Chattering rear end.

MTY55 · October 5, 2022

I have noticed this a few times last winter. This happened the other day when making a U-turn on a country road. I hit the gas on the loose gravel and the rear end locked as it should but when it straightened out the rear end didn't unlock for a while and made on hell of a chattering sound and vibration. Only 15,000 miles on the truck If I it read it right rear differential service is due at 36,000 miles. I had this happen on one of my previous trucks with the G-80 They said they added a synthetic additive and it quit. From What I have read Synthetic lube is already in the rear end.

Z45 · October 5, 2022

1-GM Fluids are from the lowest bidder. Don't believe that because GM uses it, its the best, its only good enough for them.

2-Chattering in the locker is indicative of worn out fluid, change the fluid. Use the GM junk or your favorite aftermarket brand. I recommend AMSOIL.

3-DO NOT USE friction modifier in the G80 Locking rear differential. Friction modifiers are designed to be used in Limited Slip Differential WHICH are normally installed in cars. Truck use a different system which is designed to lock up and adding more friction modified can cause problems similar to what you are experiencing. Posi or limited slip differential are designed to slip as opposed to the locker which does NOT.

GM Marketing info

Quote

¨ 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.