1995 C2500- Open Diff to Posi Swap

[Urambo Tauro]

1995 GMC Sierra SL C2500, 4L60E, 295,000 miles

I've been meaning to do this swap for a while, but here I am, having squandered away a whole 'nother summer. Winter's here and I'm still rockin' an open diff on my 2WD truck. Frankly, I don't want to do it in this cold either, but it's time to at least get the ball rolling on putting a plan together.

As I understand it, all I need to do is a carrier swap, is that right? I rebuilt a Ford 8.8 a few years back, and what I'm up against here looks pretty manageable. And if I go tearing this apart and find worn bearings, I guess I'll go ahead and overhaul the whole thing if it's time for that.

This is a budget build though, so I think I'd rather swap in a good used carrier from a junkyard or something than buy a new one. (Hopefully I can find one with good clutches, or one that's cheap enough that a new clutch kit won't be too painful on the wallet.)

I am unfamiliar with GM axles, so first things first: I need to know what to look for in a carrier. I've been learning about RPO codes, and although my glovebox sticker is almost completely unreadable, I think I see "GU6" with no sign of a G80 code. I confirmed during a fluid change a while ago that this is an open diff, and not a worn-out posi unit installed by a previous owner. Everything looks pretty original except for some excess RTV around the diff cover. So I don't think I'm the first to have changed the fluid. I looked up the diff cover pattern, and this is apparently a 14-bolt 9.5". I have no idea what the spline count is, though. Are they all the same? And are there any other details I need to provide about my truck to narrow down the right parts?

(BTW, I don't have the cover off right now. This picture is from a fluid change I did a couple years ago. I'm kicking myself for not doing the swap right then and there.)

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[JCribb]

The 14 bolt 9.5" is a 33 spline, and most if not all are 6 lug as this is considered a light duty 3/4 ton axle.

 

[df2x4]

Whatever you do, don't swap in a G80! You will regret it, they suck.

I know there's junkyard carrier options available for the 10 bolts, but I think you may have a rougher time finding a junkyard posi carrier for a 14 bolt. Interested to see what you find out here. If you do decide to buy new, Eaton has several options for the 14 bolt depending on how you want it to behave.

 

[Urambo Tauro]

In what way do G80s suck? Are they noisy?

 

[df2x4]

Just the whole design. They're not a posi, they're a sort of half-assed locker that unlocks at 15-20MPH regardless of how you're driving. Also have a tendency to not want to lock when you really need them to. They're not much better than an open carrier IMO. Both of my trucks have them and I do not like them one bit.

 

[Urambo Tauro]

Was this the only version of LSD that GM offered for these axles, or is there a better one to look out for?

 

[df2x4]

Nope. It was either open carrier or G80 in these trucks unfortunately. I'm not sure about other models that may have shared the same axle.

 

[Urambo Tauro]

Were these problems present when new, right from the factory, or do they only happen with high mileage wear? Is there any chance that these issues are created by "upgrading" to larger-than-stock tires? Or sticky tires, for that matter?

 

[df2x4]

Both of my trucks have stock wheels and tires. Both have been in the family since new. Both have always behaved this way.

 

[Urambo Tauro]

Whoops, never mind. I guess that was a silly question. I just watched a video on how the G80 actually operates, and it's totally inherent to the design. It has nothing to do with wear or tires. They really did make it to unlock at speeds over 20mph.

Not sure why they would design it like that. I think I like Ford's Trac-Loc LSD better- just a simple spring and some clutch-packs. This G80 is hardly a limited slip differential at all; it's more like a "limited grip differential". It's unlocked by default, and locks only under specific circumstances.