Locking Differential

unit731 · December 1, 2007

OK, I ordered Locking Differential in my new GMT900 Sierra 4x4.

I have no idea what it is. And is it on all the time or is there a button? Is it the rear wheels, all wheels or what?

I do, from the past, recall Positraction or limited slip. What is the difference, if any?

Thanks.

jrrod2004 · December 1, 2007

A locking differential or locker is a variation on the standard automotive differential. A locking differential provides increased traction compared to a standard, or "open" differential by disallowing wheel speed differentiation between two wheels on the same axle under certain conditions.

A locking differential is designed to overcome the chief limitation of a standard open differential by essentially "locking" both wheels on an axle together as if on a common shaft while still allowing them to rotate at different speeds when it is required (such as when negotiating a turn). This forces both wheels to turn in unison, regardless of the traction (or lack thereof) available to either wheel individually. An open differential will cease the transmission of power to one wheel if the opposite wheel has little or no traction. This may occur if one wheel comes into contact with mud, snow, or ice, or if the wheel is somehow removed from contact with the road after encountering an obstacle or area of soft ground. In such a situation, an open differential will continue to spin the wheel with the least amount of traction but will transmit little or no power to the wheel that has more solid traction. Basically, it will transmit only as much torque to both wheels as the wheel with the least amount of traction can sustain. This can result in the vehicle failing to deliver enough torque to the drive wheels to keep the vehicle moving forward, at which point it will be stuck. A locking differential solves this problem with its capability of delivering 100% of available torque to the wheel with the most traction.

dlstewart01 · December 1, 2007

The G80 is an Eaton locker or gov lock. When one wheel spins 100rpm faster that the other it locks both wheels together. At around 20 mph it unlocks. It does this automaticly. When not locked it functions as an open diff.

No trucks gets a limited slip with the exception of quadasteer. and thats G86. A limited slip had clutches so when going around corners they alowed slip as one wheel turns faster than the other. They would I think transfer traction to the wheel with the less traction.

Have a good one,

Don

Actually above post is not entirely true The G80 locks both wheels together. as in a locker It unlocks them at 20 mph so you can go around corners If you get on it in a corner and the rear locks it will pop and the wheel will skip a little. Have done this.

MS3DALE · December 1, 2007

From the service information section of the service manual....

Document ID# 1770216

Locking Differential Description and Operation

The locking differential consists of the following components:

• Differential case - 1 or 2 piece

• Locking differential spider - 2 piece case only

• Pinion gear shaft - 1 piece case only

• Differential pinion gear shaft lock bolt - 1 piece case only

• Two clutch discs sets

• Locking differential side gear

• Thrust block

• Locking differential clutch disc guides

• Differential side gear shim

• Locking differential clutch disc thrust washer

• Locking differential governor

• Latching bracket

• Cam plate assembly

• Differential pinion gears

• Differential pinion gear thrust washers

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.

Document ID# 1770216

shedberg · December 1, 2007

OK, I ordered Locking Differential in my new GMT900 Sierra 4x4.

I have no idea what it is. And is it on all the time or is there a button? Is it the rear wheels, all wheels or what?

I do, from the past, recall Positraction or limited slip. What is the difference, if any?

Thanks.

You made a wise choice.

EXSlider400 · December 3, 2007

Just be carefull on slick (rain/snow) roads. When both tires spin..can loose control quick. Cost me $$ already. It was raining and didn't notice it till it was too late.

TEE · December 3, 2007

Especially on those white painted strips at crosswalks and stop lights...you get on it and you'll think you lost your rear end when it does hook up!

Pick_up_man · December 3, 2007

I do, from the past, recall Positraction or limited slip. What is the difference, if any?

To answer your question, there is little difference. The G80 acts as a fully open differential until one wheel spins a certain amount faster than the other. At which point, the differential mechanism on the inside engages the clutch pack and starts delivering torque to the opposite (slower) wheel. If there's enough speed difference, one side axle shaft (wheel, side gear, ect.) gets "locked" to the drive shaft input torque. The two axle shafts (ie. wheels) never get 100% locked together but rather one side will always be limited by the friction of the clutch pack. My guess is the driver side locks up?

It's a good system but it's complicated and not ideal for yahoo's who shock-load the drivetrain alot.

Dixon Peer · February 20, 2010

I do, from the past, recall Positraction or limited slip. What is the difference, if any?

To answer your question, there is little difference. The G80 acts as a fully open differential until one wheel spins a certain amount faster than the other. At which point, the differential mechanism on the inside engages the clutch pack and starts delivering torque to the opposite (slower) wheel. If there's enough speed difference, one side axle shaft (wheel, side gear, ect.) gets "locked" to the drive shaft input torque. The two axle shafts (ie. wheels) never get 100% locked together but rather one side will always be limited by the friction of the clutch pack. My guess is the driver side locks up?

It's a good system but it's complicated and not ideal for yahoo's who shock-load the drivetrain alot.

I recently purchased an '09 Chevy Silverado LTZ Allison/Duramax with a locking rear diff. I really don't like the sound of it locking...BANG! Makes me think I'm going to blow an axle or something else in the rear end. The rear right tire is slipping on snow, and suddenly, I guess at a 100 rpm difference, the left side gets power, and it's on bare pavement...Bang. It works, but worries me nonetheless.

brims · February 20, 2010

I do, from the past, recall Positraction or limited slip. What is the difference, if any?

To answer your question, there is little difference. The G80 acts as a fully open differential until one wheel spins a certain amount faster than the other. At which point, the differential mechanism on the inside engages the clutch pack and starts delivering torque to the opposite (slower) wheel. If there's enough speed difference, one side axle shaft (wheel, side gear, ect.) gets "locked" to the drive shaft input torque. The two axle shafts (ie. wheels) never get 100% locked together but rather one side will always be limited by the friction of the clutch pack. My guess is the driver side locks up?

It's a good system but it's complicated and not ideal for yahoo's who shock-load the drivetrain alot.

I recently purchased an '09 Chevy Silverado LTZ Allison/Duramax with a locking rear diff. I really don't like the sound of it locking...BANG! Makes me think I'm going to blow an axle or something else in the rear end. The rear right tire is slipping on snow, and suddenly, I guess at a 100 rpm difference, the left side gets power, and it's on bare pavement...Bang. It works, but worries me nonetheless.

Don't beat the hell out of it, be gentle when you're trying to get it to lock.

Stex · February 20, 2010

See how it (G80)works in sorta real life:

http://www.youtube.com/watch?v=-sw9DwurQAs

Dixon Peer · February 20, 2010

I do, from the past, recall Positraction or limited slip. What is the difference, if any?

To answer your question, there is little difference. The G80 acts as a fully open differential until one wheel spins a certain amount faster than the other. At which point, the differential mechanism on the inside engages the clutch pack and starts delivering torque to the opposite (slower) wheel. If there's enough speed difference, one side axle shaft (wheel, side gear, ect.) gets "locked" to the drive shaft input torque. The two axle shafts (ie. wheels) never get 100% locked together but rather one side will always be limited by the friction of the clutch pack. My guess is the driver side locks up?

It's a good system but it's complicated and not ideal for yahoo's who shock-load the drivetrain alot.

I recently purchased an '09 Chevy Silverado LTZ Allison/Duramax with a locking rear diff. I really don't like the sound of it locking...BANG! Makes me think I'm going to blow an axle or something else in the rear end. The rear right tire is slipping on snow, and suddenly, I guess at a 100 rpm difference, the left side gets power, and it's on bare pavement...Bang. It works, but worries me nonetheless.

Don't beat the hell out of it, be gentle when you're trying to get it to lock.

Not beating the hell out of it at all. On the job, going up a steep incline in the driveway, snow under right rear tire, tire starts to spin, not using much throttle at all, and bang, the thing locks up and up the driveway I go. I am very careful with things I spent a lot of money on.

Z45 · February 21, 2010

Every truck I have had going back to my 1989 has had the G80 locker as its been around that long. I have not heard any banging coming from it. I rarely know when its engages.

2009SierraZ71 · February 21, 2010

OK, I ordered Locking Differential in my new GMT900 Sierra 4x4.

I have no idea what it is.

It's very cool. All you need to know. Good choice.

ken1mod · February 21, 2010

Gentlemen,

Mine is silent. Could be it's locking going up a hill is noisier. At a stop, put one wheel on ice, the other pavement. Locking should be quick and silent from a dead stop. Be rather gentle on throttle. I am not particularly easy on mine.

Ken