Residual brake valve

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If you have a disc-drum system on your car, you will need to have the right residual valves installed for the brakes to work like they are supposed to. It is true that old cars with all drum brakes had the valve built into their master cylinder, but that only works in stock systems.

The old drum brake cars did not have a proportioning valve since they used bigger diameter wheel cylinders in front than they did in back. This gave each axle the correct braking pressure.

Disc brakes need a proportioning valve to distribute pressure right when rear drums are used. Otherwise, you would lock up the rear wheels too easy. Race cars have adjustable proportioning valves to help set the ratio for each vehicle or condition.

You need residual valves no matter if you have your master cylinder under the floor or on the firewall. They keep a constant pressure in the lines behind the caliper or wheel cylinder and prevent a soft pedal or excessive travel after not using the brakes for a bit. They help insure that your drums react a little bit before your discs do to let them apply together, or else the disc brake would grab faster and the drums would have to catch up. I think it's recommended to have ten pound valves for disc and two or four pound valves for drum, if your master cylinder does NOT already have it built in.


I hope I could help some!

Sal

If residual valves were required for every system, they'd be in factory systems.

Residual valves are required in drum brake systems to prevent then ingestion of air into the system when the pedal retracts and creates a vacuum in the system.  If there isn't a residual valve in the system, the rate of return of the fluid exceeds that of the return springs and air is ingested past the wheel cylinder packing.  The residual valve is installed to force the shoe return springs to do the work of returning the fluid to the reservoir.

A drum brake residual valve should be rated at 10 psi.

Disc brake systems do not employ residual valves.  2-psi residual valves were developed for use in conversion systems where the master cylinder was moved to a position at or below that of the calipers.  2-psi residual valves are an aftermarket item, not a factory item.

Proportioning (balance) valves were developed when disc brakes fist came into use.  This is because the line pressures for disc and drum brakes are very different.  You need to be able to overcome the resistance of the drum brake return springs before you begin applying the disc brakes.  Once the brakes are applied, you need to back off on the drum brake pressure to avoid lock-up.

As with balance valves, dual master cylinders were also a necessity of disc/drum systems.  This, again, was due to the differing line pressures of the two systems.

[Phat]

Just as and ad on ,proportioning valves are the most misused brake item you will find on a rod. They DONOT turn the pressure down ..they only slow the transition and are really just a crutch.  If you size the rear wheel cyl correctly you will never use /need or have any use for one.  Sometime do the test and put a  brake pressure guage in line after the adjustable proportioning valve.  Turn the knob both ways ,you will see no diff.  Real race cars DO NOT use proportioning valves they use what is a called a balance bar system that when you turn the knob you are running a balance bar between 2 seperate brake systems as in the master cyls are hooked up to 2 complete stand alone system.  Too answer just one more question about willwood....Now this is my opinion having raced a lot of oval track stuff with my butt strapped in the seat......i would not use his stuff if he gave it too me free and yes his aluim residauls fail on the street stuff all the time.(call there sometime that with a proplem that should about cancel anythought of using his product LOL)  I have allways used the brass ones with a ball that either ECI sells or a any of the otheres that use that type.  You also have NO need for residauls if the master is on the firewall.  H ell i get away with it on some of my own stuff under the floor but you will notice some drain back if parked on and incline for a few months in the winter.  Cant take the chance on customer stuff allways residauls as close to the master as posable on under the floor rods. I also dont use factory slide proportioning valves as they are car specific.  You need to know a bunch of stuff to even play with those...it can be done but that would be a whole nother book.

[jakesbackyard]

Master Power Brakes has a wealth of info on setting up brake systems and good tech info. Check them out. Go to this link and under the technical section choose setting up brake systems.

http://www.mpbrakes.com

[Ed ke6bnl]

Just as and ad on ,proportioning valves are the most misused brake item you will find on a rod. They DONOT turn the pressure down ..they only slow the transition and are really just a crutch.  If you size the rear wheel cyl correctly you will never use /need or have any use for one.  Sometime do the test and put a  brake pressure guage in line after the adjustable proportioning valve.  Turn the knob both ways ,you will see no diff.  Real race cars DO NOT use proportioning valves they use what is a called a balance bar system that when you turn the knob you are running a balance bar between 2 seperate brake systems as in the master cyls are hooked up to 2 complete stand alone system.  Too answer just one more question about willwood....Now this is my opinion having raced a lot of oval track stuff with my butt strapped in the seat......i would not use his stuff if he gave it too me free and yes his aluim residauls fail on the street stuff all the time.(call there sometime that with a proplem that should about cancel anythought of using his product LOL)  I have allways used the brass ones with a ball that either ECI sells or a any of the otheres that use that type.  You also have NO need for residauls if the master is on the firewall.  H ell i get away with it on some of my own stuff under the floor but you will notice some drain back if parked on and incline for a few months in the winter.  Cant take the chance on customer stuff allways residauls as close to the master as posable on under the floor rods. I also dont use factory slide proportioning valves as they are car specific.  You need to know a bunch of stuff to even play with those...it can be done but that would be a whole nother book.

While we are on the subject of brakes I have doubts the the mustange II with tubular A-arms and chevy metric calipers with 11" rotors are functioning properly the truck stops but it doesn't seem to be power assisted with the power brake unit, it has vacumm from the top of the rear of the intake manafold, some time I hear a wosh sound when I apply the brakes like it is sucking vacumm.  I have drums rear with 10# residual m/c is under the floor, 2# residual for the front and a proportional valve in line with the rear drums.  ''the rear brakes are adjusted.  Seem like my 63 econoline with 4 drums and a single resovoir works better.  Any help appreciated thanks Ed ke6bnl