Disc Brake Conversion Problem

The Big Comets

Disc Brake Conversion Problem

Postby bamnow » Mon Jul 29, 2013 10:58 pm

I'm a newbie and hope you can help me with a maddening brake problem.

My car is a 1966 mercury comet villager wagon with a 289, C4 automatic, power steering and power drum brakes. I installed a CSRP front disc brake kit ( 4 piston calipers) excluding the mustang dual bowl master cylinder as it would not fit (hit the shock tower) when attached to the booster. Instead, I used a 1967 Comet dual bowl master for a power disc brake car. The original single bowl master had a 7/8" piston, and the dual bowl 67 master is a 15/16" piston. We adjusted the master cylinder pushrod to the same length as was in the original single bowl.

New calipers, new rear wheel cylinders, new master cylinder, new brake lines, 10lb. residual pressure brake valve for rear and adjustable proportioning valve for the rear. No leaks and NO BRAKE PEDAL!!!!! We even replaced the new master cylinder thinking it is was leaking internally. STILL NO PEDAL!! And yes we bench bled the master cylinder.

The only thing we have yet to replace is the booster, and I plan on picking up a rebuilt one tomorrow. The brake pedal is very slow to return to the top when we are pumping it to bleed the system and we think there maybe a problem with the booster.

Any thoughts on why no pedal? Booster issue? Wrong master? Still air in system? This is killing me!!!!

Thanks in advance.
bamnow
 
Posts: 4
Joined: Sat Mar 02, 2013 9:17 pm

Re: Disc Brake Conversion Problem

Postby talladega » Wed Jul 31, 2013 9:01 am

Hi bamnow

Do you get decent flow out of the bleeder with each stroke of the pedal? Did you start with the wheel farthest from the master cylinder?

Having changed everything like you did, it can take quite a bit to refill the system. I would concentrate on the drums first to verify master is working properly.

Let us know progress.
talladega
 
Posts: 5
Joined: Wed Jul 03, 2013 6:36 pm

Re: Disc Brake Conversion Problem

Postby bamnow » Sat Aug 03, 2013 11:01 pm

Well we figured it out- it was a bad brake booster. The booster was not allowing sufficient pressure to build in the master cylinder. We replaced the booster today- extremely hard to locate one- and bingo! Solid firm pedal.
bamnow
 
Posts: 4
Joined: Sat Mar 02, 2013 9:17 pm


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