Hard brake peddle

[qmcdugan]

Some History: F-100, original manual brake system, with drums on all four corners. Purchased in 07. First thing I did was a brake job. All four drums, and hardware pulled and cleaned. Replaced the wheel cylinders and the 3 hydraulic hoses, with new. Brakes were and had remained hard until recently when during a hard braking situation they failed. I felt a pop of sorts and the peddle went to the floor. Today, I plan to remove and rebuild the master cylinder and see what I get. This truck wouldn't have Pressure Differential Valve, would it? I will be using my Mighty Vac hand pump to bleed the system as I have before.

[Busboy]

Yes a 70 model will have a pressure differential valve. It sounds as though your master cylinder gave way. Time to rebuild or replace. I would just replace a 48 year old master cylinder rather than try to rebuild it.

[qmcdugan]

This pressure differential valve, where might it be? I've read that a pressure differential valve may contribute to a hard peddle and may be the origin of the problem, resulting in a MC failure.

[Busboy]

It's below the master cylinder mounted on the frame rail. Follow the lines from the master cylinder right to it. Plan on removing, disassembling and replacing the two O-rings in it. The rebuild kit is available from Muscle car research.

[qmcdugan]

Found it! I opted to get a re-manufactured MC, the parts guy on tonight is an old friend and he bench bled if for me.

https://musclecarresearch.com/valve-kit-whead1

All of the rubber parts are molded from a 70 durometer ethylene propylene diene monomer (EPDM) rubber compound that is fully compatible with automobile brake fluid. All parts are made right here in the USA! Are you unsure if this kit is for you? These switches was originally used on the following Ford and Lincoln/Mercury vehicles:

1967 Ford Galaxie
1967 - 1969 Ford Fairlane
1967 - 1969 Ford Torino
1967 - 1969 Ford Mustang
1967 - 1972 Ford F-100 Truck
1968 - 1972 Ford F250/350 2WD Truck
1967 - 1969 Mercury Cougar
1967 - 1969 Mercury Comet
1967 - 1969 Mercury Montego
The kit can be used to rebuild other switches of the same type if the areas where the replacement rings are used measure 7/32" in the small groove and 15/64" in the larger groove.

Complete rebuild instructions are available from the Muscle Car Research web site. Dealer inquiries are welcome - please contact us for pricing. Be sure to check out our Pressure Differential Switch Lock Tool that you can use to keep the piston centered when bleeding your brakes after rebuilding your switch!