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Problem after big brake conversion

Shocks, Springs, Brakes, Frame, Body Work, etc

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Location: Netherlands

Re: Problem after big brake conversion

Post by BigBlockMopar » Sun Dec 24, 2017 7:59 am

The size of the orifice only determens how 'quick' the engine vacuum reaches the booster. Not the amount of vacuum.


Re: Problem after big brake conversion

Post by user-23911 » Sun Dec 24, 2017 5:41 pm

All you have to do is open and close the throttle a couple of times and you've got plenty of vac.
Make sure the check valve doesn't leak.
Once you've got vac stored, it stays there until you use the brakes.

mk e
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Joined: Mon Sep 17, 2012 3:19 pm
Location: Elverson, PA

Re: Problem after big brake conversion

Post by mk e » Thu Jan 18, 2018 11:30 am

Step 1 is reinstall the proportioning valve, it is a CRITCAL part of the braking system and removing it will cause exactly the problem you are it's only purpose and reason for existing is to prevent the exact problem you're describing ;)

When the brakes are first applied or applied gently you want the % force applied to each wheel to be about the same as the %weight on the wheel. But as weight shifts forward under harder braking a higher % of the total braking force needs to shift forward along with the weight and that is the job of the proportioning valve.

The basic mechanical design will give you optimal lower pressure braking, like wet or slippery conditions, then the proportioning valve will reduce pressure to the rear as total line pressure goes up so the rears don't lock under hard braking but can still do all they can under lighter braking (wet or slippery).

When I do brake conversions I generally also switch to an adjustable proportioning valve so I know i can get the panic or limit braking working right even if the components aren't perfectly sized so they may not exactly match what the factory valve was designed for. I install proportioning valves even when I also have twin master cylinders with a balance bar because they do different need a proportioning valve on a street car and they help performance on race cars.
Mechanical Engineer

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