Limited slip or regular synthetic?

[Raptordude]

I changed the diff fluid on my 01 2500HD 2wd to 75w-90 valvoline. Full synthetic, WITH limited slip additive. That was about 8 months ago, so far everything's great. No noise, and the posi locker engages and disengages beautifully.

 

I'm about to do the same job again on a family members 06 2500HD. Should I use the same stuff? Since I did mine, I read that the limited slip stuff should not be used in the posi. However, it's worked great in mine the past few months, even in off-road, tire slipping situations. Thoughts?

 

 

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[Formulabruce]

Yours and their rear is NOT like an old school posi with a locker added, its completely different, and it doesn't matter whether you run an additive or not. It has 3 rods that move out and lock the rear after a spin occurs. Good luck!

[Raptordude]

Ahh good. That's what I thought initially but I was freaking myself out reading stuff online. I'm very happy with the way mine is performing since I did the fluid change.

 

Hopefully this 06 goes just as well

 

Thanks

 

 

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[sdeeter19555]

Yours and their rear is NOT like an old school posi with a locker added, its completely different, and it doesn't matter whether you run an additive or not. It has 3 rods that move out and lock the rear after a spin occurs. Good luck!

Hmmm...

 

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[davester]

The diagrams I've looked at for G80's show they do have a bunch of friction plates, so I would definitely put in something with the LS additive, or add some LS additive yourself (a little at a time, you want to sneak up on it from not enough to just right, if you go past to too much...it's hard to remove just the LS additive).

 

And Eaton, who makes the G80 for GM, recommends using LS additive.

[Z45]

fyi

 

 

 

¨ 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.

[Z45]

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION)

SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)

VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS

Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.

This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.

To correct this condition, drain and refill the rear axle.

 

The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.

[Z45]

Fyi GM has two versions of the G80 option in production, one for cars and one for trucks.

 

G80 for cars is a Limited Slip Differential :aka Posi, short for Positraction, a Chevy trademark name from the 1960-70's muscle car era

 

G80 for trucks/suvs is a locking differential :Not a posi

 

Both are coded G80, the vehicle line differentiates the one in use. No lockers in cars, no limited slip in trucks/suvs.

[Z45]

Limited slip differential additive use..

 

 

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.

 

 

 

 

[Formulabruce]

Here are a couple pics of what I was referencing to on the lockers.

There are some friction discs on one side in a small clutch pack. Some use carbon fiber discs now..they do not need special additive as the pressure on them with the pin system is greater than the old spring types for lock up.

This is a break down of a 2002( estimate) and up 14 bolt full floater locker ( 2500-3500HD)

a 14 Bolt FF "OPEN" Rear will have 4 Pins in it, Not 3. You can add a positrack to the 4 pin open rear if needed.

 

 

This is the older style locker Basically a car type posi with a couple rocking flanges on the carrier to lock the rear in forward or reverse. This system cant take a beating, and snow plowed trucks will ruin these fairly fast.

[Formulabruce]

Fyi GM has two versions of the G80 option in production, one for cars and one for trucks.

 

G80 for cars is a Limited Slip Differential :aka Posi, short for Positraction, a Chevy trademark name from the 1960-70's muscle car era

 

G80 for trucks/suvs is a locking differential :Not a posi

 

Both are coded G80, the vehicle line differentiates the one in use. No lockers in cars, no limited slip in trucks/suvs.

I will add that "lockers" are Low speed traction devices ONLY, and will disengage at under 20 mph.

[Raptordude]

Sheesh didn't realize I was opening a big can of worms.

 

Regardless as to what they recommend, the 75w-90 synthetic oil with limited slip works perfectly in my 01 2500hd

 

 

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[sdeeter19555]

Sheesh didn't realize I was opening a big can of worms.

 

Regardless as to what they recommend, the 75w-90 synthetic oil with limited slip works perfectly in my 01 2500hd

 

 

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I've got 75w140 Amsoil Severe Gear in mine, and it seems to work ok. That's the only Amsoil I have because I got a 5-gallon pail for $50...I wouldn't buy it at full price.

 

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[Raptordude]

I don't blame you, that amsoil is good stuff but it's way too expensive

 

 

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[jake111]

For the truck G80 "gov-locker", GM says not to add friction modifiers because they assume that, of course, you are using the GM "grape juice" gear oil which already has the proper LS modifiers in it. Valvoline also has LS. Mobil 1 also has LS. I have used Mobil 1 75-90 in mine for almost 100k miles and the rear end has behaved as it should.

 

davester (in post #5 above) is also suggesting that you can start with a non-LS gear oil and add it in yourself until it behaves. That's a sound method although I prefer the pre-mixed version in Mobil 1 because, for me, they got it right.