Understanding a Combination Valve

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Combination valves are common on most classic cars from the 1960s forward. This valve is often misrepresented as the proportioning valve, however the combination valve actually contains three distinctly different functions. Mark Simpson explains the different components within the combination valve and exactly how they function together.

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8 Responses to “Understanding a Combination Valve”

  1. Lance Helmert

    So it delays the front brakes and the rear brakes?LOL. And the bar trips the switch. Well sure it does, but isn’t the important part that it maintains brakes in the half of the system that’s still functioning? Honestly, I’d have to read a little more to be sure, but I’m thinking that was a lot of balogna. In an emergency if the front brakes apply first, the rear end will try to pass the front end.

  2. Jack15T

    I have a 71 Chevy K20 pickup. The factory comb valve only had one port for the front brakes. The brake lines split in two lower down on the frame rail for left and right front disc brakes. I replaced the comb valve with a new one that had two ports on the front for left and right front brake. I capped on of the ports an am supplying the front brakes through the one port. Will that be enough fluid and pressure to operate the front brakes or do I need to find another combo valve from that era that fits my truck. The truck isn’t drivable yet so I can’t road test it. Thanks, I appreciate any help. Jack

  3. Bill Goodner

    I have been having a long term problem on my Chevy 1985 C10. When you first drive it in the morning the rear brakes will lock up as soon as you press the brake. After several stops this seems to go away at least to where they don’t lock up. I’ve changed several components but to no avail. What would be your best guess at my problem.

    • Customer Service

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  4. Michael Waibel

    I have a 2000 Saturn and it keeps blowing rt read wheel cyls it’s been replaced many times

  5. Jerry

    Could the Combination Valve be the cause of my front disk brakes locking up upon activation…It’s an 80 model 1 ton chevy truck, I have repaced the calipers and master cylinder, and when the brakes are applied, they lock up and I have to bleed them to move the vehicle…Thank You, Jerry Lindsey

    • Customer Service

      Hello Jerry,

      There is no ABS unit in your truck, so if you’ve replaced the front calipers and master, I would probably consider replacing the combination valve.

      The seals inside breakdown over time and it is likely it has never been replaced on a nearly 40-year old truck.

      It is possible the valve is clogged of malfunctioning.

      Mark CCRC Video Membership

      • Eddie anderson

        I changed over to power brakes and a split system front and rear using a dual master stl it does stop like power brakes but has brakes

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