Heavy Hauler Diff swap

[crazyjeenyus]

I wanted this thread to cater to all those interested in diff swaps for any year / model heavy hauler.

My specific question I want to throw out for comments:

I’ve got a beautiful ‘67 C50 with a 167” wheelbase. My overall intent is to shorten the frame to fit an 8’ pickup box. I would also like the truck to be able to drive on the highway in a half-decent manner.

I also have a ‘75 C30, and I’m thinking about taking the diffs & drivetrain (get rid of the two-speed rear axle) from and putting on the C50.

Both trucks have the heavy duty ‘sm’ 4-speeds, (sm-420 on the ‘67, and sm-465 on the ‘75).

If there is anyone out there with experience on this, your comments are appreciated.

Also, if I swap the rear diff from the ‘75 C30 onto the ‘67 C50, I could theoretically mount it anywhere in the frame this eliminating the need to remove frame between the front and back wheels, and would just have to cut excess off the rear. Also, theoretically should be able to use axles and steady bearing from C30 also and not have to get a custom driveshaft fab’d up.

[Bob B.]

The C-30 probably has a 10.5 Corporate 14 bolt. It should be the right width but everything else will be wrong including the spring perches, U-joint flange, and number of wheel studs. I have never seen any 10 stud hubs for a 10.5 but I think there were (very rare) 8 stud 22.5" tubeless wheels. I think it would be a lot of effort with mediocre results. Plus what will you do with a rear axle-less C-30? Better to sell the C-30 and buy a Gear Vendors overdrive or maybe replace the SM-420 with a NV5600 5 speed overdrive (I think kits are available to bolt one to your bell housing). You got a nice truck there resist the temptation to turn it into a mechanical Frankenstein. Shortening the frame and mounting a pickup box can look really nice if done right and the truck is still somewhat useful. I think custom 9' stake beds with finished racks and floors are even better.

[1966 K10]

Im kind of in the same boat as trying to get brake parts, wheel bearings, tires and various other wear items is pretty difficult for my 64 C60. I hate the idea of 'de rating' it putting 1 ton axles on it but keeping it working on the road SAFELY is very important. My issue is the 6 lug BUDD hubs and Rh5 split rims making finding wheels difficult/expensive and if I cant find brake parts why spend more money on them.

I could use 4WD in the winder mud season and finding front 4x4 axles and medium duty transfer cases is again difficult/expensive even for modern stuff. I also have a few C30 C&C parts trucks to work with and a set of CUCV axles. The problem I see with the C&C 14 bolt dually axle is the narrow width practically requiring the axle to drop to bleed the brakes. A wider Dana 70 or a later AAM disk brake 14bolt would be a cheaper option with better freeway ratios available.

Actual use should determine the route you should take. I plan on keeping it original as long as its safe. Ive gone through the brakes, and plan on changing the tires my self since a few are dry rotting a bit. For our limited farm use it should last a few years before hard decisions will be made. When the time comes a the Dana 60 with factory trac loc and 4.56 gears along with the 14 bolt Detroit and disk brake swap will be going in. Since it has factory power steering hydroboost is a no brainer. With the SM420 getting pretty noisy and syncros NLA a NV4500 with divorced T case is the cheapest way for reasonable speeds.

[CarolinaHD]

Why not just get a late model Eaton 15k/17k rear axle? Plenty of gear ratio options and you can use standard 10 lug bolt pattern wheels, and it'll still be a real truck. Not a wimpy 1 ton


Edit: it took me several days/weeks of searching for part numbers, cross reference superceded part numbers etc to find all the brake/rebuild parts for my 67 c50. It's hard but it can be done!
I'll be swapping a ZF6 overdrive transmission this winter after I move in my new house. Keep an eye out for that thread

[crazyjeenyus]

Originally Posted by CarolinaHD

Why not just get a late model Eaton 15k/17k rear axle? Plenty of gear ratio options and you can use standard 10 lug bolt pattern wheels, and it'll still be a real truck. Not a wimpy 1 ton


Edit: it took me several days/weeks of searching for part numbers, cross reference superceded part numbers etc to find all the brake/rebuild parts for my 67 c50. It's hard but it can be done!
I'll be swapping a ZF6 overdrive transmission this winter after I move in my new house. Keep an eye out for that thread

Thanks for the info. I look forward to it. I see you’ve got a 292 in your c50. That’s what I’m planning on running in mine. It started out pretty greasy and had a burnt exhaust valve. We’ve got the rebuilt shortblock together and are now working on the head. Plan is to lump port for improved flow. I’ve got true silv-o-lite flat tops (that survived from the early 80’s) and a comp 280h cam. I’ve been waiting for several years now for one of Tom Lowe’s PES high rise intake manifolds. Good luck on the move and the tranny swap.

[kwmech]

Personally I were building one of these I'd be looking for an older 4bt with an allison. Something out of an old UPS truck or similar

[CarolinaHD]

Originally Posted by crazyjeenyus

Thanks for the info. I look forward to it. I see you’ve got a 292 in your c50. That’s what I’m planning on running in mine. It started out pretty greasy and had a burnt exhaust valve. We’ve got the rebuilt shortblock together and are now working on the head. Plan is to lump port for improved flow. I’ve got true silv-o-lite flat tops (that survived from the early 80’s) and a comp 280h cam. I’ve been waiting for several years now for one of Tom Lowe’s PES high rise intake manifolds. Good luck on the move and the tranny swap.

NICE! I got another rebuilt 292 im putting back in my 67 too. Glad you're keeping it old school and not doing something dumb and over played like a cummins or ls swap. Keep the updates coming!

[alabama mike]

Originally Posted by crazyjeenyus

I wanted this thread to cater to all those interested in diff swaps for any year / model heavy hauler.

My specific question I want to throw out for comments:

I’ve got a beautiful ‘67 C50 with a 167” wheelbase. My overall intent is to shorten the frame to fit an 8’ pickup box. I would also like the truck to be able to drive on the highway in a half-decent manner.

I also have a ‘75 C30, and I’m thinking about taking the diffs & drivetrain (get rid of the two-speed rear axle) from and putting on the C50.

Both trucks have the heavy duty ‘sm’ 4-speeds, (sm-420 on the ‘67, and sm-465 on the ‘75).

If there is anyone out there with experience on this, your comments are appreciated.

Also, if I swap the rear diff from the ‘75 C30 onto the ‘67 C50, I could theoretically mount it anywhere in the frame this eliminating the need to remove frame between the front and back wheels, and would just have to cut excess off the rear. Also, theoretically should be able to use axles and steady bearing from C30 also and not have to get a custom driveshaft fab’d up.

Just wondering if it wouldn't be easier to put the c50 cab on the c30? that would give you disc brakes in the front and you could probably use the hydro-boost systen off the c30. they make after market wheel adapters to put any size wheel you want on the 8 lug pattern.

[crazyjeenyus]

Originally Posted by alabama mike

Just wondering if it wouldn't be easier to put the c50 cab on the c30? that would give you disc brakes in the front and you could probably use the hydro-boost systen off the c30. they make after market wheel adapters to put any size wheel you want on the 8 lug pattern.

I like this idea. Does anyone have experience putting 67-72 body components on a square body frame?

Either way the 292 will drop in no problem. I’m going to investigate this option further. Thanks Alabama Mike
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