Master cylinder. Single reservoir to dual.

[AmadeusCharger500]

A friend of mine asked me to fix his 'project'. He wanted to change from the original single to a dual reservoir master cylinder, and change to a new power booster. This is on an all drum car. He had a shop plumb the new lines and change the cylinder and booster. He got it back and the brakes felt like manual. 

My 1st issue with this is, shouldn't there be a proportioning valve installed? Could a disproportionate amount of hydrualic be going to the back wheels?

2nd. There appears to be no power assist. Could the pushrod need adjusting? I am not sure how to do this. I took it off and there is an adjustable nut, but I don't know which way to turn it. I pushed the pedal with the master cylinder off and it seems to have power assist.

[John_Kunkel]

Cars with 4-wheel drum brakes don't use proportioning valves.

By "pushrod" do you mean the one from the pedal to the booster or the one in the front of the booster? Neither should affect braking but could prevent the brakes from releasing once applied.

[AmadeusCharger500]

The pushrod in front of the booster. It has what appears to be an adjustable nut. I'm wondering if adjusting that willl allow the vacuum in the cannister to open up  and assist with the braking.

Another question. If 4 drums don't need a proportioning valeve, then does it matter what reservoir goes to front or back or can they be interchanged?

[firefighter3931]

Another question. If 4 drums don't need a proportioning valeve, then does it matter what reservoir goes to front or back or can they be interchanged?

Heath, a dual master with 4 drums will still need a "distribution" block. The rear reservoir (closest to firewall) is for the front brakes 



Ron

[AmadeusCharger500]

Ok so it does need a proportioning valve? Could the lack of cause it to have feel like manual brakes?

[John_Kunkel]

A distribution block is different than a proportioning valve. A distribution block merely isolates the front/rear systems after they leave the MC without altering the pressures, a proportioning valve regulates the pressure in one system. It doesn't really matter which end of the MC powers the front or rear system, the industry standard is to have the front brakes plumbed to the rear chamber.

The adjustable pushrod in the front of the booster should be adjusted out to where it is just short of contacting the bottom of the pocket in the rear piston of the MC with the brake pedal released; if the rod is adjusted out too long it will prevent the MC piston from returning when the pedal is released and will cause brake drag but won't affect the braking per se.

If there is no boost from the booster I would look there, can you hear a "hiss" when the pedal is depressed with the engine running? Is the booster plumbed to a good vacuum source? If the booster is working properly, the wrong choice of MC will affect brake power; a piston that is too large will increase the pedal pressure needed to stop the car as will an incorrect pedal ratio. Were factory style parts used in the swap or aftermarket?

[AmadeusCharger500]

John, can you follow up on that hiss sound? I do in fact hear a hiss!

Also

They are aftermarket parts.

[John_Kunkel]

If you hear a hiss as the pedal is depressed but the hiss stops when the pedal stops, it's just the sound of air moving in the booster diaphram chamber; if the hiss continues after the pedal stops the booster is leaking and needs attention.

[AmadeusCharger500]

I adjusted the pushrod as you said. This hiss is less but still there. How do I check for a leak? I put a vaccuum guage on it and it read 20 HG. When I press on the break it goes to 10, not sure if that tells me anything.