I'm going to change my rear diff fluid this weekend. Does anyone know how many bottles to buy off hand. Thanks

im purty sure i did 4. only about 1.5 came out :0

same here, about a 1.75 came out. I put about 3.5 bottles of Mobile1 in it. I figured if GM only put 1.5 in the 3.5 i put in should be more then enough.

I went to the dealer and they sold me 2 quarts. I didn't think that sounded like enough. It was like $32 dollars a quart.

You need 4 qts. I take it the dealer sold you "grape juice" (80w90 full synthetic). Get 2 more qts if you run the G80 differential. Better yet, take the 2 qts back for return and get 4 qts of Mobil 1 80w90 synthetic and save $.

i ran the 75w140 is that bad?

i ran the 75w140 is that bad?

Not really bad. It's just going to be real stiff come winter.

My dealer parts pulled up the G80 rearend and told me it took 2.87 quarts of 75/90 Mobile One synthetic and i could get the same thing at Auto Zone a lot cheaper. I did but it took 4 quarts and the front ended up taking 3 instead of the almost 2 that he said. There was no waste as i used a pump to install it. Course i don't think you get a full quart anymore anyways. lol

When lube runs out the fill hole it's full.

From the 2004 service manual (should be the same for 2003), for rear diff:
8.6" Diff: 0.6" - 1.6" below fill hole
9.5" & 10.5" Diffs: 0 - 0.4" below fill hole
9.75" Diff: 0 - 0.16" below fill hole
11.5" Diff: 0.6" - 0.8" below fill hole.

Diesels have 11.5" but I don't know what the gassers have. For about 1/2" below the hole, mine (11.5") took about 3.75 qts. A lot of people have filled them to the fill hole with 4 qts. and not reported any problem with that.

Interestingly, the manual also lists the capacities (in qts.) for those diffs as 2.15, 2.75, 3.00, 2.75, and 3.17, respectively.

Doing the front diff? Manual says 0.5" - 0.625" for the 8.25" diff; 0 - 0.25" for the 9.25" diff. It lists 1.51 qts. and 1.83 qts. for these, respectively. Mine (9.25") took right at 2 qts. to the fill hole.

For the first change I went with genuine grapejuice (over $150 for 6 qts.) but next time I'll switch to Mobil 1 since so many are using that with good results.