Auto transmission "thuds" when changing gears after it is hot

[Devin]

My transmission in the 2004 Impala makes an audible and tactile thud after it gets hot. By hot I mean a highway drive, or a lot of idling in traffic. Usually on a summer day the car reports the temps to be just about middle of the gauge, or a little below. It never makes the noise until after I heat up the fluid, and drive around town where the is a lot of up/down shifting.

 

The first thing I want to do is check to fluid. My Dexcool turned into mud last fall and killed the water pump, and the car overheated. I fixed those issues but I can't remember if the thudding started before or after that.

 

Either way, what is the best procedure to check the fluid level?

What color should it be?

 

It's a stock 3400, but I'm not sure of the transmission model.

[AL]

4T65E trans

 

Car idling in park, pull the dipstick and check the fluid, has it ever been changed?

[Devin]

Nope. Hit about 100,000 about a month ago, though. I about got flogged when I suggested that I change my fluid at 75K and hadn't gone back to it since.

[RobertISaar]

changing your trans fluid regularly is NEVER a bad thing... i honestly would suggest a 50K change interval in normal conditions. less if it's beat on regularly, like 25K or less.

[Jssuper]

Yup I agree... I bet if you change that you will notice a significant difference in shifts and the general smoothness of the trans. Pan drop and filter change is never a bad thing. I've done mine at 50K, 80K and 102K. Its really not that bad of a job on a 4T trans.

[RobertISaar]

except for the lack of drain plug, VERY straightforward, assuming the seal for the filter doesn't get stuck in the trans, but a seal puller will rememdy that quickly.

[Night Fury]

Or just use the old one.

[Devin]

How much fluid is stored in the pan?

[Crazy K]

I use a vacuum sump device designed for removing fluids to drain any tranny I service, such that the pan has no more than a pint in it when I drop it..... makes tranny servicing hella easier.

 

6 quarts +/- ???

[tornado_735]

IDK about the 65, but my 60 held about 7 quarts after I dropped the pan.

[jman093]

I'd get the car scanned and see if it has the code P1811 "Maximum adaptive, Long shift" or something like that. It means the pressure control solenoid has gone out which is extremely common on that transmission and causes the issue you're having. The code will not turn on the check engine light so you have to scan the car to see if it's there.