What makes a cold transmission "shift" later?

[tlynch]

I still don't have any idea why when it's cold outside (below 60'ish) my transmission won't engage over drive when the airtemp outside is cold. When it's cold outside, what is it (sensor, etc.) that tells the computer to keep the trans from locking the tcc?

When it was over 60 outside, I never had this problem.

It does end up shifting, but only after I've gone about a couple of miles. It seems like maybe the fluid has to warm up before the tcc will lock

What I'm trying to figure out is if this is a problem with the trans build I had done this past spring or if it's something else.

[sherlock9c1]

Well, the ambient temp means your powertrain is also that cold when you cold-start it. Does it happen regardless of whether the powertrain is hot or not?

Second, is it OD or TCC lock that's not happening? the first is not normal. The second is.

Third, it is normal for the 4L60E to shift more softly when the fluid is cold. At least all the 4L60Es I've dealt with do that.

[WeX]

Im not 100% with the 4L60E but from experience with other automatics they dont engage lockup when they are cold (temp sensor in the fluid) to speed up the heating of the transmission, but they will shift trough all gears (even over drive).
I have also noticed that my Caprice (-94) does upshift later when its cold.

[tlynch]

Well, maybe I'm confusing OD with TCC lockup. I was under the impression that on a 4OD trans like our's, there's 4 distinct gears (1-4) and then over-drive means that the tcc locks such that the engine side and the trans side are pressed together. Am I wrong in that?

Once the car has warmed up (heck, it doesn't even have to be at normal running temp), it does not exhibit this issue. If it's 90 degrees outside, and I'm just driving the car for the day, it doesn't act weird. It only does so when it gets below 60'ish.

Either way, let me explain differently. When it's cold out and the trans fluid is air temp, I don't get the over-drive drop in RPMs when I'm cruising along. Say I'm cruising along at 55mph. When things are acting weird, I'm turning a little over 2100rpm. After a mile or two of driving, it'll drop down to 1500rpm.

Before that distance, I can slow down and back up and the rpm's will not drop. After that distance, the rpm's will always dropoff. However, if I park the car and shut it off for more than an hour or so, I'm back to having high rpms.

Does that help?

[fbi9c1]

"Am I wrong in that?"

Yes. 4th is OD. Lockup occurs in D or OD to optimize fuel economy.

"I don't get the over-drive drop in RPMs when I'm cruising along. Say I'm cruising along at 55mph. When things are acting weird, I'm turning a little over 2100rpm. After a mile or two of driving, it'll drop down to 1500rpm."

That's lockup. So it sounds like everything is normal.