Transmission Tune-up

I have a 1998 Chevrolet Cavalier Z24 with an automatic transmission. It has 100,600 miles on it. It doesn’t seem to shift into high as smoothly as it use to, or shifts at a higher speed than previously. I never had the transmission fluid changed or the transmission serviced at 60,000 miles. I wondered if changing the fluid and filter would help this. My mechanic recommended not doing it saying it may just cause more problems after going this long. Any recommendations?

Sometimes changing the fluid at this late date (40k miles overdue) will cause problems.

It’s a crap shoot.

If you are inclined to change the tranny fluid and filter (or clean screen) DO NOT FLUSH. Just drop the pan and drain/clean screen (or replace the filter) and replace the fluid. Be careful not to overfill.

A check of the pan magnet will tell if there is any problem with gears wearing.

That said, I’m going to suggest a product for rough shifting trannies that I read on another forum last night.

It’s from a very well know company called Sea Foam. Their product is called Transtune and according to those who used it the stuff works quite well.

You must follow the instructions to the letter as using too much at one time will cause problems.

Go to

Click on ‘our products’ at the top of the page.

I would have the transmission pan dropped & filter changed - probably twice in relatively rapid succession (5-10K apart) since dropping the pan doesn’t get all of the old fluid out. I would avoid a transmission “flush,” or at least if you decide to do one, make sure it is after the pan & filter.

This may or may not help. You’ve basically left fluid in your trans that is both dirty & doesn’t lubricate as well as it should. This has likely accelerated wear. Nothing but a rebuild will fix that. The thing that changing might help is electronic stuff inside of the transmission (shift solenoids). Your 3-4 upshift (4 speed?) may be sticky & getting some clean fluid through might help.

Contrary to what your mechanic says, if the transmission develops major problems after a pan & filter service, its because those problems were already there. You won’t “cause” them by doing this service.

For future reference, have pan & filter service every 30K - even regardless of the manual.

Sometimes changing the fluid at this late date (40k miles overdue) will cause problems.

I really doubt that changing it every causes problems, unless the wrong fluid is uses or not done properly.  Of course I don believe that many times when it is changed past the time it was due and after it started to show signs, changing the fluid gets blamed because it fails shortly after it was changed.  Of course it was going to fail anyway.  

I guess it does not make any real difference since the outcome is the same.

To the OP, yea I would go ahead and change it, but make sure the filter is also cleaned. I would not hold my breath that it would fix it.

Now if transmman shows up and says don’t change it, Then I was likely wrong.

In the mean time follow Roadrunner’s suggestions. They are all good ideas. I would rate the Tanstune just a little above a fluid change.

I bet you are now wishing you had changed the transmission fluid when you were supposed to.

You should change the transmission fluid ASAP and every 30,000 miles after that. Like others have said, also drop the pan and clean the filter and stay away from the “transmission flush.”

“I never had the transmission fluid changed or the transmission serviced at 60,000 miles.”

So you are 70k miles overdue…

Its funny how servicing your transmission is totally forgotten about until it starts to act up but people will change their engine oil (Not always like they should) but they seem to take better care of their engines. Are there any trouble codes coming up on the code reader?? This problem could be a drivability issue.