My '94 Bonneville has 230,900 miles. The tranny was rebuilt about 50,000 miles ago. Last summer (Kansas, July-September) it dropped out of overdrive several times during heavier loading. The only way to get it back into overdrive was to pull over, turn key off, restart. Could this simply have given it enough time to cool? Because I was having a temperature problem and/or temperature indication problem, I replaced water pump, cleaned radiator, and replaced the temp sensor. I thought this had also fixed the od problem. A few weeks ago on a trip to Texas it did it again. I pulled over and put my code reader on. I shut down to get the reader out of the trunk so of course the tranny went back to od. However, just like last time, there were no codes what-so-ever. The code reader was operating correctly as it displayed the dynamics of operation as I went down the interstate. Also, it has successfully displayed codes in the past. The only idea I have is replace the other temp sensor. Does anyone know what to do with this?

Thanks,

Jerry

So it drops out after driving for a lil bit, but u have it when the car is cool?? Or is the od completely gone?

Most of the time the od works just fine. Last summer it acted up several times during 90 ot 100 degree weather. A couple of weeks ago in Texas it was between 80 and 90 degrees when it acted up. Each time I was traveling 75 to 77 mph. It never acted up during cold weather.
Thanks,
Jerry

What does the fluid look like? (I know it'* not probable, but every bit of information helps) Do you have any form of auxiliary transmission fluid cooler?

When you say overdrive, do you mean 4th gear, or the torque converter? When you apply throttle with the TCC locked up, it will come out and feel like a downshift when you apply any significant amount of throttle.

If you're at 75-77 mph, and the transmission drops from 4th to 3rd, the rpm'* will jump up to over 3,000 rpm. If that'* not happening, and the rpm'* are only increasing by about 500 rpm, then the torque converter is unlocking upon acceleration, which is normal.

The amount of throttle it takes to bring it out of TCC lockup will vary from cold to warm temperatures.

This may be a valve body problem with the 4T60E. There is a bore and piston whose fit is just a little loose to start with. As the tranny ages, and the bore increases from wear, higher transmission temperatures induce enough differential expansion between the piston and bore to prevent the desired build up of pressure for torque converter lockup. There are aftermarket kits to re-do the bore and piston, and better-designed valve bodies to remedy the problem.

My '95 was doing the same thing. I installed a drilled 180 thermostat, and an aftermarket transmission cooler from http://www.bulkpart.com/Merchant2/me...e=tru-cool-lpd Now my engine runs cooler and I have lockup on all but the very hottest days. I bought the $45 cooler. I should have bought the $65 model (4490). Cooler trans temperatures will greatly extend the life of the trans anyway.

The cooler has (almost completely) solved my lockup problem for over a year now.

Definitely do what has been recommended to cool it down, heat is a transmission'* worst enemy. Just so we know, what does the fluid look like right now? It should be bright cherry red, if not its been overheated and oxidized. Since it sounds like you're in a very hot climate, I recommend getting the largest aux transmission cooler you possibly can, the more cooling fins it can go through, the better. Also, check for any kinked cooling lines, that can cause quite a problem. Make sure to have it flushed and filter changed when adding on the cooler. And definitely a 180 stat will keep the engine from radiating so much heat.

Also, if you can afford it, I would recommend using a newer ATF than Dexron III such as the new Dexron VI or Amsoil'* Universal ATF. They both resist heat and oxidation much better than older ATFs. Amsoil'* actually keeps the trans much cooler than regular ATF as well, and also can be run for extended intervals under severe conditions, IMHO, its worth the extra cost.

The fluid looks and smells great. The tranny was rebuilt almost 50K ago.

Thanks,

Jerry

Yes, the RPMs go over 3K. I'm certain it'* not just coming out of locking torq. I drive hills and often tap the pedal to get it out of lock after it slows 1 or 2 mph on a hill. On most of the hills I travel this keeps it from going down to 3rd gear.

Thanks,

Jerry

Thanks for the reply. I'll consider the thermostat and the cooler. You're having experienced the same problem and found a fix supports the heat problem I suspected.

Jerry