Transmission won't go to overdrive - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat

1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-09-2007, 08:45 PM   #11
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Originally Posted by wjcollier07
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.
Thanks for the reply. It looks like lowering the T-stat temp to 180 and adding the cooler is the way to go. I think I'll also change the fluid as it does have about 45-50K on it. Hopefully I can get to it this weekend. I have a long trip coming up. Family in Nawlins.

Thank you and thanks to all for the replys!

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Old 04-10-2007, 06:44 PM   #12
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Originally Posted by Jerry
Originally Posted by TrueWildMan
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.
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.


In that case, since it'* actually dropping to third, and not going back into fourth until you actually shut it off, then back on, doesn't sound like a temperature issue, since when you shut it off then right back on, little to no cooling has actually taken place.

At this point, I would suspect either the PCM, or the computer actuating the transmission.

Have you pulled any codes yet?
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