'56 Chevy Brake mystery.2. Retrofit double master cylinder costs?

Hi Guys and Gals
Just a couple questions.
1. I have been having a braking problem with my '56 Chevy wagon the past 4 months and I plan on bringing it to a different mechanic and since I've found that even good experienced mechanics sometimes just don't know what's going on with an older car, I'll ask some of you guys for some advice.

First of all 2 years ago the left (driver) front wheel started having a off/on scraping sound. My mechanic did a preliminary check, jacked it up without taking off the wheel drum, and said he thought the brakes which I just put on 2 years before was cracked. Before he had time to work on it the sound stopped and I went back to driving it about once every 10 day a few miles. My mechanic then went out of business.
The last 4 months when I would brake from a cold start the car would pull to the left; I checked all 4 wheels and did not see any sign of brake cylinder leakage. The brakes did not feel spongy or have that stepping on a plum feeling.I found that stopping a few times at low speed would bring up full braking power. I did find that the master brake cylinder reservoir; a single master cylinder was down 3/4 inch and refilled it. It seemed to work fine a couple times then went back the same thing. The master brake cylinder reservoir was still full. A couple times when I braked harder at 35 mph the left front wheel would lock up. I have'nt been driving it since.
Any ideas?

2. What is the approximate cost in parts to convert to a double master cylinder system in a '56 Chev wagon and a '64 Impala and the # of mechanic hours? What is a good long lasting brand for a new master cylinder?

Thanks
Rick

I've worked on a pristine '55 Bel Air for a friend several times and I now realize that the brake adjustment is very sensitive on the car. His has the old Treadle-Vac booster for the factory power brakes, and rebuilding that was a real education. I had to fabricate the leather booster cup from scratch.

Anyway, check the adjustment on all four wheels first.

Changing to a split hydraulic system is probably a very good idea, and shouldn't negatively impact the value of the car nearly as much as the result of lost brakes. To accomplish this you will need a split master cylinder and a residual pressure check valve. A combination unit such as was used on disc/drum setups will not be suitable. You can optionally install a proportioning valve to correct the bias between the front and rear brakes, and those are usually available as aftermarket for under $100. You might have luck with retrofitting a MC and valve from a '67 or later G-Body like a Chevelle or LeMans or Nova/Camaro parts. Many of those had drum/drum setups and no power assist. My '67 Firebird was manual drum/drum OEM. You can find a master cylinder and prop valve at several places, such as AutoZone which has split drum/drum master cylinders for Camaros for about $24 and adjustable prop valves for about $85.

After the proportioning valve you will need to fabricate brake lines to connect to the valve and head off to the front and rear respectively. I would guess that you could spend $60.00 in lines and flare fittings before you connect to the old line set at a convenient point.

I agree with the advice from Blue Bowtie. I was thinking the same thing - a 1967 Chevelle/Malibu Master Cylinder might be the one you need.
Have you pulled that LF wheel & removed the drum for a quick look at things?
Also, as BB said, the adjustment might be a bit off, which could cause your pulling/lock-up issue. Thinking you might the car on a lift, or jack the front up and just spin the front tires one at a time, see if you hear anything dragging/scraping, and also get an idea of how equally they free-wheel... Long term (desirable) action would definitely be to pursue a dual hydraulic braking system.

Hey guys,
Thanks for the advice> I'll try it out.
Rick G.