Need Help with this one.
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Senior User
Joined: Nov 2007
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Need Help with this one.
I am working on a 1995 F-350 4WD Dually Diesel. I replaced all of the brake hoses and steel lines, new calipers, pads, rear drums, shoes and wheel cylinders and a new master cylinder. Bled the brakes and got the air out. When you start the motor the brake pedal goes right to the floor. Motor not running works as it should, motor running pedal goes right to the floor. I have already changed the master for another new one. The problem is in the front wheel circuit. I isolated the brake fluid to the wheels by pinching off the hoses and then released them one at a time while my assistant (my wife) was putting pressure on the pedal. When the rear wheels were released the pedal held strong as you would expect. When I released either front wheel the pedal went to the floor. As a note this was done with the engine running. So now I know the "problem" is in the front wheel circuit. I am confused....it just does not make sense??? Appreciate your help.
Post Fiend
Joined: Jan 2005
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Your description of brakes with engine off and engine running is classic for air in the system, I would bleed them again, closing the bleed screws each time before the pedal is released. However there are other rare possibilities, one is bulging flexi hoses when full brake pressure is applied, another is caliper piston seal roll. This "roll" can occur when the piston drags the seal forward when the brakes are applied and then the seal drags the piston back too far each time.
However I still think it is air.
However I still think it is air.
Post Fiend
Joined: Mar 2002
Posts: 19,402
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From: Bonita Springs FL
pacrewchief, Did you bench bleed the master cylinder?
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