DO NOt FLUSH a high mile trans, period!

Guys, What did we do 30 years ago with our old C4s, C6s, FMXs.......there was no such thing as flushing or complete fluid exchange, we all just drained the pan, cleaned it well, changed the filter, drained the converter, then refilled with fresh fluid-right? I know I did and got plenty of miles out of those old, antiquated transmissions too-yea, there was some old fluid left in the lines, and cooler but we never gave it any thought it was so small of an amount.

 

I don't agree. Change it all. Keeping old stuff in there ain't good. You don't change your oil 1/3rd at a time, why do that to the trans? Especially when you're changing from Mercon to Mercon V.

 

I'm with Joe to change it out. I guess I should tell my Dad not to change his with 200k on the original. That must be good tranny fluid to last that long.

 

damn, 5 gallons + the PS flush is almsot $300 in fluids!

 

Huh? I just bought 24 qts at Sam's Club and it was not $300! I think it was less than $75....

 

I bought 20 quarts of Mobil1 syn Merc V for about $120. Where are you getting fluid and what kind is it??

 

so it is a personal prefrence. i am so confused the fluid does not smell to bad but it ant a pretty red.

 

If you have any doubt about the quality of fluid in there,change it,you will feel better.

 

Not trying to jack this thread but can someone tell me which trans I have? I believe its the same as op....I need to change fluid also...Its an 02 f350 crew w/82000 miles. Should I flush or just drop pan change filter and drain t/c? Not sure if mines considered high mileage or not..

 

I was looking at 25 quarts of Amsoil. Where'd you pick up your Mobil1?

 

If you have a 7.3 automatic you've got a 4R100 if you've got a 5 speed manual it's a ZF5 and a 6 speed is a ZF6.

I believe there were 5 and 6 speeds. Not 100% sure though.

 

All the SDs with manuals have the ZF-6, AFAIK.

Amsoil is WAAAY overpriced! I got the Mobil1 by the case from O'Reilly Autoparts. You might see if you can find Valvoline Syn Merc V -- It was cheaper than the Mobil1, but I couldn't find enough.

 

The gas engine trucks had the ZF-5 until 2002.

 

I used this process on my 01 4r100. What it didn't mention is that while you are running the engine and pumping fluid out, you also get a large volume of fluid coming back out of the tranny where the return line attaches. Not knowing whether it was a good idea to plug that opening, I let it come out and ended up short on my refills. No big problem but I would like to know for future reference if its ok to plug that hole while doing the procedure. Also caused a much bigger mess as at times the fluid really blew out of the hole.

Any guidance would be much appreciated!

 

It doesn't mention that because it shouldn't happen!

You probably have a restriction in the cooler circuit. When the cooler line is restricted the bypass valve opens and the fluid doesn't go to the cooler, it flows through the tube on the side of the trans.