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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.

jaycoop - According to a 1984 NAPA Brake Parts Catalog I have, it lists the rear 1-7/8" bore wheel cylinders (upper and lower) as NAPA# 19111 for your 1955 GMC Model 630. It also lists the 1-7/8" bore repair kits as NAPA# 176. Granted NAPA is very pricey, but it proved a good starting point for tracking down more info.

NAPA On line shows they are currently listed as:

UP 19111 full wheel cylinder (pic 1 below)

UP 176 wheel cylinder repair kit (pic 2 below)

Here's another link to a different parts site listing the Raybestos Part number WC19111 (and also listing lower down a cross reference of numerous other sellers part numbers) for replacement cylinders.

I could not find a Raybestos number for the wheel cylinder repair kit, but did find that even Rock Auto carries the WC19111 wheel cylinders at a much more reasonable price than anybody else.

I think these newer currently available parts should be trustworthy, whether the repair kit or new cylinders, and I think considering your EIS cylinders shelf life time is about 60 years they may be more up to the critical task at hand.

Hope this is helpful.

Wow thank you for your thorough look into this! What I may try first is the NAPA kits for the EIS cylinders - and if that doesn't result in a tight seal, I'll go for the Rock Auto complete units. Thanks again!

You are most welcome sir!

Hope you will come back and update on your experience with the NAPA kits in your EIS cylinders when you get there.

I think the older ones just always seeped a little bit. Back in the '80s when I started replacing wheel cylinders in my own 1960s cars, seemed like there was always just a little bit of dampness inside the rubber boots. Not enough to get stuff wet outside them. Still though, new rubber cups might be well advised although the NOS cylinders probably have a better factory finish inside than the modern made ones.

Thanks for the added input. I'll let everybody know how it works out in the end.

I installed the NAPA kits and the cylinders held pressure perfectly. I tested them by installing them in a vise end-to-end, without the dust boots. The vise kept the pistons from popping out. I hooked a Motive pressure bleeder to them using a metal brake line screwed into the cylinder at one end, and clamped the other end (with fitting cut off) into the pressure bleeder hose. With bleeder screw opened and facing up, I applied low pressure until the cylinder filled, then closed the bleeder, then pumped pressure up to 15 psi, then let each cylinder sit for 1/2 hour under pressure to ensure there was no leakage.

That's great news!!! Thanks for coming back and updating on the results. This should be good info for fellow Big Bolters in future brake situations.