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Transmission Flush

I had a recent transmission flush in my 96 Buick century w/100,000 miles on it. After some months it has been holding back: almost feels like it won’t make the shift into the last gear when first starting out for the day. Was flushing a possible cause for a transmission problem? Or is it just an old transmission?

Have you had a tune up? All your vacuum lines are ok? Bad engine performance can cause this. My cirrus has transmission issues but I had a shifting problem for a while. Car seemed to run smooth. I took off the plug wire covers and 4 out of 6 plugs were sitting in oil from bad valve cover seals. Bad HP output can cause the shift issue and a tune up is cheap. Trace back any vacuum leaks. Next look for a cheap 2002 car.

Flushing is the probable cause. Worst thing you can do to an auto tranny is flush it! Breaking the crud loose lets it float/flow into places it shouldn’t be … could have caused a sensor or shift valve problem which may or may not go away on its own - may or may not cost you a fortune too. Leave “flushing” to toilets and coolant systems.

Failing to follow maintenance as suggested by the manual may be your problem. It gets old, I have never done a thing recommended for my car and now I have a problem.

Yes, it has had a tune up. But vacuum lines I’ll need to look into. Thanks

A really good mechanic did the flush and I’m surprised that he didn’t warn me about this possible outcome. I actually think what you have described is what is going on. I just hope it goes away otherwise I’m just going to let it die and look for another car. Thanks

Some things you can try …

I missed the “months” part in the first reading, agreement with euryale1, check for other problems (wires, connectors, hoses, ect) also pull the computer codes, it could very weel be a sensor died, is in the process of dying or got crapped-up and isn’t reading correctly because of the flush.

If you’re mechanically inclined enough, drop the pan to drain fluid then pull the filter and see what it looks like. If the flush loosened stuff, it could very well be the filter is loaded up and not allowing enough fluid flow at high speed - replacing the filter could be all that’s needed. If the filter is clean and you feel real brave, you can drop the valve body but I’ll warn you, if things go flying you’re pretty much screwed unless you’ve got a complete professional manual to do a complete re-build. (may want to have the wrench do that work) Plausible that after some time, the filter is crapped-up and until the tranny comes up to temperature and the hydraulic oil thins enough, it can’t get enough flow to finish shifting.

Talk to the wrench who did the flush, explain what’s going on, see if he can do a reverse-flow flush to try to remove anything that may be causing the problem - also check codes & sensors …

With 100k on it, if you/wrench does find something or whatever, consider adding a quart of Lucas auto-trans additive (current fluid level must be lowered sufficiently before adding). The stuff works, I put in my wife’s Corsica with 245k on it, made a world of difference, tranny turned another 17k without any problems and it cured the rough shifting.

If this vehicle is equipped with a cooler, either/or aftermarket or in the OEM radiator, make sure it’s not plugged because that will also cause fuild flow issues. Normally the cooler is on the return flow side, if there’s a plug in it or the lines, it’ll cause too much backpressure resulting in shifting and overheating problems.

When the transmission was flushed was the pan dropped and the filter changed too?? Is this the first transmission service this vehicle has seen??


I don’t know if pan was dropped or filter changed. And since we only have had it from 54,000 miles and up, I don’t know if transmission fluid was ever changed.

Even though your owner’s manual won’t say it your best bet for an auto transmission is to have the pan dropped/filter changes every 30K miles. You went 100K miles on the same fluid. So anything could be going on at this point.

Those transmissions are really complex - both in how they operate & in they interface with engine issues. You could have any number of 100 things going on. If you’re worried about it then you need a dedicated local transmission shop to drive it & scan it.