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The Hollister Road Company disc brake conversion for HO52 and HO72 from 1947 to 1959
Due to the growing popularity of the ¾ and 1 ton Chevy GMC trucks and the lack of available brake parts in either original equipment or aftermarket for these size trucks The Hollister Road Company Disc Brake Conversion was developed to allow you to unbolt a complete brake assembly from a 2003 – 2006 2500 HD and bolt it directly on to your HO52/HO72 axle that has slide on drums. We have these bracket made on a high precision waterjet that minimizes the variance in dimensions as it cuts the 1/2 steel.
There are some important things to remember on this swap. One is that GM used the same caliper bracket for left and right, they just flipped it over so the bolt pattern on the right side is not the same as the left side. The bolt pattern on the caliper bracket is also splayed so its wider at the ebrake lever. The brake cables come out the back side of the assembly and wrap around to the front. On one side the cable will be on top and the other the cable will be on the bottom.
With this in mind you will put the C brackets we supply with the opening on top on one side and opening on the bottom on the other, this way you have both calipers facing the same direction. The GM bracket is clearly marked Front so you shouldn't’t have any problems with direction. The supplied C brackets have a rod tacked on one end across the opening. You will slide the bracket over your caliper bracket studs and tack the other side. This will ensure you keep the pattern intact when fitting it to the axle flange.
Our C bracket will mount on the right side (passenger) with the tacked rod on the bottom and on the left side (driver) with the tacked rod on the top.
C Brackets, these are as they would be on the truck. Notice that the small rod is on top on one side and on the bottom on the other
First step is to remove all the brake parts from the axle. Wire brush everything clean and tape up the spindle so you don’t damage the seal surface or bearing surfaces.
With everything cleaned on the passenger side, with a die grinder notch the top bolt holes on the backing plate axle flange as shown, at 9 and 6 o’clock, clean up any burs and screw in the Allen head set screws that have the Allen outward into those two holes lining up top to be flat with or below the flange with the hole. These will be welded later.
With your die grinder take the threads off the set screw. This creates clearance for the caliper bracket bolts.
Next take one C bracket a place it over the right side backing plate axle flange with the opening at the bottom. It will take some trimming to get it to fit. It should look like this when done. Don’t force it on and make sure your caliper bracket fits the hole before and after fitting. Once it fits nicely chamfer the edges so we have a V for welding.
Once it fits place the C bracket and caliper bracket on the axle, screw on the nuts and tighten evenly and snug them up. This will pull the backing plate and the C bracket flush on the front side.
Make two small tacks to hold it in position and tighten the nuts firmly
Double check that it all looks centered and mating surfaces are flat with no gaps. At this point you can test assemble the remaining parts. Install the hub and adjust it then assemble brake parts, if all fits well with no rubbing when you spin the hub make sure the wheel fits. Now you’re ready for welding.
Proper welding and safety procedure should be followed. The C bracket and backing plate flange are ½” steel so turn your amperage to the setting that best meets that thickness. Weld between the nuts as shown, don’t weld the nuts, and let the part air cool while still assembled so we don’t have any warping issues. Once cool remove the nuts and caliper bracket and finish welding up the bracket as shown. Only grind the weld so the nut will sit flat. Don’t grind the weld between the nuts.
Weld up the other side keeping in mind that we need this surface to be flat when done so some care needs to be take when grinding the welds so the new flange remains flat. Finish welding up to the holes and the edges on the top. Then weld the Allen head set screws on leaf spring side of the flange. These are just hole fillers so welding them on the front side isn't’t needed.
It may be necessary to clean out the bolt holes with a Dremel tool or round file.
Assemble the caliper bracket with the arrows pointing to the front
Snug up the nuts and make sure you have the new flange surface flat with not gaps. If it all looks good tighten the nuts to spec and assemble the hub and brakes.
Proceed to the other side and remember that the C bracket and the caliper assembly will be put on upside down from the previous side with the arrow pointing forward.
This is the right side of the truck . The caliper faces forward and the Ebrake cable comes out the back.. Remember the other side is flipped upside down.
ACDELCO 88965717 backing plate, 2, These are used on the left and right side
Dorman C660051 brake cable, 2
Pronto 55057, rotor, 2, See Note 2
RAYBESTOS 771PG parking brake shoes, 1 axle set
RAYBESTOS H7311 hardware kit, 1 axle set
DORMAN 924743 parking brake bell crank, 1 set
DORMAN H620722 left hose, 1
DORMAN H381276 right hose, 1
RAYBESTOS RC11021QS left caliper, bracket, pads, 1
RAYBESTOS RC11022QS right caliper, bracket, pads, 1
1. Leave the rear hub oil shield off when replacing studs. It may interfere with the parking brake spring. Use the oil shield that was on the axle tube.
2. The rotor dimension are 3.37 Over all height, 1.14” thick, 4.62” center hole, outside hat height 2.24”, inside depth to flange surface 3.04” The inner brake drum lip should be approx. .075 below the disc surface. Not all Disc makers match these dimension so measure when you get the rotor otherwise that may bind on the backing plate. The Hollister Road Company disc brake conversion for HO52 and HO72 from 1947 to 1959