Axle Options

[79vette]

I was wheeling in Johnson Valley yesterday and somehow broke my rear 12 bolt. There was no leaking when we rolled into camp last night, but when I headed home this morning the back of the truck was covered in oil after 100 miles and the axle looked like this when we stopped for lunch. I didn't hit anything, and didn't even do any wheeling today... I packed the crack with JB water weld on the side of the road, refilled the oil and drove home in front wheel drive (twin stick np205).

1 ring gear bolt had backed out and was in the bottom of the axle, and another was just starting to work it's way out. The housing is cracked all the way through, but there's no damage on the inside so I don't see how it could be related to the loose bolts. Gears and locker looks fine, but the housing is completely done. I'm trying to find another 12 bolt housing locally so I can keep my gears and ARB, but that's not looking promising so far.

Does anyone know off hand what wheel size is required to clear the brakes on a 14 bolt semi float axle (9.5" ring gear)? Looks like they come in several versions (6/8 lug, drum/disc brakes, and at least 2 widths). I can move spring perches but I need to be able to run 15" wheels.

I don't want the weight of a 14b full float. Anything else I should be looking for besides another 12 bolt or the 9.5" 14 bolt?

[kipps]

The 9.5 14bsf was used in most of the 81-91 3/4-tons. It came with either 11" or 13" drum brakes, depending on the brake rpo code(jb5 vs jb7), and depending on the gvwr(7200 vs 8600).

I'm quite sure you won't squeeze a 15" rim onto the 13" drum. There's no wasted space on those at all with a 16" rim. The 11" drum would have a chance, I would think.

The 9.5 14bsf came in some big-block half-ton gmt400 trucks, and would have been drilled for six lug. Those are probably getting quite rare now, and even if you found one, you'd have to move the spring perches.

If you have a friendly and competent machine shop locally, you could probably have a set of squarebody 9.5 shafts welded shut and redrilled to a six-lug pattern.

Also consider a gmt800 10.5 14bff axle with disk brakes. The disk brakes lose a lot of weight compared to any drum brakes, and the ring gear and housing can be shaved for an additional 2" of clearance.

[Ziegelsteinfaust]

I use 14sf's under my 3/4 tons when I would get those.

The 13" brakes are by far the most common. I only say 11's in a 454SS package.

Go buy the rear end width you want, and go for a 6 lug disk brake conversion. You may need custom axles, but would be the nicest overtime

[79vette]

Edit:. I found a 14b sf from a square body (8 lug) and a 6 lug one from a 88-98 truck.

Does anyone know if I can use the square body casting and put the brakes/shafts/gears from the 88-98 one on it to get my existing 15" 6 lug wheels to work? That seems like the easiest and cheapest way to go. I need to redo the gear setup anyway to put in an ARB, so moving the spring perches seems harder than just swapping everything I to the other housing when I have it apart anyway.

Originally Posted by kipps

The 9.5 14bsf came in some big-block half-ton gmt400 trucks, and would have been drilled for six lug. Those are probably getting quite rare now, and even if you found one, you'd have to move the spring perches.

If you have a friendly and competent machine shop locally, you could probably have a set of squarebody 9.5 shafts welded shut and redrilled to a six-lug pattern.

Also consider a gmt800 10.5 14bff axle with disk brakes. The disk brakes lose a lot of weight compared to any drum brakes, and the ring gear and housing can be shaved for an additional 2" of clearance.

So far I've found a 6 lug 14 bolt with the correct gears from an 88-98 truck. Seller wants $775, and it has the right gears. I would probably be into it $2300 or so with a new ARB, bearings seals and brakes. I would need to move spring perches. I asked about the drum diameter and am still waiting to hear back, but do you know if those drums will fit a 15" wheel?

A different guy has a square body 8 lug 9.5" 14 bolt (out of a k20) for $100, but it has the wrong gears. Would this bolt into a k5? I think the perch width is the same. This one would probably be $2000 total rebuilt like the 88-98 axle (gears, ARB, brakes/bearings/seals), but then I still have 8 lug axles that don't fit my wheels. Do you know if there is a 6 lug shaft/drum that would work, or is welding the holes in the square body stuff the only way?

Also found a 12 bolt for $600 which seems insane and is a worse axle, but all my parts transfer over. Could sell the gears and Eaton locker out of the new one and be out of pocket ~$400

Originally Posted by Ziegelsteinfaust

Go buy the rear end width you want, and go for a 6 lug disk brake conversion. You may need custom axles, but would be the nicest overtime

Are you saying buy an 8 lug axle in the correct width and covert it to 6 lug using custom shafts and a 6 lug disc brake kit? I didn't realize that could be done, but sounds great. Any suggestions for sourcing such custom shafts? Yukon?

[Ziegelsteinfaust]

Yes, if width is a big thing to you.

Myself I prefer the 4x4 versions so it's a little wider, and disk brake kits for me are a big plus.

[79vette]

I found another 12 bolt for sale for $80, so I took my crane truck for a road trip and picked that up. Fuel to drive out there cost more than the axle... That'll let me swap my ARB and basically new gears/bearings over and hopefully get a few more years out of them before I need to go to 3/4 ton running gear.

I also started making a truss for it last night, which will hopefully prevent another center section failure. Has anyone seen a trussed 12 bolt before ?

And now I've got a spare set of shafts from the cracked axle so I should be set on parts for awhile. I'll post back with more pics when I get it installed.

[79vette]

Turns out I misplaced my gear marking paste and nobody local had one I could pick up over the holiday, so I had to mail order some and it just arrived.

Just dropped the locker and gear set into the new housing, and if anyone reads this in the next couple days I'd like a second opinion on where I have the gear pattern. Again this is for a rear axle, so I'd like it to be reasonably good.
Reading the chart from Yukon (link) I think could probably take a few thousandths out of the pinion shim.

Backlash is at 0.0075" which I like.

Pinion preload is at 15 in lb (just tightened the up without a sleeve for doing the gear setup), but the Yukon crush sleeve eliminator I ordered only came with 0.010" shims... So either the pinion has 0.002" endplay (ie negative preload), or I remove a 0.010" shim and if I were to tighten the nut the pinion bearings would completely bind due to excessive preload. IMO the kit needs to have a 0.004", 0.006" and 0.008" shim to be useful, so I need to call them tomorrow and sort that out.


Photos in this old post (link below) are how I set it up a year or 2 ago (before breaking the housing in half) and it ran for ~8k miles with no problems. I think it looks similar, but gear patterns still confuse me sometimes. Any recommendations?
https://67-72chevytrucks.com/vboard/...6&postcount=18

[Ziegelsteinfaust]

Have you thought about the Moser axles for the 12 bolt?

I put them in my C10, and they are holding up better then the stock axles did with my Detroit locker.

[79vette]

Originally Posted by Ziegelsteinfaust

Have you thought about the Moser axles for the 12 bolt?

I put them in my C10, and they are holding up better then the stock axles did with my Detroit locker.

So far I haven't broke any rear shafts. I've broke 3 front D44 shafts in the last 4 years, along with one rear carrier (G80) and now the rear housing. I have an ARB locker to replace the G80 gov lock, and hopefully the new truss keeps this housing intact. I carry a spare rear shaft if I am doing any hard wheeling, and if I do end up breaking one the mosers sound good. Thanks for the suggestion!

[Duck1]

Originally Posted by kipps

The 9.5 14bsf was used in most of the 81-91 3/4-tons. It came with either 11" or 13" drum brakes, depending on the brake rpo code(jb5 vs jb7), and depending on the gvwr(7200 vs 8600).

I'm quite sure you won't squeeze a 15" rim onto the 13" drum. There's no wasted space on those at all with a 16" rim. The 11" drum would have a chance, I would think.

The 9.5 14bsf came in some big-block half-ton gmt400 trucks, and would have been drilled for six lug. Those are probably getting quite rare now, and even if you found one, you'd have to move the spring perches.

If you have a friendly and competent machine shop locally, you could probably have a set of squarebody 9.5 shafts welded shut and redrilled to a six-lug pattern.

Also consider a gmt800 10.5 14bff axle with disk brakes. The disk brakes lose a lot of weight compared to any drum brakes, and the ring gear and housing can be shaved for an additional 2" of clearance.

No 15" Wheels.