Why won't my 1994 sunbird down-shift from highway speed?

Answer 1

I am not an expert but by looking into this problem on my own car, I have discovered that the transmission on 1994 Sunbirds has a feature called "Lock-up" where instead of having a true "Overdrive" gear, the transmission "locks-up" the third gear, by use of a solenoid, into a direct drive configuration where the third gear stops slipping and drives the wheels in a direct way, which is fine at speeds above the 35 mph or so when it kicks in depending on transmission internal hydraulic pressure ( during acceleration, which calls for lower gears and high rpm/high torque).

It is an elegant solution to keep the production of the transmission more simple (and cheaper) while delivering the effect of increasing gas mileage like a true overdrive gear would do. For the most part, it has worked GREAT......or as they say, works good, last a long time. 14 years in my case with the 3.1 V6. This is the absolute BEST engine transmission combination I have ever felt.

This is what you feel when it won't downshift. It almost feels like someone is pushing the car from behind. It feels like it won't slow down.

From what I've read about it and talking to a transmission guy, there is an electro-mechanical part called the TCC soleniod which is located under the transmission cover. It is the Torque Converter Control Solenoid. This is what controls whether the transmission goes into "lock-up" mode or not. If this solenoid sticks in the "lock-up" mode, it can be the cause of what you and I have been feeling when exiting the freeway or even on faster side streets....it won't downshift.

In my case, it even stuck when stopping at a toll booth and the car died when I tried to pull away. I had to start it in the neutral position and then it would die when put into gear because it was stuck in the "lock-up" mode of third gear. Frustrating. I guess it cooled down enough to eventually come unstuck, because I eventually got it to go.

The good news is, as far as I know, this is not a major transmission overhaul. The TCC solenoid can be changed without overhauling the transmission....a much less expensive proposition. Way under $1,000 dollars I would think. I'm thinking more in the $200 or $300 dollar range. Cheaper, if you do it yourself if you are able. Then, I would think that it willl last another 14 years or so.....or approximately 130,000 miles...around there. That should be the life of the car.