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Discussion Starter #1
Hi all.

Sometimes I noticed my G80 did not lock up like it was supposed to. This always happened once in a while as long as I can remember. Sometimes when not locking, with one tire spinning, it would make a bit of a buzzing noise. But, mostly it worked just fine.

Spinning tires on wet roads today, I noticed I got some one tire fire.

My truck has 97k on it now, so I thought changing the fluid in the rear diff might do it some good. The fluid was pretty black as you would expect. The magnet had some sludge on it, and a few small metal shavings and flakes. Not great, but not particularly alarming.

After changing the fluid with synthetic 75W-90 (no friction modifier), I drove maybe 2km to a spot where I could flex and test. Grassy mound, at the edge of a gravel lot.

The diff would just not lock. Lifting right tire or left tire, forward or reverse, once one tire lost traction, I could not go further. The tire with traction would not kick in.

Finally, if I tried to to a burnout on the gravel, both tires would throw stones. Maybe a little odd. I would expect just one tire there too, but maybe both spun because traction was equal?

Maybe it was just being moody, and I should drive around, and try again some other time?

If I perform the test in this video, the tire tire does not kick back.

https://www.youtube.com/watch?v=xCwcr7Sj7Hw

I jacked it up to get both wheels off the ground. Turning one wheel slowly, the other wheels spins the opposite way. But, if I give it a rapid acceleration (as rapid as I can by hand) it does not kick back.

Anybody have any experience with this?

What should I do?

Anybody have similar experience? How did you resolve the issue?

Most online discussions seem to just be arguments about terminology, how the G80 is supposed to work, and other nonsense. Then somebody posts a picture of a grenaded one, and everyone says they suck.

Is a TruTrac the best / only option that is any better than stock? Can the G80 be repaired?
 

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I'm sure the 355 G80 can be repaired but r u positive it's not working correctly? There must be a 100 rpm difference between the 2 opposite wheels speed in order for the mechanism to engage. No such animal as "best" diff.... a Detroit TrueTrac is just another version/brand of a limited slip traction enhanced diff.

https://www.youtube.com/watch?v=AjymmXvBYsI
 

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Discussion Starter #3
I'm sure the 355 G80 can be repaired but r u positive it's not working correctly? There must be a 100 rpm difference between the 2 opposite wheels speed in order for the mechanism to engage. No such animal as "best" diff.... a Detroit TrueTrac is just another version/brand of a limited slip traction enhanced diff.

https://www.youtube.com/watch?v=AjymmXvBYsI
My testing was pretty thorough. Speeds differential between the two tires ranged from just slipping / stopped, to smoking and burning rubber / stopped.

From what I can gather, the TruTrac is really the only other option for the 8.0 axle. If it is better than the G80, that would make it the best. I don't like that it is a limited slip, but it sounds like a little parking brake will usually get it to lock up if you are hanging a wheel.
 

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Yours sounds like it's in need of repair......either the engagement mechanism is wacked, the clutches r toast or both.

If I was into serious off roading, I would look into a real/true locking diff....not a limited slip like the TrueTrac or the G80. For everyday driving on pavement a "open" diff is hard to beat for smoothness, and that's what the G80 is in most driving conditions.....an "open" diff. When it is functioning correctly, it switches to a really tight limited slip, as in torque to both wheels even when one is off the ground, as in the video. Limited slip clutches MUST be really tight AND in really good condition to prevent the wheel that's in the air (or on rollers) from spinning.
 

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Discussion Starter #5 (Edited)
If anybody can point me towards a proper locking differential for our axle, that won't cost me more than $1,500 installed, I'd be happy to take a look. As far as I know, nothing is available.
 

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I've installed 4 PowerTrax No-Slip auto lockers in various vehicles.....cost about $450-$500 and take about 2 hours to install (no special tools or ring/pinion set-up needed). Don't know if they make one for the G80 diff/case.
 

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There are no true lockers that i know of for the AAM 8.0. Just tru trac lsd.
 

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Discussion Starter #8
There are no true lockers that i know of for the AAM 8.0. Just tru trac lsd.
I have not read anything that suggests otherwise.

Has anybody successfully repaired a G80 in this state? If it's just a $15 parts kit, and some labour, I'd go for that.

Otherwise, replacing a failed G80 with another G80 does not give me a lot of confidence.

A TrueTrac might be a durability upgrade, but a slight performance downgrade.
 

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Pretty sure a rebuild would consist of new clutches and such which would probably run about $150 to $200... just guessing.

True trac would be an upgrade all around IMO
 

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Discussion Starter #10
I prefer to upgrade when things break, to avoid repeat failures. The TrueTrac may be my best option.

I'm looking for a local shop that specializes in axle work, but I don't really see much.

I'm guessing most mechanics could swap a differential in 2-4 hours. Would that be fair to say?
 

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id go for a trutrac if the g80 failed. ive never really heard of a failed trutrac, im waiting for my g80 to die to decide if im keeping my rear axle or swapping in something better, if i do keep the axle, if probably go with a trutrac.
 

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The true trac has no clutches so nothing to wear out. .Like the G80 it acts as an open carrier until wheel spin occurs.
 

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Honestly, you have already been on the path to upgrades in the drivetrain for our trucks, is say swap out to a different rear. You'll have the option for an actual locker as well as the opportunity for disc brakes and a diverse gearing selection. Plus the chance to be stronger is nice too.
 

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RKJ,
It sounds like your G80 isn't quite working properly. I found mine didn't always lock up either. It's more of a slow speed locker, and won't lock up if you're moving too fast. Anyhow, if it's not locking up it may need a rebuild or something is jammed.

Regarding the TrueTrac, it is definitely an upgrade over the G80 in all aspects. It is very simple with no parts to wear out. Additionally, it has progressive engagement rather than locking up, so you don't actually feel it engage. If one tire slips it tightens up and transfers more and more power to the other tire as needed. Like you said, if one tire is off the ground it may not engage as there is no load on the device, but feathering the brake will be enough to make it work.

If you want an upgrade, this is the way to go. You'll notice a huge difference, especially on the road in winters. Keep in mind a G80 locking up is actually a problem in the winter as it increases your chances of fish-tailing.
 

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Discussion Starter #15
Honestly, you have already been on the path to upgrades in the drivetrain for our trucks, is say swap out to a different rear. You'll have the option for an actual locker as well as the opportunity for disc brakes and a diverse gearing selection. Plus the chance to be stronger is nice too.
In a discussion with a friend, an axle swap was mentioned. While not a bad idea, my truck is a daily driver first, and an off road rig second. I'm only putting 240ft.lb of torque to 32" tires. I don't currently have any plans to evolve it any more.

I was happy with the stock setup, up until it stopped locking. Other than the G80 differential which sometimes either grenades or fails to lock, it seems like most people seem to be having good success with the stock setup.

And of course, cost is a concern.
 

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The 355 G80 disengages above 20 mph, so how snow/ice driving would be a problem is beyond me. That's another plus for the G80.....most people have SFB syndrome (don't know when to slow down) when it comes to driving on snow/ice so GM takes the G80 out of the picture at 20+ mph for the clueless drivers, ones with SFB.

The 355 G80 doesn't do "lock-up".....no limited slip diff "locks-up". Some limited slips have an engaging mechanism like the G80 and TrueTrac and some limited slips are full time always engaged like the G80 in Camaro's, etc.....but all limited slip diffs slip some......that's how they differentiate in a turn.....slippage.

Lockers, on the other hand, do "lock-up".....as in the teeth of gears are meshed together......no slip, period......kinda like a spool. Auto lockers are always engaged, until a tight turn is sensed and then they "unlock" so the diff can differentiate in the turn. A manual locker, when manually turned on/engaged, will not "unlock" in a turn. It is always locked (like a spool) until manually turned off/disengaged. When a manual locker is turned off/disengaged, it is an open diff.

Again, the G80 is not a locker no matter how many times they call it a locker in those videos. When it engages it becomes a very tight clutch type limited slip diff. It is a light duty traction enhanced diff.
 

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Discussion Starter #17
Again, the G80 is not a locker no matter how many times they call it a locker in those videos.

There are plenty of threads on the internet already debating what the G80 is, and is not.

I'm interested to hear from people who have repaired one, or replaced it with a TrueTrac.



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There are a couple of YouTube vids showing True trac installs. Also I pretty sure Kenny (Onelow1ton) installed the true trac in his 8.6... not % 100 sure but I think he did
 

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my brother replaced the G80 with a true track and loves it, Ext cab Silverado.
2 wheel dr.
 

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Discussion Starter #20
There are a couple of YouTube vids showing True trac installs. Also I pretty sure Kenny (Onelow1ton) installed the true trac in his 8.6... not % 100 sure but I think he did

There are a couple good videos showing them in action too, though often in both axles. I think it would work well for me.

At this point, I am leaning towards the TrueTrac. I found a local driveline shop, so I will contact them and see what they can do for me. In the meantime, my G80 is functioning smoothly as an open diff with fresh fluid. I might be going wheeling in a week, but I won't be alone, so it's no big deal if I get stuck.


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