The Stupid Axle Questions Thread

[Schurkey]

MY 9.5 G80 is filled with Valvoline 80W-90, with zero friction modifier in the bottle. Rated for "top-off" of positraction differentials, not a full-fill because of the lack of friction modifier.

 

[scott2093]

K1500s easily upgrade both brakes and axle strength when a 9.5" semi-float axle is swapped-in from a 6-lug K2500. Get the correct gear ratio to match the front. Need one conversion U-joint, and four U-bolts. Couldn't be easier. Shouldn't be too expensive.

Trying to figure out what rear end have on my truck since it's an implant. It's already apparent I have the duo servo drum brakes. How can I tell ? I mean my cover is a 10 bolt. I kinda remember it had a G80 before it grenaded. But what about the axles?

Dont be like me, be able to spot the difference, this measurement is the only really obvious difference in the semi float axles

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What does this mean? Which is which? That's a measurement to the spring perch?

 

[TylerZ281500]

Trying to figure out what rear end have on my truck since it's an implant. It's already apparent I have the duo servo drum brakes. How can I tell ? I mean my cover is a 10 bolt. I kinda remember it had a G80 before it grenaded. But what about the axles?

What does this mean? Which is which? That's a measurement to the spring perch?

you answered your own question its a 10 bolt. it has 10 bolts. a SF 14 has 14. or am i missing something? you can pull off the cover to check ratio if thats what your after

 

[scott2093]

you answered your own question its a 10 bolt. it has 10 bolts. a SF 14 has 14. or am i missing something? you can pull off the cover to check ratio if thats what your after

Just wasn't sure if different axles could be in a 10 bolt.

 

[Schurkey]

The 8.5" axle assembly was made in various widths. Therefore, sure, there could be different length axle shafts to match the different width housings. The '88 trucks probably had 28-spline axle shafts, I think they grew to 30-spline shafts for '89.

Go back far enough in time, and there were other GM "10 bolt" axle assemblies, but they weren't used on the GMT400 series.

But so far as GMT400 trucks, the "10 bolt" is an 8.5 axle, and they're all junk.

 

[Rocket Surgeon]

I really need to find out more NBS axles... fast!

I have a 97 and 98 k2500, both 8600 GVWR, equipped with 5.7, NV4500, and 3.73 8 lug 14bolt Full Floaters... with drums. The 97 has G80, the 98 does not.

I was offered a deal of some leftover parts from 02-06 diesel 8 lug GM trucks. This includes specifically rear axles that I was told are the same 3.73 ratio, 8 lug 14 bolt full float, with g80 and disc brakes.
I have learned the leaf spring and shock mounts may need to be cut off and relocated, but no info yet found on if the driveshaft directly hooks up.
Without opening, how can I tell if 10.5 or 11.5 gear, and does that really matter?
Can I just swap parts, such as rear disc components onto the earlier 14bolt ff axle?
Would the pumpkin swap between the axles assembles if i just wanted to move the g80?
Allegedly the newer axles are wider, but how much wider?
Anyone know of a good tutorial?

I was also offered an duramax diesel motor, but I have found some reading on that...

 

[TylerZ281500]

10.5 to 10.5 would be easy. 11.5 might use a different u joint but conversaion joints are available and easy. otherwise yes cut and reweld. pretty easy if you have the resources. not sure on widths. google should be able to tell you.

 

[Erik the Awful]

I really need to find out more NBS axles... fast!
...I was offered a deal of some leftover parts from 02-06 diesel 8 lug GM trucks. This includes specifically rear axles that I was told are the same 3.73 ratio, 8 lug 14 bolt full float, with g80 and disc brakes.

Point of note: All GMT400s came with drum brakes. Swapping disc brakes in place of drum brakes almost always requires replacing the master cylinder to function properly. If the donor truck's front brakes will swap on, your best bet would be to do a complete brake system swap. The ABS will throw a monkey wrench into that - you'll either have to eliminate it or figure out how to get it to play nice with your truck.

 

[Schurkey]

Point of note: All GMT400s came with drum brakes.

All GMT400s EXCEPT the rare C3500HD had rear drum brakes. The bigass C3500HD had rear discs.

There were Bendix 4-wheel discs available on the extra-heavy-duty job. NOT AT ALL common. I think the axles with disc brakes were also the Dana axles, not the "Corporate" 8.5, 9.5, or 10.5 AAM axle assemblies. All of the front disc/rear drum brakes were Delco, not Bendix.

The Bendix calipers are the same basic design as what Ford used for many years. Caliper held to the steering knuckle with a cross-piece, leaf spring, and one giant-headed Allen screw per caliper. They were considered "sliding" calipers, rather than the Delco "floating" calipers.

Swapping disc brakes in place of drum brakes almost always requires replacing the master cylinder to function properly.

Yes! The drum master cylinder has a tiny reservoir, which is not suitable for use with disc calipers. That's totally aside from the ratio of master cylinder bore to caliper piston bore, which may or may not be suitable.

If the donor truck's front brakes will swap on, your best bet would be to do a complete brake system swap.

Again, yes. I think there's some ball-joint-stud-hole reaming involved. This site has conversion instructions somewhere.

The ABS will throw a monkey wrench into that - you'll either have to eliminate it or figure out how to get it to play nice with your truck.

Use the ABS unit from the donor vehicle?

I'm thinking that the ABS may be compatible, but the combination valve will be different--and the combination valve bolts to, but is not integral with the ABS unit. You'd want at minimum the combination valve for the disc/disc brakes; if not the entire ABS unit and combo valve for disc/disc.

 

[Schurkey]

Can I just swap parts, such as rear disc components onto the earlier 14bolt ff axle?

Maybe. Wouldn't surprise me if the flanges on the ends of the axle housing are somehow different.

Would the pumpkin swap between the axles assembles if i just wanted to move the g80?

Sort of.

The 10.5 axle has two screw-type adjusters for the differential case; no shims or case-spreader needed. There is a "special tool" for turning the adjusters, but a medium-sized tapered punch works OK. Swapping differential cases is relatively easy. You'd want to retain your original ring gear for use with the original pinion gear. Measure the backlash before you take apart the original axle, and also measure the backlash on the donor axle. Keep track of which backlash goes with which axle.

Remove both differential cases, and then swap ring gears so the ring gear for each axle stays mated with the pinion gear it has been running on. The service manual I have for the 10.5 axle assembly says to use new lock washers on the ring gear bolts.

Put the G80 case into the axle housing of your truck, using the ring gear that came with your truck. Get the backlash the same as it was before, so the ring and pinion continue with the same wear-pattern as it was originally. It's a balancing-act, getting the backlash AND the bearing preload correct.

And then you'd do the same for the "donor" axle--the ring gear from that axle goes onto your "open" differential case from your vehicle, and then drop that case into the donor axle with the same backlash it had originally, and correct bearing preload.