this is my otion codes and what they say they are, how do you tell if you have 10.5 or 11.5

GT5 Axle Rear 4.10 Ratio (DUP With GT8)


G80 Axle Positraction Limited Slip

 

How about just getting rid of your drivetrain. Go 2wd with a short axle and 20" wide meats. Mini tubs are always cool. That way you loose some weight and mean up your trucks look. Check out these tires

http://www.mickeythompsontires.com/press_10_26_04a.html

 

The RPO codes won't help in this case. GM uses the G80 in all the rear diffs. The covers and bolt patterns are different between the two, you may be able to tell by snapping a photo and comparing it. I don't recall if there is a part number stamped on the diff case or other marks you can go by.

If you have the 8.1 / Allison I am 99% certain that you have the 11.5 in your truck. This seems to be a fairly confusing topic for the GM dealers too, I got a new cover gasket from the dealer when I put my deep pan on and even though I told them it was the 11.5 they gave me the gasket for the 10.5 ring gear.

 

In a 2500HD

6.0 = 10.5" FF Rear Diff
8.1 & Duramax = 11.5" FF Rear Diff

 

For what it's worth, the 10.5" has a design feature unique among other AAM axles made for GM - it has a third pinion bearing. The pinion gear is supported on both sides, just like a Ford 9". And, as has already been said, it's full-float with no c-clips.

The 9.5" is much stronger than a 10 bolt, but still not quite up to 800ft/pounds. I know of one 9.5" rear with 4.10's and an Eaton Posi being pushed by a RamJet 502/4L80-E with a 150 shot already showing signs of strain. The cover bolts are walking - a clear indicator the housing is flexing too much.

With a 6.0 you need a 2500HD to get the 10.5"FF rear. I think the 2500's just get the 9.5"SF. Besides the obvious Gov-Lok which fails under load in every size rear there is, the only other problem I have ever seen with a 10.5" was in a Vortec 454 Dually with a huge trailer of some sort on it going up a dirt hill. It started bouncing and bucking with the wheels spinning. It came down one time and the rear end blew apart. Turns out the 6 bolts holding the pinion assembly in saw enough force to shear the threads clean off. That was Duane's truck who used to work for Jon over at TOG.

The 10.5" dwarfs my 8.5" R&P sitting next to it:

 

i know this is the excepting by my my g80 is still working great. it gets a posi ever times other than tight cookies or if i try and hang the rear out around a corner it will kick out. it will posi from 0-90mph and will even posi from a 50mph roll.

 

I'd just get a 2500 HD RCLB>

 

it's good to use the if it isn't broke don't fix it. under the conditions you put your truck through, the 8.6 is quite strong enough. there are a couple of g-bodies that have run 8's and 9's on the 8.5 10 bolt that came in the car. more than likely if anything fails it'd be the gov-lock and even then i'd only replace that with a detroit locker. going with a larger diff is just going to add weight in 3 bad ways:

1. unsprung weight is much more
2. rotating weight is noticed in dyno numbers
3. overall weight on the truck

other than breaking because the parts are mearly stock items, your diffs should be plenty strong for what you're doing.

 

It does not matter what kind of differential is in the 10-bolt housing. The housing will flex and change the contact pattern of the gears putting too much force on the leading edges causing the teeth to break off.

It is illogical to say the 10-bolt can handle this much torque. It absolutely can not. When it breaks it will take out the trans and/or the driveshaft with it, possibly ejecting one or both axle shafts at the same time. This is a dangerous situation.

Claiming a 10-bolt will handle this much torque in a truck is every bit as irresposible as saying a 4L60-E can handle 700ft/lbs. in a truck.

These discussions always come out the same, apples get compared to oranges and the real issues become shrouded in irrelevance.

Complacency gets VERY expensive.

 

I love my 14bolt 10.5