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Getting ready to change gear oil in my 09 2500 hd. I checked on the mobil1 75w-90 and noticed that it and royal purple both have a friction modifier added to the oil already. Is this ok to use in the 2500 hd g80 locker?

 

Thanks.. Happy Thanksgiving

 

Ron

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The G80 does not need any additives so the RP is technically the wrong fluid. Obviously friction creates heat and we don't need that heat or friction with a locking diff. That friction modifier is for posi. Not us with a G80. I have posi fluid with friction modifier in my rear axle because the trans shop who rebuilt my rear axle told me that was required and boy did i give them a teaching and the guy was like 50 and im 18. I said "how many gm 1/2's you do" he said he works on about 3-5 a week and i told him he put the wrong fluid in all of them so i just left with the wrong fluid installed i dont want them working on my truck. And if it blows up i'll sue because he admitted he put in friction modifier and i have a 12K/1 year warranty

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  • 2 weeks later...
  • 1 month later...

I used the GM "grape juice" the first time I changed both front/rear diffs. (BTW, for new trucks it's a good idea to do it at about 10k miles, I waited until almost 20k I think, and you'll be amazed at how much fine metal comes out!) I've since changed several times with Mobil 1 75w-90 LS, both front and rear diffs, and haven't had a bit of trouble. The rear diff has locked a few times when I've been in dirt, and unlocked smoothly.

 

After reading LONG discussions on other sites, it turns out the G80 locker does use a clutch pack and does require some friction modifier. However, additional friction modifier to what is already in Mobil 1 or GM's fluid may also (will probably) cause problems.

 

Here's a link which explains how the G80 works, including the clutch packs and the engagement mechanism which makes it a "gov lock" diff:

http://www.bing.com/videos/search?q=eaton+differential+gov+lock+video&qs=n&form=QBVR&pq=eaton+differential+gov+lock+video&sc=0-0&sp=-1&sk=#view=detail&mid=829692A513B90470008A829692A513B90470008A

 

(link originally provided by dnewton3 on another website)

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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.

PS - The G80 in trucks and SUV's is not a posi. Posi is short for Positraction, Chevrolet's name for its limited slip differential from back in the 50's-70's, made famous in performance cars like the Camaro Z28, Chevelle SS etc. Chevrolet no longer uses the name. The other GM divsions used a different name, e.g. Safe-T-Track for Pontiac.

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I used the GM "grape juice" the first time I changed both front/rear diffs. (BTW, for new trucks it's a good idea to do it at about 10k miles, I waited until almost 20k I think, and you'll be amazed at how much fine metal comes out!) I've since changed several times with Mobil 1 75w-90 LS, both front and rear diffs, and haven't had a bit of trouble. The rear diff has locked a few times when I've been in dirt, and unlocked smoothly.

 

After reading LONG discussions on other sites, it turns out the G80 locker does use a clutch pack and does require some friction modifier. However, additional friction modifier to what is already in Mobil 1 or GM's fluid may also (will probably) cause problems.

 

Here's a link which explains how the G80 works, including the clutch packs and the engagement mechanism which makes it a "gov lock" diff:

http://www.bing.com/videos/search?q=eaton+differential+gov+lock+video&qs=n&form=QBVR&pq=eaton+differential+gov+lock+video&sc=0-0&sp=-1&sk=#view=detail&mid=829692A513B90470008A829692A513B90470008A

 

(link originally provided by dnewton3 on another website)

 

 

GM calls for no friction modifier.

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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.

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X3 on the Amsoil 75w90 Severe Gear lube. You can get Mobil1 75w90 at commercial truck outlets. My semi diffs were factory filled with it. No additives for posi. Product I would use if I didn't use the Amsoil SG

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