Flushing the transmission and overdrive

[AUSMHLY]

What would be a good product to flush the transmission and overdrive.

Once the car is up on jack stands, drain all the oil.
I've heard you could pour in a couple quarts of ATF or gasoline. Your thoughts on those?
Start the car and slowly run thru all the gears and overdrive.
Drain it and fill with your choice of oil.

Your thoughts?

 

[Keoke]

Well Roger if you feel it is necessary just leave the petro out and you will be OK--Keoke

 

[AUSMHLY]

Hey Keoke and others,

Why want to flush I guess is the question.

I have a friend who has not changed his oil in a long time, and I want to make sure there's no build up of crud or sludge in his transmission or overdrive. Plus if someone decides to change over from standard oil to synthetic oil or vise versa, I think it's a good idea to clean it all out.

Anyone want to chime in on using gasoline for flushing? Is it ok? I think that would leave less residue than ATF. However gas will not provide and lubrication when it's running thru the gears. May not be a concern, for it only being run thru slowly and for a couple minutes....true?

 

[Bob_Spidell]

The argument for using non-detergent oil in gearboxs and O/Ds is it lets crud settle to the bottom instead of floating around and blocking narrow passages (FWIW, I've used detergent oil and synthetic for over 100K miles with no problems; I prefer to keep the crud in suspension so it can be flushed with an oil change). You're suggesting putting a solvent into the gearbox to stir up any accumulated crud--maybe not a great idea. I'd just do a couple of oil changes with detergent oil.

If you're going to do it, I'd use mineral spirits or motor flush; gasoline is just too volatile--not to mention flammable--and who knows what it will do to the seals.

 

[roscoe]

Don't forget, there are several o rings that need to be functional and they are probably really old and subjecting them to gasoline(or ATF) might not be the best thing for them. Besides, if there is not abnormal amounts of stuff in the gearbox screen and if the oil doesn't "sparkle" in the sun when you change it, why flush. You are never going to get real thickened, old, gummy deposits out without a brush and compressed air in all the right places. Without scrubbing, heat or some very aggressive sort of solvent I don't think "flushing" is what people think it is most of the time. I never flush any gearbox with anything other than the fresh oil that is to be used to service it.

 

[TimK]

I opened the solenoid/accumulator box cover and cleaned the sludge out of there manually. I found quite a bit residing there. There is not enough flow through that area to flush it out by running solvent in the trans. I would never use gasoline except on a rag to clean up. Gasoline is not a lubricant and to run a transmission or engine with it is a crazy idea.

 

[Richard Dickinson]

It seems that anything more than a couple of oil changes is likely to do more harm than good . Just remember "if it ain't broke don't fix it.