Unplugging solves the lockout issue, but what should be done to correct the problem that is causing the converter clutch to remained locked when it should disengage?

 

Time to read the lockup circuit diagram/diagnostics in your service manual

Does you car have a computer ( which controls the lock up )
If not ,then there is a contamination of switches , some vac operated that enable lockup ; if some of those parts are faulty it could prevent the lockup disengaging.

In any case , lockup should disengage the moment the brake pedal is touched

 

Do a Google search on TH200's

Yours seems to be a common problem
http://gbodyforum.com/viewtopic.php?p=245455#p244685