Re: under cross member mounted power booster master cylnder

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Posted by Keith in Washington [] on Sunday, May 30, 2021 at 10:36:29 :

In Reply to: Re: under cross member mounted power booster master cylnder posted by mike [] on Sunday, May 30, 2021 at 08:24:24 :

I would consider residual pressure valves in your brake lines with the MC being that low. I did. You need different ones for disk and drum brakes. They go between the brake cylinders and any proportioning valve. The disks use a 2lb residual valve and drums use 10 lb residual valve. The 10 lb one keeps a little pressure against the drum brake springs which keeps the fluid from back flowing. The 2 lb one just keeps enough pressure to keep the check valve closed to prevent leak back. The disk residual valves don’t have enough pressure to move the caliper pistons or engage the disk pads. The residual valves need to be placed close to the master cylinder but after any proportioning valve.

Residual valves stop any brake fluid bleed back from the brake cylinder and the master if the master cylinder is level with or lower than the brake cylinders. It’s usually not a problem if the master cylinder is mounted to the firewall. With the master cylinder mounted at frame level, it is possible to park the vehicle on hill and have the master cylinder lower than the brake cylinder.

They are a nice safety item. With the drum brakes, it keeps the brake shoes under a little tension against the brake springs and results in a little less travel of the brake cylinder piston before the brakes engage.

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