Thread: front calipers wont retract

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Originally Posted by mrrilla

I popped the bleeder and the calipers retracted. I let the master cylinder push rod loose and it was adjusted full retraction so I assumed that the internal bypass valve was exposed.

I then took my front 2# residual pressure valve out and since I didn't have enough line to make a new one without the valve in it. I took the spring and rubber diaphram out and re-installed the valve which is basically open now.

My brakes work but I am concerned about not running the front pressure valve. I couldn't find anything that says the corvette master cylinder has an internal valve built in.

Mrrilla
Is this part of a front disc brake/power booster conversion Kit? This is almost the exact same set up as I got from Classic Performance Parts. They have a tech line that is great for figuring out these problems.

This is not a conversion kit. It was built from scratch for a 39 chevy.The MC is an aftermarket "street rod style" and the booster is a standard 7". I think I had the front and rear lines crossed from the MC to the proporting valve so I changed that and nothing different happend. The proportioning valve has a built in metering valve and I am 100% the plumbing is correct. I am using a DOT 3 fluid in the system.

Everything is functioning now that I got rid of the front 2# residual valve. I still have the rear 10# in there. The system works great great under no vacuum but once I start the car, I have a long pedal throw. I think that is a simple pushrod adjustment or some air in the lines though.

I have gone around and around with this brake system for a week now. I solved the front calipers not wanting to retract by simply removing the guts from the front residual valve but now I can't solve the issue of a low pedal.

I bench bled my M/C, adjusted the rear brakes and made sure I have about a 1/4" freeplay before I can feel the booster rod hitting the M/C. I bled the brake system several times and I am not getting any air out of the system.

When I think the pedal feels good, I start the car the vacuum makes the pedal feel much much worse. Everything in the system is brand new and I am thinking this issue might be caused from running no front residual pressure valve. Could this be so?