1976 14 bolt posi questions

[RaysK20]

Can someone tell me about the factory posi in the 14 bolt. I spotted one local for 50 bucks and came from a running truck thats being parted. I will probably buy it, so what kind of oil should I run in it? I assume its a clutch limited slip of some form.

[Captainfab]

The 'posi's' in the 14 bolts are actually a gov-lock. They aren't all that good and most will tell you to walk away, but it depends on what you're planning on doing with it. I used to have a '78 C20 Suburban with a weak 327 (originally 454) running 8.75 x 16.5 tires and never had a problem with the rear end....even with the 454. I don't think they require any special oil or friction modifier additive like the clutch type posi's need. I could be wrong though

Originally Posted by RaysK20

Can someone tell me about the factory posi in the 14 bolt. I spotted one local for 50 bucks and came from a running truck thats being parted. I will probably buy it, so what kind of oil should I run in it? I assume its a clutch limited slip of some form.

[RaysK20]

I just have a mild 350 with a auto behind it and 33 inch tires. Thought it might be a upgrade for out in the woods driving hunting etc. If its junk then I wont waste my money because I hate walking.

[LONGHAIR]

The Gov-Loc from the smaller 12 bolts are definately bad, but the ones from the 14 bolts are known to be better. Horsepower, tire size, and driving style are the biggest factors in it's ability to survive.

Either way, it is a clutch-type posi unit, and requires the use of the "additive" if you use a conventional gear lube. Synthetics don't need it.

Reguardless of the name, don't let anyone tell you that this is any kind of "locker"....it is NOT. It is a clutch-type unit with an mechanical means of varying the pressure on the clutches.

The single biggest issue here though is getting it installed. Used gears require extreme precision in their set-up. They have to go back exactly the way they were, no matter what the backlash actually measures. You cannot "adjust it" to make it tighter.....well, you can, but you won't like the results...

[RaysK20]

Setting it up is not a issue as its the complete rear end. I have read that some came from the factory with a detroit locker. How can you tell?

[LONGHAIR]

In '76? I don't think so. I could be wrong, but I don't think the factory used 'Lockers by then.
Many people hear "Gov-Loc" and the only thing that sticks is the "lock" part.

Any chance that you could get a picture of the internals?

[bignbad]

there were 2 diffierent 14 bolts full floater 10.5" ring gear the good one,And the semi floaters they are the smaller 14 bolts

[Mike C]

I don't think the semi-floater was around in 76. What option code is on the SPID(option code sheet in glove box)? If I remember, the square bodies only listed the code with no explanation like the earlier bodies had. Should be alphabetical. G80 is posi-track while I think G85 was the maximum traction (detroit) code. Not sure the first year the Gov-Bomb showed up, but it was 73 or later for the 10 bolt. Once again, unsure on the 14. I think 1980? 81? was first year of semi-floater.

[stomper]

Reviving this 9 yr old thread! I think I have something unusual here. A squarebody 1973 K20 with a "G56 Locking Differential". Not a G80. Is this a Detroit Locker?

[Bigdav160]

Open it up and lets see!

[Mike C]

Interested in seeing what you find, but looks like G86 to me and not G56?

Seems to be some disagreement so linked it for you to make up your own mind.

Found this Googling on the square body sight:

1973 axle:
G80 - positraction
G86 - Eaton locking diff
G87 - maximum traction (C30 camper special with dual rear wheels only)

https://www.gm***************/thread...rential.22489/

[mongocanfly]

That looks more like G86 on the sticker....

[stomper]

Originally Posted by mongocanfly

That looks more like G86 on the sticker....

You are absolutely correct mongo. My eyesight is worse than I thought.

[kwmech]

Well there is this

https://d354nuoz4t18d4.cloudfront.ne...m/rpoCodes.pdf


Really doesn't answer the question though.

[mongocanfly]

Found this.....

The biggest difference between the G86 and the G80 is the mechanical locking capability of the G80.

Both are considered "limited slip" diffs, both have clutch packs that provide power transfer to the axle with the highest traction.

The G80 has the ability to "lock" the left and right axles (using a centrifugal weight activated mechanism) if the limited slip clutches need additional help.
The G80 LSD clutches can get you out of a low traction situation, without the locker, if you don't spin a wheel.


The G86 is a high performance LSD. Because of the clutch action, the power is transfered "gently" to the wheel with the greatest traction, ideal for high hp applications.


The G80 uses a locking pawl to "hard" engage the wheel with the greatest traction, exposing the diff to a lot of stress.


The end result is the same, power is transferred to the wheel with the greatest traction, the mechanics are just a little different.

[b454rat]

The G80 is the govlock, the G86 is an old school “posi”. They went away in the mid 70s, then grenade lock after that. Only Detroit I’ve heard been used is the Eaton axles and of course 80s army trucks. Not including Dana axles.

[sweetk30]

Originally Posted by b454rat

Only Detroit I’ve heard been used is the Eaton axles and of course 80s army trucks. Not including Dana axles.

x2 in my years of playing with 14ff rears in civilian trucks unless someone swapped in a detroit or military rear .

of the gov-loc units the 14ff is by far the strongest unit . i prefer them for d.d. use and snow covered roads in the winter over a full locker .