Rear Axle Fluid

Domano 68 · July 31, 2004

Can anyone tell me the quanity of fluid for the rear axle of an 01 Silverado 1500 Ext Cab Z71? Also, would Mobil 1 Synthetic 75W 90 be a good oil? Thanks much!

westex39 · July 31, 2004

Quanity is just under 2 quarts. Level should be between 5/8" and 1 5/8" below the fill hole. I split the difference and put it at 1".

I have read posts on other forums that say that mobil 1 75W-90 works just fine.

I used Amsoil 75W-90 in my application (2001 tahoe 4x4). I didn't have any trouble with it. My brother-in-law used the Amsoil 75w-90 in his 2500HD chevy. He has about 85000 miles on it now with no problems.

99silveradoz71 · July 31, 2004

Just drained and filled the open 3.73 on my 99 Z71 today again(2nd time) with Mobil 1. No issues at all.

Domano 68 · July 31, 2004

Thanks much!

gnutruk · July 31, 2004

I would just add that if this is the first time the rear gear oil has been changed, it would be a good idea to remove the rear differential cover and clean the magnet that is attached to the inside of the cover.

That magnet is there to capture all the tiny metal bits that result from normal wear of the gears. Most of the wear happens during the first one or two thousand miles, and/or because of the first big tow.

The magnet starts looking like it is covered with fine "fuzz," and sooner or later that fuzz should be scraped off. After that, you might not have to remove the rear cover for another 80,000 or 100,000 miles.

Furthermore, if this is the first time the rear diff. gear lube is being changed, it is also a good idea to replace the rear diff. gasket. Doing so is VERY cheap insurance. Replacement gaskets are only $4.00 - 6.00 at the dealers, so cost is negligible. GM part number for the G80 locking rear differential, half-ton, 10 bolt pattern, is # 26066456. Make sure to thoroughly scrape off all the bits of gasket that will be stuck on the rear diff. housing and on the cover plate. Try not to get any of the old gasket bits in the gears. While the cover is off, take a few clean rags and generally tidy up in there.

When replacing the rear diff. cover, torque the bolts down to 40 N-m (30 ft. lbs.) in a crosswise pattern. Be sure to replace the brake cable guide in the top bolt that you would have removed when first taking the cover off.

Last, replace the bottom drain plug then fill with your preferred fluid. In my experience, the G80 locker rear differential, using the standard 10 bolt pattern found on most of the late model GM 1500 and Z-71 (half-ton) trucks, holds about 2.4 quarts. A good depth trick that others have mentioned before is to take a small, bent Allen wrench and dip it into the fill hole. Since the short arm of the Allen wrench is almost exactly one inch long, you have a reliable gauge of your fluid depth. I agree with the post above that said the “Level should be between 5/8" and 1 5/8" below the fill hole. I split the difference and put it at 1".” That is exactly what I do.

Then, go for a five or ten mile drive so your diff. comes up to normal use temperature. When you get back, put you hand on the rear cover. It should be pleasantly warm to the touch. That is the sign of a healthy diff. If any damage had previously occurred in there, it might get so hot that you cannot touch it.

Finally, AFTER THE REAR DIFF. COOLS BACK DOWN, again re-torque the cover bolts (and the drain and fill plugs) to 40 N-m (30 ft. lbs.), for they will have slightly expanded during your test run. From then on you will probably not have to do anything for another 80 or 100 K.

Be sure to take your old gear lube to be recycled. It can be recycled just the same as engine oil.

Hope this helps.

gnutruk

99silveradoz71 · August 1, 2004

Yes, good point on the cover and gasket Gnu

bballa · August 1, 2004

The whole job including removing the cover and replacing the gasket is fairly simple. I had never done it before but armed with the information from this forum I had the confidence to tackle the job. I did need to get a torque wrench first however.

Shotgun · August 1, 2004

I need to change mine. Do i need friction modifier with the mobil 1 since i have the locking diff?

bigdogs · August 1, 2004

On the 11.5" rear end you don't even need to remove the cover. The magnetic drain plug is on the bottom of the case so when that is removed all the gunk comes out too. I used Amsoil Series 2K 75-90 in my (took 4 quarts). Those 4 quarts still cost less than ONE quart of the grape juice..