changing and flushing tranny fluid

[Cheeky]

i'd like to DIY changing my car's tranny fluid/filter.

from what i've seen on DIY sites, you can either drain the fluid at the pan, or you can disconnect one of the tranny cooling lines (and subsequently add more ATF which will get rid of the residual fluid).

any thoughts on the best way to perform an ATF change?

any tips, like using gasket sealer on the pan gasket?

[jseklund]

I have done this, and it is a really messy job- just so you know. If you have a fluid evacuator of some sort, it is a HUGE help.

You are correct- there are two normal ways to do the change- drop the pan, pull the filter and refill the pan. This is good as it puts a brand new filter, and in some cases a brand new gasket, in the oil pan. It is bad because it leaves over 1/2 of the fluid in the torque converter.

The second way they normally do it is to disconnect the line and either turn on the car to move the fluid through, or use a power flushing machine (wish I had one!). Either way, you need to make sure you add enough fluid through the dip stick as you flush through as you don't want the fluid to run dry. You get all the fluid out, but you still have an old filter in there and whatever gunk was on the bottom of the pan.

Then there's the way I do it. I normally drop the pan (this is REALLY messy, even if you suck a lot of it out with a fluid evacuator through the dipstick tube first), pull the filter, replace the filter, clean the pan out REALLY good (i.e.- make it shine. I don't remember at the moment, but I believe carb cleaner works well.), put on a new gasket unless you have a reusable gasket (a new one usually comes with the filter kit- I look for rubber gaskets, not cork), fill the pan, disconnect the line and then pump through. This way you get almost all of the fluid out of the torque converter, get a clean pan, and get a new filter.

Be prepared for a big mess, and have plenty of degreaser handy. Don't use a red rag- the little pieces get in the tranny and reak havoc at times. If you notice an abnormal amount of metal in the bottom of the pan- it is a warning sign (which is another reason to drop the pan).

Good luck!

[Tarhead]

www.bobistheoilguy.com (I'm not joking!) has the best discussion forum for anything related to motor oil, transmission, brake, radiator fluid and general maintenance.
Based on the advice I've gleaned from this group I now drain whatever tranny fluid comes out (~2.5 qts) from the tranny drain plug and refill each time I do an oil change. I was amazed at how nasty this fluid can get after ~30,000 miles and now after 4-5 drain and fill routines on a 2001 Mazda Tribute the fluid is like new and no mess. The filter in most new transmissions is nothing more than a screen which self cleans so replacing it after dropping the pan and getting a shower of fluid is probably not required in most vehicles like the old days.

Mark

[Black wallnut]

Drop the pan, change the filter then clean up the mess! Do not worry about the fluid that is in the torque converter. Jim Boyd said long ago that IIRC in his experience as a Auto Service manager that often folks that flushed their trannies with a power flusher would soon have tranny problems. As auto trannys wear some contaminates in the fluid is a good thing to keep parts functioning. Or so it seems to be the case. For years all mechanics would ever do is drop the pan. Newer tranmissions may react differently to this approach so it would be wise to check in a good service manual for your specific vehicle for the proper proceedure.

[jseklund]

Drop the pan, change the filter then clean up the mess! Do not worry about the fluid that is in the torque converter. Jim Boyd said long ago that IIRC in his experience as a Auto Service manager that often folks that flushed their trannies with a power flusher would soon have tranny problems. As auto trannys wear some contaminates in the fluid is a good thing to keep parts functioning. Or so it seems to be the case. For years all mechanics would ever do is drop the pan. Newer tranmissions may react differently to this approach so it would be wise to check in a good service manual for your specific vehicle for the proper proceedure.

This is correct as far as the fact that most service managers will only drop the pans. The procedure in the book on my car (and the one that the dealership uses) only has you dropping the pan.

However, I think that the "flushing will kill your transmission" statement is a myth. The problem is that most people NEVER service their transmission, and then it starts acting up. When it starts slipping, they want to change the oil and have everything back to normal. It's too late, but they flush and two weeks later their car won't go. They blame the flush. Seems logical enough- I flushed and then my tranny died. It's not how it works though. Contaminates are NEVER good for your oil, and if shards of metal are holding your tranny together, you're in trouble.

I personally would flush it all out, or try to get as much out as possible. Tarhead's method from BobIsTheOilGuy.com is also an OK method. He is correct that SOME cars have nothing more than screens, so replacement is not exactly necessary. Cleaning may not be a bad idea though. My car has a replaceable filter- so I replace it. If you don't want to mess with the TC, then change the filter (if applicable) and clean everything up every 20-30K and get a fluid evacuator to change out the fluid in the pan every 5,000 miles or so. I personally like messing with the messy tranny fluid as infrequently as possible, so I opt to do it all at once and be done with it. I have to do it 1-2 times a year with the mileage I put on the car.

[Bruce Cohen]

I was always led to believe that if the fluid remained cherry red , not brown and didn't smell burnt, not to mess with it. Just keep the level (check it with the engine running) topped off.

Bruce