Can anyone tell me what type of differential this is?

I am Trying to remove an axle on what I believe to be a 1991 Chevy 1500. but upon coming apart the rear end it looks completely different from pictures I’ve seen. I know this must have something to do with the four by four mode locking in my wheels but I have no idea what it’s called. Does anyone know what this setup would be called so I can look up a manual on how to take it apart? here are some pictures of it…

It is a rev-loc limited slip differential. Acts like a locker style positraction until the truck gets to about 25 mph and unlocks.

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Many GM trucks use(d) what is called a “governor lock” limited-slip differential. In '91, the factory manual referred to it as an Eaton Locking Differential. I don’t know how long Eaton made it or if they still do.
Here’s the working description from the manual:

The locking rear differential allows for normal differential function as indicated in the standard rear axle description. Additionally, the locking rear differential uses multi-disc clutch packs and a speed sensitive engagement mechanism that locks both wheels together if one wheel should spin excessively during slow vehicle operation.

Full locking is accomplished through the use of a heavyweight governor mechanism, cam system, and multi-disc clutch packs. The flyweights on the governor mechanism move outward to engage a latching bracket whenever the wheel-to-wheel speed varies by approximately 100 rpm or more. This action retards a cam which, in turn, compresses the multi-disc clutch packs locking both side gears to the case. The 100 rpm wheel-to-wheel speed allows for cornering without differential lock-up.
At vehicle speeds above approximately 32.2 km/h (20 mph), the latching bracket overcomes a spring preload and swings away from the flyweights. At this vehicle speed or greater, the differential will not lock, as the added traction is generally not required.

Note that while the differential may not lock above a certain speed, the limited-slip still works via the clutches (I think).


Not in the last 3 GM trucks I’ve had did they still have a limited slip function. Once it was open, it stayed open. Truck guys think it tows better that way. I’d rather have a Torsen or a Tru-Trac.

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This comment spurred me to do a little more research. Looking further into the GM factory manual’s description and operation of the locking axle, it states: “Under normal conditions, when the differential is not locked, a small amount of limited-slip action occurs.”

And from Eaton’s (they do still make this diff.) brochure on their MLocker G80 diff. (MLocker = mechanical locker, G80 = GM’s RPO code for the locking diff.), they state: “Functions as a light bias limited slip differential during normal driving conditions.”

This implies that, while it may not act as a “full” limited-slip, neither is it fully open. It’s somewhere between.


Did you work on that in a past life?

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No, just suffered with them!

Years work of cars and trucks with various types have colored my opinions.

Pure lockers slam when the engage… my 3/4 ton Suburban. They work but not smoothly.

The rev locs work ok but drop out at too low a speed, IMHO

Cone types work until they get hot. Clutch types are ok with manual trans but can snap spin with automatics.

Torsen gear types are my favorite. Had one in my Honda S2000. Put one in my current Mustang. Super smooth. Drives like and open diff with traction like a good clutch posi.