3.42 To 3.73 In 2000 Sierra G80 Diff

[Willshire]

I'm sure someone out there has done a 3.42 to 3.73 (gu6 to gt4) swap. I am looking for a good brand of gears and associated parts i will need to complete the job. Also my g80 diff does seem to want to lock in the left tire when the right starts to spin (on pavement) are the clutches perhaps wore out? the truck does have 280000k (160000miles) on it. I don't want to order the gears and forget any parts, left with the truck on a hoist and blah blah blah. I purchase alot of stuff from summit. Do they offer a decent gear manufacturer? What size is the diff? Long post but get'r all in in one shot.

[rodram]

...... Also my g80 diff does seem to want to lock in the left tire when the right starts to spin (on pavement) are the clutches perhaps wore out? ........

 

I can't help you on specifying parts or part manufacturers, but I am curious about your question here.... only comment I can think of is... if you have 4wd then you need parts for both front and back...

 

The G80 in your truck is an Eaton mechanical locker (... no clutches) that engages when one wheel begins to spin faster than the other .... so based on your description, the locker appears to be working....

[Willshire]

Sorry i just read my post and i meant to write that the left tire does NOT lock in when right begins to spin

[Z'06]

Ron's Machining Service (eBay) sells complete gear packages with master install kits.

 

AAM gears are OEM and are widely considered the best manufacturer. Yukon is apparently the brand to get if you can't get AAM.

 

On a separate note, it is not going to be worth your time/money/effort to switch from 3.42 to 3.73, especially if you have 4WD. Consider 4.10 if your tires are in the 31-33" range.

[rodram]

Sorry i just read my post and i meant to write that the left tire does NOT lock in when right begins to spin

 

... so if there is no lock-up when one wheel spins then it is likely that your G80 is no longer functioning... they work well right up to the point that they fail... there is no wearing out so to speak... they work well on slippery road surfaces but are not intended for any level of abuse ...

 

you can buy parts to replace the G80.. or you can buy other rear locking devices to install when you have everything all apart... lots of information on these on other threads in the forum.

[dlstewart01]

LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109

SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)

VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS

Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.

This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.

To correct this condition, drain and refill the rear axle with SAE 75W-90 GL5 (P/N 12378261). 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.VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80.

SERVICE PARTS INFORMATION:

Part Number Description ----------- ------------------ 12678261 Lubricant, Rear Axle (1 litre)

Parts are currently available through CANSPO.

WARRANTY INFORMATION:

As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.

© Copyright General Motors Corporation. All Rights Reserved.

 

How the G80 works...

 

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 open diff 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.

__________________

 

 

 

 

[Willshire]

ok, so if i want to just locate a rear end to replace mine (rebuilding seems time consuming for a guy with one day off per week) i believe i have a 8.5" 10 bolt ring gear in my 2000 sierra 2wd (10 bolt round cover). If i get a junk yard axle, what years should i search for? and where on the axle is the diff type(posi) and gear ratio stamped on. so i know what to tell the wrecking yard. Thanks