93 Lumina won't downshift when hot

[jrocket613]

My 93 Chevy Lumina, 3.1 with automatic tranny (not OD) runs fine for about 10 minutes, then, when I stop or slow down, the engine stalls. It seems like it is locked in high gear. Once it cools down, after about 10-15 minutes, it's ok for another 10 minutes.
Is there a shift modulator or solenoid that can be replaced without pulling the tranny? The car is worth less than a tranny rebuild, but it's in nice shape. How do I identify the tranny? A tranny guy said a TH440T4 is easy, and to forget about the 4T60 and 4T60E. Underneath only says "Metric HydraMatic" on the pan.

[jeffcoslacker]

Your torque convertor lockup has failed. The convertor is staying mechanically locked up, just like forgetting to push the clutch in as you stop with a stickshift.

Once it sits for a few minutes and the pressure bleeds off, the convertor unlocks, and it will drive again.

You can unplug the TCC plug, this will stop that from happening until you can get the solenoid replaced. This will cause the Check Engine light to stay on, and you won't get the best mileage without it.

There is a square four prong plug going into the transmission case in front, facing the radiator. Unplug it from the case to disable the TCC.

[jeffcoslacker]

Parts stores have a tranny ID chart, you can tell what you've got from the shape and number of bolts in the pan.

[jeffcoslacker]

4TS60 and 60E the solenoid is under the side cover pan on the driver's side. You don't have to pull the tranny, but it has to drop down far enough to access it.

[jeffcoslacker]

http://autorepair.about.com/cs/doity.../aa011703a.htm

[jrocket613]

Originally Posted by jeffcoslacker

Your torque convertor lockup has failed. The convertor is staying mechanically locked up, just like forgetting to push the clutch in as you stop with a stickshift.

Once it sits for a few minutes and the pressure bleeds off, the convertor unlocks, and it will drive again.

You can unplug the TCC plug, this will stop that from happening until you can get the solenoid replaced. This will cause the Check Engine light to stay on, and you won't get the best mileage without it.

There is a square four prong plug going into the transmission case in front, facing the radiator. Unplug it from the case to disable the TCC.

Thanks, Jeff. I disconnected the plug, but have to wait until tomorrow when I get a dealer plate from my friend in order to test it out. You sound like you really know your Chevys.

[jeffcoslacker]

That's been a problem with lots of GM FWD cars for many years. When they first started having problems with them, we at the shop were stumped. I knew what it felt like was happening, but didn't even know there was a lockup mechanism on the convertor back then. Called a tranny shop, and described it just like I said above, like driving a stick and forgetting to put the clutch in as you stop, and the guy knew what it was and enlightened me.

Since then, I've seen literally dozens of them with the same problem.

I don't know how far you looked on that link I supplied, but there is a very good description of the procedure to verify that it is the solenoid (it almost always is) and not wiring or ECM doing it.

Hope you get it figured out. Good luck!