disc brake bleeding problem on 73 Brave

[blkhwk039]

I changed out my disc calipers and master cylinder on my 73 brave and I can't get the front disc to bleed???  Rear wheel cylinders bled no problem.  Tried everything, pedal and vacuum bleeding, even gravity bleeding.  Does anyone have any thoughts???  Also the chassic manual I bought from the website is missing page 5-24 that just happens to be about disc brake bleeding. Any help would be greatly appreciated

[Oz]

Did you bleed the boosters first?  Did you bleed the master cylinder before doing the brake lines?

Check the master cylinder to see if it is two compartment.  One is for the rear and the other is for the front.  One is pretty small and doesn't hold a lot of fluid so you have to watch that you don't let it go empty while bleeding.

[DaveVA78Chieftain]

Link to Page 5-24

Dave

[TripleJ]

What exactly is the problem you are having? Is there no fluid coming out the bleeder screws? Or is there fluid coming out but still a low pedal?

[blkhwk039]

I have gone thru the gravity and pedal bleeding procedures like you normally do and cant get any fluid to the front disc. Master cylinder was bench bled three times. No issue there. I was wondering if the metering or proportioning valve could give me a problem? Really frustrating when you have done this many time on other vehicles and now its not working. Any help is appreciated. Thanks for the missing page too, Dave.

[blkhwk039]

Rear brakes bled no problem. Just cant get any fluid out of the front caliper bleeder screws. Master is full of fluid. Cant even get any fluid with a hand vacuum pump on either the left or right caliper.

[Mr. T]

If you haven't all ready, take the bleeder screws off and clean them.  They may be completely clogged with crud.


Don T.

[DaveVA78Chieftain]

Do you have this style of Power brake system?


or dual brake boosters?

[blkhwk039]

I have the single master cylinder with the booster like the diagram.  I can't get any fluid to come thru the lines to the disc brakes only.  Rear bled no problem.  I changed the calipers, master cylinder and flex hoses to all brakes.  Lines are all clear.  I was just wondering if anyone had a problem with the proportioning/metering valve?  Can it lock up and cause a problem bleeding??  Never encountered this problem before.  I have a 73 Duster with similar brakes and never had an issue, also an older Ford.  Just wondering if that valve set up could be an issue.  Really frustrated after two day of work cuase I really like this old rig.

[EarlJr]

Just a question... please don't get offended.

Did the new flex lines come with plugs or caps? New lines often come with dust plugs to keep the line clean during shipping.

Also, I've got one of these and I cannot recommend it enough. Pulling the fluid to you is so much easier than yelling at your kid "Push the pedal! *wait* Let go of the pedal! *wait* Push the pedal!" while lying under the car in the shop.

[blkhwk039]

No caps on lines. Had them made at hoseman. I have done the hand vacuum pump to try to get fluid drawn to them and nothing. I sucked the lines dry of residue fluid. Also done the gravity and pedal method with no luck. Anyone know if the valve (proportioning/metering)could have caused this??

[Froggy1936]

YES ITS THE PROPORTIONING VALVE!!!!!!!!!!!!  Read on how it works its just doing its job when you opened the frt bleeders It shut off all fluid to frt syestem . Wile holding the pedal down and opening a rear bleeder it should reset the other way then you can bleed the frt with your vacuume bleeder then reset the valve to the center position That is the tricky part !! You also should have a brake warning light on that wont go out when releaseing the parking brake . Frank

[blkhwk039]

Thanks a million for the insight Frank. I will give it a try. Was going to remove the whole assy and clean it but I will try this first.

[DaveVA78Chieftain]

From the Service manual:

COMBINATION BRAKE WARNING/METERING VALVE

Metering Valve Unit Operation          

The metering valve holds off hydraulic pressure to the front disc brakes in the 35 to 135 psi range to allow the rear drum brake shoes to overcome the return springs and begin to contact the drums. This feature helps prevent locking the front brakes on icy surfaces under light braking conditions. The metering valve has no effect on front brake pressure during hard stops. Checking Metering Valve

   
• A slight "bump" can be felt by the foot as the brake pedal is stroked. This bump will occur after the pedal has been stroked about 1 inch.
• A visual check will show that the valve stem extends slightly when the brakes are applied and retracts when the brakes are released.
• In case of a metering valve malfunction, remove valve and install a new combination valve assembly.

Brake Warning Switch Unit

The brake warning switch used in these combination valves are latching types. If a pressure loss occurs in one side of the dual brake system the piston in the valve will move toward the failed side and latch in that position. This will cause the brake system warning light to come on and stay on until the brake system is repaired. After repairing and bleeding the brake system, applying the brakes with moderate force will hydraulically recenter the piston and automatically turn off the warning light.
DO NOT DISASSEMBLE THE VALVE TO RESET THE PISTON. Testing Brake Warning Switch Unit The brake warning light bulb function can be tested by starting the engine. The light will go on when the ignition key is turned to the extreme right START position and will go off as soon as the engine starts.
To test the service brake warning system, raise the car on a hoist and open a wheel cylinder bleeder while a helper depresses the brake pedal and observes the warning light. If the light fails to light, inspect for a burned out bulb, disconnected socket, a broken or disconnected wire at the switch. If the bulb is not burned out and the wire continuity is proven, replace the brake warning switch in the brake line Tee fitting mounted on the frame rail.

BLEEDING VEHICLES WITH METERING VALVES
(Combination Brake Warning Switch / Metering Valve) Due to operating characteristics of the valve, which causes complete shut-off of the flow of brake fluid between approximately 3 to 135 psi, front brake bleeding procedures should be done as follows:

   
• Gravity Bleed: This method of bleeding is not effected by the metering valve, as fluid pressures are always below 3 psi. Remove master cylinder reservoir cover and gasket, then fill reservoirs with approved brake fluid. Open disc brake bleeder screws, and allow fluid and air to drain until stream of fluid is free of air.
• Pedal Bleed: This method of bleeding is not affected by the metering valve, as fluid pressures are in excess of 135 psi. Follow normal procedure of pumping pedal and opening bleeder screws. Do not pump master cylinder dry.
• Pressure Bleed. This method of bleeding is influenced by the metering valve. Bleed pressure, which is normally about 35 psi, is high enough to cause the metering valve to close, stopping the flow of fluid to the front brakes. However, the valve (Fig. 2) can be held open manually by using Tool C-4121, to pull the valve stem out.

RESIDUAL VALVE

A residual valve is required to maintain light hydraulic pressure in the rear wheel drum brake hydraulic system to keep the wheel cylinder piston cups sealed against the piston bore during "off" brake" periods. Residual valves are located as follows.

On RM300 and 1975 M300 models the valve is located in the master cylinder (rear) outlet supplying the rear brakes.

On RM350, RM400, M400, M500, and M600 models the valve (formally installed in the front outlet of the master cylinder) is located in the rear brake system outlet of the brake warning metering valve assembly

Dave