residual valve

[rob63mess]

hey guys,
My 31 truck was converted over to hydralic brakes by the previous owner..it appears to be a basic master cylinder and the work looks neat and clean....my question is should there be a residual valve somewhere in the system and exactly what is its purpose?

[Bob Johnson]

My pickup was converted to hydraulic brakes before I got it. A few years ago I had to replace the master cylinder. When I installed the new one i had problems with air getting into the lines after repeated bleeding. The master cylinder I installed was set up for a residual valve but it did not come with one. I purchased a repair kit for the master cylinder, which includea residual valves, and installed the residual valves and since then I have not had any problems with air getting into the system.

The purpose of the residual valve is to keep a small amount of pressure in the lines. It is enough pressure to keep air from leaking in through the wheel cylinders. But not enough to move the shoes. This is important if your master cylinder is mounted low on the car. On cars where the master cylinder is mount high on the firewall there is enough pressure due to gravity to keep the air out. But if the master cylinder is mounted under the floor boards there is not enough pressure to keep the air out.

Bob

[Tom Wesenberg]

It holds the pressure so you can pump up the brakes if need be.

[Randy in ca]

Many master cylinders had an integral proportioning valve. Any idea what your's is from? If you're not having any problems, chances are you don't need one.

[rob63mess]

It's from a 60 Olds strangely enough....fits nicely......the problem i'm having is that when i step on tne pedal for the first time when stopping, it is very soft....like go to the floor soft....but after one pump I have plenty of pedal.....the master cylinder was replaced and the system was bled really well.

[Tom Wesenberg]

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If the pedal is solid on the second pump, then I'd say the brakes need to be adjusted tighter.

[Bob Johnson]

See the following link for info on residual valves. It should help you understand your problem.

http://www.thebrakeman.com/valvetechi


Bob

[Patrick L.]

There is a difference between a proportioning valve and a residual check valve. A drum system needs a residual valve to add some pressure to the system which is overcome by the shoe return springs. Disk systems do not use them as there are no pad return springs as the pads are supposed to rub on the rotors unless the master is mounted very low and then a very low pressure residual valve may be needed.

[Jim Brierley]

Patrick L. I think you have your terminology mixed up. Drum brakes on all 4 wheels require only a residual valve, it's main purpose is to keep air from entering the system when your foot is not on the pedal. A proportioning valve adjusts pressures to drum and disc combinations for even braking at the wheels.

[Patrick L.]

Jim, you're right. I should have proof-read before I posted. Just another brain fart. Good catch.

[hardtimes]

Originally Posted by rob63mess

hey guys,
My 31 truck was converted over to hydralic brakes by the previous owner..it appears to be a basic master cylinder and the work looks neat and clean....my question is should there be a residual valve somewhere in the system and exactly what is its purpose?

Hey Rob,
YES is the (simple) answer to your question!
Now WHERE is that valve First, identify your master cylinder and its' location ! If located on the firewall (up high), the residual should be up there nearby also. However, in most of these old cars converted to hydraulics, the master is under the floor..driver side. Therefor, the residual can be INSIDE the master (depending on how late model it is) or it will be IN the line coming out of the master nearby! Most guys, like me, don't know squat about replacing great working mechanical brakes with great working (when knowledgeably installed) hydraulic brakes.
Listen to Jim B contribution here also. Good luck.
Finally, if you have a properly installed residual valve....IS IT WORKING

[Patrick L.]

The residual check valve should/will be in the master cylinder. Its a little brassy/coppery valve. A proportion valve will be on the outside of the master or remotely attached somewhere.

[hardtimes]

Originally Posted by Patrick L.

The residual check valve should/will be in the master cylinder. Its a little brassy/coppery valve. A proportion valve will be on the outside of the master or remotely attached somewhere.

Hey Patrick,
As I stated...depends on whether your using a NEW enough master cyl...as to whether it is inside or not.

[Bob Johnson]

Here is a picture of a repair kit with internal residual valves.

Bob