I have a 1977 F600 that I am about to start work on. I will be converting it to a Cummins 24V and extending the cab. For now, the truck is in a farm truck version, with flat metal bed and stake rails on the sides.
I want to use a 1977 F250 bed to convert to, and change the stock rear to a modern F250/350 SRW axle with diesel gearing.

Question....

Can someone give me an idea as to the ease of replacing the old 2-speed axle with the modern axle?

 

Welcome to FTE.

When you find the Cummins, take the trans and rear axle, springs and all related hardware. If you put a newer smaller axle under those existing springs, your "pickup truck" will ride so poorly that you will not want to drive it.

You might even consider transplanting the Ford cab and bed to the donor rolling chassis.

As far as pulling that old axle, beware that it weighs over 1000lbs with the duals attached. Don't let it roll away, and if it does, get out of the way!

There is no "ease" in dealing with such a beast. Plan it out, have the proper equipment, blocking, and a back up helper.

 

Thanks for the welcome and the info... I was recommended to airbag the suspension so will likely go that way. The Cummins is in an 2001 HD Dodge and would rather have the Ford 5R110 auto trans than the Dodge unit.
I am using a conversion kit from Diesel Conversion Specialists and it appears that from their recs, the 5R110 would be a great tranny.

 

In the rear, just take a few leaves out of the pack and replace with a block, since the f600 has a torque leaf, you should be good.

Here's the rear end of a 79 F600. Badd *** frame and leaf pack. Axle is about the same size as my 5ton rockwells are, which are beast:

 

Thanks, 78. I wanna take the front upper/lowers and rotors from a donor 2011 F250 and use up front. Do you think that would be too hard to do?

 

U talking 2WD?

I would not use F250 suspension/axles on this frame/cab combo.

I would say an F450-550 chassis cab rear Dana 135 would be a great idea to lighten things up. Then.....widen the 2wd front axle to match f600 body width. This was my thought on what to do with my 1960 F800 since I wanted it to be a low street truck.

You need to post a lot more info about what you want the end result to be. I'm confused about your goals here. You can't have a SRW f250 axle under an f600, it doesn't compute.

Also, Pics

 

Ok. Thx. That's what I was wondering. My goal is to have a dependable, ext/crew cab with the ability to tow my single car trailers and boat (boat weighs less than 2500#). I want to be able to cruise comfortably at interstate speeds. I initially wanted to keep the truck low, but now would like to have a more rugged profile with 33's or 35's.

 

You know, 35's are gonna look tiny in the F600 Wheelwells. What size tire & rim combo do you have at the moment? 11R22.5 tires are almost 42 inches in diameter. Keep in mind you need a load range of at least 6,000 lbs for this combo.

I'm not sure about the rest of the USA but here in Kalifornistan, a CHiP might pull you over to 'check out' your rig, spot tires less with less than the needed load range, then impound it until you fix the tire problem. Just happened to a friend with an F550-based trailer hauler/weekend toy.

For things to look right, your box would need some kind of dually-style flares to match the width of your front fenders. You're kind of stuck with that wide front axle (for looks) but a later big Ford truck front axle with disc brakes could be substituted.

Removing leafs or going to bags will fix the incredibly stiff ride. I would however caution against using anything from a truck smaller than an F550. Undersized axles will not be strong enough for that heavy beast you're contemplating.

You mentioned the Dodge as your donor vehicle. Well, get the engine, its harness and computer if it has one. If you want the seats and the dash cluster (or whole dash), take them. Now sell off the rest to finance your project.

Of course, these are merely my honest and humble opinions gleaned from over forty years of working on various morphadite abortions that family, friends and neighbors have dared to call cars or trucks.

I would suggest trying to find a late F550 with a gooched cab to drop your cab onto. You can then put the Cummins in it and have fun in a safe and reliable manner.

Food for thought, your mileage may vary.

Ray

 

Thx guys... In my humble knowledge, just goes to show how much I know... That's why I came here for opinions and ideas. Please keep'em coming.

 

My F700 looks like it had the same Eaton axle and suspension as yours. MY new Rockwell is a 20K setup.
The brakes (Air 16.5 X 7 drums) on the new axle are exactly the same size as my old one.

Late last year I found a air ride rear axle and suspension for
$125 . It's out of a 92 freightliner and of course It needed
New air bags and shocks.
This is the axle I bought.

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I worked for about 8 hours cutting off the (21) 3/4 inch rivets
Holding the brackets to the frame. The gears were 4.10s
I'll get it apart the bearings are fine to reuse.
I have found a used 3.58 gear set for $307
This last winter I got a new set of air bags and Monroe shocks. After I got the one new brake drum , I then got is the gears installed in the pumpkin and I bought a brand new set of brake chambers. $38.50 each at Webb's truck parts.
I took the rails that came with the new axle and used them as a template to drill my Ford frame rails. Its working quite well. I used bi metal hole saw bits withe the pilot bit removed.
The truck rides like a dream compared to the old spring setup.

this is last years pic with 3.70 gears.
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I have a NON-OD 6 speed and have 255/70R22.5 tires (36.6 tall) it will cruise
@ 65 all day long. With my new 3.58s instead of 70MPH in the above pic it does 73MPH at that same RPM.
This is a RR20-145 rockwell axle and are quite common under large trucks.
Gear are avalable for them.

I have a set of 3.70 gears for a Eaton AND a set of 4.10 gears for a rockwell 145 series if you are interested.
PM me if so.