On my '54 GMC 630 gasser(503) , I was able to get new brake cylinder cups, I had already found master cylinder(1.5") cups on eBay. My truck('54 GMC fire truck) has Type FR-3 rear brakes. They may be identified by 2 wheel cylinders, served by 2 brake lines from a 'Y' at the first cylinder, adjustment by 3/8" Allen wrench, two locations.

Upon disassembly, the wheel cylinders are identified by casting number: FD 9572; 1.875" ID. These data are from disassembly, they do not appear anyplace else, certainly not by looking under '54 GMC, forget about going that way.

My wheel cylinders were labeled 1 7/8, which is 1.875". I found on:

Powerbrake-drivetrain.com, new cups which I received today, verified, 1 7/8" , so I am all set. Of course I need to hone the cylinders, etc.

They have other associated items, too. Ah, for air brakes!!

Good luck,

Ed


'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.