Tranny question I have been meaning to ask

I have always heard once an automatic gets a certain amount of miles on it, it is NOT a good idea to change the fluid. I keep hearing stories of peopl e with 100,000 miles on their tranny and getting the fluid changed and the transmission suddenly lcoked up. What exactly would cause is and is this tr ue?

Reply to
stryped1
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not always, but potentially, for extreme cases, yes. seals, including those in valve bodies, age with the fluid. new fluid, with its seal conditioners, can potentially cause valve body rubbers to swell and therefore lock. this won't happen if fluids are changed regularly, and to some extent, it's dependent on the quality of the rubbers, but if the seal chemistry is at the point where its cross-linking is starting to break down, then seal conditioner can cause it to swell much more than normal, hence the problem.

it's not that common though, and less common on modern electronic control transmissions though - different controls, different valve bodies.

similar things happen with brake fluids to cause leakage after fluid change. often this is blamed on "pump bleeding" - this is untrue unless the cylinder is actually corroded and it physically tears the seals - which would happen on /any/ extended pedal movement anyway [emergency braking]. new fluid, in this case, shrinks seals, and when a little worn [as is natural with use], this can be sufficient to case leakage.

Reply to
jim beam

The argument is that by removing the old fluid and putting in new fluid, you can move some of the residual particles of crap around inside the transmission and possibly move some from a place where they are doing no harm to a place where they are doing harm.

In addition, there may be seals which are held together only with varnish.. put new fluid in, some of that varnish may dissolve and things start leaking.

Some folks use a complete flush, and the flushing process is even more apt to dislodge junk.

My recommendation is to never, never, allow your transmission to get so messed up in the first place that fluid changes will ever be a problem. If you do regular changes you will never get into this sort of situation.

If you have a car with 100,000 miles on the transmission and the original factory fluid (and there are a lot out there), my inclination would be to change the fluid, don't flush it but just change it, then do it again after about a year, and then do whatever changes are recommended in the manufacturers' extreme service schedule. Yes, you are taking a risk when you do that first one. But if changing the fluid causes the transmission to fail, you're better off with a new transmission anyway because the old one was pretty badly abused.

Then again, I drive a manual, so what the hell do I know?

--scott

Reply to
Scott Dorsey

is NOT a good idea to change the fluid. I keep hearing stories of people with

100,000 miles

lcoked up. What exactly would cause is and is this true?

The cause most of the time is coincidence. That combined with the likelihood that of the 100,000 people who do this it's only the 10 people who's transmissions go bad shortly afterward that bother posting anything that we remember for more then a day. Nate? just said he did it at 135K and no problems. No one will remember that the next time someone asks about this issue but everyone will remember the guy who posted that he changed his fluid and a week later his transmission went out. Also, the reason most people who would let things go so long without a change decide to change the fluid is because they are starting to experience some transmission problems. Provably 9 times out of 10 their transmission would have gone out "soon" whether they changed teh fluid or not.

Reply to
Ashton Crusher

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