Over the last few days I installed a G80 locking differential in my 2000 GMC Jimmy Diamond Edition, AWD/4WD. I had pulled the differential from the junkyard 3 years ago and just got around to tackle this job.

I removed my original open differential and removed my ring gear and transferred it to the G80 differential. The install was straight forward. The critical aspect is setting the backlash correctly. Factory service manual specification is .002-.009 in. I thought I had the differential in specification but during my test drive I had a ticking/grinding noise during turns.. I was not sure of the cause but I suspected the differential side bearings as I did not replace them before installing the differential. I ordered new bearings from NAPA (BR72), I removed the differential from the car. I removed the side bearings while I was waiting for NAPA to get the bearings in. The bearings came in yesterday afternoon and I was able to press the new bearings on to the differential. Today was spent installing the differential into the axle again. I decided to check the backlash again and I was way out of spec. I spent quite a bit of time trying different shims and checking the backlash. After about 2 hours I managed to get the backlash to .003 in. I installed the axles, connected the drive shaft and before I put the cover on I checked the backlash one final time and the backlash was confirmed at .003in. Reinstalled the cover, sway bar, rotors, brake calipers, tires and re-hung the spare tire. This time the test drive went perfect. No noise from the differential. I am not sure if the noise was from the side bearings or the incorrect backlash settings.

As part of this overall installation I replaced the axle bearings and seals. Replaced my rusty dust shields with junkyard replacements. I blasted painted the differential cover and the dust shields.

 

Sweet! The G80s get a lot of hate, but I've always had good luck with them. And man, do they make a huge difference both on and off road

 

Nice! There are better locking diffs but the G80 is a major upgrade from what you've had.

 

II understand the limitations of the G80 as a slow speed traction device. It is a true locker when it does engage.

 

To answer your question the backlash was your problem. The stuff you replaced is always nice to have when swapping gears/carrier. Just to be clear, a G80 is NOT a true locker, ever, it's a limited slip differential.

 

When the G80 engages both axles are locked together. It does not transfer the drive wheel from one side to another. You tube has videos exactly how the G80 works.

 

I agree that the backlash was his issue, but I have to disagree about the g80 not being a locker..

yes, it engages using clutches as a limited slip does, allowing some slip before it engages. However, once fully engaged they (when functioning properly) deliver a 50/50 split of power to each rear wheel- just as a "true" locker does. It is also designed to disengage over a certain speed to keep you from spinning out in high speed, low traction conditions (one of the dangers of a locker).

so in my opinion it is somewhere in between a posi and locker, but being that it delivered a 50-50 split, it is a true locker by definition

edit: I we mr.vls already explained while I was typing. Ooops!

 

In my experience, the G80 holds up fine in most stock applications. But I've seen plenty of them explode spectacularly when subjected to high horsepower, big tires, or hard use. They're also fairly complicated, so it's not that uncommon for some of the small moving parts to fail and keep it from locking like it should.

 

I'll go out on a limb here and try to explain a LSD like the G80. Limited slip differentials usually use spring loaded clutch-style friction plates to help keep the tires moving at the same speed. When engaged they are a very low speed traction device. When both tires are on the ground and one tire loses traction it will start to spin. When one axle spins approximately 100 rpm faster than the other, the G80 kicks into action and effectively locks the axles together. If you get a LSD like a G80 stuck with one tire in the air you'll see how well it works for getting traction, you'll be in for a rude awakening, no traction. When you add big tires to the equation and the skinny pedal is pressed down hard, when you do get traction something will give and more than likely it will be the G80. Lockers on the other hand are fixed in the locked position until a high enough differentiating force causes them to unlock temporarily, then it's right back to being locked. If you have a selectable locker it uses air, an electric current, or a cable to switch between an open and locked state, not mechanical like a standard locker. A locker that is working properly will always transmit power to both wheels at the same time, regardless if both wheels are on the ground, regardless of speed. A spool will do the exact same thing as a mechanical locker but there is not differentiating action (it has no way to release one side) so both axles are permanently locked together mechanically.

 

You've done an excellent job explaining how a limited slip works and with the exception of the fact that the g80 is, by definition, a locker- I agree with everything else you've said in the explanation. I'll try to explain a bit further why it is a locker.
As you've stated there are multiple different style lockers, some engage in different ways than others. What defines a locker vs a limited slip is not the means by which it engages or disengages, but by the fact a locker delivers the same amount of power to both wheels while locked. A properly functioning g80 will do exactly that.

yes, limited slip differentials use a clutch style engagement system- just as the g80 does. However, unlike the g80, limited slip differentials only delivers a small percentage of the power to the 2nd wheel once the first one loses traction.

the "jack one wheel up" trick won't prove anything with a g80, because as you explained earlier there are very specific conditions that need to be met before it will actually lock for this particular style differential. which are not going to be met by spinning a wheel by hand

I hope I'm not coming across as argumentative or rude, I'm just hoping to help explain the reasoning behind the fact that the g80 is considered a locker despite functioning in a substantionally similar manner as a limited slip