Transfer Case And Differntial Fluid Flush... Or Change.

[flstc4me]

Thinking about changing the fluid in the transfer case and differentials on my 04 Tahoe Z71. The transfer case is the NP8 unit. I called the local dealer to get a price on having the fluids changed to which the service writer replied "We don't just change it, we flush the differentials and the transfer case. It's much better. It will run you $380."

 

Needless to say the price seems a bit steep and I noticed that many people on this forum change the fluids and I could find no reference to anyone flushing the differentials or transfer case.

 

How important is it to flush these components?

 

I assume my front differential has standard mineral based gear lube based on all of the information that I can find. I removed the fill plug and it stinks like good old fashioned gear lube, but I have never smelled synthetic gear lube so I can't make the determination. Is it likely mineral based gear lube?

 

I have had the transmission flushed a while back instead of changing the fluid.

 

Any insights on flushing vs standard changing appreciated.

[zaac]

The only insight I have is changing it yourself will cost about $30. Each of them only holds about 2 quarts. I don't think flushing would be a big benefit, imo.

[markw8]

I don't see any reason to flush any of them. Just change the fluids.

 

Mark.

[Z45]

Flushing is just a way for them to make more money from you. That's the big money maker for the shops these days, sell a flush.

 

It should not cost this amount of money. I had the 2 diff, the trans and the TC fluid changed in my 2008 to synthetic last year. It took the trans shop 1.5 hrs to do it and I supplied the fluids. They charged me $90 labor. Sound like this dealer charges $150 hr.

[Spurshot]

I see no benefit from "flushing" these components, nor do I believe they were being honest or conveying correct information to you. I am not aware of any method to "flush" any of the differentials or transfer cases. They are basically open case resevoirs although the transfer case does have a simple oil pump system of sorts. But a transfer case doesn't have an elaborate pressure oil system like a auto trans. The auto trans flush methods are intended to get the old fluid out of the torque converter since these typically don't have drain plugs.

 

Just drain thses components and change the fluids. That's all they will do, I am nearly certain.

 

It's very easy to change the fluids in these components since they all have drain and fill plugs easily accessed.

 

The front axle should take SAE 80-90W GL-5 gear oil (about 1.75 quarts)

The rear axle should take a SAE 75-90W Synthetic gear oil meeting GM Spec 9986115 (about 2.2 quarts)

The transfer case should take a Dexron III Automatic Transmission Fluid.

(about 2.3 quarts)

Fill them to the bottom of the fill plug.

 

This is simpler than changing the oil and filter on any common engine.

[flstc4me]

Thanks for all of the advice and comments on the value or lack of value of flushing.

 

I crawled under the Tahoe this morning and drained and replaced the fluids with no real issues. I didn't even get a bath in gear lube.

 

I do have one question, what do you seal the transfer case plugs with? I know there is some GM part number but I don't have that stuff at my disposal.

 

okay, so I have another question also. I bought the Auto Trak II fluid the other day for the transfer case, but when I pulled the drain plug some amber/brown stuff came out, not blue as I expected. It looked more like motor oil, did not look like transmission fluid and did not smell like spent transmission fluid. It have very little odor to it at all. I looked at the tag on the transfer case and it says New Process NP246 followed by two letters that were either CM or GM I believe. This equates to the NP8 transfer case. The glove box sticker lists the transfer case RPO code as NP8. Well it has blue fluid in it now. Should I be concerned about the amber/brown fluid?

 

The front differential drain plug was fuzzy, but there were no chunks of metal only the shavings so I assume this is normal.

 

Now to think about the transmission fluid. I like the idea of pulling the pan, changing the filter and filling with 4 quarts or whatever it takes. I read through the Amsoil site and don't think I am ready to do the flush myself.

 

Thanks again for all of the help.

[Spurshot]

Good job on the diffs and x-fer case. The fluid could have been anything some lube shop put in. No telling what it was. You did the right thing with the blue/purple synthetic Dexron III. My 4wd pro says the Chrysler syn ATF is the same stuff.

 

If you have a 2500, the transmission likely has a drainplug. You won't get the oil from the torque converter or the cooler lines etc by changing it yourself. But it's still better than not changing. If you change it more often, I think the flush can be substituted by a drain change.