Thread: 125C buildups and tech help

I have built plenty of these and they came in a lot of the mid 80s GM cars and were even used up to almost current date in a few of the smaller cars like the Cavilier and Sunfire. While they are very light, reliable, and inexpensive they also do not have overdrive which will hurt highway fuel economy. On the inside the appear pretty fragile but do handle their share of power. The most common problem on this transmission is the TCC solenoid failing which causes lockup to stick on once the transmission warms up. Unplugging the TCC plug on the trans case will be a quick fix to keep your car from dying while pulling up to a stop but replacing the solenoid is the correct fix as no TCC operation will cause the trans to run hot and hurt highway gas mileage.

Do you know if this transmission came in the 88 Corsica?

If it is just a 3 speed or only as D-2-1 on the shifter than yes, this was the only 3 speed that GM used.

I don't remember. We bought it new and had it in to the dealer 36 times for different issues. Two things that plagued me were the rough idle (2.8l) and a stumbling. I kept telling them that when I slowed down the car chugged like a manual would if you didn't push in the clutch. In 95 for the first time it actually died when I came to a stop. Took it to the Ford dealership a block away and they replaced the TCS. No more problems with the chugging.

TCC replacement guide. Althou for a Fiero, it applies to ALL 125C trannys..
Lockup solenoid

IM considering putting in a 125C into my TGP if the tranny blows. I have been hearing that the 125C, in non-computer controlled form, holds the power, and transfers it better than the 440T4. And since the TGP is mainly a track car until I get the body redone, I am not concerned about MPG.