transmission ??? 2000 grand prix 3800
 

After I drive longer distances 70 + miles sometimes I lose overdrive.

When I check the fluid at that time ideling ,hot, and in park the fluid seems above the full line with some bubbles in it. I does not feel hot or smell bad.

I am wondering if it is maybe overfilled a 1/2 quart or so and that when expands it messes up some line pressures or something. or is it a sign of it going bad?

It has 130,000 on it and I changed the fluid and filter at 110,000 when i bought it. not sure of previous maint.

when it is cold it runs normal, even when it will not shift into overdrive it still shifts smooth in the first 3 gears.

It does sound like it is overheating. The pcm will take you out of OD in an overheating situation.

it stayed out of 4th this morning while cold, so I dont think its a temp thing, maybe a stuck selonoid.

Any way you can get a scan tool to see what it is doing? Or possibly have a transmission shop diagnose to help you out?

You may also want to pump a little of the fluid out and see if that takes care of the foaming problem.

follow up

its been a while and finally fixed. problem was the shaft that engaged the 4th gear clutch was worn. had to pull tranny to replace and decided to rebuild at same time as it has 130000 on it only $500 bucks more. now its happy.

I was running in 3rd for a few weeks but when it got above 90 degrees, running 3500 rpm's on the freeway was heating things up a bit too much and gas milage dropped 5-6 mpg. so the fix was in order.

thanks for the follow up....I wish I had the know-how to rebuild my tranny....it cost me $2800 to get it done at aamco