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Phillio99
12-08-2010, 02:08 PM
I've got a 93 Mark VIII with a 156,000 4r70w in it. J-Modded, and filled with Mercon V by the previous owner. I'm starting to get a little the 3-4 rumble strip phenomenon and I'm considering changing the fluid.

I've heard rumors it's unwise to replace all the fluid in an older transmission as some of the clutch material in the old fluid extends transmission life. I'm guessing this is some garbage but let me know whether you guys think I should flush the whole system or simply drop the pan.

Thanks,
Phil

90coug
12-08-2010, 02:14 PM
For what it's worth I've heard the same info about flushing the whole transmission. I'd say do what your most comfortable with and maybe just start by just dropping the pan.

TbirdSCFan
12-08-2010, 02:32 PM
Was the 4r70w originally made with Mercron V? If it was originally equipped with Mercron III/Dexron, they are not interchangeable. Might want to research it a bit for yourself.
Anyways though, if you are beginning to experience some shifting problems, they won't go away with a fluid change, nor will they go away without one and if the wrong type of fluid was used, its iffy that the correct type would fix anything either.

Usually, from my experience with the AOD+Mercron 3, shifting/holding problems come from clutches worn past their tolerances. That doesn't necessarily mean worn down to metal, but charred up enough to not grip the steel rings. Upping the line pressure might buy you some time, but usually you're looking at a rebuild. In that case if it were me, I would just leave it alone until I could get the time to do the job.

Ddubb
12-08-2010, 03:16 PM
Mercon V is the recommended fluid for all 4R70W Transmissions.

Could be the torque converter clutches slipping if its not the transmission clutch pack if the fluid hasnt been broken down past its usable point.


- Dan

frdlvr30
12-08-2010, 06:53 PM
Flush the whole thing. If it continues....replace the converter...If its just starting to rumble into overdrive it may cure the issue.

Phillio99
12-08-2010, 07:57 PM
I reread through Jerry's 4r70w thesis over on the TCCoA and it sounds like either method is acceptable to flush transmissions. I think I'm just at the limit on the service life of this fluid. Going to have it flushed and go from there.
Thanks,
Phil

Dirtyd0g
12-08-2010, 08:58 PM
93 were a bad year for the converters, you want a 96+ converter as a bare minimum or the problem will keep resurfacing.
Alan

TbirdSCFan
12-09-2010, 01:13 PM
I'd say do what your most comfortable with and maybe just start by just dropping the pan. Or to avoid the mess, siphon most of it out the fill tube first. a 8' length of 1/2" clear plastic tubing from the HW store works great.

White Lightning
12-09-2010, 08:34 PM
Don't forget the trans cooler! It collects a lot of trash and will only contaminate your nice clean fluid, I have had good luck with talking to my local trans guy, he has given me a lot of good advice! Great guy! cheers Frank H.

Phillio99
12-13-2010, 11:32 PM
93 were a bad year for the converters, you want a 96+ converter as a bare minimum or the problem will keep resurfacing.
Alan

Hey Alan, If I am dealing with a breakdown of torque converter clutch surfaces, would I be better to just wait on this until I can replace the converter or change the fluid and hope that works as a bandaid in the meantime? I need the car to commute this winter and I doubt I'll be able to replace a converter until this spring. Appreciate the help.
Phil

Dirtyd0g
12-17-2010, 04:35 PM
If it were a late model that might work, the early model is just going to clog the filter int he transmission the more it flakes off.
Alan

None2Slow
12-18-2010, 05:07 PM
I've heard rumors it's unwise to replace all the fluid in an older transmission as some of the clutch material in the old fluid extends transmission life. I'm guessing this is some garbage but let me know whether you guys think I should flush the whole system or simply drop the pan.

Thanks,
Phil

This is true. Had a 74 Ford 4x4 that had a leaky pan gasket. Replaced the gasket and filled with new fluid. About 5 miles down the road, it was done. Drained the fluid again and it was really really dark, chunky and metallicy. Suprisingly, didn't smell burnt.

91BLOWNBIRD
12-18-2010, 08:57 PM
its not always good to flush auto trannys

Ddubb
12-18-2010, 10:31 PM
its not always good to flush auto trannys

But not changing your fluid is even worse ... ;)


- Dan

91BLOWNBIRD
12-19-2010, 03:47 AM
flushing is bad...changing is good