Disc Brake Conversion - Out Of Proportion

Tips For Choosing The Correct Valve For Your Disc Brake Conversion

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In 1967 all cars went to dual masters, and disc brakes were an option. Older cars had a single master with drum brakes. On the right is a '66 distribution block that cannot be upgraded to the dual master because there is no inlet for the second line. The block on the left is also a distribution block but for the '67 dual master cylinder. It does have the provision for the second master line but cannot be used on disc brakes alone because it does not proportion any fluid; it's still just a distribution with a low-pressure warning light lead.

Proportioning valves come in all shapes and sizes and vary considerably depending on the car you are working on. But the most common problem you'll face is which valve should be used on which car. To help you make the right choice when doing a disc brake upgrade we asked the experts at Inline Tube and received the full scoop, from installing a used valve to buying a new one.

There are plenty of disc brake systems available today. Just take a look on e-Bay, at the swap meet, or in the junkyard. But most people don't know what system will fit their ride. First off, it's important to know the exact year, make, and model of the car the brakes came off of. Most of the parts cross over to work on a number of different vehicles, but knowing what to look for is the hard part. Whenever we see a disc brake setup at the swap meet and ask what year it came off, the standard answer is: "A '72 Chevelle." Take a close look to determine the exact year. The '69-72 GM A-Bodies and the '67-69 Camaro are not the same system.

The first year for disc brakes on GM products was 1967. Almost all cars before then had four-wheel drums. Discs were introduced as an option on passenger cars from '67-72. Starting with the '73 model year, front disc brakes were standard and front drums were no longer available. When disc brakes were developed, so was the dual master cylinder. But because discs required different pressures, the master was divided into two halves to provide pressure to the front and rear separately.

All '67-68 factory disc brake cars came with dual-piston calipers. Those from '69-72 had a single-piston design. The majority of aftermarket systems come with the later, single-piston caliper, but this is not technically correct for '67-68 cars. The single-piston setup will bolt on all the '64-72 GM A-Bodies and '67-69 F-Bodies.

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Which valve do I need? There are so many to choose from, they are all different sizes, and the fittings change as well. This is why it is difficult to pick out the right valve for you car. Some valves are used in conjunction with others, and many are singular units which require no other valves. Most people call these items "proportioning valves," but very few are just that. Some are distribution blocks and others are hold-off valves.

The first issue to converting a car to disc brakes is what kind of car it is. If it is factory correct and that is a concern, single-piston calipers on a '67-68 car will certainly catch the judge's eye. If the car is a driver, no one will care. The first question Inline Tube asks is: Are you looking for original appearance or for something that just bolts on and does its job?

That brings us to the issue of the proportioning valve. The valve released in 1967 was still being worked out for the next few years and could be made up of as many as three pieces. In 1971 the design was used on most cars late into the '80s. This is why it is important to know what the correct pieces are for your car.

People generally refer to all blocks as proportioning valves. This is incorrect. There are metering blocks, hold-off valves, adjustable proportioning valves, and residual valves. What's the right combination? Once you get past the spindle and calipers, the brake lines will drive the average guy insane. With the wrong caliper the hose may not fit. With the wrong valve combination the lines may not fit properly.

The fitting sizes change with the year of the valve, and valves that look the same are not. Factory lines do not work with aftermarket valves, and in some cases, headers will hit blocks located on the frame. We've put together a set of photos to make anyone the expert. Next time you go to the swap meet you will know what to look for. Inline Tube makes lines to work with all the valves, but you still have to know what valve your car has on it. Remember most of these cars are over 30 years old and parts have been changed.

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