Rear end oil change

[Z15]

Although the G80 in trucks and sport utilities uses clutches, it is a full locker. If you use a friction additive this can reduce torque / load carrying capacity and is not recommended. IT IS NOT A LIMITED SLIP DIFFERENTIAL. those are typically installed in performance cars such as the Camaro, Corvette, Cadilac V series! G80 is the open code for both types.

Per GM Service Info - Important: Installing any friction modifier causes the clutch pack in the locking differential to slip and miss engagement. A fluid flush can often remove debris that is a contributor to clutch chatter. Adding friction modifier additive can cause a loss of locking differential functionality.

 

[Pcpurvis]

That old number from your owner's manual, 12378261, has been superseded by 88900401 or 10-4016. Your axle takes 2.15 quarts and requires no limited slip additive.

I replaced the rear differential gear oil last weekend using 75w90; it took right at 3qts. The old oil looked very good for the miles (at least 170k miles); the differential was like new with only a very small amount of metal filings on the magnet (like putty in fact). Got it cleaned out and put a new gasket and filled it up. That’s when I noticed that the new gear oil had the limited slip additive in it. So after a mild freak out I read on the bottle that it could be used on either limited slip or open slip differentials.
Is that true or do I need to drain and flush the differential and replace the oil (w/o the additive this time)?

Thanks in advance

 

[swathdiver]

I replaced the rear differential gear oil last weekend using 75w90; it took right at 3qts. The old oil looked very good for the miles (at least 170k miles); the differential was like new with only a very small amount of metal filings on the magnet (like putty in fact). Got it cleaned out and put a new gasket and filled it up. That’s when I noticed that the new gear oil had the limited slip additive in it. So after a mild freak out I read on the bottle that it could be used on either limited slip or open slip differentials.
Is that true or do I need to drain and flush the differential and replace the oil (w/o the additive this time)?

Thanks in advance

Well, what brand and part number did you use?

 

[Pcpurvis]

 

[Pcpurvis]

View attachment 394963

The note about the limited slip additive is on the back

 

[nonickatall]

The limited slip additive is important for the clutch in the differential, if a certain type of locking differential is installed there. The locking differential also has normal gears and bearings like a normal differential. If the Limited Slip additive does not interfere with these gears and bearings there, this will not be a problem with your differential either.

In other words, it is bad to operate a differential that requires limited slip without this additive, but it should not be a problem, to operate a normal differential, with a limited slip additive, as far if the type of oil is correct and has the correct viscosity.

 

[Z15]

Lots of misinformation about the limited slip additive and what its purpose is. Again, truck and suvs DO NOT have a limited slip differential!

Chatter is essentially the build-up and release of energy between the differential clutch packs in a limited slip differential during operation. This phenomenon often occurs when torque is transferred between the clutches or when rotational speeds change. During the stick-slip phase, energy is built up to a point where contact between the clutch plates change between static friction (stick) and dynamic friction (slip), resulting in noticeable vibrations. It is this vibration that causes an audible chatter or ratcheting to be heard within the differential. While certainly an annoying characteristic, there is typically no mechanical damage occurring to the differential. It is most often noticed in parking lots or slow driving while turning where the outside wheel turns faster than the inside wheel.

In an effort to control this chatter, friction modifiers are often used. These additives result in a smoother transition between the two states of friction: static and dynamic. Static friction occurs when the clutches physically lock together, while dynamic friction occurs as the clutches are slipping, ergo Limited Slip Differential.

¨ Optional Equipment (G80 Order Code) on all GM two-wheel and four-wheel drive light trucks and sport utilities.

Benefits

¨ Improved traction differentiates the vehicle relative to other rear wheel and four-wheel drive vehicles on the market.

¨ Maintenance free; requires no lube additives.

¨ Enhanced towing and off-road performance.

¨ Patented carbon friction disc technology enhances performance and durability while reducing warranty claims.



Principles of Operation

¨ Wheel speed difference (left to right) in excess of 100 RPM will cause a flyweight mechanism to open and catch a latching bracket.

¨ The stopped flyweight will trigger a self-energizing clutch system, which results in the cam plate ramping against a side gear.

¨ Ramping increases until both axles turn at the same speed (full lock), which prevents further wheel slip.

¨ At speeds above 20MPH, the latching bracket swings away from the governor and prevents lockup from occurring.



Technical Specifications

¨ Automatic locking takes place within a fraction of a second, so smoothly that it is unnoticed by the average driver.

¨ Unlocking occurs automatically, once the need for improved traction is gone, and is unnoticeable to the average driver.

¨ Compatible with anti-lock brake systems.

 

[Pcpurvis]

The limited slip additive is important for the clutch in the differential, if a certain type of locking differential is installed there. The locking differential also has normal gears and bearings like a normal differential. If the Limited Slip additive does not interfere with these gears and bearings there, this will not be a problem with your differential either.

In other words, it is bad to operate a differential that requires limited slip without this additive, but it should not be a problem, to operate a normal differential, with a limited slip additive, as far if the type of oil is correct and has the correct viscosity.

Good to know.
So how can you tell which type you have if you have an automatic transmission? My TJ is a manual 6 speed and the wheels spin in opposite directions when rotating a wheel by hand (open slip).

 

[nonickatall]

Good to know.
So how can you tell which type you have if you have an automatic transmission? My TJ is a manual 6 speed and the wheels spin in opposite directions when rotating a wheel by hand (open slip).

There are two possibilities. In the glove compartment is a sticker, where you can see the equipment features codes, there is also a code somewhere for the differential, e.g. g80. I don't know exactly which ones these are for the other differenzials, but someone here can definitely tell you.

The second option is: Simply change the differential oil, and remove the coverto do this. If you look inside the differential, you can see immediately whether it is a limited slip differential or a normal differential.

 

[JonnyTahoe]

Both my 2000 Tahoe and 2000 Yukon have the same G80 with the factory Drain plug on the bottom of the Differential. I have changed the rear diff fluid 3 times in a little over 3 years in the Yukon using Valvoline 80W-90 non-synthetic gear oil in the white plastic bottle. Reason for the fluid changes was a leaking cover got a new GM steel cover and used better gaskets no more leaks. Did plenty of Differential testing on my garage floor and the street. From a stop both rear wheels will spin the exact amount and leave the exact amount of rubber in a straight line however in the rain if I go around a corner I can get one wheel to spin. Up my driveway with snow on it they both will spin most of the time. I would agree these are not Limited Slip and I do not see any Clutch Packs.