Does a stock 4 wheel drum brake Maverick have a proportioning valve???

I basically have two QUESTIONS that I hope someone can anwser for me.
#1 does a stock 4 wheel 9 inch drum brake (4 lug) car have a proportioning valve???

#2 can someone read what I am writing below and tell me what they think could still be wrong with my cars brakes AFTER I have replaced 95% of all the parts in the brake system.

Here's the scenerio. My yellow 72 sat for a month or two and when I went out and jumped in it one day the brakes went clear to the floor, if you pumped them 2 or 3 times really quick they would come back up and stop the car and hold fine as long as you keep some pressure on the brake pedal. You literally could keep your foot on the pedal for 10 minutes or longer after pumping them up and the would not bleed down and go soft so I mentally eliminated a leaky line. The minute you release all the pressure from the brake pedal and then try to hit the brakes again the pedal goes to the floor, then if you pump, pump, they come up again.

I figured it was just an air bubble int he line for some reason because there is no brake fluid anywhere on the ground under the car so I was going to just bleed the brakes and see what happened, well all the bleeders were frozenrusted and wouldn't break loose so I just bought all new brake parts I essentially replaced everything, front to back, from the master cyl. all the wheel cylinders, all the hardware kits, self adjusters the front rubber lines, shoes, the whole 9 yards you get the point. The only thing I didn't replace was the the one rear rubber line because it looked ok and appeared to have been replaced not too long ago. and if the car has one I did not replace the proportioning valve.

Well my Bro-in-law did the work and everything was great for 2 days. Brakes worked well everything was right with the work\ld because I had my maverick back to drive to work.

I drove the car approximately 200 miles in a course of two days and on my return trip home last night the brake pedal went clear to the floor again.
Same scenerio as before, it goes to the floor the first time you push the pedal, then if you pump it 2 or 3 times real fast it comes up and holds as long as you keep some pressure on the pedal.

So I am thinking that since a proportioning valve for a disc-front/drum-rear brake car part of the job of the valve is to keep pressure in the lines going to the drum brake wheel cylinder that maybe if the 4 wheel drum brake car has a proportioning valve that maybe it is screwed up and not keeping the pressure in the line going to the wheel cyl.

The left side of my brain is saying that it is an air bubble in the line and the brakes just need to be bled again and it is just a coincidence that the brakes are doing the exact same thing they were doing before I had ALL new parts put into the brake sytem..

So what does everyone think is it still an air bubble in the line that worked it's way to one of the wheel cylinders or does the car have a proportioning valve and that is the culprit? Is there a pin hole leak somewhere that is sucking air but possibly not big enough for me to notice the fluid loss on the ground under the car? What do you think?

Also for the guys that have a disc-front/drum-back brake setup where is the proportioning valve located? Is it under the car or is it under the hood next to the master cylinder??

 

Any 4 wheel drum brake car I've had, had a proportioning valve.
Did you replace the master cylinder?

 

I am not positive if you call it a proportioning valve or a distribution block. On the F100's with all drums there is a block where all of the brakes lines come together, then one line runs to the rear and the 2 front lines go their way. That block also houses the brake warning light in it in the case you loose pressure in either the front or back the valve moves one way or the other causing the warning light to come on.
Did the master cylinder get bench bled before it was installed?
Too me it sounds like it is master cylinder related. Like the 1st time you step on the brakes the piston in the M/C doesn't have enough seal to compress the fluid. After a pump or 2 it gets it's seal and holds the pressure until you release it. Usually though if the M/C is bad it will bleed done under steady pressure. Also a M/C can leak and never drip on the floor. Look up under the dash where you can see the master cylinder boot, pull the boot back and see if there is fluid running down under the carpet.
clint

 

Those are symptoms of a bad master cylinder. Did you replace it? Your list says from the master back. I assume you did the master first. Regardless any time you open up a system with an old master and bleed it you should replace the master. When you bleed brakes the master goes beyond its normal range of travel and its really common to damage the seals inside.

Yes it has a prop. valve. If it was stuck you wouldnt have got fluid at all 4 wheels when you bled it. If you did replace the master dont rule it out as bad. Seen many rebuilt masters fail. Some out of the box. Tough to diag over the net but I hope that helps.

 

Ford uses what they called a COMBINATION VALVE. The combination valve has four jobs: 1. Distributing fluid, 2. Proportioning, 3. Pressure differential sensing, 4. Metering valve. All cars from mid 60's and up used this valve

 

Yes, I did replace the master cylinder. I just went out and pumped the brakes up and held my foot on the pedal for at least 5 minutes and they do not leak back down, the pedal stays completely firm, I did this at least 5 or 6 times and then looked under the hood and all around under the car and cannot find a drop of fluid anywhere.

I do se the "proportioning" Valve under the hood next to the master cyl. but I am assuming that on a 4 wheel drum prake car it is more of a distibution valve/place to put the brake warning light sensor

 

I would bleed the brakes again.

 

Also look under the carpet under the driver's side. The Master cylinder can leak and the fluid run down under the carpet.
clint

 

check the brake light warning switch for leaks...it was sucking air with little notice of a leak.

Exactly what mine done

 

Drum or disc it still has the same function just a different calibration. Any car needs more front brake than rear. Thats its job. The valve inside is held in center by front and rear pressures. If the pressure drops front or rear you should get a warning lamp assuming it works. If they pump up and stay hard for 5 minutes your not likely looking at a leak. Even a tiny leak you'd be surprised how fast the pedal drops. Try a bleed to see if you get any air. Did you bench bleed the master first?? You said it was fine for 2 days though right?? So what would have changed after 2 days of use?? Something must have failed. I would still be suspect of that master. Seen too many fail. I wont even install a rebuild at work apart from one local builder who is not cheap but good. They did a clutch master for me for a 500 horse Pantera I work on. Thats how much I trust that re-builder. Short of that everything gets a new unit.

 

another vote for the mastercylinder. the described problem is clasic master cylinder failure.

 

I didn't get to do anything with the brakes this weekend. was busy on Saturday and my back was acting up on Sunday. So I guess I will try bleeding the brakes again and see what happens. I am not positive but I do not think anything was bench bled before installing which I know leaves a lot of air to get rid of. My guess would be air in the line that finally worked its way to a spot that it is now affecting something. But my second thought was the master cylinder.

I guess I will start with bleeding them again and see what that does. If that doesn't fix them I guess it is time to take the master cyl. back and get a new one even though I just bought the one that is on there. I have dealt with these parts places enough that I do know that even though you just bought a part there is no gaurantee that it is not bad right our of the box.

Thanks for all the opinions, you all just helped to confirm my thoughts on the subject... It's always nice to have asecond opinion

 

You got to bench bleed the master first. You can bleed the wheel cylinders all day and never get the air out of the master

 

...and another vote for the master cylinder. Over the years had lots of master cylinders fail this way...and they don't have the be leaking on the outside, then can leak internally. I also agree with the bench bleeding. You've gotta bleed a new (remanufactured, rebuilt, whatever ) M/C on the bench 'till you don't see any more air bubbles, otherwise you'll be pulling your hair out trying to get it to work. I've also had rebuilt master cylinders fail right outta the box...

 

My Bro-in-law did the work and he is normally pretty good and thorough. so he very well may have bench bled the master cyl. I am not positive. I'll ask him when I get a chance.