68FastbackGT

What do you guys think about changing the automatic transmission fluid on a transmission with over a 100k miles since the last change. I have heard that if you do not change the fluid within 30K, that you should not do it. The reason stated is that the varnish build up will be greater and the detergents in the new fluid might break the varnish free and clog up the transmission. This clogging would precipitate a rebuild, which is what was trying to be avoided with the fluid change in the first place.

Please let me know what you think.

coda618

IMHO, you risk more by having varnish/sludge build up, and deteriorated fluid will not do wonders for your trany either. Also, how clean do you think the original filter is at this point. That will hinder the flow of the fluid and cause wear. By your thinking above, you are avoiding something that might happen (sludge breaking loose) for what you know is going to happen, general decline of the trani fluid, worn filterand associated problems. Just do it. Your trani will thank you.

scott_m_mil

You could always change it , run it for a few hundred miles then change it again if your worried about a sludge/varnish break down you may even add some of that cleaning junk the to the first batch ...It'll cost a little more(not too much i think a filter at a ford dealership is like 5 bucks) but you dont have to worry

boeing747arowair

+1. u dont want stuff to continue grinding in there huh?

OhioMachIRunner69

I agree with these guys, you are better off changing the fluid than running the car on old tranny fluid.

Soaring

You not only need to change the fluid and the filter, you also need to drain the torque converter. Ask if you don't know how.

scott_m_mil

Good call soaring.

68FastbackGT

Tanks for all the input guys. I posted another sight and got just the opposite advice, that is to not change the oil after running it for so long without a change unless it is having problems. (Ahh, what do they know)

A compromise suggestion I have been given is to only drain the pan and change the filter. The idea being that you lower the rate at which the new oil cleans the transmission and lower the risk of large pieces of a deposits braking off and creating an embolism. I guess this is kinda like putting a quart of automatic transmission fluid in the oil to quiet sticky lifters.

I know that some torque converters have drain plugs accessible from the inspection plat. Alternatively for torque converters without a drain, I have been advised to remove the cooling line from the transmission, let it drain into a bucket, start the engine and stop it when the flow of fluid slows. Then fill the transmission with new oil and start the engine again until you see the new oil come out. Then put every thing back together and top off the transmission.

ZZmustang

You can even do it lazyer than just changing the fluid in the pan.
Just unhook the trans line from the radiator and start the engine, Don't rev it or put it in gear. when the fluid stops flowing shut it off, replace the amount that is in the pan that you drained it to. You will have to do this a couple times in a week to get more new fluid in than old. but, it's easy and really , really lazy mans way of doing it.

andrewmp6

soaring how you change it in the converter