75 F100 - Calipers locking
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Joined: Aug 2004
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75 F100 - Calipers locking
I have a problem with my 1975 F100 front calipers locking. My truck was not braking very well and the pads and shoes looked a bit worn so I did some brake work this past weekend. I just replaced my rear brake shoes and replaced both front calipers and pads. I bled the system and cranked it up for a test run and I noticed that I was having trouble moving the truck. Both front calipers were locked. Initially I thought the new calipers were bad so I put the old ones back on but I had the same symptom. I have determined it is some type of hydraulic problem because once I release the pressure on the line the cylinder will go back into its bore and the front wheels turn happily for as long as you don't apply the brakes again. Once you hit the brake pedal, the fronts lock up and remain locked for an uncertain amount of time (I let it sit for a few hours and came back and the wheels would turn). So my question is - wth am I doing wrong here? 
I read some stuff about the proportioning valve but nothing really describing my situation - most of the complaints related to that appear to be about not getting brake fluid through the lines. My fluid flows like a champ when I press the pedal to bleed the lines. One other thing I found from searching the forums says something about bad brake lines possibly collapsing and causing such symptoms. If the brake lines were bad shouldn't I have seen this before the recent brake work? I have never had a problem with calipers locking before. Not sure what to replace first.
I read some stuff about the proportioning valve but nothing really describing my situation - most of the complaints related to that appear to be about not getting brake fluid through the lines. My fluid flows like a champ when I press the pedal to bleed the lines. One other thing I found from searching the forums says something about bad brake lines possibly collapsing and causing such symptoms. If the brake lines were bad shouldn't I have seen this before the recent brake work? I have never had a problem with calipers locking before. Not sure what to replace first.
Posting Guru
Joined: Aug 2000
Posts: 1,984
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Dswan, did you lube the caliper slides when you reinstalled everything? I had a brake grabbing on my 78 Bronco, and thought it was the caliper piston sticking. After removal, I found that it was sticking on the slides. After wire brushing and lubeing, the problem was solved.
Tuned
Joined: Feb 2003
Posts: 495
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From: Cincinnati, Ohio
Dswan,
I would replace the front brake hoses since if they are collapsing they will not retract the piston back into the caliper bore. They don't retract completely but just enough to release pressure on the pads. Not really sure why your original pads didn't drag but I had the same problem on the rear pads on a Lincoln after I changed pads and it turned out to be the brake hoses.
John
I would replace the front brake hoses since if they are collapsing they will not retract the piston back into the caliper bore. They don't retract completely but just enough to release pressure on the pads. Not really sure why your original pads didn't drag but I had the same problem on the rear pads on a Lincoln after I changed pads and it turned out to be the brake hoses.
John
