I have always been amazed at brake theory discussions-

paul2748 Posted-

"If you don't have a combination valve or a residual pressure valve that that may be your problem.  The combo valve is both a residual pressure valve and a proportioning valve (combo_.  Disc/drum masters generally do not have a residual pressure valve so you need to install them in the system.  10 lbs for the drums, 2 for the discs  ...

THANX for the kind words Paul, but ...

There seems to be confusion concerning OEM Systems and aftermarket parts. FORD (during this period and introduction of DISC/DRUM) had the RESIDUAL VALVE mounted in the MC, later DBL RSVR in the outlet line to the drum brakes.

A COMBINATION (or PROPORTIONING) VALVE is not used in four wheel drum brakes (although it was used in some GM SYSTEMS). A 2lb residual is used with a DISC BRAKE CONVERSION only if the MC is mounted below the caliper level to prevent brake fluid returning (draining) to the NC (gravity). The DISC BRAKE design is self adjusting, no valve (of this type) needed.

FORD DEARBORN has the best description of the system.

The RESIDUAL VALVE's purpose is to prevent the slamming of the wheel cylinder piston cups (by retracting spring pressure), possibly distorting them and allowing air to enter the wheel cylinder. Their other purpose is to keep a steady 10lb pressure on the system to allow for quicker shoe movement when applying the brakes.

So is the need to re-check shoe adjustment again after bleeding the system (shoe position will change).

The style of your MC oldcarmark. I cannot remember if it is GM or MOPAR but if the guy will give you the origional application, you can probably find on the internet a breakdown and see if a residual valve was in the MC. The INLINE VALVES you see are mainly for conversions or custom brake systems.

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I have always been amazed at brake theory discussions-

paul2748 Posted-

"If you don't have a combination valve or a residual pressure valve that that may be your problem.  The combo valve is both a residual pressure valve and a proportioning valve (combo_.  Disc/drum masters generally do not have a residual pressure valve so you need to install them in the system.  10 lbs for the drums, 2 for the discs  ...

THANX for the kind words Paul, but ...

There seems to be confusion concerning OEM Systems and aftermarket parts. FORD (during this period and introduction of DISC/DRUM) had the RESIDUAL VALVE mounted in the MC, later DBL RSVR in the outlet line to the drum brakes.

A COMBINATION (or PROPORTIONING) VALVE is not used in four wheel drum brakes (although it was used in some GM SYSTEMS). A 2lb residual is used with a DISC BRAKE CONVERSION only if the MC is mounted below the caliper level to prevent brake fluid returning (draining) to the NC (gravity). The DISC BRAKE design is self adjusting, no valve (of this type) needed.

FORD DEARBORN has the best description of the system.

The RESIDUAL VALVE's purpose is to prevent the slamming of the wheel cylinder piston cups (by retracting spring pressure), possibly distorting them and allowing air to enter the wheel cylinder. Their other purpose is to keep a steady 10lb pressure on the system to allow for quicker shoe movement when applying the brakes.

So is the need to re-check shoe adjustment again after bleeding the system (shoe position will change).

The style of your MC oldcarmark. I cannot remember if it is GM or MOPAR but if the guy will give you the origional application, you can probably find on the internet a breakdown and see if a residual valve was in the MC. The INLINE VALVES you see are mainly for conversions or custom brake systems.

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According to the Shop Manual Pedal "Free Travel" prior to the Pushrod contacting the Piston inside the Master Cylinder should be minimum 5/16" and Maximum 7/16". This is determined using  Hand Pressure on the Brake Pedal. If the Correct Pushrod is being used  this Adjustment is made using the Eccentric Bolt. There is a Spring at the front of the Master Cylinder Bore that returns the Piston to full "release" Position when pressure is released from Brake Pedal. If that initial Adjustment cannot be done correctly then that that is the place to start  diagnosing the Problem of low pedal Height. When I get around to replacing my Manual Brake Master with the replacement Booster / Master I will be adding the inline Residual Valve. I believe the rest of my System is in good shape with the Drums being within Specs and not Oversize. I am in the Process of pulling Engine/ Trans so I won't be doing brakes over for Awhile.

  

There can be issues if the brake pedal push rod is too long. It's been thousands of year so please correct me if I'm wrong, but as I can recall after much thought:   When the pedal is released, the MC cup must move back enough to uncover the compensating port (the smaller forward of the 2 holes)  to arm the MC with a full charge of fluid for the next application. When the pedal is released, the MC piston returns faster than fluid is returned from the wheel cylinders. Fluid flows around the MC cup to relieve the momentary low/negative pressure until fluid begins to return from the system. That may possibly explain why it takes a couple rapid pumps to get a taller pedal???  Another reason that comes to mind for the residual valve is to prevent, due the momentum of the returning fluid, the possibility of air entering from the wheel cylinders when the pedal is released and to keep the wheel cylinder cups against the bore. However, I doubt air is in the system, though. If the shoes are contacting the drums by adjustment, then any excessive travel should be eliminated.  As stated in another post, the residual valve may be faulty and also check that the MC piston is returning all the way home.  Hope this helps and not add more confusion, JEFF....................


64F100 57FAIRLANE500

I’m just thinking out loud here, and maybe not clearly. But if you have no or a malfunctioning residual pressure valve and crack the fitting open from the master to the brakes you’ll get no or little fluid. If you’ve got even 10lbs you’ll get a little spurt. Not much, fluid isn’t compressible, but maybe enough to see?

I’ve had larger motorhomes where the brakes were fine, but if you did some hard corners you needed to pump them slightly, like you’re describing. I was told that was the side load pushing the pistons back in and requiring they be moved back out. I know I’m talking disc here, but if the brake friction device isn’t close to the rotor or drum you’re going to run out of travel before you get full braking.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

If you don't have a combination valve or a residual pressure valve that that may be your problem.  The combo valve is both a residual pressure valve and a proportioning valve (combo_.  Disc/drum masters generally do not have a residual pressure valve so you need to install them in the system.  10 lbs for the drums, 2 for the discs  KULTULZ is right


54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ

A spongy pedal is an indication of air in the system. I would guess the master cylinder if it wasn't bench bled.

  Ron Lane,  Meridian, ID

After driving a bit and I mash down on the brake pedal to slow or stop the pedal goes about half way to the floor.Give it 3 quick pumps and I gain about 1 and 1/2 to 2 inches that feels where I would like it to be. After the 3 pumps the pedal remains firm and does not sink to the floor as it would with a bad master cylinder. Advice that I have received on this topic and the fact that I have bled the brakes several times have led me to believe that perhaps I need to arch the shoes which no one does any more or buy shoes with oversized linings.

George can you help me to understand what it is about your brakes that concerns you. If I understand it is the pedal is too close to the floor and not that there is something wrong with the braking action.
Is that your issue?  The movement of the piston inside the master cylinder forces brake fluid to each wheel cylinder so when the wheel cylinders are fully expanded the brake pedal can not move further.
Will a longer rod from the brake pedal to the master cylinder solve your issue? Brake pedal travel will REMAIN THE SAME just start higher and finish higher. If not can you explain. Pete

oldcarmark Posted -

"Back to my Question regarding the Residual Check Valve. The Supplier of the aftermarket Master I purchased has told Me there is no check Valve in this Master. Check Valve is not required unless the Master is mounted under the Floor (which in my Case it is Firewall mounted)

Any opinions?

Yeah, I have an opinion. The guy you are buying from is clueless or feeding you false information for a sale.  

Residual Valve

Residual valves are used to maintain constant pressure on the brake system. 

For drum brakes, a 10 lb. residual valve is used to hold pressure against the springs in the drum.  This allows the drum brake to engage more quickly and reduces pedal travel. 

For an under-the-floor master cylinder brake system, a 2 lb. residual valve is used for disc brakes to keep brake fluid from flowing back down into the master cylinder. 

SOURCE -   https://techtalk.mpbrakes.com/how-to-series/four-things-to-know-about-brake-valves

The MC you boiught is not FORD but regardless, a residual valve was somewhere in the system.

Most of these sellers (especially on EvilBay are dangerous) IMO.

That's the best I can do for you. GOOD LUCK with it !

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