1946 Dodge HD rear end swap

[Fat Red Truck]

I’m looking for someone that’s done a rear end swap from the original heavy duty dually to something that will get me more than 40mph 😊 The truck is completely original for power train and I want to try and keep as much of it that way as possible. Thanks to anyone that can give me some suggestions. 

[lostviking]

How much rear end do you want? Do you want dualies?

[47 1.5 ton]

What size truck are you working with? You can add an auxiliary trans with overdrive behind what you have if enough frame length.

[Fat Red Truck]

I do want to stay with duals and would prefer to just swap the rear end. The rear brakes were decommissioned before I bought the truck and I really don’t want to mess with trying to find parts. The truck is a 1.5 ton. My goal is to just make this a nice easy driver to take out on a weekend or drive to work once in a while. 

[Dave72dt]

Tire size?  7.50 x 20?  8.25 x20?  That's important info as to the type of trucks to start looking at.  If you have the 20" wheels, I'd start looking at single axle units with 22.5 wheels.  Check your inside tire to tire dimension to make sure you clear the springs.  School bus axles might be a good choice.  Be aware you may not have enough under the hood to be happy with the swap when done.

[47 1.5 ton]

  Does yours have a 2 speed or single rear? With 7.5x 20” tires it will make 50mph and I’m told stories up to 65mph. With a strong motor will do a little better. As mentioned, you can go to 8.25’s but will loose a little strength pulling but still in a good range. 
 

  I get around the back roads fine around 45-50mph but you really need to make sure your brakes are all there as the fronts will slide pretty easy. When I started with mine, I was convinced 40 was it (5.625 ratio) but that was due to not pushing it harder and motor was short on power(it is no Cummins). I recently was working with a friend in his B series and he added a Brownie with OD, gave it a half gear up /under and very nice to operate. His was a little noisy to my liking so I’m looking at a Gear Vendor unit now. 
 

 Going to be hard to keep those 5 bolt 20’s and make any real upgrade on rears. Just some thoughts—

Edited September 21 by 47 1.5 ton

[Old CWO]

This might be a good time to think about converting to axles that use more common bolt pattern, tire and rim sizes as well as brake parts that are still in production.  It wouldn't surprise me at all to find a dually GM 14 bolt or Dana axle with similar dimensions to your original rear under a much newer chassis.  I'm thinking delivery van, mini motorhome, cab & chassis, stuff like that. The front will probably be a little more challenging but not unachievable.  

 

 

 

 

[MBSoPaB]

FRT, I used to go round and round with this very same question on my 1.5 and 2 tons.  My multivariate analysis boiled down to two questions; which bolt pattern could I live with, and how wide was acceptable in the rear.  

 

Truth is, our Job Rated medium duty trucks are pretty narrow, when considering modern rear axle swaps.  Front axles, too.  Narrowest I could find in modern hardware came under cab & chassis setups from the big three.  Think ambulance, wrecker, box van.  Beware their ring and pinion ratios are wildly different by intended use and original powerplant.  The width in question here is WMS to WMS (wheel mounting surface), unless you're in love with one axle setup and are willing to have tubes and shafts cut down to the width you seek.

 

Lug pattern.  Our 5-lug pattern is an 8" on center.  The newest axles I ran across were a brief two or three year blip of Dodge motorhomes (MH) circa 1972/1973.  The axles and hubs are expensive, and the wheels (19.5" tubeless), expensive as well.  I think the last set of MH wheels I came across were 17.5, but I may be misremembering.

 

For rears, my '47 COE runs a Dana 60 with an 8 on 6.5" pattern.  My buddy's '59 Montpelier (Dodge flathead 1.5 ton chassis) step van runs a Dana 80 out of a wrecker, and runs slow, with the Furd 10 bolt wheels on it.  A 5-lug problem solver, maybe, I had a '58 D400 with an Eaton 1350 or 1380 rear end, single speed, 5 lug on 8" circle matching the pattern under your Dodge now, it had Budd 20" lock ring wheels.

 

And, the front axle; on my '47 COE, I run motorhome disk brakes, thanks to a spindle swap at the kingpin; the kingpin on the COE's and buses were 1.12" diameter, the same as the class A Dodge motorhome chassis from the '70's.  M375 or M400 chassis, usually with the 413 and industrial cooling setup, knock the pins out, swap the knuckles over, put the pins back in and put in fresh welch plugs.  All Mopar parts, and the engineering didn't outpace the application in those 30+ years.  So, for my COE, that runs 8 lug on 6.5" bolt circle, plenty of wheel and tire options there, just not as large as an 8.25 R20 setup.  Did this on the Montpelier, too.  There's single and dual piston calipers, so size yours accordingly for your needs and intended uses.

 

As far as keeping it original, my buddy's original '41 COE travels at 48 MPH.  Crank the windshield out a bit, and it's a nice, cool, airy ride.

 

Good luck with your pursuit!

 

MBSoPaB 

[Old CWO]

2 hours ago, MBSoPaB said:

... on my '47 COE, I run motorhome disk brakes, thanks to a spindle swap at the kingpin; the kingpin on the COE's and buses were 1.12" diameter, the same as the class A Dodge motorhome chassis from the '70's.  M375 or M400 chassis, usually with the 413 and industrial cooling setup, knock the pins out, swap the knuckles over, put the pins back in and put in fresh welch plugs.  

 

That was a really elegant solution for upgrading the front brakes.  Bravo.  Out of curiosity, what size are those rotors?

[MBSoPaB]

13" Rotors.  They fit snugly under the old 16" Accuride dually wheels, * barely *.

 

FRT, thinking back on it, and the complexities of mismatched systems and parts, if all you're looking for is to break out of the 40 MPH club, and you think your brakes are up to the task, maybe a good old brownie (auxiliary transmission) is worth considering?

• Brown - Lipe, say 5231 size.

• Watson, with overdrive (not just underdrive).

• Spicer.

 

They're just as much obsolete and unobtanium as changing out an axle, plus you'd have an extra shift lever to grab!

 

MBSoPaB