I'm rebuilding the rear hydraulic brakes on a 55 GMC model 630 with Eaton floating axle/Dayton wheels. Each side has two 1-7/8" bore wheel cylinders. I purchased NOS EIS cylinders, probably made in the 1960s. They were clean, no rust and very supple rubber components. I disassembled them, lubed the internals with brake fluid, installed them, bled and pressure tested just the two cylinders at one wheel with a Motive pressure bleeder at 15 PSI. I'm getting very slight seepage out of the cylinders. I'm not going to reassemble the drum and axle until I know the hydraulics are right. The rubber seals may or may not seat in better with a little use. I would rather try to find modern kits for these if available, or just buy new complete Raybestos cylinders. I'm stuck because I don't trust what I installed but I'm also leery of the stuff that's on the market nowadays. Your input would be greatly appreciated.
