2.5 Ton Axles for 1974 K20

[Scott Vincent]

I've made a decision to get rid of the wimpy 10 bolt in the front of my K20. The truck already had 37" mil tires, however I am probably going even bigger since the truck is now taking an 8" spring lift. I originally looked at a D60 for the front, but after researching them, and reading some cases of breakage, I realize that the 2.5 may be the way to go. So Rockwell 2.5 Ton's are what I'm looking at. I have 3 places that I can get a set, front and rear, for cheaper than 1 D60 for the front, so that helped the decision.

So here is the question.

How in the hell do I do this?!?!? I have looked and looked for information on how to fit these axles for a squarebody and found nothing. I cannot imagine that they come ready to bolt up, so relocating spring perches and shock mounts are in my mind. But where can I find the information? Are there templates or jigs? Is there any site, vide, book,...anything on this topic?? Or....is this some prize secret kept by the truck builders shops?

I am very committed to doing as much of this truck myself as possible, even to the point of learning welding this winter, so I want to do these axles myself.

What resources can I use to do this properly?

Thanks in advance.

Scott

 

[Hilllbilly]

Boyce Equipment | Rockwell 2.5 Ton Axles

We sell used and rebuilt Rockwell axles that fit the m series 2.5 Ton military truck.

www.boyceequipment.com

Better off looking at and studying pictures of conversions, than asking on a internet forum

Why not just get dana 60 front , 70 rear?

 

[nvrenuf]

Do a LOT of research before moving forward. Find someone that's done it on a forum, Facebook, Instagram, etc and start asking a lot of questions. Military axles are very different from light duty truck axles and are not at all ready to bolt in.

Things to consider -
* They have driveline brakes vs wheel brakes, I believe the DOT requires brakes at the wheels which can be an expensive mod.
* They have a large 6 bolt lug pattern so wheel choices are limited unless you convert to 8 lug, again $$$$
* Overall width is considerably wider than regular axles, most people modify / flip the bearing hubs to narrow them to a normal width.
* The diff is tall so there is a minimum lift needed to run them, at 8" you'll probably be ok but check.
* You'll have to add leaf spring perches and shock brackets.
* You'll have to figure out how to adapt the steering, likely requiring at least going to crossover.
* Locking hubs?
* 6.72 gears! You'll need a tall tire and overdrive to make this more than 45 mph street-able. 4.10's are available but good luck finding a local shop that will set them up.

Ultimately, IMO, regular 1 tons are a far easier choice for a truck that sees any street use. If this is an off road trailer queen then this might not be so bad but anything can be broken if you put a big enough tire or motor in it.

 

[idahovette]

@Vbb199 Vince has done this ....maybe he will chime in

 

[Grit dog]

@Vbb199 Vince has done this ....maybe he will chime in

But he can weld and fabricate and it was an off-roader only.
This is a poor, ill conceived idea on many levels on the OPs part.

 

[idahovette]

yeah, I KNOW all that @Grit dog, I just answered a question....OK?.....plus I'd like to hear from Vince

 

[waterpirate]

Hold my beer moment. If the op is truly committed and there is no time restraint, have at it imho. This statement assumes that the op has some serious skill to back up the vision. A monster truck fab shop would be on my call list for info.
Eric

 

[PrairieDrifter]

But he can weld and fabricate and it was an off-roader only.
This is a poor, ill conceived idea on many levels on the OPs part.

Agreed. Can't even weld and wants to do 2.5 ton rockwells by himself?

Especially for anything other than off-road thrashing, and I mean bouncing through mud holes and blasting through rocks. Totally unnecessary for big tire street driving, anything other than rock bouncing really.

 

[Grit dog]

Ya pretty much only the baddest of the baddest mud buggys and crawlers run 2.5 ton axles.
Be easier to convert a Super duty D60 if a squarebody D60 isn’t available. Guessing they’re easier to find.
Plus, yeah can’t even street legal a Rockwell equipped vehicle.

 

[Grit dog]

yeah, I KNOW all that @Grit dog, I just answered a question....OK?.....plus I'd like to hear from Vince

Not directed at you. Said it for the OPs purpose.

 

[PrairieDrifter]

Just want to say I'm all for learning, but learning has to be done in increments. Starting with a huge project like that is not only extremely hard(not something to learn how to weld on) but is also dangerous for everyone(if street driven)

A mudbogger? Off-road vehicle? Sure. It's your money, if your axles fold under the truck and you roll it, that's your life and money in your hands, all I can say is ya probably shouldn't learn on that project.

 

[bucket]

@Scott Vincent what is your intended use for the truck and what size tires do you plan to run?

 

[Vbb199]

yeah, I KNOW all that @Grit dog, I just answered a question....OK?.....plus I'd like to hear from Vince

Heyoooooo

Here i am

Now I gotta read this post lol

 

[Vbb199]

OP i'd definitely look for a D60/D70 set for 37" military tires

2.5 tons is kinda big , especially for leaf springs with nothing else to keep them under the truck like track bars or links, not to mention the gear ratios available in a 2.5 ton.. 6.71 is standard gearing, which is deep for 37's... gonna have a whole top speed of 45mph before your motor is slinging a rod out, and with a 700r4 or something, 1st would be so low, you'd move 1 tire rotation then shift into 2nd lol

Im not trying to discourage you from your dreams, but 2.5 tons is a bit extreme for 37's , even in the military variant with the heavy sidewalls

 

[Strick]

I've made a decision to get rid of the wimpy 10 bolt in the front of my K20.

The 74 K20 should have a decent Dana 44F and a 14FF rear; those are two great axles to use for a general purpose wheeling truck. The obvious upgrade would be the Dana 60F and do some gearing to accommodate for larger tires. I have wheeled the crap out of 44's, 60's and 14FF's with no real problems. Sure, when hanging a big meat off the axle (@SquareRoot) end and adding a heavy right foot can lead to carnage but using the factory style axles is certainly the least intrusive, most economical and most manageable upgrade to do.
I agree totally with some of the other post contributors in stating that you'd be well advised to do plenty of research before diving off into the Rockwell swap. There's a giant F-rd here locally with those and there are only pinion brakes on it and it takes two-weeks notice to get the thing to stop. Perry has 54 Boggers on 20's and homemade spring hangers as well as 8" springs along with homemade blocks and traction bars. He would take his truck to the local mud pit and cruise it in Benson at "Mule Days" (which is happening this month BTW). The truck was originally a '74 with a built 429/SM435/NP205 with Dana 60F and 14FF from a CUCV. He ran this truck and could actually use it with 44's before doing the swap. He did have the biggest truck around after the mods though.
Unfortunately he has gone on the meet the Maker and his sons still have the truck. I see it sitting under the shelter at the homestead when going past in the Driver's Ed route. I wish you well in your built but urge you to do plenty of research and PRICING before you pull the trigger on the revamp. These folks here can offer plenty of advice as mentioned already.

HS