73 z1 rear brake issue

ok were almost finished with the friends 73 z1. were having a issue with the rear brakes. its got aftermarket brakes and its a hurst airheart master cyl. NOS from the late 70's. all parts are new... master, hose, caliper, pads and rotor. the issue is when we started bleeding the air out we have found that piston in the caliper movers out when pressing the brake but also returns when you let off the brake. I know the caliper does let off the pressure so your not dragging the brakes but i m getting the piston to fully return into the caliper ...... so we can never get the pads to touch the rotor. Im stumped.... there is no air in the sys that i can tell.
HELP?

right brake pads?

PLUMMEN wrote:

right brake pads?

yep!
i guess a really good way to describe it is when i press the brakes the piston moves 1" (just a number not real travel)... when i release the brakes the piston travels 1" back into the caliper. when it should just hardlymove back at all just enuff to not drag the pads and rotor.

did a check valve get left out?

PLUMMEN wrote:

did a check valve get left out?

all parts are new... and is there a valve in there? i know theres not 1 in the hose or the caliper but not sure on the master cyl.

Guessing m/c has two ports at bottom of reservoir for transferring fluid between reservoir and bore.

One of the ports might be obstructed.

Good Fortune!

Patton wrote:

Guessing m/c has two ports at bottom of reservoir for transferring fluid between reservoir and bore.

One of the ports might be obstructed.

Good Fortune!

2 small ports... yep and i dont see anything in there but im going to open it up and see again... was also told maybe the boot on the piston is sticking and pulling it back in..... ok that sounds realistic also so ill see about checking the rubber boot too. ill let yall know what i find.... but a waterpump is calling my name right this sec.

Is the cap on the reservoir vented?

Try doing this: crack bleeder, apply brake, close bleeder, let off brake. Do that a few times to push fluid through.

Kidkawie wrote:

Is the cap on the reservoir vented?

Try doing this: crack bleeder, apply brake, close bleeder, let off brake. Do that a few times to push fluid through.

nope the cap is a polished alum. rectangal with 2 screw/bolts to hold it down. I have bled it with the cap on and off. i have bled it when the system was under load(normal kinda bleeding) and open it then put on a load like you said. I do know i get a larger discharge when i open the bleder and then press the brake.

Try blocking the caliper with some wood so the piston has something to push up against.

And like Patton said, recheck those small ports that they are clear of any debris.

well we got it working right. we ended up pushing the piston almost all the way out of the caliper then with the hose removed from it we filled the caliper with fluid. the master and hose had been bled so we kept the open hose end up so no fluid drained out and then hook it all back up and bled it with a wrench acting as the rotor(was the same thickness). then we reinstalled it on the bike and with a few small adjustments on the linkage we had strong rear brakes.