1951 GMC Maintenance Manual shows rear brakes are 12"x2" on 3/4 ton (150 model) and 14"x2.5" on 1 ton (250 model). Same book shows 4.57:1 as standard rear gear ratio for the 3/4 ton rear axle, but a 5.14:1 ratio (same as in your 1 ton) was available as an option, so be sure to verify the ratio before you put any money or time into a 3/4 ton axle.
I understand that brake drums for either axle are pretty scarce. All early '47 thru '52 3/4 ton rear brakes use the same drum.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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