The Stovebolt Site Forums The Parking Lot Tons 'o Fun 1 Ton dually rear drum swap

Hey folks,
My rear drums and brakes are currently ok, but I've been preparing for when they may need to be addressed.
According to this tech article: https://www.stovebolt.com/techtips/axles/1%20Ton%20Upgrade/ the authors mention:
I have a dually with the HO72. If I'm reading this correctly, does that mean I can have a modern set of of rear drums if I can source all the parts from a 90's 3/4 or 1 Ton?
When I got new 19.5" rims, I had clearance issues with my stock rear drums, so I started playing around with this. The 90's dually drums are way too wide. They fit the on the hub perfectly and clear the rim, but extend way back almost to reach the leaf springs.
The backing plate also fits perfectly. I tried using a single wheel drum, but it didn't clear the rim, so I didn't pursue checking axle clearance. I ended up using a wheel spacer to make the rims clear the original drum.
I'm thinking about experimenting with this again. It would be nice to have rear brakes that use parts that are more plentiful.
Before I embark on finding parts and stuff, has anyone done this? Can you just bolt up a full set of rear drums from a 14bolt on an HO72? Any tips?
Thanks in advance for the collective wisdom!
Greg

I think I'll let someone with a little more hands-on experience with this swap open up that can of worms. To the best of my limited knowledge of the situation, there are some issues concerning the diameter and width of brake drums, clearance between the spring leaves and the backing plates, and some issues with parking brake linkage if the donor brake system has the parking brake incorporated into the rear wheels rather that at the back of the transmission. It's definitely not a bolt-on swap.
Jerry

Thanks Jerry - I figured if it was an easy swap there would already be an article on how to do it. Who knows - there's a first time for everything. I'll see if anyone else weighs in.
Greg

The 72 on back used the HO52/72 rear ends. 73 up used a different rear end. The 72 back parts are more likely to interchange with the earlier models.
George

Thanks George. I guess the easier question is - what pre '73 parts do I need to convert to not so obsolete drums? Seems like the drum back plate is not readily available from most parts places, but it seems like you can get drums, shoes, hardware etc. If I can find the right back plates it seems like I can swap over to a '72-ish rear drum setup. Is that accurate?

I am not that familiar to know just what interchanges. There are many options on these brakes. The backing plates will have to be bought used. Some drums are not available new.
George

I think I found some used backing plates with all the hardware attached. I'm going to look into those more. New drums and stuff for that year of truck seem pretty easy to find. This might be promising. Thanks for the info!
Greg

As Jerry said in the first response, it appears these backing plates I found are for trucks with the parking brake on the transmission. They might work but now I'd have to figure out what to do for a parking brake. Hmm, more to ponder.

You could carry a big block V8 and a length of chain, and "Drop Anchor"!

Jerry

Heheeh yeah really Maybe carry around some rubber chocks. As is the parking brake pawl is pretty worn, so often times if you bump it it releases anyway. I don't trust it to hold any place where leaving the trans in gear wouldn't stop the truck from moving, haah. THe drop anchor method might actually be an improvement!

Not sure what your looking for but, I have 1954 DRW rear end coming out for a 14 bolt swap. If your are worried about having parts
for the future ??? Also in CT.

Hi Jim,
Thanks for the offer. My goal of this effort is to figure out if we can retrofit the old rear ends with modern, readily available, off the shelf drum parts without needing any customization.
My curiosity got the best of me and I ordered a variety of brake parts. I've been playing with different parts from 1990's 3/4 and 1Tons and might have actually found a solution!
I'm still waiting on a couple more pieces but I'll post an update soon. If it works, I'm going to do a video and list all the part numbers out.
Thanks again for the offer, I may take you up on it if this retrofit craziness doesn't pan out.

My truck has a one ton leaf spring dually rear. I plan to run a single 17.5 rear wheel on it. I was able to order all the parts I needed for the brakes from Rock Auto. It wasn't easy or cheap but I used the brake dimensions to make a kit. One side is installed while I work other issues and it all appears to fit. I've collected two more 3/4 ton leaf spring axles - These are slightly wider than the dually and have smaller brakes. I am in Oxford CT also if you want more info or want to come by and have a look. Also I am searching for a good 4.56 or 4.10 center section - HO52/72. Everything I have is the low low gears.

I was really close to getting it, but I gave up. I had a dually back plate from a 90's 1 ton, and a drum and brake hardware from a 90's 3/4 ton single wheel. The deeper dually back plate in combination with the 13"x2.5" single wheel brakes allowed the 14bolt brakes and drum to fit on my '49 dually HO72.
I ran into issues when I assembled the brake shoes. The dually back plate is expecting 3.5" wide shoes, so the 2.5" shoes sat crooked because they didn't reach the spot they are supposed to ride on in the back plate. So the top of the shoes by the wheel cylinder were out at the right distance, but the bottom of the shoes by the self adjuster were at an angle back in towards the back plate. They are supposed to be parallel to the back plate but aren't.
I thought of welding on a spacer or doing something with a flat carriage bolt but figured that might create an opportunity for the shoes to get hung up on something. If someone wanted to get creative they can probably create a shim or guide plate to go on either the shoes or the back plate. I still think it might be possible, although not too practical especially with the rear disk kits that they have now.
Lessons learned:
New back plates don't come with the brake shoe anchor pin. That's the thing near the wheel cylinder that the shoes rest on, and the various return springs attach to. They are not carried by the common supply houses. I finally found some at wholesalegmpartsonline.com
The brake hardware kit, and self adjuster repair kits, while complete and inexpensive - do not have the parking brake lever. That's the part that attaches to the rear shoe and gets pulled on by the park brake cable to actually set the brake. Also not carried by the common supply houses, but found some at wholesalegmpartsonline.com/
You'll also need brake shoe guide plates (which go on the brake shoe anchor pin), and a brake bar lever, which goes from the park brake lever to the front shoe.
Wheel cylinders don't come with the brake shoe push rod/push pin. Got some of those at Napa, I don't have the part number handy though.
The rear park brake cable (the last run that goes from the frame and into the drum) will need to be figured out. The newer drums have the round hole where the conduit snaps in and is held on by metal spring tabs, where as the older ones have the metal plate with two screws that hold the conduit to the back plate. I found a cable that looked like it was going to work. It was the right length for both the cable and conduit. I ground off a ferrule to get the right amount of travel. It fit in the drum and connected up to the park brake lever. It might have worked, but I was figuring that out around the time decided to give up.
Here are the part numbers, all from RockAuto unless otherwise noted:
Back plate: GM GENUINE 15622343 (left side, I never ordered a right side. Only difference is where the hole for the park brake cable goes. Single wheel plate has 2 holes, one with a rubber plug, not side specfic)
Drum: ACDELCO 18B111
Shoes: POWER STOP 451R
Brake hardware: ACDELCO 18K561
Self adjuster kit: ACDELCO 18K39
Parking brake cable: RAYBESTOS BC95182
Brake shoe guide plates: DORMAN 13896 Drum Brake Shoe Guide
Brake bar lever: DORMAN 21152 {#3898059} Brake Bar Lever
Brake shoe anchor pin: GM 14009982 (wholesalegmpartsonline.com)
Parking brake lever: left - GM 15649193, right GM 15594177 (wholesalegmpartsonline.com)

It was a fun experiment though. I learned a ton about drum brakes and found that wholesale GM parts website. If I ever have a 1960s+ truck(or whenever they settled on the self adjuster brake design) I'm good to go with the drum brakes.
I used this Youtube video to help me figure out assembly. The guy had a good trick for assembling the self adjuster spring in a vice rather than trying to do it on the truck. It worked like a charm.