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Brake issues..... |
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dpimm
AMC Apprentice Joined: May/03/2014 Location: Tampa Status: Offline Points: 157 |
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Posted: Nov/11/2016 at 10:47pm |
I have been having some brake issues on my 68 AMX... I have 77 Matador 11" discs with the 3.1" single pistons calipers on the front. Originally car was
pulling to driver side. I replaced the passenger side rotor and swapped
the brake pads, bled the system 2X and now... no brake pedal. Someone
suggested that at least part of the problem might be that I am using
DOT5 brake fluid... but then I have read on other forums where plenty of
guy are using DOT5 with no issues. I have read some people imply that
with the silicone brake fluid the pedal always has a spongy
feel because the silicone fluid compresses more... but that is somewhat
hard to believe. HOWEVER, I decided to swap to a 76 Matador MC due to
its 1-1/8" bore instead of the 1" bore on the 68 AMX MC ( essentially will push 125% more fluid) and am swapping
in a new driver side caliper too. I also decided to add a line lock (just a
personal decision) and because I do not want to run another line from
across the entire firewall to run the front line for the line lock AFTER
the differential valve (not the proportioning valve) I am considering
doing away with the differential valve all together... not sure a light
on my dash is necessary to tell me I have lost brake pedal pressure. I
could move it over to the driver side inner fender wall near where I am
going to put the line lock, but not sure I see the need. BACK to the
DOT5 issue, I was thinking about flushing the system and going with DOT4
but not sure if that is really necessary. If I do flush the system,
what do I use, that will not destroy any/all the rubber seals in the
system????
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FuzzFace2
AMC Addicted Joined: Jul/05/2007 Location: Angier, N.C. Status: Offline Points: 10356 |
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Ok when you said "swapped pads" hope that was for new pads?
I would never do half a system like 1 rotor and then 1 caliper! Do both calipers, both rotors at the same time. I would also replace BOTH rubber hoses seeing the system is down now. On the master did you bench bleed the master before you installed it? If not you will never get a pedal. Sometimes once the master is benched bleed and cant get anything at the wheels you have to start at the master and at the first fitting after the master crack it to bleed. Once you have fluid move on down the line to the wheels. You also did not say how you were bleeding the system. I see your point on the removal of the valve for the light, don't need it to tell me I have no brakes when pedal is on the floor! As for the line lock if you are not drag racing the car every weekend WITH slicks don't add it. It just adds more things to the problem. BTW how old are the rear wheel cly and rubber hose? If old I would replace them with the new front parts and your brake system is like new. Dave ---- |
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TSM = Technical Service Manual
75 Gremlin X v8 for sale 70 Javelin 360/auto drag car 70 Javelin 360/T5 Street car |
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6768rogues
AMC Addicted Joined: Jul/03/2007 Location: United States Status: Offline Points: 6241 |
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I don't bench bleed the master. I open the bleeders one at a time starting with the closest to the master. Then I let it gravity bleed until fluid is running out with no air. It takes a while but I never had it fail.
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Located usually near Rochester, NY and sometimes central FL. |
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dpimm
AMC Apprentice Joined: May/03/2014 Location: Tampa Status: Offline Points: 157 |
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Fuzz- Everything in the brake system is new or rebuilt and was installed less than 200 miles ago. And I mean EVERYTHING. Rotors were turned, rebuilt calipers, new drums, new wheel cylinders, new pads, new shoes, new MC (this one is a 1 1/8th" bore MC from a 76 ( I thought perhaps the additional fluid it pushes might be good with the 3.1" piston calipers), rebuilt booster, new front and rear metal (not stainless) brake lines, all new brake hoses, pedal assembly was rebuilt/restored as was bell crank that goes from pedal linkage to booster, new proportioning valve (on rear frame frail). Literally EVERYTHING in the brake system had already been gone thru once already, again under 200 miles ago. As of last night I have put new (rebuilt) calipers on both sides, a new MC, swapped in another rebuilt booster I had for the other AMX that is in paint. I have gone around, cracked and re-tightened every fitting, gone through the TSM brake bleeding procedure 3X and pushed 2 bottles of DOT5 fluid thru just to make sure they were thoroughly bled.. I can get a pedal if I pump it a few times but on initial push it goes to the floor. I am not getting air when I bleed and do not see any obvious leaks that should be causing this. Perplexing... |
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Gelalthedamned
AMC Nut Joined: Nov/28/2014 Location: Athens ga Status: Offline Points: 376 |
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I'm dumb and had my calipers on the wrong sides upside down when I changed from drum to disc...are yours facing the "right way"?
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Calamity - 73 Gremlin X zombie rod (daily driver)
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dpimm
AMC Apprentice Joined: May/03/2014 Location: Tampa Status: Offline Points: 157 |
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LOL- yeah, mine are bleeder side up, but I can see how that could happen.
Dennis |
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mmaher94087
AMC Addicted Joined: Apr/01/2008 Location: Arizona Status: Offline Points: 1690 |
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"I can get a pedal if I pump it a few times but on initial push it goes to the floor." I could be way off here but do you have the correct length push rod for the master cylinder? I don't remember the length so I'm out of suggestions. Ross???
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Mike
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tomj
AMC Addicted Joined: Jan/27/2010 Location: earth Status: Offline Points: 7553 |
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silicone fluid (DOT5) does not have a mushy feel. it's an incompressible liquid, done and done. i ran it for 20, 21 years in my old classic wagon.
the 1-1/18" master cyl will make for a hugely stiff brake pedal, unless you have power assist. * larger bore = shorter travel + more force. * smaller bore= longer travel + less force. you may have gotten away with not bench-bleeding the master cylinder in the past, but i'd bet that's the source of your trouble now. i've had soft pedal on brake systems that i DID bench bleed, only to take it out, and do it again, and even though no more air than a 1mm diameter bubble came out, that fixed it. master cylinder bleeding is more subtle than it has any reason to. if it had enough air in it, for example a new master cyl filled with air, and the pedal is pushed, the rubber pistons can fold backwards and then it will never seal until its disassembled and repaired. been there, done that! for whatever reason, a tiny bit of air in the master cylinder ruins everything. a tiny bit in a wheel isn't as debilitating, and easily bled. |
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1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5 http://www.ramblerLore.com |
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dpimm
AMC Apprentice Joined: May/03/2014 Location: Tampa Status: Offline Points: 157 |
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UPDATE- re-bleeding the front reservoir of MC on the car. Pedal is great
until about the last inch of travel and then goes away just at the end
of the stroke. If I have the MC bleeder line submerged in fluid, the
pedal just goes slack... if I have it out of the fluid squirting into
it.... kinda looks like air is coming out. I thought this might possibly
be related to the rod length issue that had been mentioned by several
folks. I adjusted the rod all the way in and... pedal still
does the same thing. If I have the MC bleeding line submerged in fluid
it just goes slack at the end of pedal travel but will continue to pump
fluid after that with each time you depress pedal. If you you take the
bleeder line OUT of the fluid it will pump fluid, go slack at the end of
the pedal travel then it will not pump fluid anymore... Anyone ever
experienced this before? Never had this much of an issue with any brake
system I have EVER done. lol
Edited by dpimm - Nov/18/2016 at 10:24pm |
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White70JavelinSST
Supporter of TheAMCForum Joined: Aug/08/2012 Location: Minnesota Status: Offline Points: 4866 |
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FYI, it is somewhat critical that the master cylinder be mounted in the vice absolutely flat to ensure the bleeding process doesn't trap a bit of air in the master. I use a known accurate level for this purpose and place it on top of the master with the lid removed.
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70 Javelin SST, second owner, purchased 1972
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