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Front brakes stay engaged

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72_AMX View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72_AMX Quote  Post ReplyReply Direct Link To This Post Topic: Front brakes stay engaged
    Posted: Jul/26/2020 at 6:36am
Morning. I need some assistance The Front disc brakes on my 72 AMX staged slightly engaged. So far I have replaced the master cylinder both front rotors, calipers, pads and brake hoses. Any ideas or suggestions on what could be wrong. When the car is moving I can put it in neutral and the car will come to a stop and stay in place even on a upward incline. the petal has almost to travel to it and is stiff. Thanks

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6768rogues Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 10:28am
Are you sure you have a disc brake master and not one for drum brakes?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 10:50am
Disk brakes need the residual check valve removed at the master cylinder just inside were the disk brake supply line attaches to the master.
Many masters will ship with residual check valves installed regardless of intended use. I'd be check this first.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote purple72Gremlin Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 11:58am
And or did you make sure the slides are free?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 5:09pm
Thanks for the info. I will check on the check valve and slides. I thought the slides where free but will check again. I did not know about the check valve. Thanks again for the info.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mramc Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 5:36pm
Also check the front brakes hoses, some times they collapse internally . You may not see it, but if your brakes hoses have not been changed in 50 years , time to do so. They are not good forever. LRDaum  
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 5:51pm
Thanks will do
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Fluffy73 Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 5:53pm
Check to make sure you were given the correct master cylinder. I chased the same issue for years.  Turns out there is a master cylinder available that looks identical to ours but has the reservoirs swapped. Make sure yours has the small reservoir to the front.

For years, my car had issue with the fronts dragging and under hard braking the rears would lock up.  After I changed out a broken axle, I went to bleed the brakes and opening the rear circuit, the large reservoir in the master began to drain. Wrong Circuit!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Twisted70amx Quote  Post ReplyReply Direct Link To This Post Posted: Jul/26/2020 at 6:13pm
Not sure what your history is with the car but if it wasnt checked when replacing the MS the brake booster pushrod length might be too long. That'll cause a firm pedal and keep the brakes engaged. There's a tool to check it but it you go to push your MS onto the booster and there a small gap before you apply pressure or tighten the nuts I'd say it's likely your cause. The tool checks with it disassembled. Good videos on YT on how to set it up. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72_AMX Quote  Post ReplyReply Direct Link To This Post Posted: Jul/29/2020 at 4:24pm
Thanks for the follow-up. I did check the Master Cylinder and the small reservoir is in the front. I talked to the mechanic who installed the MC and asked him about the push rod. He stated that there was not a problem that he could tell when he installed it. I still have the original MC and will send it off to be rebuilt just in case. We are going to replace the brake hoses and see if that works. Any ideas on if the hoses are bad could the interior pieces of the hose contaminate the channels in the calipers? Any suggestions on a good brake MC and Caliper rebuilder.
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