Would it be a bad idea to change the fluid and filter on the old GM 3-speed automatic transmission that's in my 1979 Pontiac Catalina? The car has a little over 113,000 miles on it. I have not driven it yet to gauge forward driving shift quality, but it seems to have no problem going into reverse.
no
You would change it? I thought about what Scotty has said a few times about American transmissions- they like to shed clutch material and asbestos inside, and would hesitate on doing it for that reason
If the friction surfaces are worn and shedding the fluid will be dark and gritty. If the fluid is clean or just a little bit dark but still slippery it should be OK to change the fluid. (Not flush, just drain and fill.)
Scotty said around 200k. I doubt there’s asbestos. The environmentalists would have a conniption. (then again you have a '79) You want abrasive clutch material OUT of your transmission,not inside . You also don’t want burnt fluid. But I doubt your clutches are completely burned out at 113k. You would know. So keep it that way. Change the fluid. Anyway my 2nd generation transmission guy says fluid change problems are “extremely rare"
I'll look into doing it, once I can get the car onto a paved area to safely work underneath. It's on an old, compacted gravel driveway right now. I set a sheet of half inch plywood between the gravel and jack stand when I was doing the brake work, it held fine. I wasn't really under the car for any length of time, either, so there was minimal chance of an accident. I don't trust that setup and being fully under the car, haha.
yeah get secure and comfortable first. You don't want that nagging voce in the back of your mind while you're trying to work on car.