brake problem

I searched first but did not find an answer to my problem. I have disc brakes on the front of my 51 and drum on the rear.The master is hanging on the firewall.I noticed the front brakes were dragging when I came home the other night.I jacked the car up and found the fronts to be dragging.I can push the piston back on both sides of the car with a screw driver and they will spin free.I tried bleeding them and it appeared the master was not right so i got a new one.I tried it today and found that it was not the fix.I broke both the lines free that run from the prop valve to the calipers and they spun free.The interesting thing was when I put the lines back on the prop valve the brakes worked correctly a couple of times. It acts like when the lines are full of fluid that it does not return correctly to fully release pressure.I am at a loss right now. I am leaning towards the prop valve, it is a non adjustable one and is mounted on the frame. I would appreciate any help. Thanks

 

If your master is on the firewall then you dont need a residual valve on the disc brakes.

 

So your saying I can remove the proportioning valve and run the lines right into the master?

 

The valve may be sticking in the bore of the master, or the little return hole or holes are pluged in the resevoir not allowing all the fluid to return.


My Speedway 40 style master didn't come with the hole drilled. It acted almost like a one way check valve.

 

Sounds like the gap that needs to be between the master cylinder piston and push rod is not there or something is not allowing it to release properly when your foot is not on the brake pedal. You can check the gap with clay or maybe by feel. MP Brakes make a checking gauge, but it does not fit some masters. The clue is that when you crack the bleeder, the pads release the rotor

 

I bench bleed the master and it worked good as it is new. I can crack the bleeders and the calipers will not retract on their own only if I push them with a screw driver.When I had the lines off the prop valve and I pushed the pistons in fluid did come out of the lines as it should.

 

Proportioning valve and a residual valve are not the same thing. A residual valve holds pressure in your lines when you release your pedal. I think you have a bad valve or the wrong pressure valve. Drums take a 10lbs valve abd discs take a 2lbs valve.

If the master is higher than your caliper, you don't need a residual valve on your discs.

 

I have a tough time thinking it is a blocked/not drilled correctly master cylinder since you replaced it. 1 being that way? Ok, maybe. 2 in a row having that same issue? Not likely.

 

So the valve that I have on the frame is a residual valve? It is about 5 inches and has the lines from the master running to it and the line to the rear out of it as well as the lines to the front.

 

Its more than likely a combonation valve. What is it out of? What is the master out of? It sound to me like you have a 10lbs (drum brake) residual (check valve) on your disc brakes.

Basicly, it sounds like your valve is one that was designed to have 4 wheel drums.

 

Was this a fresh build? Or was it a 4 wheel drum brake car and you just added discs?

 

It came with the set up and it has mustang 2 front and 8 inch drum rear.I drove the car for awhile and it worked fine.I will try removing the valve in the morning. Thank you.

 

Before you go eleminating blindly, do a search on residual valves. It sounds to me like they gave you the drum/drum combo valve and not the disc/drum one or it is no longer working right.

 

what master is it????, it sounds to me as if it is a drum master and not disc drum master, pads on disc always rub slightly but not to the point they get noisy, id say residual in cylinder all the way here

 

Not sure what master it is but it is a typical large reservoir in front and small in back. I am not sure what make the system is , I did not build car.

 

if as you say you open the bleed screws and the wheels still drag then i say it is your calipers sticking, opening the bleed screw eliminates everything but the calipers as a problem.

 

I thought about that but seemed odd both would be bad at the same time.

 

1. How much drag? Disk brakes will always have a slight drag on them as there are no springs to retract the pads like drum brakes have for the shoes.

2. Going back to what Dane wrote in post 3. Do you have a bit of slack in the pushrod from the pedal to the master cylinder piston. If not it will keep the return port to the cylinder covered and not allow the fluid to flow back in the master cylinder properly.

3. Disk brakes usually take a 2lb residual valve while drum brakes use a 10lb residual valve. Usually with the combination valve you shouldn't need any additional residual valve.

 

I think that is the issue right there.

 

Normally drum/drum masters have equal size reservoirs, disc calipers need more fluid so have masters with a larger reservoir for the discs. Make sure you have the disc brakes plumbed from the larger reservoir and going to the correct ports on the combination valve. Pictures would be a big help.

 

The rotor will not make a half a revolution when turned. I know that is too much drag but why is what I am wondering.The master is correct. I adjusted the rod from the pedal so it has no pressure on pedal and it did not help.I will crawl under car and check valves.It looks to be plumbed correctly when I took the lines off. I thought I saw what I thought was a coupling but it just might be a residual valve.

 

If it is, does it say 10 or 2 anywhere on it? What color is it?

 

Well the mystery piece was just a coupling , brass about an inch long.The combo valve is plumbed as follows.... the lines come into the top on each side of the idiot light switch. The bigger line is to the rear and the smalleis to the front... Straight out of the rear is the line that goes to the rear brakes...9/16 I think. The other 2 lines go to the front brakes idependently of each other..there is no T in the front lines they each go straight to the rubber lines...

 

Proportioning valve or Combination Valve

Residual valves-

 

yep looks just like the proportioning valve

 

Ditto, Remove the residual check valves. #14 is also correct,...Calipers do not "retract" when brakes are released. And, as stated, be sure the pedal pushrod is correctly adjusted. That alone, can produce the problem you're having.

4TTRUK

 

I do not have residual valves only the combo valve.I can pull pedal up so it does not touch rod and issue is still there.I am pretty annoyed at this point. I just do not want to toss more money at it until I kow it is right.

 

I agree with budd .When you opened the bleeders you eliminated the rest of the system.Calipers are your problem.

 

just a jump in the woods here but are those lines to master in the right port there is a front and a rear, now just say for instance they are, the internal residual valve( which most have for rear drums) in the actual master cylinder would be holding drum pressure to the fronts (if its a disk /drum master) therefore causing excessive drag

i would take the line from front port out and check if theres one in the port, you can take rear out also and compare the two ports to see if theres a big difference or not in the hole inside the port????? just throwing ideas here


also disconect that valve in the line and see if it releases the calipers a bit more, they are definately dragging to much from sounds of it, u should be able to get a good 180 spin with a flathead screwdriver in ur wheel studs if this makes sense, and with wheel on u should be able to get 360 spin or more with ur hands

 

All of this is on the right track. Residual valve where one is not needed, drum/drum master cylinder, wrong plunger adjustment, lines reversed, and one more thing to consider. Check the rubber lines up front. Have seen cheap one go bad. Lining swells up and restricts the back flow of the brake fluid.

Good luck