Rear end oil change

[Retired Cop]

Good evening everyone. I want to change the oil in my rear end. Do I need to use the GM fluid? If not any recommendations? Should I use the additive no matter what fluid I use? Thanks in advance.

[dr_ws6_00]

I would use the additive for sure

[Mr. Luos]

2 quarts of whatever 80w-90 and the additive.

[NavdeepWS6]

i use 75w-90 buy two quarts but you'll only use 1.5 quarts and put in the limited slip additive
get synthetic oil just go to an auto parts store and get some just see which brand you like
dont forget get a gasket i hate scrapping of silicone when the shops use it cause if you ever got to change it again gasket=less work

[jesseheel]

how do you change it. never done it.???

[side2000]

use synthetic---most of companies that make synthetic blend additives in. i use amsoil and i use no additives.

[NavdeepWS6]

how do you change it. never done it.???

the way i was told to do it
1.jack up car from rear diff and put it on jack stands then lower jack and remove
2. start taking off bolts starting from bottom
3. after all bolts are off pry open diff from bottom but keep hands on it let it drain
4. remove diff scrape off gasket/silicone off diff cover and rear end
5. put gasket and diff cover back on and tighten
6. using ratchet unscrew the diff plug/bolt
7. put in limited slip additive
8. using a pump put in 1.5 quarts of oil and when getting near end try not to overfill.
9.plug the diff back up and clean up with a rag
10.drive around and check for leaks

[Too Fast]

GM recommends synthetic for the OE differential, probably to help the weak link last longer. 75w90 I believe, it should be in your owners manual. And yes, use the additive. You do not have to use the GM OE fluid, any synthetic will work, use what you like.

[Retired Cop]

ok, thanks

[jesseheel]

thats great thanks

[side2000]

there is an advantage to not using additives w/ a brand like amsoil. . . .more oil. . . .i dont use additives w/ mine and i've never experienced chatter. read the bottles when you go into the store, hopefully there is an amsoil distributor around you.

[CompSyn]

there is an advantage to not using additives w/ a brand like amsoil. . . .more oil. . . .i dont use additives w/ mine and i've never experienced chatter. read the bottles when you go into the store, hopefully there is an amsoil distributor around you.

Amsoil gear lubes already have friction modifiers blended into them so they are compatible with most limited slip units right out of the bottle. However, some like to use a limited slip additive with the Amsoil anyway. And although Amsoil doesn't generally recommend the use of oil additives, they do have a proprietary limited slip additive that is compatible with their gear lubes for certain application that may need extra friction modifiers. The recommendation is, if you don't experience differential chatter, you don't need the extra additive.

CompSyn

[02transamce]

can you buy the additive at a parts store or is it a dealer only item?

[NavdeepWS6]

can you buy the additive at a parts store or is it a dealer only item?

you can get it at a parts store

[GatorSS]

the way i was told to do it
1.jack up car from rear diff and put it on jack stands then lower jack and remove
2. start taking off bolts starting from bottom
3. after all bolts are off pry open diff from bottom but keep hands on it let it drain
4. remove diff scrape off gasket/silicone off diff cover and rear end
5. put gasket and diff cover back on and tighten
6. using ratchet unscrew the diff plug/bolt
7. put in limited slip additive
8. using a pump put in 1.5 quarts of oil and when getting near end try not to overfill.
9.plug the diff back up and clean up with a rag
10.drive around and check for leaks

Don't forget to inspect the magnet for metal and clean everything inside before reinstalling the cover.

[INMY01TA]

2 quarts of whatever 80w-90 and the additive.

+1. GM actually doesn't recommend synthetic (neither do I) cause the manual does not know whether you have Auburn or Torsen. Neither Strange, Moser, nor Eaton recommend syn for their Eaton posi 12 bolts. Not necesary and I've read mineral dino oil has it's advantages in the rear. So I say any ole 80/90 will do fine.

[BlackSS1]

Don't forget to inspect the magnet for metal and clean everything inside before reinstalling the cover.

3 questions:

Is the magnet the plug itself, or elsewhere in the diff?

How often should one change the oil in a 10 bolt?

Any benefit to adding a girdle rather than the stock cover?

Thanks Navdeep for the step by step

[INMY01TA]

Magnet is on the backside of the stock cover. The girdle is basically an appearance mod imo, the fact that it does have a drain plug will make future fluid changes easier.

[CompSyn]

+1. GM actually doesn't recommend synthetic (neither do I) cause the manual does not know whether you have Auburn or Torsen.

GM doesn’t recommend synthetic? That’s interesting because they SELL synthetic based oils.



GM may have said something like that in days of old but now they sell and recommend synthetic differential lubricants .

The application for Retired Cops 2002 Firebird is a API GL-5 specified 75W-90 synthetic gear oil. When a manufacture calls out for an API GL-5 specified gear oil, they do so in reference to API GL-5 specification and related ASTM STP-512A performance tests.

API Lubricant Service Designations for Automotive Manual Transmissions, Manual Transaxles, and Axles

The designation API GL-5 denotes lubricants intended for gears, particularly hypoid (see note) gears, in axles operating under various combinations of high-speed/shock load and low-speed/high-torque conditions. Lubricants qualified under U.S. Military Specification MIL-L-2105D (formerly MIL-L-2105C) satisfy the requirements of the API GL-5 service designation, although the API designation does not require military approval. Performance test details are in ASTM Publication STP-512A.

Note: Frictional requirements for axles equipped with limited-slip differentials are normally defined by the axle manufacturer.

ASTM STP-512A Performance Test Details

Section 1 (L-33 Test): Performance Test for Evaluating the Moisture Corrosion Tendencies of Automotive Gear Lubricants

Abstract
This test method describes a test procedure for evaluating the rust and corrosion inhibiting properties of a gear lubricant while subjected to water contamination and elevated temperature in a benchmounted hypoid differential housing (carrier) assembly. The customary test is a seven-day test; an abbreviated test of one day may also be run.


Section 2 (L-37 Test): Performance Test for Evaluating the Load Carrying Capacity of Automotive Gear Lubricants Under Conditions of Low Speed and High Torque

Abstract
This test method describes a test procedure for evaluating the load carrying, wear, and extreme pressure properties of a gear lubricant in an axle under conditions of high-speed, low-torque and of lowspeed, high-torque operation.


Section 3 (L-42 Test): Performance Test for Evaluating the Load Carrying Capacity of Automotive Gear Lubricants Under Conditions of High Speed Shock Loading

Abstract
This test method is used for determining the antiscoring properties of gear lubricants under highspeed and shock conditions.


Section 4 (L-60 Test): Performance Test for Evaluating the Thermal Oxidation Stability of Automotive Gear Lubricants

Abstract
This test method describes a test procedure for determining the deterioration of gear lubricants when subject to severe thermal oxidation conditions.

So whether you have a GL-5 mineral based gear oil or a GL-5 synthetic based gear oil, they both have to meet the minimum specifications required in order to be qualified as an API GL-5 lubricant.

Neither Strange, Moser, nor Eaton recommend syn for their Eaton posi 12 bolts.

Manufactures of limited slip units are concerned about getting the right ratio of friction modifiers (FMs) in gear lubricant so that the clutch packs will work properly. In the days of old, it may have been observed that an improperly formulated synthetic gear lube did not have a proper formulation of FMs, which could cause improper operation or premature failure of the limited slip clutch packs. Actually, the same would occur with a mineral base gear lubricant if the right amount of FM's were not present. This is why many manufactures came out with limited slip additives to supplement the lack of FMs in off the shelf gear oils. Today, some manufacturers formulate FMs into gear oils so that they are compatible with limited slip unites right out of the bottle. For example, check out the recommendation from Amsoil in regards to their SEVERE GEAR® lubricant.

Recommended for use in differentials, manual transmissions and other gear applications requiring any of the following specifications: API GL-5, MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037), Mack GO-J, or the differential (hypoid) gear oil specifications from all domestic and foreign manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in axles where an API GL-4 lubricant is recommended.

AMSOIL SEVERE GEAR® is compatible with most limited slip differentials. If limited slip differential chatter occurs, add Amsoil Slip-Lock friction modifier additive.

The recommendation is one thing, but how does it stand up in real world use? See also:

there is an advantage to not using additives w/ a brand like amsoil. . . .more oil. . . .i dont use additives w/ mine and i've never experienced chatter. read the bottles when you go into the store, hopefully there is an amsoil distributor around you.

Not necesary and I've read mineral dino oil has it's advantages in the rear. So I say any ole 80/90 will do fine.

Exactly what advantages do mineral based gear oils have over synthetic based lubricants? Recent testing conducted in accordance with the American Society of Testing and Materials (ASTM), Society of Automotive Engineers (SAE), and Federal Test Method Standards would seem to indicate otherwise. To review the complete study, check out A Study in Automotive Gear Lubes, HERE.

CompSyn

[side2000]

i'd never put mineral based fluids in ANYTHING except motor break-in. . . . .my lawn mower even has used amsoil in it.