Technical Brake issue

Model A with Boling Brothers hydraulic conversion. Wilwood dual master.
Can pressure bleed system, no air.
Two new master cylinders, both bench bled per Wilwood instructions.
Checked pushrod travel, bottoming per Wilwood instructions
Residual pressure valves installed, front and rear. 10#
When I press on pedal, no front brakes. Disassembled front brakes, everything looks good, no leaks.
Pressure to front wheels doesn’t release. This problem stated about thirty days ago, after 6 years of working flawlessly.
question, can the residual check valve fail to release pressure over its 10# ?

thanks for any feedback
Ken

 

Anything can fail. Could be the RP valve. Could be the brake line.

 

Flexible break lines can fail. HRP

 

^ yup the first suggestion here is always an internally collapsed flex line. It can act like a valve and not let the fluid back flow

 

@Tim beat me to it! Just to clarify. Brake flex hoses can fail without showing an external leak. The internal lining of the hose can break down with age and flexing. The loose section of the lining can then act as a restriction or one-way check valve to the flow of brake fluid. This could make the brakes harder to apply or keep the brakes from releasing properly.

 

Okay, based on your description, you seem to have two problems that don't make sense. First you say you do not have any front brakes, then you say they won't release. Which problem do you have?

 

When I pressure bleed the front brakes, great fluid flow, no air.
Test drive in driveway, brakes work for one apply, then lose half pedal.
Front brakes aren’t releasing , both wheels.
When I open the bleeder, I get fluid flow, again, both sides.
I did this same test, removing the mc pushrod, eliminating the mc from the issue.
Two new masters (Wilwood), only part not checked so far is the check valve
I also tested front brakes with the drum off, can only see left front. Shoes expand but don’t retract, again retaining pressure.
I’m going to change brake hoses (Aeroquip), just in case.
I did find reference to failed rpv, during a search of this site.
Call into Wilwood, waiting for return call.

 

If you did the bonehead thing of pushing the pedal with the drum off you may have pushed the pistons out so far that they got stuck or cocked.

1 wheel acting up would be a flex hose, two wheels acting up would be residual valve or master cylinder.

 

Follow-up:
Drove over to Summit Racing, bought new RPV,
Problem solved.
Tested old valve, would allow fluid thru from mc, but no return.