Brake Repair

Had to find and issue with the brakes that the mechanical inspector noted. Symptom observed was brake pedal slowly lowering when pressure is applied.

Looked around for a while, and found that brake fluid was leaking slightly around the proportioning valve I have installed. I purchased the adjustable prop valve from Flyin’ Miata, and it came with metric M10x1.0 to SAE adaptors, as the Miata brake lines are metric and the prop valve is SAE.   The fluid leak appeared to be between the adaptor and prop valve body. I tightened the rear and began to loosen the front brake line when the adapter sheared off.   Will need to get more adapters and am looking at getting a different adjustable proportioning valve that has a built in sensor to indicate when there is hydraulic fluid pressure loss/differential from front to rear.

I think this one will work,

But I need to confirm that the sensor is not just a brake light switch. Summit confirmed that the sensor is a low pressure sensor for detecting brake failure.


Brake proportioning valve from Summit Racing linked above actually just has a brake light switch, not a failure warning switch.

Found a standalone brake failure warning switch from an older Chevrolet (photo below).

Differential pressure warning switch.

Generic diagram below:

Rock auto seams to have something like these here:

***UPDATED June 30 2018***

Hooked up the brake system and found a leak at the willwood proportioning valve again. Took a look at the CPP prop valve I ordered from summit tools and the front and rear plumbing are seperate so we used the CPP prop valve to just run the rear brake lines thru.  Hooked it up and bled the brakes to get all the air bubbles out. Went thru about .5 litre of brake fluid. Brakes are firm now with no leaks at the prop valve or elsewhere.