ATF flush in old trans, yes or no?
 

Tahoe has about 175k on the clock. I bought it 2 years ago with about 145k the weekend I bought it i took it up to my dads shop and tuned it up, install new shocks, tires, brakes and dump and replace all the fluids. After I did the oil change I grabbed the trans filter kit and all of a sudden one of the techs came over and asked me how many miles were on the truck, I said 145 he then asked how the fluid looked and smelled, i said its red and smells fine, he then advised me to leave the fluid alone. I said, isnt that just an old wives tale? He said no, another one backed him on it and my dad threw me out of the shop. Fine whatever, i left it. Lately I noticed it was banging when shifting, especially if I have been driving for a while, like if the trans was hot, so friday I pulled the dipstick out. Fluid was level and smelled fine but was all brown. I was pissed cause I wanted to change it two years ago and i was told not to. So despite their warnings I droped the pan at home, installed a new filter and 4 quarts of fresh ATF (700r4 takes 12 quarts in total) of course when i started it up the 4 quarts of fresh fluid mixed with the 8 quarts of old brown fluid but it shifts fine now. I pull teh dipstick and the fluid is still brown. I drove it up to my dads shop and asked to use the trans flush machine to suck out all the brown fluid and install fresh red fluid and again with the "i wouldnt do that if i were you" or "dont do it man" comments, so i didnt. WTF? How is dirty better than clean? Has anyone ever flushed a high mileage trans to get the brown fluid out and put red fluid in and had problems after? Anyone on here with personal experiance? I think its BS

I've seen flushes do bad things...engines & tranmissions, cooling systems...esp engines...you force crap out of places it is stuck in and it circulates through everything. IMO if you have to flush it you have to rebuild it.

My $0.02 - change the oil & filter again in a few thou if you must and call it a day.

This is my understanding:

In a trans that is in good shape, a flush is not a problem. There aren't too many particles suspended in the fluid modifying the friction and the internal clutches and such are still in good shape.

In a higher milage trans there is more wear and the particles suspended in the fluid may be preventing slippage since the fluid is not as "slick". Trans anti-slip additives work this same way, kind of like a limited slip additive for a clutch posi.

do not flush, just a simple change of fluid and filter at the most.

I guess Ill just leave the brown crap in there until she breaks

my friend had a cutlass with 195k miles on it when a trans line rotted out... got the line replaced and had to add some new fluid obvioulsy.... a weak later the trans went byebye

well if it has an auxiliary trans cooler, you could remove the output hose and drain a quart then replace a quart with it running. its a pita but works, its how you do some cars too by the book. on another note, my dad's 96 suburban had a troublesome trans the way you described. if it does bang into gear when hot, i would bring it to a trusted trans shop. i think its something with the planetary gears. also scan for tranny codes. could help!

Well thats sorta how the trans flush machine at my dads shop works, you just disconnect the trans cooler lines from the radiator, hook the inlet line up to the fresh fluid and the outlet line to the empty jug and start the car. The trans is a big pump and pumps out all the old and sucks in all the new.

It stoped banging as soon as I dumped the fluid and changed the filter

well if everyone is steering you away, have them sign something that says they will replace the trans when it blows. but scan the computer, it never hurts.

why is the fluid brown? Isnt that a sign of slipping clutches, etc? I always thought any color other then red was a problem in transmissions??

True if the trans had a computer, i shoud have mentioned that its a 1992

Constant heat cycles burn the fluid, but yes, clutches that slip more than they should gan generate excess heat

oh ok 92. trans fluid is a powerful degreaser and the color doesn't say as much as the smell, but can mean some.

You are better off taking that trans pan down and welding in a drain bolt. Change the fluid as often as possible until it is always red. Then change that filter. Once you have done that, change that fluid and filter every 10,000 miles.

I don't know about that. All flushing does is replace the old with the new. I've heard about problems with leaks when changing fluid types. I flushed out my 175K transmission with synthetic and all is fine. That was 50K ago and I tow about 10% if the time (about 6K a year towing).

I put in a shift kit over 100K ago and all has always been fine with the transmission.

Art.

I wound up flusing it. It shifts smoother now, pistons engauge and disengauge with out sticking or any more clunking. Should of did it a while ago. Must be an old wives tale. Clean is better than dirty in a pressure sensitive componunt with tiny orifaces in the valve body. I ruled out the theroy that a flushing dislodges particals because the actual flushing is less pressure than what is created in normal driving conditions. The old clutch material acting as a friction modifier makes a little sence, But the fact that oil breaks down and loses its lubricating properties is a fact. New oil will lubricate better than old oil. I personaly think people who flush a trans who are not careful and allow the pan to run dry whan the trans is pumping out the old flud and the front pump sucks up a nice air bubble frying the clutches. Thats probably the culpret. You get some just out of high school kid working at jiffy lube operating a machine between getting high on coffee breaks and he doesnt fill the pan fast enough and you burn out a clutch... that sounds more practical to me. If 1000 transmissions get flushed today and 1 breaks next week we hear about the one that broke, we dont hear abouty the 999 that run better. Then again who knows, my truck may be on the back of a flat bed by the end of the week and i will be eating my words...

I agree that running the pan dry would negate any benefits to replacing old fluid with new fluid. The machine my buddy uses is idiot proof. You disconnect from the radiator, the "in" goes to one port, the "out" goes to the other. Start the engine and the little green light, lights upif the fluid is flowing in the proper direction. The "start" light lights up if the fluid is going in the correct direction and the "fill" fluid hopper is full. If all is good you select the amount of fluid to replace and hit the start button. A valve changes direction and it starts draining old fluid into a reservoir and replacing it with the new stuff at the same rate as it’s taken out. If the new stuff runs out the valve changes back so that you are pumping from the pan again.

I’ve seen the old timers do it by draining it out while having someone pour fresh stuff down the dip stick and then turning the engine off once fresh fluid starts coming out. I wouldn't try it but the old timers seem to have been doing it that way for a long time. Who am I to criticize?

Art.

how much does a flush go for these days?

It depends. I think they usually charge about $100 I'd think. Also depends on how much needs to go in and what type of fluid.

Art.