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Front axle for a 2 ton bus? KP60 too light?

thatbus

Well-known member
Joined
May 1, 2022
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5129
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143
Long story short, I'm building a 2 ton GMC bus into an expedition/4WD vanlife/whatever you want to call it, rig. I'm looking for a suitable front end. I've got a Chevy Kingpin D60 under there currently, but am thinking I need something bigger.

I know what the 60 bible says about KP60 GAWR, but I've been told conflicting information; some tell me the Kingpin 60's of that era were nominally 6,000lbs, others tell me they were not de-rated to 4,500lbs due to tires/springs by GM, and are in fact "only" a 4,500lb GAWR axle. On the other hand, I know that OKA 2 and 3 ton trucks came with identical axles to the Chevy kingpin 60's, and those have been used successfully for many years except for bent inner C's and knuckles, something which can be addressed by gusseting and I suppose upgrading to Reid or Solid knuckles.

I can't think of many other alternatives, beyond going with a SD60 or Super60, or somehow finding an open knuckle 70 - I've found closed knuckle 70's with discs, but I understand those are still junk. For a bunch of reasons, Humvee BFG's are the perfect tire for this build, and I want to keep them - mine are the 24 bolts rated at 4,540lb's each - for a bunch of reasons, I need to stay with tires around 37" to 40". I am aiming for a GVWR of 14,500lbs, front GAWR of 5,500lbs to 6,000lbs. I have a 10" drop airshift M35 tcase that can be clocked for a 4" offset to either driver or passenger side. With the KP60, driveline angles work out well despite the front end being passenger drop.

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Would gusseting + trussing this KP60, be my best option? I figure I could also do a Jana 76 conversion, 35 outers, and drive flanges to get some cheap-ish beef.
 
The Fat Boy, SD60 from a 2005+ F550 has the highest GVW and is in trucks that handle more weight than that.
What's the front suspension in that? Big assed brakes, thick wall tubes, 1550 ujoints, etc.
Can leaf spring them with grinding and a Barnes 4wd kit.
8 lugging, to keep your rims isn't hard.
May need a spacer to clear brakes.
 

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I do have a Kodiak open knuckle 70... but they're spendy.
 
Chevy/dodge kp60 was 4500#. The ford obs 60 was rated at 5k#. 05+ superduty at 6k# and same era 450/550 for 7k#.
 
blakes said:
X2

It's not like it's gonna be a rock bouncer.
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Yeah this thing is mostly going to live on BLM land in the states/crown land in Canada. Forest roads, some mud, that kind of thing. No rock crawling in a bus lol.

u2slow said:
Chevy/dodge kp60 was 4500#. The ford obs 60 was rated at 5k#. 05+ superduty at 6k# and same era 450/550 for 7k#.
Click to expand...
Interesting. Any reason for the difference between Ford/Chevy KP60's? Aren't the tubes the same dimensions, knuckles and C's practically the same? I assume it's just tires/springs then?

Grendel said:
The Fat Boy, SD60 from a 2005+ F550 has the highest GVW and is in trucks that handle more weight than that.
What's the front suspension in that? Big assed brakes, thick wall tubes, 1550 ujoints, etc.
Can leaf spring them with grinding and a Barnes 4wd kit.
8 lugging, to keep your rims isn't hard.
May need a spacer to clear brakes.
Click to expand...
I'll probably stick with what I've got, truss it, gusset the C's, and go from there... but if I did go with a SD60, any opinions on redrilling the unit bearings, versus 8x170 to 8x6.5 adapters, versus redrilling the DRW adapters to 8x6.5? Are they forged or cast? Either way, I know I'd need 3-4" more backspace to clear the brakes on 05+ axles from what I've read...
 
Run it. OEM ratings dont matter.

Most of the weight rating of the components, back in the day, was the sum of the weakest link. Bias ply 7.00-16? No sense on rating an axle for more.

Guess you could dive into wheel bearing specs if it concerned you.
 
TRINDU said:
Run it. OEM ratings dont matter.

Most of the weight rating of the components, back in the day, was the sum of the weakest link. Bias ply 7.00-16? No sense on rating an axle for more.

Guess you could dive into wheel bearing specs if it concerned you.
Click to expand...
this
 
thatbus said:
Interesting. Any reason for the difference between Ford/Chevy KP60's? Aren't the tubes the same dimensions, knuckles and C's practically the same? I assume it's just tires/springs then?
Click to expand...

I think the spring spacing factors in - i.e. leverage on the outers; given a common tube size/thickness. Ford had Dana make the 50ttb to 4600#, so the 60 of course had to be stronger.

Another figure I have is the 2ndgen dodge 60 (ya, the CAD one) at 4850#.
 
TRINDU said:
Run it. OEM ratings dont matter.

Most of the weight rating of the components, back in the day, was the sum of the weakest link. Bias ply 7.00-16? No sense on rating an axle for more.

Guess you could dive into wheel bearing specs if it concerned you.
Click to expand...
Yeah, I'll just stick with it. I did look at bearings actually; the Ultimate 60 has the same inner and outer bearing ID's and OD's as the kingpin axles, and the Ultimate is rated at something crazy like 7350lbs. The only difference with a trussed KP60 would be the strength of knuckle castings, and kingpins vs balljoints themselves, I guess.



Anyone have opinions on the Solid vs the Reid knuckles? Can't get shit up north here without paying out the ass for shipping, the Solids are a bit easier on the wallet though...
 
With the value of Chevy 60's these days I would sell it and go Ford SD rather than start upgrading parts and swapping gears and be money ahead. Then again you would have to switch transfer cases
 
TRINDU said:
Guess you could dive into wheel bearing specs if it concerned you.
Click to expand...
Wheel bearings on driven axles with a proper spindle are clown shoe sized compared to the same GVW non-driven axle. You need room for the axle. Then the spindle needs to be thick enough. And that leaves you with a bearing that is large enough to not give a fuck.

Dana 44 bearings dwarf the stuff you get on the front axle of a MDT dump truck, panel van, class A, etc.
 
I vote the Fat Boy Grendel suggested. Big brakes to stop the pig on the dime, tight turning radius(!) and the GAWR. It probably will make sense to swap the matching rear axle too, for the matching wheel bolt pattern and the big brake.
 
thatbus said:
<snip>

I'll probably stick with what I've got, truss it, gusset the C's, and go from there... but if I did go with a SD60, any opinions on redrilling the unit bearings, versus 8x170 to 8x6.5 adapters, versus redrilling the DRW adapters to 8x6.5? Are they forged or cast? Either way, I know I'd need 3-4" more backspace to clear the brakes on 05+ axles from what I've read..
Click to expand...
The 2005+ Fat Boy is 10 lug , has 10 lug unit bearings, too. Can swap on the 8x170mm ones ones and keep the really big brakes and they're easy to re-drill.

They're also a lot wider, which would help your turning radius. Brakes are so much better than your Chevy 60.

You'd probably want to re-drill the adapter/ factory spacer.

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thatbus said:
Yeah this thing is mostly going to live on BLM land in the states/crown land in Canada. Forest roads, some mud, that kind of thing. No rock crawling in a bus lol.


Interesting. Any reason for the difference between Ford/Chevy KP60's? Aren't the tubes the same dimensions, knuckles and C's practically the same? I assume it's just tires/springs then?


I'll probably stick with what I've got, truss it, gusset the C's, and go from there... but if I did go with a SD60, any opinions on redrilling the unit bearings, versus 8x170 to 8x6.5 adapters, versus redrilling the DRW adapters to 8x6.5? Are they forged or cast? Either way, I know I'd need 3-4" more backspace to clear the brakes on 05+ axles from what I've read...
Click to expand...
The fords and special buulds had the beefiest c's.
Most fords also had a wider perch width which puts the weight closer to the c/tires.

You got the gm so running it is obviously the easiest. But as said, +05 are bigger axles and you could sell the gm and pocket cash but youll spend more making all the ford parts work.
 
thatbus said:
Yeah, I'll just stick with it. I did look at bearings actually; the Ultimate 60 has the same inner and outer bearing ID's and OD's as the kingpin axles, and the Ultimate is rated at something crazy like 7350lbs. The only difference with a trussed KP60 would be the strength of knuckle castings, and kingpins vs balljoints themselves, I guess.



Anyone have opinions on the Solid vs the Reid knuckles? Can't get shit up north here without paying out the ass for shipping, the Solids are a bit easier on the wallet though...
Click to expand...

Solids are beef also, I don't think you'll hurt either.
 
What's the intended usage?

If you really want to go stout just because, as mentioned above by others, the Ford Super 60 or the Kodiak 70 are your best choices.
 
ChiScouter said:
With the value of Chevy 60's these days I would sell it and go Ford SD rather than start upgrading parts and swapping gears and be money ahead. Then again you would have to switch transfer cases
Click to expand...
The SD60 is further offset from center-to-driver than the chevy is from center-to-passenger, correct? That could be a problem. With the Chevy 60, the diff is centered enough that I get great angles for the front and rear diffs by clocking the t-case outputs 4" to the passenger side (they both have a 10" drop). I don't want to get rid of this t-case; a T-136-27, given how beefy it is, it's airshifted, and it's already divorced.

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That said, rear angles are more important to me than front angles. 4WD would only be used at low speeds in snow and mud and not nearly as often as 2WD high or low.
Tech Tim said:
What's the intended usage?

If you really want to go stout just because, as mentioned above by others, the Ford Super 60 or the Kodiak 70 are your best choices.
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I will be living in this thing. Mostly up north in remote parts of Quebec, Ontario, and BC. Lots of snow and mud, but nothing too gnarly. The worst I'd see is crown land with no trails at all, when I visit family/friends on our mining claims. It's an expedition rig, I guess you could say. The axle concerns are there, not really because I'm going to abuse this thing, but because I'd like some extra beef and capability when somewhere alone with such a large rig and the expectation that you can't call for help.
rockota said:
not one has asked for a full build thread yet? :confused:
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Yeah I'll make one tonight ;) Gonna spend the day checking out a 6BT and DT360 first though... Need to rip that little gasser out of the bus and get something better.

Some more pics in the meantime:
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Right now, I have 47" chevy leaf springs up front. Air sprung seats help, but it rides pretty well, actually, and has much more flex than in the pic above. Adapting SD60 radius arms wouldn't be too difficult...
 
Yes, SD60 is more offset of center, but also high pinion. Maybe a moot point?

What rear end, you sure it's perfectly centered?
 
YotaAtieToo said:
Yes, SD60 is more offset of center, but also high pinion. Maybe a moot point?

What rear end, you sure it's perfectly centered?
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It'll be a Dana 80 for the rear, and it's about 1.5" offset to passenger, I think.

(Still got the massive 13k, 6.40/8.72 two-speed rear end under there if anyone wants it lol)

Could be a moot point because of the long wheelbase of 153". I think the front driveshaft would be about 36" long. Definitely fine with the KP60. But would need to measure for the Super 60...

1651718498841.png


Pic and measurements were taken with the old SM420 in there, the Eaton FS will probably bring the t-case back another 10".
 
Grendel said:
If all else doesn't meet your requirements, I have a 14B front here, trussed and set like a Chevy 60, with all Ford outers and 8 on 6.5. :flipoff2:
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If you were a syrup sucker like me I'd be interested, 🇨🇦:flipoff2: otherwise the logistics of that might be difficult. Also, trying to do this build on a budget.

Assuming same knuckles and tube strength, is there an advantage to a 14 bolt front vs. a Jana 76?
 
thatbus said:
Assuming same knuckles and tube strength, is there an advantage to a 14 bolt front vs. a Jana 76?
Click to expand...

The pumpkins physically fit different OD tube, so no sense in assuming same/same.
 
I knew the older 14bff to have 3-3/8" tubes, and the ribbed centers may have been 3.5".

Kp60's were 3-1/8". 05+ went to 3.75".
 
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