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Brake system rebuild

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Jska View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jska Quote  Post ReplyReply Direct Link To This Post Topic: Brake system rebuild
    Posted: Nov/18/2017 at 8:47pm
Looking for help. First time brake rebuild on 1968 AMC Rebel. fr/rr drums both redone in the last 1-2 years, I am in the middle of changing out master cylinder and brake booster. I changed out both parts(both purchased from American Parts Depot) with no real problem, the pressure valve is out and I am at the bleeding stage. I bled the master cylinder, The problem is the peddle is firm, almost too firm to bleed the lines. While I am getting some bleeding action, it is taking a good bit of pressure on the peddle. The only thing that seemed different is that the control rod on the booster was about 3/16 or so inch longer than the original one on the car which took a little finesse to install but does fit.  Have i missed something ? could the booster be bad? rod too long? Any help is greatly appreciated
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Jska View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jska Quote  Post ReplyReply Direct Link To This Post Posted: Nov/19/2017 at 1:02pm
A follow up: I did the standard booster test and held the pedal down mid way and then started the car. there was no further downward movement in the pedal.
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tomj View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Nov/19/2017 at 10:34pm
the too-long pushrod could be a problem. it may be depressing the master cylinder piston with your foot off. is there a reason you couldnt use the original one?

do you have vacuum on the hose to the booster? it sounds like it is not working..

1961 roadster american
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Lyle View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lyle Quote  Post ReplyReply Direct Link To This Post Posted: Nov/20/2017 at 10:32am
Another place to look at.
You stated the pressure valve is out. Removed completely or just the switch and nylon pin?
The differential pressure valve may have moved and be stuck to one side blocking front or rear lines. These things stay in one spot and when doing a rebuild I like taking them apart to ensure the gunk is cleaned out, the pistons seal and are free to move.  Found a few with a heavy ridge in the bore that had to be fixed by boring/sleaving the bore.
 
 
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Jska View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jska Quote  Post ReplyReply Direct Link To This Post Posted: Nov/20/2017 at 8:55pm
Follow up: So I continued with the bleeding rotation with the stiff pedal. When I got to passenger side front wheel, the stiff pedal released when I began bleeding it and it began bleeding correctly and the pedal felt normal. I continued to the front drivers wheel and it bled as well. I went back and redid the rear wheels and they bled correct this time as well. The brake pedal feels good and a rode test was good. I failed at my attempts to re-install the pressure differential valve. It would not drop in. I initially took out the wire terminal, plunger, and spring. could the piston be tripped? and how do I correct this bleeding system again?
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