[twins_two]

i have a brake question for everyone. i used a chassis for a rod that had 4 wheel manual drum brakes. i found front discs off of the same kind of trunk and now i have no pedal at all. The master cylinder is new as are the front calipers. the master cylinder is mounted on the firewall and not frame. The only way i have brakes is to block off the front lines and run rear only. My question is do i need a residual pressure valve or is my problem the master cylinder designed for drums? i have asked the local parts store and they say the part number is different but they look the same. thanks for any help

[427v8]

The problem is most likely that you have a MC designed for drums.
the disks need more fluid than the drums. The residual pressure valve should also not be used with disks.

give Master power brakes a call and they should be able to set you up with a disk/drum MC. Might want to know the diameter of the piston in the disk caliper.

Keith
Corvette Engineering

[pepi]

do you have a proportional valve plumbed in the system? That is a must have.

[ROCKABILLY WHITE BOY]

it sounds like you need a propartional valve for disc brakes set up

[Centerline]

Although a proportional valve is pretty much required you main problem is your master cylinder. You NEED an MC that is designed for a disk/drum setup. Using a drum/drum MC won't work. Also make sure you have the front calipers mounted with the bleed valves up and that they have been bled correctly.

[pepi]

[QUOTE=Centerline]Although a proportional valve is pretty much required

it is more then pretty much required, it is a must, as long as you have a dual MC meaning a reservoir for each brake system. The front set of brakes and the back set of brakes, two places to put brake fluid. The proportional valve will do the metering and proportion the brake application providing the larger percentage of stopping power to the front system, brakes. All brake lines front and back go through the proportional valve, also referred to as a combination valve and plumbed lower then the MC.

[427v8]

A prop valve is an easy way to fix a porly designed brake system, but it shouldn't be over used. It should be used to fine tune the bias. Slapping a prop valve in the OP's car won't fix his problem.

He needs a new MC.

Keith

[twins_two]

thanks for the help the new master cylinder worked.