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Brakes won't let go!

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IowaTom View Drop Down
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    Posted: May/04/2021 at 3:33pm
Getting a bit discouraged over my front (Scarebird) discs on the '59 Super.
I replaced hoses, again, and just now bled out rebuilt calipers from NAPA only to have the problem continue.  After running the car to rebuild pressure in the vacuum booster, I pump the brakes a bunch of times to get a good pedal then try to move the rotors by hand.  No luck.  I take a screwdriver and between the studs try to move them - only with great effort.  (Wheels and tires not back on yet)
You might think I have a residual check valve in my M/C but I don't, and no check valves on the way to the wheels.  Just direct lines from the master to the calipers.
I even removed the fitting at the reservoir to the front discs on the master and inserted a small but stiff wire.  It went in at least an inch, maybe near two with no resistance telling me there NOT a residual check valve.  The brakes bleed easily and freely but the wheels seem to tighten up way too much.
Any thoughts?  Thanks, Guys!
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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2021 at 3:58pm
Do the brakes release when the engine is not running? No engine running, do the brakes operate as would be expected, harder pressure to clamp but releasing when foot is off the pedal?

A link to some diagnostics, scroll up and then back down to read the complete article:


Edited by Trader - May/04/2021 at 4:49pm
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304-dude View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2021 at 4:54pm
Some new master cylinders need the apply rod adjusted. I did a wee tare down to show an OEM master has multiple shim washers on some units, keeping the piston further in, while at rest. Without the shims, the piston will cause the fronts to apply, without pedal travel, on booster brake systems.

I think there is a thread on the apply adjustment.

Edited by 304-dude - May/04/2021 at 4:56pm
71 Javelin SST body
390 69 crank, 70 block & heads
NASCAR SB2 rods & pistons
78 Jeep TH400 w/ 2.76 Low
50/50 Ford-AMC Suspension
79 F150 rear & 8.8 axles
Ford Racing 3.25 gears & 9" /w Detroit locker
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Trader View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2021 at 5:11pm
As 304-dude states, even if mix matching, manual or boosted brakes, there should be 0.025" free play between the pin and the master cylinder. This can be measured before installation. Though on some systems you have to be a little creative to get this measurement from the mounting surfaces.
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IowaTom View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote IowaTom Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2021 at 6:08pm
Guys, I think that's been my problem.  I loosened the nuts holding the M/C to the booster and the wheels turn as they should.  I bought one of those H shaped tools for finding the .025" and actually did, but it's time to readjust.  Sheesh, I thought once adjusted you were good to go.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: May/04/2021 at 6:29pm
Good to hear Tom.
I have one of those silly tools and still use an old push rod to measure to the back of the master cylinder and then measure to the mount face of the master cylinder to get my depth. Then measure and set the pin from the booster.
The "H" tool I bought years ago for $10 is worthless except for collecting dust!
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farna View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: May/05/2021 at 6:55am
If all else fails you can use a washer or two between the MC and booster. Won't hurt a thing, and on the positive side is the pushrod seal on the MC starts to leak you'll see it, won't leak into the booster! If the rod isn't adjustable that may be an option...
Frank Swygert
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IowaTom View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote IowaTom Quote  Post ReplyReply Direct Link To This Post Posted: May/14/2021 at 9:30pm
Exactly what I did, Frank!  Works like a charm.
I kick myself for replacing hoses and calipers when all I needed was two 3/8ths washers.
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