Differential/TC Fluid Change Question

[Coloradolawdobe]

Hello all,

I have found multiple "how to" guides on changing the transfer case/diffential fluid and I believe I am all set. However, I wanted to double check something. I have heard/been told that for instance if you do not ever change your automatic transmission fluid that you should not change it because it may blast out what little is holding the transmission together. Hopefully this theory is not the same with the Diff/TC fluids. My TB has 118K miles and the only time the Diff/TC fluid might have been changed is when I bought it at 40K miles as a certified used from GM. So, am I safe changing these fluids even though they may never have been changed/ might have been changed almost 80K miles ago? Any advice is greatly appreciated! Thank you in advance!

~~Rich

[Trail X]

The theory on the transmissions is that grit gets built up inside the transmission, and it becomes essentially 'friction aids' for the clutches. The theory is that if the fluid is changed, it will clean the transmission, and the built up grit. The general thought is that the transmission therefore may slip.

The other way to think about it is, if the transmission fails after the fluid change, it probably would have failed soon anyways.

I don't think it counts as much for the TC and diffs. Change those fluids immediately.

[Coloradolawdobe]

James,

Thanks for the quick response. Yeah, they are getting drained this weekend for sure. I just wanted to make sure I didn't take any life away from whatever is left!

~~Rich

[navigator]

I also think most with the old tranny theory will agree that a drop the pan, change the fluid/filter is ok but a general power flush might be bad.

Our tranny's aren't due for a flush until 100k anyway for normal driving so at 118k you aren't in too bad of shape.
Mine is at 90k and is still pretty and pink.
I bought the supplies to do a drop/drain/replace and plan to do that soon.
I think after that I'll just do drain every 25k and have thought about adding a cooler as well.

[The Roadie]

... for normal driving...

What is this "normal driving" of which you speak?

Sorry, had to.

[DJones]

I think I was around 110k when I changed the rear and 140k when I changed the front. Somewhere in between I changed T/C and I highly doubt that it is the reason why it clunks.

[Coloradolawdobe]

Hello all,

Thanks for the input. It sounds like I'm good to go for the Diff/TC fluid. I still feel very "iffy" about the transmission fluid. My 78K of the total 118K miles on the vehicle have been fairly "hard." I have made countless trips up to the mountains, one very heavy tow from NOLA to Denver, and multiple heavily loaded cross country trips. If I were to do anything I suppose it would be a mere fluid/filter change and not a flush. Is there any way, other than looking at color and smelling the fluid, to determine if I have passed the proverbial point of no return? Thanks!

~~Rich

[Trail X]

aa1car is always one of my favorite resources for things like this:

http://www.aa1car.com/library/atf.htm

[bartonmd]

The theory on the transmissions is that grit gets built up inside the transmission, and it becomes essentially 'friction aids' for the clutches. The theory is that if the fluid is changed, it will clean the transmission, and the built up grit. The general thought is that the transmission therefore may slip.

The other way to think about it is, if the transmission fails after the fluid change, it probably would have failed soon anyways.

I don't think it counts as much for the TC and diffs. Change those fluids immediately.

That's the theory a lot of people have, but it's not what causes old transmissions to fail when you flush the fluid...

The new fluid has all of the new additives in it, to get rid of the deposits... The deposits break free and pretty rapidly with the new fluid, and clog up the filter (which is usually original, because people often "flush" instead of flush and drop the pan and change the filter), which then starves the transmission for fluid, which kills it...

So if you're doing it on an old vehicle, you want to flush all the fluid, then drive it for a few days, then drop the pan and change the filter, and top the fluid off...

Mike

[Trail X]

Ah, thanks for the clarification. Mike's got better knowledge of the transmissions than I do. Isn't some of your family trans engineers?

My last flush, we ran a good bit of DEX 3 through the transmission to clean it out, then dropped the pan, changed the filter and fluid to DEX 6 because I was a little worried about the previous change interval. Sounds like a similar method, which I've heard is good for also cleaning out the torque converter.

[bartonmd]

Ah, thanks for the clarification. Mike's got better knowledge of the transmissions than I do. Isn't some of your family trans engineers?

Yes, but I read this in an SAE paper some time ago...

Mike

[Coloradolawdobe]

Hello all,

Changed the Rear Diff, Front Diff, and TC today. The entire process took three hours from start to finish, and then another 30 minutes trying to get this stuff out of my hair. All the write-ups on Trailvoy are incredible, I have saved so much money from these sites!