if drum brakes are used as above, but another option and upgrade is adapting modern disc brakes (with parking inside) to the 14 bolt axle.
See this Previous thread
working up to the following:
13" rear disc brakes with internal drum parking brakes from a ~2007 GM single wheel AAM 11.5" axle, (3/4 ton pickup). These brake parts are also used on many years and models of GM 3/4 and 1 ton trucks, vans, and SUV's roughly from 1999-2017.
I've checked fit of these brakes adapted to a 14 bolt hub/axle in 18" dual wheels and 19.5" dual and single wheels, no issues. These brakes on a 14 bolt should fit easily in the wheels you have on your AD 3/4 or 1 ton, but it'd be smart to test first. (Dual wheels however will not fit the modern AAM axle originally fit with these brakes, explanation below)
Caliper brackets, same left and right side, GM part number 15949892 or 88965717 come complete with dust shields, studs, and parking brake lever boot.
You'll need a flange to weld on the axle tube with the appropriate bolt pattern for the new caliper bracket.
It's an odd mounting pattern, drawing attached, center bore needs to be (likely) larger to suit your axle tube. I had flanges waterjet cut to these dimensions and will bore the last little bit to suit, and turn the pilot.
The flanges are welded to the axle tipped at seemingly odd angles, the following is how they were on my donor axle. This assumes, but have not confirmed, that the spring pads on the donor were close to level
with the truck in normal operation (which is the case for an AD 1 ton). The idea/result is caliper bleeding screws are on top and also provides convenient routing for parking brake cables. It's not real critical and should be close enough to duplicate these angles on your new axle.
With spring pads level and while viewing the caliper bracket mounting flange on axle:
--View from driver side the drivers side flange has the widely spaced holes up, and tipped clockwise, 22.0° from horizontal.
--View from passengers side the passengers side flange has widely spaced holes on bottom, and tipped clockwise, 8.0° from horizontal.
GM # 15712803, Bendix # PRT5260, ACDelco # 177861, or NAPA # 86828CR is the new 13" rotor with ~4.836" bore.
It does not fit the pilot on back side of 14 bolt hub but there is room to install a bushing on the hub to correct the fit and properly center the rotor.
After extensive searching no other possible rotors are a satisfactorily snug fit on the old 14 bolt hub, some have less slop, but are still not accurately piloted.
An adapter bushing is the proper way to go, duplicating the hub to rotor fit GM designed for this modern brake setup.
The bushing would be a shrink fit on the hub with a nominally 4.593" inside diameter.
Outside diameter ~4.830" aiming for 0.004-0.005" clearance in the rotor.
Approx 3/8" thick, or same as pilot projection on back of hub.
Finally the donor rotor originally fit over the AAM 11.5 hub just behind the wheel, and we're going to install it behind the hub, held on by pressed in studs same as the old 14 bolt drum was fitted to the hub. This is why dual wheels don't fit over these brakes on the newer AAM axle but will fit over them on a 14 bolt axle; the rotor and caliper are moved further from the wheel.
To make it work out right the backing plate mounting flange gets welded onto the axle tube 5.25" from the inside rotor/drum mounting surface of the hub. See angles above for orientation of backing plate. ....For reference or curiosity, the donor axle with these brakes had the caliper bracket flange set in 3-15/16" from outside surface of hub where the rotor slides on. To that dimension I've added AAM hub thickness of 0.910" and rotor flange thickness of 0.400" to arrive at 5.25" in our case with rotor behind hub.Parts list:
Caliper bracket flange, have made, drawing attached
Centering bushing for rotor on hub, have made, dimension considerations above.
Rotor GM # 15712803, Bendix # PRT5260, ACDelco # 177861, or NAPA # 86828CR
Caliper bracket with dust shield, studs, parking brake boot GM # 15949892 or 88965717 (difference in ABS sensor mounting or not, we don't care, buy the available or cheap ones)
Caliper with carrier and guide pins _______
Brake hoses ______
Brake hose clips ______
Brake hose bracket left ______
Brake hose bracket right ______
Bolts, brake hose brackets ______
Nuts, for caliper bracket studs ______
Parking brake shoes ______
Parking brake boot alone GM # 12473096
Parking brake lever GM # 88965732
Parking brake adjusters and hardware ______
Parking brake cables ______Further details to come as I figure them out