G80 Rear Diff Fluid Change.

[WilliamBos]

Hi All,

 

Getting prepared to change the rear axle fluid on my G80. Wondered if you are buying new fastners like GM suggests?? Are you getting them from the dealer??

 

What about fluid?? Going to Use 75W90 Syn, maybe Amsoil, but do I need an extra additive for the G80??

 

[brims]

Only reason I used new bolts was because they were longer for my MagHytec cover. You're not supposed to use an addative with the G80.

[Spurshot]

Hi All,

 

Getting prepared to change the rear axle fluid on my G80. Wondered if you are buying new fastners like GM suggests?? Are you getting them from the dealer??

 

What about fluid?? Going to Use 75W90 Syn, maybe Amsoil, but do I need an extra additive for the G80??

 

 

 

Huh? Really? What? Do they wear out or somethin?

[MS3DALE]

You're not supposed to use an additive with the G80.

 

+1 DO NOT use any additive.

 

New fasteners/bolts is not necessary.

[C. Charles Hahn]

You're not supposed to use an additive with the G80.

 

+1 DO NOT use any additive.

 

New fasteners/bolts is not necessary.

 

 

Seriously? That's a new one on me. I've always been told by mechanics that you have to use LSD additive with the G80.

 

What problems does using additive cause? Luckily the Royal Purple I use is already compatible with limited slip and open differentials so I've never had to put additional additive in, but I'm curious what the deal is.

[MS3DALE]

You're not supposed to use an additive with the G80.

 

+1 DO NOT use any additive.

 

New fasteners/bolts is not necessary.

 

 

Seriously? That's a new one on me. I've always been told by mechanics that you have to use LSD additive with the G80.

 

What problems does using additive cause? Luckily the Royal Purple I use is already compatible with limited slip and open differentials so I've never had to put additional additive in, but I'm curious what the deal is.

 

 

Absolutely not,The G80 is not considered a limited-slip (Although some limited slip action occurs) its a locker.

 

From SI in the GM service manual (And this might be more info. than you want,but never the less).....

 

 

#PIP4054C: Eaton Locking Differential Chatter Shudder Noise on Turns - keywords bind grab grind - (Aug 26, 2008)

 

 

Subject: Eaton Locking Differential Chatter Shudder Noise on Turns

 

 

Models: 2004-2007 Buick Rainier

 

2000-2009 Cadillac Escalade, ESV, EXT

 

2002-2009 Chevrolet Avalanche

 

2004-2009 Chevrolet Colorado

 

2003-2009 Chevrolet Express

 

2000-2009 Chevrolet Suburban, Tahoe

 

2000-2007 Chevrolet Silverado Classic

 

2007-2009 Chevrolet Silverado

 

2002-2009 Chevrolet Trailblazer

 

2004-2009 GMC Canyon

 

2002-2009 GMC Envoy

 

2000-2009 GMC Yukon, Yukon Denali, Yukon XL

 

2000-2007 GMC Sierra Classic

 

2007-2009 GMC Sierra

 

2003-2009 GMC Savana

 

Equipped With a Locking Rear Differential RPO G80

 

 

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

 

Condition/Concern:

Customers may comment on a chatter or shudder from the rear axle on vehicles equipped with an Eaton locking differential. This condition would be noticed in parking lot maneuvers, turning, or during locking differential engagement and may be more noticeable when the differential is hot. Locking differential clutch chatter may be causing this concern.

 

Note 1: This does not apply to vehicles equipped with RPO QS4 (Quadrasteer) which is part of option package NYS. Quadrasteer vehicles use Dana axles and have a different fluid requirement.

 

Note 2: This PI does not apply to vehicles equipped with a RPO G86 limited slip differential.

 

Recommendation/Instructions:

If differential clutch chatter is encountered in a vehicle equipped with an Eaton locking differential, flush, drain and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on. If the condition returns replace the rear differential clutch plates and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on. Refer to eSI for clutch plate replacement and set up procedures.

 

Note 1: Eaton locking differentials used in 10.5" rear axles are equipped with steel clutch plates. It is a design characteristic of these steel clutch plates to exhibit more clutch chatter than other models.

 

***Important: Installing any friction modifier causes the clutch pack in the locking differential to slip and miss engagement. A fluid flush can often remove debris that is a contributor to clutch chatter. Adding friction modifier additive can cause a loss of locking differential functionality***

 

 

And heres some general information.......

 

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.

[WaterGuy]

You're not supposed to use an additive with the G80.

 

+1 DO NOT use any additive.

 

New fasteners/bolts is not necessary.

 

 

Seriously? That's a new one on me. I've always been told by mechanics that you have to use LSD additive with the G80.

 

Adding the LSD additive is that it has to do with the clutch packs.

 

As a side note, LSD in not in the approved abbreviation listings.

Besides, it would depend on how old you are as to what LSD means to ya.

[MS3DALE]

Besides, it would depend on how old you are as to what LSD means to ya.

 

[Mossyoakglock]

I used M1 75W-90 and just put a small big of locktite on the bolts just incase.

[CapitalTruck]

When I did my diff fluid I used the old bolts. However, looking at them now I see why they suggest to put in new fasteners. These small little bolts get to rusting and looking like they might be a P.I.A. to remove later (because the rust is kind of making the heads rounded out). I'll be putting new ones in the next time I do a fluid change.

[bossier62guy]

Hi All,

 

Getting prepared to change the rear axle fluid on my G80. Wondered if you are buying new fastners like GM suggests?? Are you getting them from the dealer??

 

What about fluid?? Going to Use 75W90 Syn, maybe Amsoil, but do I need an extra additive for the G80??

 

 

I did as the service manual stated and used new bolts.....amazing how many people will change their fluids above and beyond what GM calls for but when it comes to the small things they totally blow it off.....

[cliobogger]

where do you look to see if you have the g80 or not?

[MS3DALE]

where do you look to see if you have the g80 or not?

 

In your glovebox on the SPID label,If you have it you will see the code "G80"

[Dirty Chris]

They are not Torque-to-Yield. I assume GM recommends new bolts beacuase they come with threadlocker on them. If your bolts are in good condition, you can reuse them after cleaning the threads/heads and puting new threadlocker on the threads during intall.

[brims]

They are not Torque-to-Yield. I assume GM recommends new bolts beacuase they come with threadlocker on them. If your bolts are in good condition, you can reuse them after cleaning the threads/heads and puting new threadlocker on the threads during intall.

 

I agree with this completely. If the bolts are messed up somehow, the threads messed up, the head rounded over, etc then you should replace the bolts. If the bolts have some surface rust and threadlocker in the threads, clean them up and off you go.

 

Do you replace your lug nuts every time you take a wheel off? The same applies here.