Are your brakes parts assembled correctly? You have the 'short shoe lining' (primary) toward the front of the vehicle/ the 'long shoe lining' (secondary) towards the rear of the vehicle. (You DON'T have 2 shorts on one side and 2 longs on the other side!- There should be one of each on each side!) Pic below shows a short and long lining on one side, even way back in 1946!
Did you disassemble or push on the cylinder's pistons and make the gut's jump out while installing it?
Are the shoes adjusted outward enough to where the drum will sorta 'barely' go over them (BUT NOT ACTUALLY CONTACTING THE SHOES) In other words, much more adjusting would make the shoes start scraping the drum.
If the shoes were too far inward, the innards of the wheel cylinders would have to "Over-extend" (travel a long way) in order to push the shoes against the drum.
This over-extension may make the seals inside the cylinder push past it's smooth machined bore. When the shoes are adjusted outward correctly, the guts of the wheel cylinders barely move to make the shoes contact the drum.
If you installed a rebuild kit (instead of a new unit) The bore of the old re-used cylinder needs to be honed with a wheel cylinder hone to remove any pitting/ rust/ buildup in the bore. You must insure the kit is the right size for the size bore you have.
Lemme know if this info helps,
I like a happy ending!
I happen to have a few pics (9) of me "cheaping out" with 'rebuild kits'/ honing for my 1946 Willys Jeep wheel cylinders. These are real simple brakes with 'manual' cam adjusters for shoe adjustment (there are no automatic adjusters!)
Images (Click to enlarge)
Wednesday, April 5th, 2017 AT 7:08 PM