The Stupid Axle Questions Thread

[Schurkey]

I heard a rumor that only the 8.5” rears got sway bars on the utility GMT400.

I haven't heard that...but I don't know everything.

The OE sway bar mounts are integral to the shock mounts. See picture of an 8.5” below.

Thanks for that.

The 8.5" axle tube OD is 3.125" and the 9.5" OD is 3.375" (at least on the two that I have, pictured).

Do they require different saddles to conform to the OD?

GM uses bigger U-bolt plates to go with the bigger U-bolts, which are needed with the bigger axle tubes.

 

[zzyzx]

I decided to put in a rear locker since I've been hitting the trails more. I was going to use a spartan, but turns out I'd need a new carrier since my 8.5" has a g80. Would I be better off going with one of the full carrier lockers or sourcing an open carrier so I can use the spartan? I'm on a bit of a budget hence why I'm not going with a selectable locker.

 

[Schurkey]

I was going to use a spartan, but turns out I'd need a new carrier since my 8.5" has a g80. Would I be better off going with one of the full carrier lockers or sourcing an open carrier so I can use the spartan?

You have an 8.5" rear axle. The original differential carrier in an 8.5" axle is the most-fragile part of the axle assembly--either the open, or the G80 carrier. Both are known to explode under normal use.

So the LAST thing you need is to invest money into a locker that goes into a "glass" 8.5" differential carrier.

OTOH, there is no Spartan "Lunchbox Locker" for a 9.5" axle. That means when the 8.5 you have explodes, or you scrap it prior to it exploding, you should upgrade to the 9.5" axle, and then buy a "real" high-traction differential for it. I'm using the Gov-Lock that came in mine, in an '88 K1500. The 9.5" and 10.5" Gov-Locks don't have the poor reputation of the smaller ones. I replaced the open differential in my 10.5" K2500 with an Eaton Truetrac.

You could put an aftermarket differential carrier into the 8.5" axle, which eliminates the worst of the problem--the original "glass" differential carrier. That still leaves the rest of the 8.5" axle's marginal qualities, such as the typically-horrible 254mm (10") leading-trailing shoe rear brakes.