76 Highboy brake issue.
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New User
Joined: Feb 2002
Posts: 16
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76 Highboy brake issue.
I've got a bit of a problem with the brakes on my 76 highboy. Everything except the lines and booster is about 2 months old. They worked great until the other day when I tried to stop and the pedal suddenly dropped to the floor. After 2-3 full pumps it'd build and hold good pressure. My first guess was that I had a front wheel bearing coming loose. Both were loose and were subsequently adjusted. I also re adjusted the rears while I was at it. Problem still exists but it's down to 1 pump and then a nice high and tight pedal. If I push it to the floor during the initial application the LR will lock up, but nothing else. No leaks, MC is full. The symptoms and sudden onset of the problem have me leaning towards a bad MC. The only piece that doesn't really fit is the lack of a falling pedal under pressure. I'm assuming that the cups are bypassing, but still seal well enough that they'll hold pressure once there's some back pressure to expand them. Anyone agree, disagree, have any other ideas? I'm open to suggestions. Thanks.
Postmaster
Joined: Oct 2008
Posts: 3,026
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From: Renton, WA
I had a simalar problem that turned out to be the master. My pedal would randomly drop to the floor on some brake aplications or if I held my foot on the pedal in anticipation of stopping, but the pedal didn't fall under constant pressure. So I guess I agree master.
But one thing to try, push the parking brake down a click or two, not enough to stop the truck but enough to put a little pressure on the rear pads. Then try the brakes, do they feel better, if so it's in the back.
But one thing to try, push the parking brake down a click or two, not enough to stop the truck but enough to put a little pressure on the rear pads. Then try the brakes, do they feel better, if so it's in the back.
