Technical Master Cylinder Issue

So, some master cylinders have a residual valve internally... the reason for a residual valve is to hold the shoes a little closer to the drum to limit pedal travel in a brake application.
Lets say the master cylinder has a internal valve and there is a external valve added.
I say loose the rear brake residual valve and see what happens...I believe 10 psi is too much thinking out loud and you master cylinder may already have a residual valve in that circuit

 

Wrong, the residual valve is to keep air from coming past the wheel cylinder cups upon brake release. And 10 psi is good for drum brakes.

This is all false.


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Boy since you are the hall monitor, you need to be careful about falsely stating that this is all false.
So if he has a residual valve in line and a residual valve in the master cylinder is my major point.
Also there is no cup to hold against the piston wall in a disc brake and it is uncommon to use one on a disc application.
I stand corrected on the original basis for a residual valve...though that has changed over the years. However I am questioning if his master cylinder is a equipped with a residual valve AND an inline valve plus having a residual valve on the discs
I have no idea what he has

 

I’m sorry, it was all false, like it or not, if he has two residual valves I don’t think it would make any difference at all, it’s strictly a one way check valve. You only need a two pound residual valve on disc brakes if the master is below the calipers but it won’t hurt anything.

The purpose on drum brakes has not changed over the years, sorry again. They were phased out with the advent of cup expanders in wheel cylinders.

Please tell me what part I was wrong stating it was false?


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Hey all sorry for delay in response life got,in the way...i re plumbed the front resevoir to the rear and the rear resevoir to the front and all is well...i am guessing it has to do soemthing with the spring pressure but its working fine now..thanks all for the info..very informative

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Well there you go...now I’m on a mission to find out why...

Glad you got it fixed


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And that's why I said what I said in post #70. I bet if you had bleed the front brakes first with how you had it plumbed before all would have been well. You were try to bleed secondary prior to doing primary end of master. But want does brake fluid care.

 

Could it be the fluid volume difference between the primary and secondary? Just pokin' the bear.

 

It doesn't matter the bleeding sequence with a dual master cylinder; primary first or secondary, front or rear axle.

 

^^^^^ Did OP ever say he never got a pedal? Reread post #1. OP doesn't understand what he's feeling while bleeding. Then find post where OP states master was a working unit from a donor vehicle. As most do they'll start at the back then work forward when bleeding. That's text book 101 single circuit ideology. Sure one can bleed the other way around. But understand what going's on and why. Again, as @31Vicky with a hemi has said...

 

Just as long as it’s perpendicularly parallel while remaining level to the intersecting slope.
Oh wait that is driveline angles My bad.
What’s this one about again?

 

The affect's of thrusting and exchanging of fluids from one to the other. Oh wait, wrong tab was open.

 

so.... does a 1968 or 1976 mustang have these expanding sealing cup
what is actually 'modern'
when was the article written

 

TODAY, my friend and i were trying to find why i couldn't beleed my rear brakes, a 1967 mustang mc mine is early ford hyd bks, so i need a drum,drum MC, both resivors the same size. the MC i have was a new one made in china, the front piston was froze up, rong size cups, Oh! the fromt line goes to rear brakes, if it was mounted on firewall.

 

The one with the 'Vette master has it right: large res. to front discs. After many tests with similar & worse problems we (@ my shop) never used propor. valves if running larger tires on rear. Really ! And we never used Chinese residual pressure valves. Try it (if still problems) removing the porpr. valve. They are each designed for diff. weight & configuration of vehicles. & try it ! good luck The off the ground check is a good idea too.

 

Really hard to know without taking it apart and looking for the cup expanders, the cup seals are the same there will be a metal disc between the spring and seal or the end of the spring will be wound in a taper that fits inside the seal


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That's all I've ever done. Not saying it works for all applications. Sure in hell works with 165 15 to 235 thru 295 15 combo's.