Will GM ever get rid of the G80?

SierraHD17 · December 7, 2019

That video is neat and all but that's not actually how a Trutrac people talk about operates. There is no spur gears on the ends of the worm wheels to lock the gears together in a Trutrac and they actually run parallel with the drive gear on the axle shaft. Instead if you spin one faster than the other the principal is the worm wheel will be forced into the wall of the case and bind as the two will separate under wheel speed difference. The worm wheels spin with about half the gear overlapping the one on the opposite axle. That's all fine and dandy but it's pretty mickey mouse in the long run as it heavily depends on friction to the case of the differential. In that sense its much like how an Auburn limited slip relies on the side gears having teeth on the back side that dig into the case. Here is the Eaton exploded view video.

Edited December 7, 2019 by SierraHD17

Nanotech Environmental · December 7, 2019

15 hours ago, SierraHD17 said:

That video is neat and all but that's not actually how a Trutrac people talk about operates. There is no spur gears on the ends of the worm wheels to lock the gears together in a Trutrac and they actually run parallel with the drive gear on the axle shaft. Instead if you spin one faster than the other the principal is the worm wheel will be forced into the wall of the case and bind as the two will separate under wheel speed difference. The worm wheels spin with about half the gear overlapping the one on the opposite axle. That's all fine and dandy but it's pretty mickey mouse in the long run as it heavily depends on friction to the case of the differential. In that sense its much like how an Auburn limited slip relies on the side gears having teeth on the back side that dig into the case. Here is the Eaton exploded view video.

I had a G80 in my last truck. It was always inconsistent & it eventually stopped working properly. It would often stay locked up, which becomes a real PITA.
I replaced it with a Torsen Truetrac, which worked much better and was always very consistent. It always worked. Always. It's also a lot more tractable and predictable. It's far from mickey mouse, as the design will work reliably after 200,000 miles...

The G80 I have in my '17 is also inconsistent. It's better than the last one, but far from perfect.
The inherent design of the G80 is neat on paper, but not great in the real world. It's also a time bomb, due to its design.

IMO, a good test of a rear diff, is to back up a snow/ice covered grade in 2wd. That will tell you how good a posi/locker design really works. A G80 will send the rear sideways(if it even decides to engage). If it doesn't engage, you sit there. You need wheel speed to make the G80 work, which is often not a good thing on snow, as it creates ice under the spinning wheel.. A torsen will do a much better job of keeping the truck going where you want it. It works almost from 0 RPM & does a much better job of getting you going up a slippery hill. A small downside of the torsen is that it can create a shudder at low speeds as it quickly sends power back and forth between sides. No big deal & it's a small price to pay.
The torsen also works fine going forwards, even if you want to screw around and hang the rear end out. It will help you do that when you want.

Edited December 7, 2019 by Nanotech Environmental

SierraHD17 · December 7, 2019

I run Detroit lockers in every truck I own minus my 2013 because i haven't installed it yet. Even my 2017 has one. Does what I want it to do every time and is predictable as hell doing it. The Trutrac is pretty mickey mouse... and honestly lots of people get 200000 + miles from Auburns too... or oem G80s... or anything really. I use a Trutrac in one of my trucks front diffs as it better than being open... and they work well at that. Even the OEM's only use the Trutrac in front axles as that is where it does well on a truck... Not my cup of tea but its better than an open diff until it ultimately becomes one all on it's own.

The old Gov lock has been around since 1973 in GM trucks and likely will still be used until they replace the axles with electric wheel motors. People mostly like it and it is what it is. If you dislike it you can replace it with whatever suits your fancy and enjoy it.

Edited December 7, 2019 by SierraHD17

Grumpy Bear · December 7, 2019

I've seen both the worm and worm wheel and the helical gear styles of Truetrac. Now. Until you posted that video I'd never seen the helical gear style. I will look into this.

Edited December 7, 2019 by Grumpy Bear

swathdiver · December 7, 2019

G80 in our trucks is a system, not an actual part, that has been in production since the mid 1980s. It is part limited slip, part locker. In the GMT400, 800 and 900 pickups and SUVs it was in the 8.5, 8.6 10-bolts and 14-bolt 9.5 axles. The K2s went with 12-bolt Salisbury axles, 9.5 and 9.76. What are the T1s using?

Pressure from those who don't know will likely cause GM to adopt those more complicated and costly systems, just like they're doing with the IRS for the SUVs.

If only Uncle Sam would let the automakers make throwback cars and trucks, a K5 Jimmy with no airbags, side reinforcements, manual locking hubs, solid axles, etc. like the old days, they'd sell a ton of them.

America's President is listening though, he's rolling back regulations to make future cars less costly and for those of you who are old enough to remember, we're going to get real light bulbs, shower heads that actually shower us with water and toilets that actually work on the first flush again.

SierraHD17 · December 7, 2019

The G80 RPO code for locking differential has meant the Eaton Gov lock since it's introduction in 1973 in a pickup truck... not the mid 80's. G80 also is the same code used for a limited slip in a passenger car application until today. If you had a limited slip after 1973 in a truck it's RPO code G86. I would have to go look in my RPO code guide to see what the Detroit Locker's RPO code was because it was an option in the 10.5" 14 bolt through the 90's.

GM recycles RPO codes constantly and uses them in multiple applications. It's just a code... If you had a 1969 Chevy truck with positraction as per the sticker in the glove box ( it's a clutch pack limited slip back then) it's RPO was still G80.

The 9.5" and 9.76" 12 bolt is a redesign of the 9.5" 14 bolt which debuted in 1979. Yes you could install a Gov lock from a 1979 model year truck in your 2019.

mistaare · December 8, 2019

I am still confused is it good or not?

Seems like a a lot people here don’t like for whatever reason but the fact that they have used it for 20+ years seems to speak volumes.

SierraHD17 · December 8, 2019

1 hour ago, mistaare said:

I am still confused is it good or not?

Seems like a a lot people here don’t like for whatever reason but the fact that they have used it for 20+ years seems to speak volumes.

Try 47 years actually.. it turns 50 in the 2023 model year so it's not new.

You either like it or you don't. It's as simple as that. Considering I have replaced it in 5 vehicles with something else speaks to what side I'm on. I don't like how it operates and never will. Maybe you do? It's all about choice here. The 9.5 and 9.76 won't explode like the 10 bolt version does.

Edited December 8, 2019 by SierraHD17

RaisedByWolves · December 8, 2019

On 12/5/2019 at 4:08 PM, BlaineBug said:

That 40 mph figure might be wrong, I don't know. I was watching this build yesterday on Power Nation, below. At 12:40 he starts talking about the G80 and mentions that it becomes an open differential at 45 mph. Of course the show is like a commercial, as they advertise for manufacturers and sellers of upgrades, so, take his trash talking with a gain of salt.

At any rate, the Ford Ranger seemed odd. If it had the limited slip I would have felt it should have done better with their tests based upon my own ownership of a Crown Victoria with a Ford 8.8 3.55L. I rebuilt with stock clutches, non-carbon fiber, and even reused the original S spring and it was a great limited slip. The spring is a lot beefier in the F150s and Explorers but really doesn't do anything beyond initial preload. A lot of people would "upgrade" to the truck's version of the S spring thinking it would do wonders but in reality it was just for the initial wheel spin before centrifugal force takes effect and compresses the clutch packs.

I never spun out, either, although in slick conditions I was mindful of throttle application during turns. I suppose the G80 is built for idiots and soccer moms, which is probably true.

Yeah, that show is crap and Im pretty sure his info is off.

The G80 is basically an every mans locker.

You could not give a soccer mom a standard manual locker equipped vehicle and expect her to keep it on the road.

Edited December 8, 2019 by RaisedByWolves

RaisedByWolves · December 8, 2019

On 12/6/2019 at 11:09 AM, Grumpy Bear said:

It's the 1XX rpm to lock that gives me pause. I understand it wouldn't be an issue on a slippery surface like mud or snow. Thing is, the only personal use I have for it is acceleration on dry pavement. I like it to leave straight.

Trust me, it will.

One tire chirps, it locks, done!

100rpm is about 12mph.

RaisedByWolves · December 8, 2019

16 hours ago, mistaare said:

I am still confused is it good or not?

Seems like a a lot people here don’t like for whatever reason but the fact that they have used it for 20+ years seems to speak volumes.

It is very good.

swathdiver · December 8, 2019

21 hours ago, SierraHD17 said:

The G80 RPO code for locking differential has meant the Eaton Gov lock since it's introduction in 1973 in a pickup truck... not the mid 80's.

The 9.5" and 9.76" 12 bolt is a redesign of the 9.5" 14 bolt which debuted in 1979. Yes you could install a Gov lock from a 1979 model year truck in your 2019.

For those asking if the system is any good or not, in my opinion YES! Never had a problem with its performance in 30+ years.

I think you're right about that. I was thinking of the torque limiting disc which is mentioned below.

According to AAM, you cannot use the center section of the 9.5 14-bolt in the Salisbury 12-bolts.

My comments are directed to 1500 or 1/2 ton series trucks and SUVs, I grew up with G80s in my Buicks, while the center section is the same and cover, they did not have the governor and were a true limited slip.

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.

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

SierraHD17 · December 9, 2019

Most if not all of the current aftermarket carriers for the 9.5" and 9.76" are just 9.5" 14 bolt carriers. You just get a spacer plate and some bearings to use it.

According to GM you can't use LT connecting rods and crankshafts in an LS block either which is totally bogus. It happens.

Edited December 9, 2019 by SierraHD17

Grumpy Bear · December 9, 2019

On 12/6/2019 at 8:39 PM, SierraHD17 said:

That video is neat and all but that's not actually how a Trutrac people talk about operates. There is no spur gears on the ends of the worm wheels to lock the gears together in a Trutrac and they actually run parallel with the drive gear on the axle shaft. Instead if you spin one faster than the other the principal is the worm wheel will be forced into the wall of the case and bind as the two will separate under wheel speed difference. The worm wheels spin with about half the gear overlapping the one on the opposite axle. That's all fine and dandy but it's pretty mickey mouse in the long run as it heavily depends on friction to the case of the differential. In that sense its much like how an Auburn limited slip relies on the side gears having teeth on the back side that dig into the case. Here is the Eaton exploded view video.

Haven't heard back yet from my source but I've watched the video a number of times and don't find it Micky Mouse at all.

Those pinions are nested in close fitting bores just like your crankshaft is spinning in the mains and just like your crankshaft it is being forced in directions every which way and yet I don't see that as MM either. These are hardened gears in hardened bores spinning at or near zero rpm. They don't rely on case friction but gear friction. Clutches in you LSD rely on friction. Clutches in the AT or for your MT or your brakes all rely on friction. Two gears on opposite shafts in a MT are trying to force themselves away from each other. The sun and planetary gears in your AT ditto. None of that is either MM nor is it even avoidable. Eaton designed for this just like anyone else does when friction is the operative means for functionality. This is about as seamless a system as has been devised. Millions of these units have outlived the powertrains they control. I'm in.

SierraHD17 · December 9, 2019

Meh... I have plenty of actual personal experience with the units which I know from others that have left this forum is meaningless to talk about....but still. They peg easily and rely heavily on using inferior fluid to allow the friction required to operate. It's like the Gov Lock... love it or hate it.

Edited December 9, 2019 by SierraHD17