G80 Locking Differential in K5

[scouthead]

The RPO on my 78 K5 shows G80 Locking Differential with HE4 3.40 ratio Rear Axle. So far 140K miles on the original rear axel and locking differential. I just don't want it to go kaboom.

yeah might wanna order a new gasket and some oil... can of brake parts cleaner. drain, and inspect what you have to make sure nothing is damaged. should be able to slap a new set of spider and side gears, if they are damaged, without having to change backlash or messing with the gears???

 

[tarussell]

The RPO on my 78 K5 shows G80 Locking Differential with HE4 3.40 ratio Rear Axle. So far 140K miles on the original rear axel and locking differential. I just don't want it to go kaboom.

G80 is just the RPO ( regular production order ) code for GM’s so called “locking differential “ but if I recall correctly that code was used on older vehicles that had the Eaton clutch type diffs. and they were fairly stout for the size that they had to work with.
Pop your cover and see if your diff looks like this - it was replaced by the Gov-Loc sometime around 1979 or so.

 

[dyeager535]

Yes, G80 is a generic code GM used for cars and trucks. Depends on the application as to what G80 actually is. G80 in cars was always posi (clutch type LSD) later half tons didn't get anything but the gov-lock. Apparently earlier trucks could have clutch style?

"What would be better then the G80 in the rear differential?"

*IMO* for the average rig that sees a lot of street use, but is used for light offroading, the gov-lock is essentially about as good as it gets in terms of operation. The downsides are that in the half ton its weak, it's a fairly complex mechanism for failure, and it's "unpredictable" since it locks up based on wheel speed differential. But in snow and muddy conditions, I generally push the truck as far as I can in 2WD, knowing I have 4WD to get me out of what I get into. With the gov-lock, as anyone with a locker probably knows, I can get much, much further in 2WD than I can with an open diff, and without having to use a ton of throttle to keep moving. I also don't worry a bunch about the rear end trying to come around on me, nor do I have to stop movement to get it to engage.

The electric lockers are cool, except you aren't supposed to engage when moving. All the clutch/Torsen types are not "positive"...in some conditions they can/will fail to provide traction to the wheel that needs it. True lockers are squirrely on ice and can be a bit rough on the street.

All have their downsides and upsides. GM/Eaton must have done something to solve the exploding problems on the later G80's (edit: half ton), I'm sure they were seeing much more power than ours ever saw, and there seems to be no epidemic of these axles self-destructing.

For the "average" person that needs some sort of better traction, but doesn't need/want a true locker, IMO the Truetrac is the best choice in a truck if the gov-lock is out of the question.

The G80 in the 14SF and 14FF axles is significantly stronger, I did this to my 8.5" on the street, while the G80 14SF in the same truck has been going for almost two decades without issue. These are expensive failures.

 

[AJMBLAZER]

14SF and FF parts are just bigger than a 10 bolt. First time I opened up a Ford 8.8” or Chrysler 9.25” I was surprised by how much beefier the parts were compared to the 8.5” 10 bolt or even the Dana 44 and 12 bolt.

My ‘19 1500 has a 9.5” 12 bolt semi floater. Basically a 14SF with less bolts. The G80 works great so far and I don’t worry about it. If it was a 10 bolt with 385hp and 33” tires I’d feel differently.

It ever blows up I’ll explore my locker options though.

 

[Bigb55]

The G80 gov lock is a very capable and street able traction device.

You have to know how it works and what it was designed to do though. Or they have tendency to go boom.

It functions best at low tire speed only. It was also not designed to be forcefully shock loaded.

Off-road it works best at low crawl speeds. In loose dirt/mud/snow, it's best to apply steady throttle from a stop until traction is attained. Diff will stay locked until tire speed increases to a point and then it will release. If traction not obtained, It's best to let tires come to a stop before applying throttle again. Or the G80 can be shock loaded at high RPM. This is when they normally break.

When moving, the G80 again will function best at lower speeds. Be smooth with throttle application when crawling and avoid shock loading.

With this in mind it will last awhile. My 1993 k1500 Blazer has 240k on the OEM G80. It's done about 20k of those miles on the trails over the 20 years I owned it.

 

[tarussell]

The Gov-Loc is fairly unique in its ability to lock up ( and as stated above it’s intended to be done by very careful low wheel speed moments ) but the problem is when the unit locks up unintentionally on the street because the flyweight mechanism engages because of centrifugal force and not by wheel speed alone.
If the unit is working as designed this condition should never happen but for any mechanic that worked on squares and GMT-400’s this is all to common on trucks that are street queens and have never been abused. These models are very well known ( and documented ) for the flyweight being faulty and causing shock-loading and the internals and case housing just can’t handle it.
If it were only abused applications with big tires , high power and maximum traction or someone who does not understand the finesse that it takes to activate a Gov-Loc it would be unfair to give a 10-Bolt 8.5 on down a bad name. But this is not the consensus among those in the industry - they have more of a reputation for catastrophic destruction under normal driving conditions than they do for lasting a lifetime as they should.
A Gov-Loc is very effective but sadly not a reliable means of traction aid on the smaller applications. Some folks had good results but the majority have had lesser experiences and I would assume that ANY unit that has been abused has most assuredly died a violent death - “KABOOM”…..
Anyone can roll the dice but history has taught that these are not the best traction devices to be trusted.

 

[Chickntrk]

What would be better then the G80 in the rear differential?

Anything

 

[ZooMad75]

G86 actually was an option for a clutch type posi in later years. Pretty rarely used as most packages like the Z71 included the G80.

The problem I have with the mechanism is the fact that it needs 50-100 rpm difference in wheel speed side to side for it to engage.

Think about that, one wheel is stoppped with traction and the other wheel is on ice spinning. Once that threshold of rpm difference is met then it locks in and now the stopped wheel is going to match speed of the spinning wheel. Sure sounds like a damn good way to shock load everything involved.

The first time I really felt that happen was in my GM days. 2001 they were hyping up the launch of the new Duramax and Allison trans in the new gmt800 trucks. Had this rolling dog and pony show called the Power Launch Tour set up for Gm employees to check out. One of the demonstrations was to show the effectiveness of the G80 locker vs the other guys open diffs. There was a “track” made with landscaping Timbers that were setup at alternate levels side to side. As you drove up these it would force the rear axle to articulate and hang the right side tire a foot or two in the air. Driving up in a open diff ford, progress ceased as all power went to the wheel in the air. You backed up and switched to a Gm truck and got to the same point. The guys running the show would direct you to ease into the throttle and the G80 would eventually lock up once the speed difference was reached. Every time that lockup was indicated with a loud bang from the rear of the truck. The truck lurched forward and was driven off the lumber.

It was not smooth by any stretch. That demonstration was probably the most extreme way to show it but to me it’s just not an ideal way to lock a differential. It’s really no different than performing a neutral drop in a automatic or dumping case he clutch with a manual. You just are doing it to one wheel and side gear. If that wheel has decent traction that’s where the crap hits the fan.

The 14b versions survive better because the size of all the parts are bigger. The 8.5/8.6 versions are puny. And we fixed our share in gmt800 trucks and express vans too.

My ZR2 S10 has an 8.5” 10b with a G80 that I’m mildly concerned about. But even with the 31’s that are the stock size the 4.3 doesn’t have enough power to do any damage. Plus I drive it like an old man so it will probably live forever. It can’t spin the tires on pavement unless I did high rpm clutch dump anyway so I’ve yet to feel it engaged on anything but snowy roads.

 

[scoots90245]

Not that I’m pro G80, im not (tho im fortunate enough to have one in my k5), but are there really issues with them in stock truck, with only occasional use? Sure they arent meant to be beat on and you need to tip toe around with 35’s and offroading. Said another way, will they crap themselves in a “normally” driven stock truck?

Bought my 89’ with 150,000 opened the diff to change the oil and discovered a nice crack. Stoked I was in my garage.

 

[scouthead]

Bought my 89’ with 150,000 opened the diff to change the oil and discovered a nice crack. Stoked I was in my garage.

View attachment 432871

lol, that photo is actually kind of beautiful... its like you captured a very special moment in time... that split second as the soul was leaving the body (differential / whatever)

 

[tarussell]

lol, that photo is actually kind of beautiful... its like you captured a very special moment in time... that split second as the soul was leaving the body (differential / whatever)

He caught it right at the point of “Ka” and avoided da’ “BOOM“ !

 

[muddybuddy]

Literally stars aligned. Just think, if the diff had been turned 180* when you pulled the cover, you probably wouldnt have seen any indication of the damage lurking on the otherside.(unless it was on jackstands and you were spinning wheels to inspect diff)

 

[tarussell]

The retaining bolt for the center pin must have already sheared and was on its way out too.
Nice catch !

 

[scouthead]

Literally stars aligned. Just think, if the diff had been turned 180* when you pulled the cover, you probably wouldnt have seen any indication of the damage lurking on the otherside.(unless it was on jackstands and you were spinning wheels to inspect diff)

note to self:

when i get around to the 14sf inspection... make sure to spin that carrier around even if it stops in a place where I can already see the side gears and spiders!