Rear end fluid. Again.

[GMCTRUCK]

I have done a search on this but, there doesn't seem to be a consensus on what to do. My 03 manuals don't make any reference to rear axle break-in. As far as fluid goes it says: SAE 75W-90 Synthetic Axle Lubricant (GM part # 12378261) or equivalent meeting GM spec 9986115. Also no reference to the Locking diff. The dealer doesn't seem to know much. I've got 1200 miles on the truck and haven't towed yet but, will be towing on a 5 hr trip (each way) at the end of the month. What should I do?

[Alli-max]

Mobil 1. ~$7 a bottle at Autozone.

[Captain Mal]

4 quarts of Mobile 1.

I have 100,000 on mine with 1/2 of it towing heavy. Changed the rear end fluid three times (the last time 2,000 miles and 2 days ago) and the front ( two quarts) once. All seems fine.

I say nuts to all the talk of what is or is not "acceptable" in the differentials. Mobile 1.

[LanduytG]

The Amsoil Series 2000 75W-90 works very well.
http://www.lubespecialist.com/products/tgr.htm
Greg

[mowser]

I think it says to check it every 7,500 miles in the manual. It's synthetic so you don't have to change it, if GM wanted you to change it why would they put synthetic in it?????? Eaton says as long as you break in the rear end properly [no towing for 500 miles or long trips for the first 500 miles or so] you don't have to change it.

mowser ;)

[Turbo Al]

GMCTruck; Hi. I brought the rear end breakin procedure back up to the top of the forum for you and others.

[SoMnDMAX]

Change it before your trip. Your rearend will thank you!!

Mobil 1 75w-90 or Amsoil Series 2000 75w-90 are both excellent choices.

[Luis]

Change it now! If GM didn't want you to change it, they would not have put a drain plug under it! Use the Amsoil or the Mobil 1 GL5 75w-90. Don't forget to clean the magnet attached to the drain plug. When yo do this you will SEE why you need to change it and, by the way I seem to recall a lettter from Eaton which says to change the fluid after a 500 mi. break-in. Cheap insurance and it will help you in the Bonding process with your new truck. :D

[imported_]

Can the 74/140W HD rear differential gear oil (part# 12346140) be used in the front differential?

Gmpartsdirect.com sells it in 6 qt. packs $14.23/qt. $83.38 USD for the 6 pack.

Since the rear takes 4 qts. and the front takes two qts. it would work out just right.

Otherwise I guess I'll just change out the mustard stuff for synthetic Mobil 1 75/90W.

[GMCTRUCK]

Thanks guys. I will change it this week. If GM stuff is obscenely over priced I'll go with the Mobil 1. Unless the Amsoil cult gets me first.