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Brakes won't let go! |
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IowaTom
AMC Nut Joined: Mar/07/2018 Location: Kent Washington Status: Offline Points: 448 |
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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
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6762 |
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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
AMC Addicted Joined: Sep/29/2008 Location: Central Illinoi Status: Offline Points: 9081 |
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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 |
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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
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6762 |
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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
AMC Nut Joined: Mar/07/2018 Location: Kent Washington Status: Offline Points: 448 |
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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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Trader
AMC Addicted Joined: May/15/2018 Location: Ontario Status: Offline Points: 6762 |
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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
Supporter of TheAMCForum Moderator Lost Dealership Project Joined: Jul/08/2007 Location: South Carolina Status: Offline Points: 19611 |
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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...
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Frank Swygert
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IowaTom
AMC Nut Joined: Mar/07/2018 Location: Kent Washington Status: Offline Points: 448 |
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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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