Yeah order the 8.5 gear, Remember though you have to have your computer retuned and dont forget to get the full installation kit, with the bearings..

 

I would get an 8.5 if I had an 8.5 and an 8.6 if I had an 8.6.
Thats just me though.

 

Naked, if your rearend is the AAM 860, which I think it is, the actual ring gear is 220mm, or 8.6614 inches.

 

Dung - I have HP Tuners so I can do the gear swap update myself.

Grip - How do I know which rear end I have? And if I have the AAM 860, where do I find the 8.6" gears?

 

Yes, could be the drive wasn't long enough.

Maybe you should go to a dealer and test drive both to see what you think.

About strength, I think the 4.10 uses a smaller pinion than the 3.73, so there is less gear tooth contact to spread the load between teeth. I haven't heard of anyone busting gear teeth though, so it's probably not a concern.

While you're in there an Eaton clutch type posi would be a good idea. I have one and you can see the case is alot stronger than the G80.

 

Email AAM, thats what I did to find all the info I needed.

 

The 10-Bolt rear in your truck will accept an 8.5" or an 8.6" ring gear. Same differential and housing.

I have not taken the time to read through all the other replies, but at a glance it looks like you are getting good information from both sides.

There is one paramount concern you should have since your truck is supercharged - strength. You've got a truck almost the same weight as a Suburban and a lot of power. There is a lot being asked of that rear end...

In my opinion you should stick with the 3.73 gear but upgrade the differential to an Eaton Posi. The 3.73 gears will not put as much stress on the axle shafts and the housing as the 4.10 gears would. Going with 4.10's or more will multiply torque more. It's a lot of fun to gear the rear real low if it can handle it, but a 10-bolt cannot under boost. The ring gear is too small for numerically high ratios to hold up under power. The larger the ratio is the smaller with less teeth the pinion gear becomes. This minimizes contact between the pinion and ring gear teeth and creates more heat. The extra stresses will flex the housing more than than a lower ratio would. I'm sure you've heard of many people that say they have 4.10's in a 10-bolt with a supercharger and no problems at all. That's an opinion, this is mine.

The G80 is a compromise between power-handling and road manners and versatility. It works by a shaft inside with a centrifugal flyweight on it that spins faster in proportion to the difference in RPM between the left and right tire. When enough of a difference occurs, the weight fly out enough to engage a pawl which activated the lock-up mechanism. The lock-up gets it's energy from driveline torque. This torque is used to tighten the lock-up clutches until slippage stops, and then the unit will automatically de-energize. When the unit is locking up force is exherted internally against the sides of the housing from the inde out. The mechanism works in such a way that it will only stop supplying energy to the lockup mechanism once wheel slip has stopped. With a heavy SUV and supercharged torque it is possible to create wheel spin at torque levels beyond what the G80 can counteract. When this happens they can be enough force inside the carrier to literally explode the housing into tiny pieces. Everything in the rear end will be ruined and it will probably take out the transmission with it. An Eaton Posi works differently and handles much higher levels of torque. The G80 is not a performance piece, it's intended to be all-purpose and all-weather, but specialized in nothing. The Eaton Posi is a true street performance piece that also happens to be very well-mannered and streetable.

So, if it were me a bigger rear end was not in the budget I would get the Eaton Posi and stick with 3.73 gears.

(I have 4.56 gears with only 29" tires. It's a blast to drive but I had to get a 10.5" rear end to be strong enough to handle that ratio.)

 

Thanks James, I knew I could count on you to give me a well-informed reply. That sobers me up a bit. The excitement of having more off-the-line torque is mitigated by the prospect of having to replace the whole rear end if I decide to go that route and play around with power. My truck tips the scales at nearly 3 tons so of course I need to realize the added stress that much weight puts on the stock 10-bolt rear.

Can anyone tell me what the difference is between an Eaton Posi, an Auburn Posi, a Detroit Locker, and whatever else is comparable? Also, what does this stuff look like? I'd like to see the difference between the ring and pinion (which I believe is what comprises the gears, correct?) and the G80/posi/locker components. Does anyone have a link that will educate me? I'm pretty damn lost in this rear end stuff.

 

I wonder if it would be better to just get a new rear end.

 

Found this guy on EBay for both gears and Eaton posi....has good feedback.