How a G-80 Works

HARDTRAILZ

Original poster
Moderator
Nov 18, 2011
49,665
In some discussion on G80s and their merits and faults, I thought...we need this on the Nation, so

How a 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.

Videos

http://www.youtube.com/watch?v=p8nAb...eature=related


[video=youtube;OmrQWfWCXKQ]http://www.youtube.com/watch?v=OmrQWfWCXKQ[/video]

http://www.youtube.com/watch?v=rGlac...eature=related

Also feel free to discuss this or add any info.
 

n0kfb

Member
Dec 8, 2011
104
There's a whole bunch of animations and other videos on You Tube outlining how a G80 works. It's a pretty nifty peice of engineering.

-- Dan Meyer :coffee:
 

Wyle

Member
Dec 4, 2011
200
So what type if rear differential do I have if I'm not fortunate enough to have a glowing "G80" emblazoned in my glove box?? :hissyfit: Are the standard ones open :frown: or some form of limited slip?

And since I don't have a locker, does that mean my dash switch should truthfully read 3HI and 3LO?

There's a pretty cool G80 animation from Eaton on youtube as well and a couple informative/entertaining ones on differentials in general. Thanks, HARDTRAILZ. "Finally understanding differentials". Like I need something new on my to-do list. :raspberry:
 

rjpoog1989

Member
Dec 4, 2011
116
Wyle said:
And since I don't have a locker, does that mean my dash switch should truthfully read 3HI and 3LO?

technically it would be 1HI 2HI and 2Low because your front wouldn't be locked either, unless you installed an aftermarket locker.
 

The_Roadie

Lifetime VIP Donor
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Nov 19, 2011
9,957
Portland, OR
Wyle said:
So what type if rear differential do I have if I'm not fortunate enough to have a glowing "G80" emblazoned in my glove box?? ...
You have the kind of differential that RECEIVES the recovery strap when you get stuck offroad. :rotfl: I have the kind that GIVES the strap. :wootwoot: :biggrin:

Seriously, been offroading multiple times in groups that include a 4WD without a G80, and 2WD WITH the G80. The non-G80 4WD needs assistance far more often than the other guy. It's sad to be him, really. :redface:

Limited slip was an option only in the SS. And they didn't have a locker option, and nobody takes them offroading. Yet.
 

DJones

Member
Jan 21, 2012
701
St. Petersburg, Florida
the roadie said:
Limited slip was an option only in the SS. And they didn't have a locker option, and nobody takes them offroading. Yet.

That's interesting. My 2007 Saab 9-7x brochure says "Rear Limited Slip Differential".
 

Wyle

Member
Dec 4, 2011
200
rjpoog1989 said:
technically it would be 1HI 2HI and 2Low because your front wouldn't be locked either, unless you installed an aftermarket locker.

Oh yeah. I was thinking the splined disconnect handled that, but its still an open differential. doh! <scratching head> Then the disconnect just keeps the front driveshaft from spinning in 2HI when both front axles are spinning?! Wait. Then why do you get front binding and crow hop if the front wheels can spin at different speeds with the spline engaged? I'm back to being confused again.
 

Wyle

Member
Dec 4, 2011
200
the roadie said:
You have the kind of differential that RECEIVES the recovery strap when you get stuck offroad. :rotfl: I have the kind that GIVES the strap. :wootwoot: :biggrin:

:thumbsup: Touche. Technical understanding can be a bad thing. Open diff means 0WD if one gets light. Chaining wheel spokes to the frame probably isn't a good method to transfer torque to the other wheel.
SIGH. Ok, just add G80 to the mod list. Hmmm. Wonder what's in my son's 2WD, er, 0-1WD TB. He never leaves the pavement. "Hey son, let me look in your glove box."
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
If he has a G80, you can offer to change diff oil for him some weekend. 4 hours later, present him his vehicle with YOUR old axle in it. :wootwoot:

Changing entire rear axles is the cheapest way we've found to install G80s in trucks that didn't come with them. If you have a SWB I6, it's also a good time to upgrade to the stronger 8.6" ring gear diff. Almost never a change in price at the junkyards. I got mine for $400.
 
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million-miles

Member
Jan 10, 2012
189
If we dont have the g-80 does anyone make a locking rear or just better to go to pull apart and find one
 

djthumper

Administrator
Nov 20, 2011
14,950
North Las Vegas
million-miles said:
If we dont have the g-80 does anyone make a locking rear or just better to go to pull apart and find one

The only locker available for the 8" IIRC is the Eaton G80
 

usmc

Member
Dec 30, 2011
11
the roadie said:
You have the kind of differential that RECEIVES the recovery strap when you get stuck offroad. :rotfl: I have the kind that GIVES the strap. :wootwoot: :biggrin:

Seriously, been offroading multiple times in groups that include a 4WD without a G80, and 2WD WITH the G80. The non-G80 4WD needs assistance far more often than the other guy. It's sad to be him, really. :redface:

Limited slip was an option only in the SS. And they didn't have a locker option, and nobody takes them offroading. Yet.

roodie....help me understand what you posted about the G80 option only on the SS. I have a '04 ext V-8 & the option lists the "GT4 - REAR AXLE - 3.73 RATIO & G80 - LOCKING DIFFERENTIAL". Do I have the same as what's in the video?
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
Wyle said:
Then the disconnect just keeps the front driveshaft from spinning in 2HI when both front axles are spinning?!
Exactly. It cuts down the wear on the front differential because fewer parts are spinning. But a closer analysis reveals that SOME parts are spinning in 2WD mode. The left CV shaft turns the left differential end gear. That spins two spider gears. They force the passenger side end gear to spin the intermediate shaft that goes through the oil pan in REVERSE. The splined disconnect is not engaged, so the reverse spinning intermediate shaft doesn't do anything inside the splined disconnect. All this happens because the front diff gear carrier (and its ring gear) are being held still by the superior friction of the pinion seal and front driveshaft seal on the transfer case. It took a mechanical engineer to explain it well enough to me.
Wait. Then why do you get front binding and crow hop if the front wheels can spin at different speeds with the spline engaged? I'm back to being confused again.
EVERYBODY who thinks deeply about the problem runs into that wall sooner or later. Congratulations! I had to figure it out years ago.

The reason is because the transfer case in 4HI has very low slippage. Almost locked. Not like a slipping AWD transfer case as on a Subaru, for instance.

The front and rear diffs are open, but all that means is that they AVERAGE out the RPM of the front wheels. They are allowed to rotate at different RPMs on the inside and outside of the turns, but the differential driveshaft spins at a rate that's the average.

BUT the front and rear differentials arc out different radii in turns because the vehicle's turning point is in line with the rear axle. The transfer case locks the front to back driveshaft and forces them to turn at the same RPM, so that's why you get scrubbing, even with open diffs. Viola! Let me know if this needs more explanation.

envoyturning.jpg
 

The_Roadie

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Nov 19, 2011
9,957
Portland, OR
usmc said:
roodie....help me understand what you posted about the G80 option only on the SS. I have a '04 ext V-8 & the option lists the "GT4 - REAR AXLE - 3.73 RATIO & G80 - LOCKING DIFFERENTIAL". Do I have the same as what's in the video?
If anybody EXCEPT SS has a G80, it's the Eaton Automatic Locker shown in the video. Full lockup. Fragile.

What I said about the SS was the Eaton Automatic Locker wasn't an option. They have a limited slip different unit available. They also have a larger ring gear not shared by any other vehicle except the Saab SS clone.
 

usmc

Member
Dec 30, 2011
11
Thanks....I see now that the "limited slip" is not the same as the "G80 Locking Diff". I wasn't aware of that. I thought they were all the same. Good info.
 

HARDTRAILZ

Original poster
Moderator
Nov 18, 2011
49,665
I believe the SS have a G86 limited slip but mine will have a lockright
 

lovesrugers

Member
Jan 25, 2012
30
Now that was an interesting write up. From it I learned that my 02 Bravada has a G80 in the rear. I don't know why because I have never considered the Bravada as a great off road vehicle when compared to other vehicles I have owned. Mainly this is due to the AWD system. What I do know is that so far with the AWD inoperative at the moment the G80 rear got me through stuff that would have most likely got me stuck nice and good.

Jerry
 

MDBT

Member
Jan 26, 2012
223
DJones said:
That's interesting. My 2007 Saab 9-7x brochure says "Rear Limited Slip Differential".

All Saab 9-7x and the TBSS do not have the G80 option, they are G86 which is a limited slip.
 

HARDTRAILZ

Original poster
Moderator
Nov 18, 2011
49,665
GM in their infinite wisdom would refer to either of the G80 or G86 set-ups as limited slip in different vehicles or configurations. They don't differentiate as much as we do.

They typically would call it what they thought sounded better to potential buyers...Truck guys like to hear a G80 called a locker...implies strength...Buick buyers want to hear it is a G80 limited slip...implies smooth operation and safety.
 

DJones

Member
Jan 21, 2012
701
St. Petersburg, Florida
MDBT said:
All Saab 9-7x and the TBSS do not have the G80 option, they are G86 which is a limited slip.

Found it: a 5.3i with the G86:
(from August Pohl auto parts)
View attachment 18362

Now it makes more sense.
 

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MDBT

Member
Jan 26, 2012
223
Just to clarify, while the 4.2 and 5.3 saabs have the same g86 LSD they use a smaller 8.6" vs the tbss and aero which I think are 9.5".

As for the g80 designation, the way I understood it is that g80 was an LSD in cars and the eaton locker outlined above for trucks and SUVs. But I'm not 100% on that it's just how I thought it worked.
 

HARDTRAILZ

Original poster
Moderator
Nov 18, 2011
49,665
The 9.5 is a decent semi-float 14 bolt. Has lots more options and strength than the smaller rearends. Was on many heavy 1/2 and light 3/4 ton trucks. I think the 454SS pickups had it too. Thats why I picked one up, but the g86 would be about worthless for me.
 

gmcman

Member
Dec 12, 2011
4,655
Is there a 4:10 option for the 8.6" or even possibly the 9.5" in the SS?

I'm thiking if mine ever goes then I would want the SS if possible just to have all the strength.
 

HARDTRAILZ

Original poster
Moderator
Nov 18, 2011
49,665
SS had 4.10 standard but only the G86 limited slip. However, I got one but also got a locker and open carrier so mine will be strong and functional for me.

I know some of the LTZ's and ext/xls had 4.10s as well.
 

Cable810

Member
Dec 5, 2011
690
Good Info Hardtrailz :thumbsup:!! I looked in my TB and I didn't see a G80 but I saw the Gu6. I searched on Trailvoy and from what I read, the Gu6 is or has the G80. Is this correct anyone?
 

The_Roadie

Lifetime VIP Donor
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Nov 19, 2011
9,957
Portland, OR
Cable810 said:
..the Gu6 is or has the G80. Is this correct anyone?
Sorry, no. The GU6 code is a gear ratio:

GU6 = 3.42
GT4 = 3.73
GT5 = 4.10


The G80 option is separate, and is in addition to one of the three gear ratio codes. The glove box sticker will ALWAYS have one of those three codes, and may or may not have the G80.
 

northcreek

Member
Jan 15, 2012
3,263
WNY
Initially I thought that the difference between the two sizes(8.0-8.6) was the ratios (3:73-3:42) and since my G80 is optioned with GU6(3:42) gears I assumed that I would have the smaller(8.0) ring gear but, this is not the case.My cover is stamped 8.6 and actual ring gear measurement is 8.6
So my question is: are these two sizes a result of two different units(I didn't want to say;two different differentials)and if so what's the diff between the two diffs?(other than .6")....Mike.:confused:
 

djthumper

Administrator
Nov 20, 2011
14,950
North Las Vegas
Basically those .6" and what is available for lockers and gears. The 8.6 you can get 4.56 gears for them.
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
northcreek said:
So my question is: are these two sizes a result of two different units(I didn't want to say;two different differentials)and if so what's the diff between the two diffs?(other than .6")....Mike.:confused:
The diffs are indeed different. Short wheelbase I6 vehicles get the weaker 8.0" ring gear version with 28 spline axles. All long wheelbase, regardless of engine size, and V8 SWB get the 8.6" with slightly stronger 30 spline axles.
 

northcreek

Member
Jan 15, 2012
3,263
WNY
Makes sense now,thanks for getting me a little closer to understanding my new ride.As a precaution I'm going to put some new OEM bags in the back to try and avert the dreaded compressor burn-out.At 5 years I can't be too far from a slow leak...Mike.
 

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