Differential Fluid Change

woyster_00z71 · May 20, 2003

This weekend I am going to change the front and rear differential fluids in both the Silverado and the Tahoe. I have read several old posts and the guides and am going to get:

5 quarts of 80W-90 Valvoline gear oil for the Front Diffs

5 quarts of 75W-90 Mobil 1 Synthetic gear oil for the Rear Diffs

and 2 gaskets for the rear diffs

The gasket number that I have is 26066456. Is this the same for both a 4.10 and a 3.73 rear differential? Is it the same number for both models and years? Is this number still correct?

Just want to make sure before I start rounding up parts and oils.

Thanks,

B.J.

woyster_00z71 · May 23, 2003

Well, I bought two gaskets at the dealer and then drove all over Northwest Houston looking for gear oil. Finally found what I was looking for.

This morning I changed the front and rear differential fluids on the Tahoe and probably tomorrow morning I will do the same on the Silverado. The rear magnet looked great with no shavings on it at all but the front diff magnet had quite a bit of shavings on it. Also, there was a alot of silver grease on top of both of the magnets. Does anybody know what this was? Is this something done at the factory/dealer? Maybe a sign to let them know the fluids have never been changed?

Anyway, I used the allan wrench method of checking fluid levels. The rear worked great...2.5 qts was perfect. The front however took a little less than 2 qts. Then when I was checking the level, I dropped the allan wrench and feared it had fallen into the diff. Thankfully it fell into my oil pan instead.

All in all it was a fairly easy job and hopefully it will last me another 50,000+ miles.

B.J.

DJinCO · May 23, 2003

B.J.,

Howdy, Why didn't you use Mobil 1 for the front diff also?

Thanks,

Doug in Colorado

2001 Tahoe 4x4

bigtruck21 · May 27, 2003

i'd say the 80w90 causes more wear than the 75w90 based on your magnet test. When i change mine, i'll use synthetic in both. The silver grease your talking about is probably very fine metal shavings. It looks like that when i pull the oil plugs out of new vehicles during first time oil changes.

bassdog · May 27, 2003

The silver grease your talking about is probably very fine metal shavings. It looks like that when i pull the oil plugs out of new vehicles during first time oil changes.

Could very well be. Another possibilty is anti-seize compound from the threads.

woyster_00z71 · May 27, 2003

Thanks for the replies. I didn't use Mobil 1 in the front diff for two reasons. First, the front diff doesn't have synthetic from the factory and GM doesn't recommend it. Second, I couldn't find Mobil 1 80W-90 and had a hard enough time finding 75W-90.

I did change the differential fluids on the Silverado on Saturday afternoon as well. The rear magnet was about the same as the Tahoe even though it had 20,000 more miles on it. The front magnet had less shavings. In any case, the fluids were changed and it took me about an hour less than what it took me to do the Tahoe (I guess I learned something).

Now for the tranny and transfer case on both trucks. Has anyone noticed that the owner's manual only says to check the differential fluid levels...never to change them? And it doesn't mention the transfer case at all! Tranny is mentioned to check levels and to service at 50,000 mile intervals. Just a bit of interesting information.

B.J.