1998 K2500 limit slip or locking?

[dmg92001]

Short story: Safety first. Verify suspension, steering, brakes. Replace all fluids and filters (except for A/C refrigerant and desiccant, assuming the A/C works.) Flushing the brake fluid will require a scan tool to get all the old fluid out of the ABS system.

Everything rubber is suspect: Hoses, belt, tires, mounts, suspension bushings.

Then a proper and complete engine tune-up. Connect a scan tool, verify EVERY sensor and computer output. Look at fuel trims, misfire counts, and so forth.

There's multiple reasons for low brake pedal. You're right about the adjuster(s), and you'd want to remove the drums to verify. But that's just scratching the surface. Air anywhere in the system--including inside the ABS--is another possibility. Oversized (worn) drums. Weak brake hoses. Weak master cylinder--in particular the third chamber or it's check-valve.

Your truck likely has JB6 brakes, therefore low-drag calipers in front. This requires a Quick Take-Up master cylinder, and replacing that with a standard, but larger-piston master is popular but crazy.

I'm expecting that axle to be a 9.5" semi-float; G80 represents a Gov-Loc differential.

But the easy way to put this to bed, is to remove the differential cover, drain the fluid and take a look. Look at the gear ratio and gear condition while you're in there. Inspect the magnet for debris.

Thank you for all this detailed response - so from what I understand now, the two main types of differentials are open and limited slip, with gov-loc and posi being two different types of limited slip.
If I remove the cover and it is a gov-loc I will see this:

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and if It is a posi I will see this:

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And if it is gov-lock I use 80w90 gear oil with no additives
and if it is a posi, then I use the same oil with a friction modifier additive?

I assume I should not reuse the old oil/mix it with new- previous owner replaced the cover after it rotted out and said he used whatever GM recommended (and I have no idea what that is exactly).

I will definitely need to a lot more research into working on the brake lines (most I've ever done is bled them after changing a caliper).
I have a basic scanner but I don't think it will do what you mentioned about flushing the ABS.
An electronic tester indicated the brake fluid was bad so I'll definitely be flushing it soon.

I am changing the front shocks today (hopefully) and will open the rear diff cover this weekend.

 

[GoToGuy]

My dads old 96 had one. I never realized it had the locker until right before he sold it. I borrowed it in the winter and wondered why his 2wd shortbox with wide-ish tires seemed to do better in the snow than my 1-ton 4x4 with AT tires, but with an open diff.

So a locker or posi doesn't limit slip.

 

[Sean Buick 76]

So a locker or posi doesn't limit slip.

More accurately they “limited turn”. There is no slip in the locker style G-80 diff. Once one of the wheels starts turning faster than the other one centrifugal force allows the locker to engage the other axle. While they function ok for a daily driver type of situation they don’t put up with burnouts, drags racing and off road abuse for very long. In fact I think the main reason the 10 bolt Chevy rear axle is known as a week rear end is because of the catastrophic gov lock G-80 explosions that occur and take out the whole diff. While off roading I was trying to get my 01 Yukon with a 10 bolt G-80 out of a challenging area and the Gov bomb went off and not even the housing was salvageable. It blew a hole in the cover, just a mess.

When a good aftermarket locker, spool or limited slip is added the 10 bolts can be durable especially with stronger axle shafts with a higher spline count.

 

[99xcss4]

the g80 seems to hold up better in the 9.5 10.5 14 bolt and aam 11.5 then in the 7.5 8.5 and the 8.6 10 bolts the old 8.875 truck 12 bolts seem to share the blowing up problems with the various 10 bolts

 

[Cadillacmak]

More accurately they “limited turn”. There is no slip in the locker style G-80 diff. Once one of the wheels starts turning faster than the other one centrifugal force allows the locker to engage the other axle. While they function ok for a daily driver type of situation they don’t put up with burnouts, drags racing and off road abuse for very long. In fact I think the main reason the 10 bolt Chevy rear axle is known as a week rear end is because of the catastrophic gov lock G-80 explosions that occur and take out the whole diff. While off roading I was trying to get my 01 Yukon with a 10 bolt G-80 out of a challenging area and the Gov bomb went off and not even the housing was salvageable. It blew a hole in the cover, just a mess.

When a good aftermarket locker, spool or limited slip is added the 10 bolts can be durable especially with stronger axle shafts with a higher spline count.

When I put the 94 454 and 4l80e in my daughters 74 chevy, I went out in the street and did a burn out. Gov bomb went off! She was all upset but I had another Gov bomb laying around so she wasn't down long.

 

[454cid]

So a locker or posi doesn't limit slip.

A locker locks and unlocks. An LSD slips in a limited amount. An open diff slips in an unlimited amount.

 

[evilunclegrimace]

More accurately they “limited turn”. There is no slip in the locker style G-80 diff. Once one of the wheels starts turning faster than the other one centrifugal force allows the locker to engage the other axle. While they function ok for a daily driver type of situation they don’t put up with burnouts, drags racing and off road abuse for very long. In fact I think the main reason the 10 bolt Chevy rear axle is known as a week rear end is because of the catastrophic gov lock G-80 explosions that occur and take out the whole diff. While off roading I was trying to get my 01 Yukon with a 10 bolt G-80 out of a challenging area and the Gov bomb went off and not even the housing was salvageable. It blew a hole in the cover, just a mess.

When a good aftermarket locker, spool or limited slip is added the 10 bolts can be durable especially with stronger axle shafts with a higher spline count.

NOT true Gov locks have clutches, and one wheel will slip under the right conditions after the loc is engaged.

 

[Sean Buick 76]

NOT true Gov locks have clutches, and one wheel will slip under the right conditions after the loc is engaged.

Yes there are clutch disks that cushion the engagement once the locker is triggered but the initial activation is from the locker not the clutches. My point is that with these junk Gov bombs the tire that doesn’t have enough traction starts to spin violently and then a tiny BS locking tab engages sending power to the other wheel which is cushioned by the tiny inadequate clutch disks.

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For a daily driver without any real power the G-80 is a bit better than an open diff but for anything with power or that gets tire spin off road or on ice the Gov bombs are terrible.

An actual limited slip diff (LSD) that uses clutches as the main function is a much better way to get an equal distribution of power to both tires without any downsides except clutch wear over time. A good LSD allows very little lag time before the second tire gets power.

A real locking diff like a Detroit locker offers a more positive engagement without the worn out clutch issue. These may click around corners which some people may not like.

Air lockers are great because they can be set to fully open for great turning ability or fully locked without any slip.

Or for drag racing or on a budget when pushing big power or hard core off road the spools give you 100% equal push to each tire. My drag car is spooled and I still drive it on the street. You can feel that the rear wheels scrub a bit when making tight turns but the tires are 20” wide and surprisingly they don’t chatter or make noise when doing tight turns in a parking lot. For a daily driver using a spool will increase tire wear.

 

[evilunclegrimace]

I agree with part of this, But the clutches are not tiny they are roughly the same size as clutches in a LS diff. They do not wear out any faster than a LS diff. And as far a violent engagement the governor engages the locking mechanism at a 200-rpm difference and unlocks at 20MPH. A Detroit locker has a much more "violent ' engagement, especially under throttle on a turn. The clutches are there so that when the vehicle makes a turn one wheel can spin faster than the other without the wheel hop that you get with a Detroit locker in a turning situation under moderate power on a dry road condition.

 

[Sean Buick 76]

I agree with part of this, But the clutches are not tiny they are roughly the same size as clutches in a LS diff. They do not wear out any faster than a LS diff. And as far a violent engagement the governor engages the locking mechanism at a 200-rpm difference and unlocks at 20MPH. A Detroit locker has a much more "violent ' engagement, especially under throttle on a turn. The clutches are there so that when the vehicle makes a turn one wheel can spin faster than the other without the wheel hop that you get with a Detroit locker in a turning situation under moderate power on a dry road condition.

I’ve been wrong before but I’m pretty sure that the Gov bombs act like a fully open diff until the wheel speed between the right and left rear wheels hits a 200 rpm difference in speed at which point a flimsy 1” pawl engages the locker. And if your really getting the tires spinning at that point with the locker engaged it disengages over a certain speed leaving it an open diff again. The clutches don’t control when the locker engages they only cushion the transfer of power. If babying the vehicle the Gov bomb isn’t so bad, it allows open differentiation and gives power to the other wheel if you get stuck and have one tire spinning helplessly. But if you have a powerful engine or you drive aggressively they just won’t last, and they self destruct taking out the whole diff normally.

A real locker isn’t violent when it engages because it’s already engaged. The only time the locker clicks is when you go around a corner when not on the gas. If you floor it you get 50% to each tire until you let off even around a corner.