No front brakes!

[351carlo]

So I was driving the mustang and noticed the rear brakes were doing most of the work, if not 90 percent of it. They were locking up before the fronts, and I could barely stop.

Well, I thought it might be air in the system. Bled the system. Got new Calipers.

Thought it might be the master cylinder leaking internally. New master cylinder. Bled the system. Shoots the fluid out of the bleeders.

Still have barely any front brakes, and the rears keep doing all the braking. I can lock the rears up, and still not feel a damn thing up front.

Any ideas? I've never heard of a proportioning valve just going bad, but that looks like the answer at this point.

 

[2nd Mustang]

What kind of brake setup and what kind of car?

 

[351carlo]

Sorry about that...

70 Mustang, Disc/Drum, Stock all around, Power Brakes.

 

[StaffAmerica74]

You could try adding an adjustable proportioning valve.

 

[ron67fb]

When did this start happening?
Did this happen suddenly, or did it get progressively worse? Do the rears lock up coming to a "normal" stop such as a light or stop sign, or a panic stop?

If what you say is true, that the front brakes are "not working", then a proportioning valve won't help a thing. It sounds like the front is working but the rears are just locking prematurely.

 

[krash kendall]

Sometimes, when fluid has been lost, the proportioning valve hourglass-shaped rod travels completely to one side of the journal locking out one resevoir. You have to open up the ports on it and use whatever small tools neccessary to move it back to center before re-bleeding your system. Pumping the pedal too fast while bleeding can do this too. Just to clarify, the ones with the hourglass-shaped rod trigger a sending unit to a brake/parking brake warning lamp in some cars (not specifically mustangs).

 

[Alarus]

Could the rear drums be too tight, i had to tigheten mine on my 73, i replaced the brakes and they were too loose i had to tighten them with the adjustment screw in the drumb (just a thought)

 

[grego37]

how much vacuum do you have

 

[351carlo]

I have a warning light. My problem occured after the car had been sitting for about a month, and the car had no fluid in it (Bad leak at rear of master cylinder).

The fronts are grabbing, just not nearly enough. The rears only lock if I slam the pedal, not on a normal stop. I'm assuming I'm just not getting the proper fluid pressure to the fronts.

I've bled them more than once. My only thoughts are the proportioning valve as it's the only thing I haven't done.

My vacuum is lacking, 244 duration .560 lift camshaft in a 351c motor. Still not the problem though, I can lock the rears up with the booster disconnected and the fronts still won't do jack.

 

[ron67fb]

How are you bleeding it? Did you try gravity bleeding it for a while? Sometimes the old pump-and-squirt doesn't get all the air out, especially if it ran dry at one point.

 

[351carlo]

How are you bleeding it? Did you try gravity bleeding it for a while? Sometimes the old pump-and-squirt doesn't get all the air out, especially if it ran dry at one point.

Bench bleed new master cylinder, pump 3 times, and one at a time afterwards. It's not air, I can almost guarantee it.

 

[2nd Mustang]

Just a thought, but when the brakes lock up, does it stop straight? My 67 power disc/drums used to do that after changing the booster. Found out the pushrod from the booster to the master cylinder had too much play in it. You have to get it just right or the brakes will lock up. The first time it happened, tapping the brake pedal helped, also stabbing the gas pedal released the brakes, so I assumed it was the rears that were locking up.

 

[67coupestang]

got me thinking about mine. so i cracked open the prop valve, sure enough the rod had traveled all the way towards the "front" end, severly limiting the pressure applied to the front brakes. I havent re-bleed the front yet but already I can tell a huge difference.

 

[Platonic Solid]

I have a warning light. My problem occured after the car had been sitting for about a month, and the car had no fluid in it (Bad leak at rear of master cylinder).

The fronts are grabbing, just not nearly enough. The rears only lock if I slam the pedal, not on a normal stop. I'm assuming I'm just not getting the proper fluid pressure to the fronts.

I've bled them more than once. My only thoughts are the proportioning valve as it's the only thing I haven't done.

My vacuum is lacking, 244 duration .560 lift camshaft in a 351c motor. Still not the problem though, I can lock the rears up with the booster disconnected and the fronts still won't do jack.

Getting brake fluid on the shoes can cause them to lock too. Replace them if they've had brake fluid on them.
.

 

[ron67fb]

Bench bleed new master cylinder, pump 3 times, and one at a time afterwards. It's not air, I can almost guarantee it.

That's what I thought too while chasing a low pedal on my car after changing the master. After hours of swearing I cracked open the bleeders, gravity bled an entire container through it then fabricated a home-made bleeder on the spot, and I cured it. The time it takes you to tighten the screw and yelling "pump" to your assistant, the air bubble has already gone back up.

Anyone can make one of these. A real time saver!