Front and Rear Diff Change

[foghorn23]

Finally took the time on Saturday to look into the front and rear diff to change fluid. I have the limited slip rear end so I went by the dealer to check on fluids (especially the 8oz additive for the LS rear end). I was amazed to find that the dealer was going to charge $118 for the fluids required. I politely bought the 8oz GM additive and left for Wally World and Autozone. I bought 3 qts of Castrol 80W-90 @ Wally World for approx $9 and 3 qts of Mobil 1 synthetic 75W-90 at Autozone for approx $22. The two guides on the site:

 

Front Diff Guide

 

and

 

Rear Diff Guide

 

were very helpful. The allen wrench trick was super advice. All in all the front diff held a little over 3 pints of new fluid. and was exactly 1/2 inch below the fill hole. The rear held the 8 oz bottle of Limited Slip additive and two quarts of fluid. It was exactly 5/8 inch below the fill hole. I was able to return a quart a Wally World and a quart at Autozone. Total cost around $29. $118 vs $29; now I know why they're called "stealers."

 

All in all this is a very simple job. (I didn't remove the cover from the rear diff, probably should have, but didn't have time this weekend) Just make sure you can get your fill plug out before you drain the diff. ( On the rear the fill plug was super tight and required a few four letter words before it would budge.) It would be a crapper to drain the diff and not be able to refill it.

 

Anyway, thanks to all who developed the guide on the site. You can learn so much about these trucks here!

 

Thanks again

 

Vroten

[RyanbabZ71]

your truck is on 01? You do not need the rear diff additive.

[foghorn23]

Yes I know that's supposed to be the case, but since I wasn't using the "genuine GM fluid" I thought I'd go ahead and add it.

 

vroten

[RyanbabZ71]

all you need is synthetic fluid which the mobil 1 is. The additive is unnecessary.

[seadoons]

Ryan, is the additive necessary in a 2002 model? I also have the limited slip and didn't add it when I did the original change at 30K, but I am about to do it again now that I am close to 60K.

[RyanbabZ71]

the additive is for the old body style trucks because they used regular oil and not synthetic like the new trucks

[biznotch]

What about a 2000? Additive needed?

[budhayes3]

The Additive is not necessary from 99 NBS and up, or if you switch to synthetic.

[AZ-Z71]

I agree with everyone about about the rear diff additive.

 

Anyway, did mine on Friday and it went really well. Don't know if I seen it here or read it somewhere else but when removing the plug it is a good idea to make sure you can get the fill one off first. I did that, but all my plugs came out really easy.

 

The blue transfere case stuff was only like $6 and change from the dealer. Said I needed 2.1 quarts but after draining it I only got like 1 and 3/4 back in before it came back out the filler hole. (I bought 3 just in case)

 

The rear diff is supposed to be like 3 quarts but only could get like 2.5 in to take it to 5/8" below the fill hole.

 

The front diff is supposed to be like 2 quarts but maybe only got 1.5 in before filled.

 

I'm assuming that the capacities are for a total tear down and totally dry. I could re-check them in a couple days and make sure they are all still filled.