Long pedal and grabby

[Sixt8Chrgr]

I took the car to the shop today. Good thing I was taking it today because the brakes were really bad. When stopped the pedal would go to the floor about 3 out of 5 times. I had to pump up the pedal to get brakes.

What are the pressure valves?
Where are they?
What do I do with them?

Thanks,

Lawrence

[Musicman]

I took the car to the shop today. Good thing I was taking it today because the brakes were really bad. When stopped the pedal would go to the floor about 3 out of 5 times. I had to pump up the pedal to get brakes.

What are the pressure valves?
Where are they?
What do I do with them?

Thanks,

Lawrence

These 10 PSI valves are used in a drum brake system to prevent air from being ingested into the hydraulic system when you release the brake pedal. Typical wheel cylinder seals only seal when there is pressure behind them. Rapid release of the brake pedal creates a vacuum in the system which causes the seals to relax and air is ingested into the wheel cylinders. Maintaining 10 PSI in the system at all times prevents this. They also hold the brake shoes closer to the drum, maintaining a higher brake pedal, so you are not constantly pumping the brakes to stop. Older drum brake master cylinders had 10 PSI residual pressure valves installed internally behind the tubing seats, but in-line replacements can be purchased and installed "if necessary". Also, some newer style wheel cylinders have cup expander's which eliminate the need for the residual pressure valve.

Get a new master on there, flush everything real good, inspect everything, and then see what you get. You can always add the residual valves later if you feel you need a higher pedal.

Oh yeah... Here's a couple of shots of a typical drum brake assembly front & rear, just in case you don't have anything to go by already.

[Sixt8Chrgr]

Is a master cylinder rebuild kit an option or should I just put a new or rebuilt mc on the car?

Thanks,

Lawrence

[Musicman]

Just put another one on there... new is better. Many times rebuilt units are not all that they should be.

[Sixt8Chrgr]

Just put another one on there... new is better. Many times rebuilt units are not all that they should be.

Ok I will go with a new one.

[Sixt8Chrgr]

Musicman if I need to install in line pressure residual valves, are they installed inside or outside the master cylinder? Can you give me some details about this if in the event my wheel cylinders don't have the internal valves you spoke about earlier?

I want to ensure that I have a hard pedal at the top of the pedal travel. I need some insight on this please.

Thanks,

Lawrence

[Musicman]

The 10 psi aftermarket valves are installed in the brake line tubings themselves. You can install them somewhere in the lines coming out of the master if you like, one for the front drums, and one for the rear drums. They can be purchased at any number places : MP Brakes, Pirate Jacks, SSBC, etc...

[Sixt8Chrgr]

OK thanks

[Sixt8Chrgr]

Musicman thank you for all the help on the brake rebuild in my 68.

This is what we found:

Leaking master cylinder at the back of the unit
Installed a remanufactured unit from Auto zone because they had no new ones in stock. The remanufactured unit is working fine and was only $31 with no core replacement. I will probably rebuild the original and put it back on when I restore the car.
The rear brakes were not working at all. The rubber hose on the rear end had collapsed and no fluid was going to the rear brakes at all! Once we got the fluid to the rear brakes the wheel cylinders leaked so we put new wheel cylinders on the rear. The front wheel cylinders and the rear ones were very new looking but I guess the rear ones failed because they did not have any fluid in them? Who knows, but I now have 4 new or like new wheel cylinders.
The fluid was old and nasty looking when we pulled it through the system. We flushed the entire system with good fluid during the rebuild.
The brakes were horribly out of adjustment. We fixed all that and now my brakes work perfectly. The car is a pleasure to drive now. The power drum brakes are not that bad actually.
Again thanks for all the help.

Oh we did not have to put in the 10 psi valves.

Lawrence

[b5blue]

There you go! (or stop going)  The drums work well as long as you don't expect 100mph stopping power.

[Musicman]

Laurence

It's good to hear that you got everything going again. Congratulations on a job well done

Mike

[Sixt8Chrgr]

Thanks b5Blue and Musicman