I need brake help!

[BigRed76]

The problem I'm having is actually with my 72 cutlass, but this is such a great board that i figured i could get some help with it. I recently did a front disc brake conversion which works really good, but now when braking the front brakes apply long before the rear brakes do. The conversion kit i bought came with an adjustable proportioning valve, but idk where I am supposed to install this. Should i try to find a stock prop. valve or is the adjustable one ok to use? Any help is appreciated.

[raycow]

A standalone prop valve would be installed in the line to the rear brakes, but if you don't have it in there now, I don't think it will do you any good to install it. On a normal disc/drum system, the rears want to apply first. The prop valve delays applying the rears until the fronts have reached a predetermined pressure. It sounds like you have the opposite problem.

Have you determined that your rears are actually getting pressure? For example, could the shuttle pin in the distribution block have moved off center and closed off the rears? Is your warning lamp hooked up and working?

Ray

[DKN]

The front brakes will begin to slow the car as soon as you build brake pressure. The rear brake shoes will not engage the brake drum until they have enough pressure to overcome the return springs and the friction of all the moving parts in the system. This is why the factory proportioning valve assembly includes a metering valve. The metering valve will prevent the front calipers from getting pressure until the metering valve opens, usually around 100psi. This allows the rear shoes to engage the rear drums just before the front calipers engage the rotors.

The adjustible valve is plumbed between the master cylinder and the rear brakes. It works by reducing the pressure coming out of the valve. The adjustment only changes the point at which the valve begins to function.

There is a good detailed explanation about the valves on page 4:
http://www.classicperform.com/Instru...brakeguide.pdf

Danny Nix
CPP

[BigRed76]

The rear brakes are getting pressure, but only when the brakes are applied fairly hard. So i guess what i need to do is get a combo valve?

[DKN]

A combo valve may help. It should only make a difference when lightly appling the brake. You may have an obstruction in the brake lines that knocked loose when bleeding the new brakes. I assume you switched to a disc brake master cylinder so that the reservoir is large enough to allow the front pads to wear without running out of brake fluid. You may try switching to a different brake shoe material, the soft shoes stop well, the long life hard shoes require lots of effort to work. Also check the rear brake adjustment, and that all of the moving parts move freely.

Danny Nix
CPP

[BigRed76]

Originally Posted by DKN

A combo valve may help. It should only make a difference when lightly appling the brake. You may have an obstruction in the brake lines that knocked loose when bleeding the new brakes. I assume you switched to a disc brake master cylinder so that the reservoir is large enough to allow the front pads to wear without running out of brake fluid. You may try switching to a different brake shoe material, the soft shoes stop well, the long life hard shoes require lots of effort to work. Also check the rear brake adjustment, and that all of the moving parts move freely.

Danny Nix
CPP

I did switch to a disc brake master cylinder, and recently put on new ceramic pads to replace the metallic ones that came with the kit. Once the new pads were on the problem was way more obvious. The car still has the original combo valve for drum brakes in the front so i'm assuming it wasn't equipped with a metering valve.

[cdowns]

you need to get rid of that drum brake combo valve and replace with a proper disc/drum combo valve //if you've driven for any distance i'd worry aboiut the condition of the front discs due to overheating// combo valve has residual valve that keeps those discs applied at all times and leads to overheating and hardening of discsc and warpage

[LONGHAIR]

Originally Posted by BigRed76

The car still has the original combo valve for drum brakes in the front so i'm assuming it wasn't equipped with a metering valve.

That's your problem right there, you need the disc/drum valve. Wasn't that part of the kit?

[BigRed76]

Originally Posted by LONGHAIR

That's your problem right there, you need the disc/drum valve. Wasn't that part of the kit?

Unfortunately that did not come with the kit and im not sure why. Thanks for all the help with this. Now i'll try to find the disc/drum combo valve.