I have a 49 Desoto that has a power disk brake conversion. It has new MC, booster, proportioning valve, lines, rear wheel cylinders, and calipers, with a Rusty Hope conversion. The problem is almost no pedal pressure. I have tried 3 different MC's and 2 p-valves, MC's were properly bench bleed and hole system vacuum bleed. The MC and booster are a 75 Cordoba setup, the Rusty Hope conversion uses 80's Camaro calipers.If I clamp off both lines to the front wheels I have a solid pedal. If I remove one or both clamps I have very little pedal pressure. There is enough to stop the car at very slow speed. The bleeder valves on the calipers are on the very top. There are no leaks anywhere in the system. I know the booster is good because when I start the motor I lose all resistance on the pedal. I have done brakes many times before and this is the first time I have had this problem.

 

Just a wild thought ? Could the pro valve be hooked up to the wrong side of the master. Did it ever work properly ?

 

Is this a newly installed system? Or a system that needed some work and you replaced all the parts? And did it work good before at and point with this conversion?
I'm Guessing all the new parts matched up with all the old parts You replaced?
As far as I know, Rusty Hope is still around.

 

Yes the pro valve is hooked up right. This is an all new system everything is new, there are no old parts. even the rear end is from a 91 Cherokee.

 

Does it stop ok if you pump the system a couple of time?
Look at the Residual Valve Pressure in the system and see if that is holding.

 

No it don't build pressure with pumping. It says about the same.

 

I would say faulty M/C OR The system needs Residual valves.

 

As I stated before I have tried 3 different M/C's. The M/C and booster are mounted on firewall so no residuals were installed. The pro-valve is under the M/C and has 1 outlet for the rear and 1 for each front wheel with steel lines from pro-valve to rear cylinders and to hoses at wheel well in front. where would I put residual valves in this setup. I know it will take one 10 for the rear and two 2's for the front.

 

Install them rite out side the master cylinder.... Check with who you got the master cylinder from and see if the master came with them or without them internally.

 

I think I found my problem. My M/C's bore is to small. The bore of the Cordoba N/C is 1.031 and I have Camaro calipers and the bore of the 80's Camaro M/C is 1.25 so I'm not pushing enough fluid to have pressure. Thanks for trying to hslp.

 

Keep us posted if that was the fix...