Yukon

Recently had a chance to get some transmission fluid all over me (installing my tranny cooler) and was lucky enough to catch some in a cup. Now I've wanted to do a flush of the fluid in my 99 limited for some time now, and have read that some say you can mess things up if your transmission has dirty fluid already. So here's what I have, what say the masses, should I go ahead and flush, or hold on to what I have?

Old in a cup


New and Old


More new and old


(sorry for the relativly crappy pics, its hard than you think to get good pictures of this stuff)

I have 120k on the clock, un-known if a flush has been done before. The fluid smells like I would expect old stuff to smell like...

What say the masses?

swampfox

if it was mine i would change it. trans fluid loses it effectiveness over time. if it has a burned smell there could be other problems. a good additive is extra insurance when you change the fluid.

scuba

Yes.

Ardent

Just do a drain and refill along with the next 3 or 4 oil changes. You'll get most of the old fluid out that way.

Yukon

Well I think I should re-phrase.. Obviously its nasty fluid. I know I should change it, but will flushing it all do any damage? Possibly a drain and fill every two weeks with cheap stuff to slowly introduce new fluid, then a full flush of everything once ive drain and filled 16 qts?

snobdds

There are some that would say don't do it with that many miles on the truck. However, I am of the opinion that fluid changes, if done right, should not contribute to a failure. It does loosen stuff and clean junk up, but most problems are there before the fluid change was done.

If it was me, I would flush the tranny with new fluid for a week, then I would drop the pan and clean that real good and replace with new fluid. Then all the large chunks aren’t floating around.

J2F42C

IMHO, I'd do this:

1. Drain and refill the tranny two times before the end of October with new but not expensive tranny fluid like Castrol Import ATF.

2. Before the end of the year I'd drop the pan and change the filter.

3. Then within a week flush the tranny with 16~20qts of new fluid such as MaxLife ATF.

pendrag

I've got a 99 and mine looked much like yours. When I installed the cooler, I flushed out 12 qts of old fluid at the output line before I connected the cooler to it. With each qt out, I cut the engine and added a new qt of Castrol Dextron VI. By the 12th qt, it was coming out clean. I didn't drop the pan - just drained from it initially, and then finished the flush at the output line as described above.

She's been running just fine since then (~2 months) with no leaks so far. I also included an inline magnefine filter during my cooler install.

mmml4

X2 on what pendrag did plus drop the pan and clean the strainer.


IIRC it is the power flush machines that cause the problem with a complete fluid exchange not just fresh fluid. Of couse I have $%&%^ for memory so I may be thinking of something else.

pendrag

I'm a lot less worried about dropping my pan to clean the strainer since I installed the inline filter. I figure anything that gets loose on the strainer and gets into the fluid is going to get trapped in the inline filter. I'll be replacing the filter once a year or so.

brian2sun

Flushing does not break trannies! Idiots who don't service them for 10 years break trannies - and then they like to blame it on flushing. Flushing may point out a problem after years of neglect, but that's a lot better than finding out something's wrong while it strands you unexpectedly on the side of the road in 110 degree summer heat or at 3:00am in a snowstorm right?

Drop the pan, replace the filter, and do a full DIY flush of the system, it WILL prolong the it's life.

skjos

Mine looked worse, and I had no problems after the full DIY flush.

http://home.centurytel.net/stevenjac...sh/tranny.html