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AndreiMustang
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Aug 3, 2017, 5:45 PM
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Brake calipers stick
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1969 Ford Mustang 6 cylinder 200 ci
Hi guys, I have a 69 mustang coupe and I just installed front disc brakes. They were wilwoods from cjponyparts and came with braided lines. After installation, I also replaced the master cylinder with a new one from AutoZone and I bench bled it no problem.
I bled the lines for the front (ignore rear brakes since its a dual bowl master cylinder) and pushed the brake pedal. It felt firm and stopped the brakes as it should. However, once I let go of the pedal and it sprung back to it's original location (like it should again) the brake calipers retained pressure. I couldn't move the wheels in the front. So i released the pressure on the bleeder valve on one side and then they worked again.
However, every time I push the brake pedal the calipers stick because there's built up pressure somehow. And I have to release the bleeders to get them to move again. Any idea how this is happening? I have manual brakes and I used a new master cylinder designed for manual brakes drums all around.
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Hammer Time
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Aug 3, 2017, 6:33 PM
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Re: Brake calipers stick
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Is it possible there are any kinks or sharp bends in the flex hoses?
Did opening one bleeder release both wheels?
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Sidom
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Aug 3, 2017, 8:08 PM
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Re: Brake calipers stick
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You can also double check the pedal height..... The the rod off the pedal and see if that releases the calipers...
You say you installed disc brks... Were you replacing frt drum brks and if you did, did you also install a proportioning valve into the system?
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Hammer Time
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Aug 4, 2017, 5:44 AM
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Re: Brake calipers stick
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The next time the brakes lock up, instead of opening the bleeder, loosen the mounting bolts for the master and pull it away about half an inch. If that releases the brakes, then your problem is the pushrod for the master is too long and not allowing the master to relieve.
There must be a very small amount of free play before it moves the internal piston.
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(This post was edited by Hammer Time on Aug 4, 2017, 5:45 AM)
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Tom Greenleaf
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Aug 4, 2017, 6:52 AM
Post #7 of 23
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Re: Brake calipers stick
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Question on this whole thing? From top, "I added disc brakes" -- does that mean this had drum brakes before that? I plead I can't know but many vehicles didn't have disc brakes unless you also had a V8 - Mustang may be an exception?
This would mean there's residual pressure from proportioning valve to keep wheel cylinder cups from leaking plenty of return spring force to overcome that but not a disc style?
Are these 4 piston calipers or two piston calipers or unique and one piston floating calipers now? 4 and two as I recall were on Ford products and drums on some but no floating one piston ones yet for 1969.
It was already mentioned to release pressure and see if they free up - I would do that. Now just see how little pressure with your hands (engine off) it takes to make a rotor drag with hands only - it's a lot. In use they would get hot and the pressure even worse but limited not locked tight if no serious kinks or parts failures.
I can't know they made a zillion Mustangs with assorted options that varied wildly - lame 6 cylinders that were plenty to nuclear powered V8s with alterations and components that could barely handle that.
(explaining the 'residual pressure thing') like a "T" handle old air pump with a cut if pressure was applies fast it held cup tight. If slow it allowed air to pass without making pressure - same idea with cups of wheel cylinders for drums vs disc brakes that don't use springs to retract can't take residual intention force at all,
Tom
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Tom Greenleaf
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Aug 4, 2017, 9:53 AM
Post #9 of 23
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Re: Brake calipers stick
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Follow the brake lines - this should/must have a proportioning valve! 1967 DOT mandatory dual systems front and rear the reservoir closer to firewall is for fronts has its own line is separate in essence from the rear or should be.
This ends a decade or so of the platform it's on which is that of the original Falcon shares a lot. That all changed in 1970. You have dragging brakes for the exact reason I said if not done via a proportioning valve it's done at the master cylinder but don't recall that?
As I said and just look at a wheel cylinder how it's cupped pointing one direction. That would collapse and pour out brake fluid early if it wasn't under pressure from the last touch of the brakes - it has to do that all makes.
So it's not that 4 piston caliper at fault with your test proved it wasn't.
Techno trivia fact: A disc brake retracts just the smallest bit from the torque on the squared "O" ring seal of each piston. You don't see that but look at a disc brake with another person applying them then releasing them it will move back just a smidge right in front of you.
Side note on that caliper: Do change out fluid often on those when this is solved. They froze early from just water, moisture, humidity just not very well sealed up but the idea is even pressure on pads vs super simple single piston floating calipers that came later. It's very sensitive to bearing adjustment and a very true rotor as they can't "float" with any warp to them sometimes just when warm/hot. When perfect you do get far superior braking that is almost not going to fill with dust or dirt nor pull for a mile of braking if wet from like a puddle as drum brakes about all do.
Look for or add the right proportioning valve for a disc brake model even if it has none now the disc brake version had to,
T
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Hammer Time
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Aug 4, 2017, 11:15 AM
Post #10 of 23
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Re: Brake calipers stick
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I don't think a proportioning valve is the issue here.
An incorrect proportioned system may apply too my pressure to either the front or the rear but will not keep the brakes applied after release. There is a real good chance the proportioning is built into the new master anyway.
This could be as simple as adjusting the push rod for the master.
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Hammer Time
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Aug 4, 2017, 11:16 AM
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Re: Brake calipers stick
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Then try cracking the line open at the master and see if that releases them.
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Hammer Time
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Aug 4, 2017, 11:26 AM
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Re: Brake calipers stick
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That means the master is the source of the problem. It could still be related the the pushrod length. Just because the rods are the same length, doesn't mean the piston socket in the master is the same depth. It's one or the other to blame.
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Tom Greenleaf
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Aug 4, 2017, 11:27 AM
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Re: Brake calipers stick
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Pushrod if even any question must have some free play. You may think it's identical and if touched or changed may not be. Loosen it while intact if suspect if that would also release brake pressure.
Wear on just how it's pushed inside too,
T
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Hammer Time
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Aug 4, 2017, 11:33 AM
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Re: Brake calipers stick
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That's not what I asked you to do. I asked you to loosen the master cylinder mounting bolts. There is a difference.
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Hammer Time
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Aug 4, 2017, 11:37 AM
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Re: Brake calipers stick
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If you're that confident, change the master.
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Hammer Time
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Aug 4, 2017, 11:52 AM
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Re: Brake calipers stick
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No, you either have a bad master or a pushrod not releasing all the way.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
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Aug 4, 2017, 12:23 PM
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Re: Brake calipers stick
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By now I'd just change it. Order it for the model with DISC brakes. The reservoir should be larger towards the firewall as that section is fronts first, larger because as pads wear fluid displaces the wear - drum brakes don't use squat to displace wear is why. Those old type calipers do take some fluid just by themselves to fill.
"Not all the familiar with brakes!" You will be. Bleed master on bench first as per instructions that are usually with it or ask. Then ALL wheels in order, RR, LR, RF then LF. Calipers tap on them to get last bubbles out,
T
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