Transfer case Fluid change

89 Suburban with 139,000 miles


In changing the transfer case fluid, when I removed the top fill plug, about 1 quart of ATF fluid came out of the TOP FILL hole.

My questions are:

1)how did they get that much in the unit?

My only guess is that is filled by other means during a repair and installed with fluid?

2) does overfill do any damage?

I did notice this unit is leaking and would drip fluid on the exhaust pipes after I had used 4wd.


3) Is the transfer case connected to the transmission in any way that would cause this overfill?

There are 1 maybe 2 reasons why transfer case is overfilled.

1 - Somebody did infact overfill it.
2 - Trans fluid is getting past the seal from transmission and filling transfer case. Not too sure about this one though. Was your trans low on fluid?

Shouldn't do any damage to TC.

Transfer Case is connected to Transmission taking place of Tailshaft housing. Tailshaft Housing would be used on 2WD.

Was your trans low on fluid?

Yes, the transmission was down about 1 1/2 qt which was about the overfill amount.

Is one safe to assume this is normal and that the transmission and transfer case are connected? And that if you want a clean transmission fluid change, you need to do the transfer case at the same time.?

As Fireplug informed me on a different thread and confirmed by my mechanic, I probably do have a bad seal.

Does it cause a problem? Mechanic said I will probably blow a seal on the transfer case from the overfill which is evident now from leaks. This leak will cause the transmission fluid to run low and ruin my transmission if I don't keep on top of things. So.........need to get it fixed when I find the $ but until then check the tranny often and have tranny fluid on hand.

This problem is common on all C/K Trucks and all S-10 trucks.
The transfer case will over fill and blow out ALL the seals on the unit and also drain the transmission and burn it up so get it fixed as soon as you can
Even though you are not using the 4+4 the main shaft is still turning and building pressure and will blow out at the weakest link the seals.
Fireplug

Thanks for all the good info here. Neighborhood mechanic helped fix this on the drive way. Cost of seal was $11.00 and he spent about 7 hours on it. Thanks to fireplug for getting me set straight on this.