Replacing open diff in '00 Silverado

BlaineBug · December 6, 2021

https://www.eaton.com/content/dam/eaton/products/differentials-traction-control/mlocker/eaton-mlocker-brochure-2009-en.pdf

that1nerd · December 6, 2021

10 minutes ago, BlaineBug said:

I apologize. I was formerly under the assumption that it was a "maintenance free" locking differential. It also does NOT need limited slip additive. I know that part for certain at least.

3 minutes ago, BlaineBug said:

https://www.eaton.com/content/dam/eaton/products/differentials-traction-control/mlocker/eaton-mlocker-brochure-2009-en.pdf

Hey, it's all good. No worries! That brochure is awful misleading at first glance, it got me too!
I love how it says "Maintenance free; requires no lube additives" than says "Patented carbon friction disc technology enhances performance and durability" a couple bullet points down. Again, quite misleading. It probably worked on the executives at GM, too.

I'll just stick with the Truetrac.

Z45 · December 6, 2021

I have owned 5 GM trucks in the last 25+ yrs and every one had a G80 and I never once had any issues with it. Millions of trucks and SUVs have been successfully using a G80 for the many years. It is an excellent product. Like anything, it can be misused, misrepresented and blamed for things that are not its fault. Then there are some individuals that just seem to have a hatred for it and will repeat unfounded rumors to discredit it.

Edited December 6, 2021 by elcamino

that1nerd · December 6, 2021

3 minutes ago, elcamino said:

I have owned 5 GM trucks in the last 25+ yrs and every one had a G80 and I never once had any issues with it. Millions of trucks and SUVs have been successfully using a G80 for the many years. It is an excellent product. Like anything, it can be misused, misrepresented and blamed for things that are not its fault. Then there are some individuals that just seem to have a hatred for it and will repeat unfounded rumors to discredit it.

You're absolutely right, and I'm not refuting that. If they've been in production for this long, then they obviously are doing well in most street/daily driving use-cases. I was just simply remarking about how that specific brochure can be misinterpreted very easily.

As for me, I'm just being very picky about what I want for my truck and my use-case. Although the factory G80s work very well, I want a literal "maintenance free" limited slip differential where I don't have to worry about clutch packs a few years down the road. The Truetrac fits that use-case perfectly for me.

BlaineBug · December 7, 2021

2 hours ago, that1nerd said:

Hey, it's all good. No worries! That brochure is awful misleading at first glance, it got me too!
I love how it says "Maintenance free; requires no lube additives" than says "Patented carbon friction disc technology enhances performance and durability" a couple bullet points down. Again, quite misleading. It probably worked on the executives at GM, too.

I'll just stick with the Truetrac.

With that being said I haven't had any issues in 2 years of ownership and a stock SUV. Although it is apparent when it engages, you can feel a good clunk when the locking pawls catch! I've also rebuilt a Ford 8.8 limited slip, but that is always under tension and never operates as an open differential unlike the G80.

Edited December 7, 2021 by BlaineBug

swathdiver · December 7, 2021

The G80 in a trucks since the mid 1980s is not the same as a 1970 Chevelle or a 1980s Monte Carlo SS G80. The truck G80 is a combination of a locker and limited slip. It requires no limited slip lubricant.

From the shop manual:

The optional locking differential (RPO G80) enhances the traction capability of the rear axle by combining the characteristics of a limited-slip differential and the ability of the axle shafts to "lock"together when uneven traction surfaces exist. The differential accomplishes this in 2 ways. First by having a series of clutch plates at each side of the differential case to limit the amount of slippage between each wheel. Second, by using a mechanical locking mechanism to stop the rotation of the right differential side gear, in order to transfer the rotating torque of the wheel without traction to the wheel with traction. Each of these functions occur under different conditions.

Limited-Slip Function

Under normal conditions, when the differential is not locked, a small amount of limited-slip action occurs. The gear separating force developed in the right-hand clutch pack is primarily responsible for this.

The operation of how the limited-slip function of the unit works can be explained when the vehicle makes a right-hand turn. Since the left wheel travels farther than the right wheel, it must rotate faster than the ring gear and differential case assembly. This results in the left axle and left side gear rotating faster than the differential case. The faster rotation of the left-side gear causes the pinion gears to rotate on the pinion shaft. This causes the right-side gear to rotate slower than the differential case.

Although the side gear spreading force produced by the pinion gears compresses the clutch packs, primarily the right side, the friction between the tires and the road surface is sufficient to overcome the friction of the clutch packs. This prevents the side gears from being held to the differential case.

Locking Function

Locking action occurs through the use of some special parts:

A governor mechanism with 2 flyweights
A latching bracket
The left side cam plate and cam side gear

When the wheel-to-wheel speed difference is 100 RPM or more, the flyweights of the governor will fling out and one of them will contact an edge of the latching bracket. This happens because the left cam side gear and cam plate are rotating at a speed different, either slower or faster, than that of the ring gear and differential case assembly. The cam plate has teeth on its outer diameter surface in mesh with teeth on the shaft of the governor.

As the side gear rotates at a speed different than that of the differential case, the shaft of the governor rotates with enough speed to force the flyweights outward against spring tension. One of the flyweights catches its edge on the closest edge of the latching bracket, which is stationary in the differential case. This latching process triggers a chain of events.

When the governor latches, it stops rotating. A small friction clutch inside the governor allows rotation, with resistance, of the governor shaft while one flyweight is held to the differential case through the latching bracket. The purpose of the governor's latching action is to slow the rotation of the cam plate as compared to the cam side gear. This will cause the cam plate to move out of its detent position.

The cam plate normally is held in its detent position by a small wave spring and detent humps resting in matching notches of the cam side gear. At this point, the ramps of the cam plate ride up on the ramps of the cam side gear, and the cam plate compresses the left clutch pack with a self-energizing action.

As the left clutch pack is compressed, it pushes the cam plate and cam side gear slightly toward the right side of the differential case. This movement of the cam side gear pushes the thrust block which compresses the right-hand side gear clutch pack.

At this point, the force of the self-energizing clutches and the side gear separating force combine to hold the side gears to the differential case in the locking stage.

The entire locking process occurs in less than 1 second. The process works with either the left or right wheel spinning, due to the design of the governor and cam mechanism. A torque reversal of any kind will unlatch the governor, causing the cam plate to ride back down to its detent position. Cornering or deceleration during a transmission shift will cause a torque reversal of this type. The differential unit returns to its limited-slip function.

The self-energizing process would not occur if it were not for the action of one of the left clutch discs. This energizing disc provides the holding force of the ramping action to occur. It is the only disc which is splined to the cam plate itself. The other splined discs fit on the cam side gear.

If the rotating speed of the ring gear and differential case assembly is high enough, the latching bracket will pivot due to centrifugal force. This will move the flyweights so that no locking is permitted. During vehicle driving, this happens at approximately 32 km/h (20 mph) and continues at faster speeds.

When comparing the effectiveness of the locking differential, in terms of percent-of-grade capability to open and limited-slip units, the locking differential has nearly 3 times the potential of the limited-slip unit under the same conditions.

Locking Differential Torque-Limiting Disc

The locking differential design was modified in mid-1986 to include a load-limiting feature to reduce the chance of breaking an axle shaft under abusive driving conditions. The number of tangs on the energizing disc in the left-hand clutch pack was reduced allowing these tangs to shear in the event of a high-torque engagement of the differential locking mechanism.

At the time of failure of the load-limiting disc, there will be a loud bang in the rear axle and the differential will operate as a standard differential with some limited-slip action of the clutch packs at low torques.

The service procedure, when the disc tangs shear, involves replacing the left-hand clutch plates and the wave spring. It is also necessary to examine the axle shafts for twisting because at high torques it is possible to not only shear the load-limiting disc, but to also twist the axle shafts.