I hear this a lot. I was just talking to my BIL. He's got a 04-ish 1500 work truck. 260k miles currently. Bought it with low 100k. Works as a HVAC technician and tows a trailer occasionally. Not a huge weight, but he drives a lot. Stop and go, etc.

I was talking to him recently and he said something like, "I never serviced the transmission because they said if you change the fluid it will cause it to slip." Something about if you remove the old fluid with all the clutch material, the "grit" goes away and leads the clutches to slip. Me thinking: A particle that has already been removed from the clutch or band backing and is suspended in the fluid can't help the clutch pack engage, can it? How?

Is there any truth in that? I would think doing regular scheduled fluid changes is the best thing to do to prolong the performance of your unit. I've serviced my transmissions (4 speeds) well into the 200k mark w/o any issues. There's always a bit of clutch material on the magnet, which seems normal.

What say the transmission experts? I realize there's very different designs in these units. TH350/400, 4Lxx, 6Lxx... don't really know anything about the 8Lxx and 10 speeds.

 

Let me start by saying, this is the DUMBEST rumor out there. period.
I'm not calling you or your family dumb...this rumor is passed around so much I can see why someone would believe it if they heard it that often

You are absolutely right, regular fluid changes are the best thing.

This is true for ANY automatic transmission.

"grit" in the fluid is absurd to even think about

 

Thank you! Exactly what I was thinking! Not to mention all that clutch material causing pump body wear, bushing, journal, and bearing wear. Yuck!

 

The filter removes a lot of grit.
I have purchased used vehicles before and had to replace rear main seals, etc
and have drained the converter and transmission on these.
I've also flushed transmissions by putting a big pan under the transmission, cutting a filter neck off and attaching a hose that goes into a one gallon bottle of fluid and ran it til the fluid came out clean(er).

Never had a problem.

 

With that thinkin'...
Take the Pan Magnet out so that the "Grit" can circulate betta!
And make dems performance mo betta!

 

That rumor happens for one simple reason. Many times people change fluid because they feel a problem and of course after that problem gets worse and they blame the change rather than the fact they didn't change it for 100k miles or more.
Now in the old days before modern trans fluids it could be somewhat true with high millage units as varnish would build up on valves etc and act as a sealer of sorts and new fluid could wash this off and cause some issues. But that was long ago.
Frank@PerformaBuilt

 

Wow, Grady just flipped my world with his awnser.
It is not the grit. i was told by shops, that the old fluid has some clutch material in the fluid, thats why it starts slipping when you change the fluid.

But from now on, i know the right awnser.

Thanks Grady!

 

Grady is Maroon Monster, not vorteciroc, for the record.

 

I also think this myth is horse apples. I've been doing full flushes (through the cooler line) for over a decade now with no ill effect. i normally pay attention to whats in the pan and the colour of fluid before i make a decision on flushing or not.