Customs Disc Brakes Holding Pressure

I acquired a 63 Galaxie recently. Previous owner did a front disc brake conversion (booster with dual master cylinder that looks like it is from an early 70s mustang, drilled slotted discs with braided lines). My test drive of the car went well and the brakes were solid. Now that I've owned the car for a little bit it felt like the brakes were dragging. Sure enough, I jacked the front and the wheels turned, but there was significant drag. I unbolted the master from the booster thinking that the rod was adjusted too far, but that didn't release the brakes. I cracked the bleeder at one of the calipers and they released. Thinking it might be the master cylinder, I picked another one up at the local parts store from a 72 mustang with front disc brakes. Changed it out and bleed the system well, but still holds pressure. Interestingly, the car does not have a proportioning valve, but stopped well without locking up the rear. Any ideas on what to do? Why is it not releasing the pressure?

 

Good chance it's the rubber lines collapsing internally.

 

Pedal return not allowing the MC piston to return al the way, blocking port?

 

I pulled the MC away from the booster (brake lines still connected) and the brakes were still dragging. And the flex lines to the calipers are steel braided flex lines, not rubber. Can those fail?

 

Are there check valves in the master cylinder?

 

Loosen the nuts that hold the booster to the firewall, and see if the brakes release.

Also, check the bolt that holds the pushrod to the pedal.

A lot of Fords in that era had an eccentric bolt that could be used to adjust pivot position, and thus the effective length of the pushrod.


If this is misadjusted, it will stop-out the pedal on the bracket, and apply the brakes.

 

Not sure. Looks like a regular MC to me. Two pot. Large reservoir to the rear for the disc brake circuit.

 

I was thinking that initially and was going to troubleshoot that more, but I pulled the MC away from the booster and the brakes didn't release. That would eliminate any pedal to boost issues. One thing that I noticed is that there is a four way block for the front brakes. One line comes down from the MC to the block, two lines go from the block to the calipers and the last line as about a 6" line coming up and terminating into a brake pressure switch. I wonder if there might be a column of air in this that is not allowing the calipers to retract all the way. I'll have to try and bleed that tomorrow.

 

The large reservoir is runs to which circuit exactly?

 

Try cracking a bleed screw on the other side [and check both wheels to spin freely]
Flap in the brake hoses should only effect one side.

If it has an early Mustang Drum / Drum Master Cylinder it will have 2 residual valves

 

You will need to check something, and that will involve disconnecting the front brake line from the master cylinder.

The inverted flare of the brake hard line sits against a cone at the base of the threads in the hole where it attaches.

You need to observe the cone and see what it is made of. If it is the same Iron that the remainder of the master cylinder is made of, you're ok.

If that seat is made of brass, then the master cylinder has a residual valve in that port.

Report back what you find. If there is one there, there is a procedure for removing it.

 

Brass cones:

Those have residual valves behind them.

 

Yes, I promise you, they are not steel through their core.
A common occurrence is that the innards can decay and cause a blockage of returning fluid.
the result is dragging pads.
I would invest in new flex hoses. ( either type )

 

It will be simple to find out if it is the residual valves in the master or the brake hoses. Crack the lines at the master and if it releases the brakes it's the master or the residual valves. If that doesn't release the calipers, crack the bleeders on the calipers. If that releases the calipers it's the hoses.

 

Exactly what I had to do on a 70’s OT car recently. In my case it turned out to be the flexible lines.

 

Is that four-way distribution block possibly a residual pressure block?

 

The " braided" is a covering , inside that is the fluid carrying " hose" summer plastic/ rubber product that can collapse . start at the m/c ,open fittings until you find what relieves the pressure .

 

So they release when you crack a bleeder. That means there is a blockage somewhere in the system. If both calipers release when you crack a bleeder, then the blockage is somewhere in the single line part of the front brake system. I would apply the brakes to the point that you can get them dragging when the pedal is released and crack the line at the master cylinder. If the brakes release, the problem has to be in the master cylinder or the pedal. If they do not release, follow the line to the next connection and crack it there. Keep doing that until you reach a connection that releases the brakes when cracked. Your problem is in that section of line.

 

Update. I bleed the line that goes up to the brake switch from the 4 way block. No help. I can release the pressure from that block to release the brakes and I can crack the line from the MC and release the brakes. Tells me there is an issue with the MC I guess. The MC is casting number 2227091 (late 60s early 70s mustang). I found the casting number for the calipers which is 499 (late 70s -80s GM). Would the Ford MC hold pressure on the GM calipers? Something built into the MC? Or do I have 2 bad MCs and need a 3rd?

 

Take off the line for the front disk brakes from the master cylinder. Shine a light in the port in the master, and if you see a brass piece, it is a residual valve. Screw a sheetmetal screw into it and pull it out. Re connect the the line to the master and see if that fixes the front brakes dragging.

 

You need to reuse the brass piece for the mating surface
@smokinjoe3 This shows removal on the rear circuit, but it also applies to the front circuit

 

Thanks for the tip. Wouldnt think that there would be a residual valve on the disc brake side of the MC becuase it is a disc/drum MC but you never know. I'll take a look at this tomorrow and let you all know. And thanks for the tip!

 

Post a picture of the distribution block when you get a chance. What did a factory '72-ish Mustang use?

 

Looks like a factory 1963 piece. I don't think there is any valving in it. As stated, brakes release when I crack the line at the MC. I'll be checking for a residual valve in the MC later today.

 

Thanks for all of your responses. Residual valve found and removed. Brakes bleed. Success! Brakes work good!

 

See post 20. Your welcome.

 

Every so often I get it right.

Happy motoring!

 

50/50 You either get it right .............. or you don't

@smokinjoe3 Glad it's all sorted [Now you can drive the wheels off it]