[79bird]

Alright, so one day my brakes were all of a sudden not working. I inspected everything at it looked fine. Tested the master cylinder and booster..Then my dad was apparently worried for "safety reasons", which i understand so he took it to a shop and they told us the master cylinder and the proportioning valve was bypassing. So I ordered the parts and my neighbor who helped me install them said its almost impossible for a proportioning valve to break, so we replaced the master only and bleed the system WITHOUT USING TUBING. Then when I first rode the car, the brakes felt better than when they were broken, but about 1/2 strong as they used to be.. To save cash i got a $25 master cylinder of Rock Auto, and im thinking that the cheap master cylinder doesn't work very good?? Or could it just be the PP valve that needs to be replaced? I checked the booster as well and its fine n dandy . Thanks!

Also, when I slam the brakes (when I was checking them) the wheels will not lock up anymore! It just decelerates when i slam it..

[LATECH]

Sounds like cheezie brake pads on the front (low friction co efficient) and possibly frozen wheel cylinders in the rear. Have you looked the entire system over?
Also if the pads in the front are rusted into the mounting area and wont move(without a hammer) then they wont apply well either. Believe it or not that is a common issue, especially in the rust belt.
Service the fronts pads/mount area, making sure the pads slide freely, check the rear to be sure the wheel cylinders move when you step on the brake.

[79bird]

Yeah but im pretty sure the wheel cylinders are ok, because the shop checked all of that..Isnt it true that the proportioning valve will only really affect the rear drums?

[LATECH]

If a system looses pressure, the valve shuttles and stops the fluid to the failing system top keep the operable sytem functioning, as a safety device.
Check to see that pressure is being sent to each system, front and rear alike. pressures will be different of course, but as long as you get action that would be an indicator the valve is not shuttled to one end closing down one system.
A RED BRAKE warning light on the dash that is illuminated( after bulb check) is a good indicator that the valve has shuttled and not operating both systems.

[79bird]

Ok.. Ill check that..But could it also be that the master cylnder is a cheap one?

[LATECH]

Probably not a defective master, its possible. Probably something you missed.
If the parts store will give you another ,throw it on, then youll know for sure
I bet its something else.

[66SSImp454]

You can pinch off all the rubber brake lines with some pinch off pliers or vise grips and see if the pedal is firm.

Make sure all air should be out of the system. I like to gravity bleed.

If firm, the problem is below the clamps. Then remove one at a time or only from/only rears and see if the problem is found.

If still soft with the hoses clamped off, then there are ways to isolate each components between, but if this is on your 79 then it can really only be the master or adjustments if available. You can use the plugs you used to bleed the master with it still on the car and see if it is still soft.

I have my doubts on a proportioning valve, all that does is control the pressure so that the rear brakes get a little more force. I think more of a lock up issue would happen.

Sometimes safe hard stops fix it all. Like something gets pushed into place.

Let us know.

[alkey]

diyou bench bleed master cyl before installing?