Hard brake pedal with rear Disc Rail Buggy

[2381Buggy]

Thoughts please. Have had a hard brake pedal on my 73 Rail since I bought it. Brakes stop, but not well. Was converted to a rear disc set-up that I think the former owner got from J C Whitney. It has dual tractor brakes that are split from the one line running from the master cylinder. They work well. It has a single line master cylinder from a 66 Chevy truck, I believe. Could it be that this master cylinder is mismatched to the rear brakes? It has about a 1/2 play in the rod. No front brakes. Doesn't even have a brake light switch output on the master cylinder.

Not sure if I should put a buggy type master cylinder on it or not. Pulling on the tractor brake levers works pretty well so I don't believe I have a rear hose issue.

[cbeck]

Mine had a 5/8 bore master cylinder with just rear disc on mine. What bore is the mc you are using?
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My cut in half and rebuild thread
www.thesamba.com/vw/forum/viewtopic.php?t=647779

[2381Buggy]

I'm not sure but when researching this on line for this year model cylinder, it appears it might be a 1 inch bore.

[viiking]

The bigger the MC diameter the LESS pressure you can develop for the same pedal pressure! Not an issue if they are power assisted brakes but if you are non assisted then the pedal had to be pressed much harder.

From memory an original VW bug MC was ~19mm so 1” (25mm) means braking will be harder!
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1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[2381Buggy]

Rehashing this older post I did a couple of years ago. I am about ready to try and solve this brake problem of a hard pedal. The current 1966 Chevy truck master cylinder does have a 1" bore. So if I drop to a smaller bore unit, hopefully that will give me a softer pedal with some give to it.

The Chevy cylinder that is on it supposedly has a fitting size of 7/16-24. It looks like the vw master cylinders are 10x 1.0 I would like to just use the same brake line and fitting that is there now. I can't find a 7/16 to a 10x1 adapter, but could go from a 7/16 to a 3/8 then to a 10x1. So, two adapters in between the brake line and the replacement cylinder. Is this a problem?

How small of a bore should I go to on the master cylinder to work with rear disc brakes (only)? I think the "buggy" cylinders are a 22 bore.