Hi, I have a 91 Buick Lesabre, 90,000 miles with a 440T4 (4L60) transmission. When driving from a cold start, the transmission will drop into neutral when coming to a stop. It may do this 1 or 2 times within the first 5 miles of driving. Once warmed up the transmission works fine. When it does drop into neutral, it will re-engage within 5-10 seconds. Manually shifting in the 1st will also re-engage the transmission.

I have replaced the vacuum modulator – no change. I have also removed/cleaned the pan, changed the filter and refilled to the proper fluid level – no change. The fluid is clean, not discolored and no burned odor.

Is there anything else I can do to service the transmission in the car or am I looking at a rebuild to correct the problem?

Thanks in advance!

Try overfilling the trans by 1 quart as a test as you are describing a classic low fluid condition.

Did this just start happening?

Has been happening for the last 3-6 months. I did notice that the problem only exists when the transmission is in OverDrive. In Drive, the transmission does not drop into neutral.

Did you check the fluid with the engine is hot, running and on level ground?

Even if it is actually full, still add the extra quart and see what happens.

Hi,

Overfilled transmission, no change in the way it drives.

Sounds like you have an internal problem.

Thats exactly what One of the symptoms of my tranny would do to a 'T' when I 1st bought it with 125K Orginal miles on it. Dirty Dirty Fluid. BUT.....

Lil'Ole Lady told me that her heater never worked the last few years. So I pulled & replace the thermostat, lo-an-behold the thermostat was stuck open. Immediately after replacing thermostat (old one was Was stuck open). I disconnected my battery and pulled the ECM fuses for a few..put it all back together and even though I have yet to change my fluid I did notice that it was shifting into/out of overdrive more frequently...seemed to shift better.

I only drove it 30-50 miles before I changed my tranny fluid but before that it never popped out of OD and/or since! and had to be pulled into D. Coincidence?

I Believe that engine temp plays important factor in how that tranny up/down shifts...sure stopped my 'popping' out of OD issue.

My 2-cents

Take care
Mtfork
91 Buick La sabre Custom 132K

Yes, your engine temperature does have an effect on the way your transmission shifts.

With a stuck open thermostat, the PCM is thinking that the engine is having a hard time warming up and it changes your shift patterns. I guess depending on the platform, it keeps the trans from going into OD.

Your fuel mileage will be affected by this also. Not just due to lack of OD, but your engine is running richer.

I just bought a 1993 LeSabre and have the exact same issue. At the first stop of the morning which is in approx. 2 miles from my driveway, the car will appear to be in neutral and will shift into 1st in 2-3 seconds and will not do it again for the rest of the day.

It'* funny....it looks like it'* running cold and my milage is down about 10% from where I think it should be....so I thought I'd throw in a thermostat and see what happens. It'* hard for me to believe that this may be causing the trans problem, though.

At any rate, did you ever fix this problem and, if so, what was the fix?

Sincerely,
Garret

Hi, thanks for the post. My Buick Reatta is starting to drop into "neutral" when i stop at a
stop sign but when i put it in neutral and back into drive it is ok. The fluid level is a little
above full after driving 10 miles and checking while running . Any clues what could be wrong?