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Flatty 03-24-2002, 06:56 PM So here is my problem. I have a 1991 Ford F250 Diesel, and as I step on the brakes, the pedal slowly goes to the floor. If I let off and step on them again, the same thing happens. Is this the Master Cylinder? I can't find any leaks in the system, so I know it is not a leaky line. There is a little fluid leaking out of the master where it meets the booster. Is this a rear seal going out on the Master, and air is getting in it? Dimitri desertCJ 03-24-2002, 07:12 PM Either that or your brake booster? I had a similar problem in my '79 F350, totally different I know, but after going downhill with low RPM's my pedal would go to the floor.Pretty scary when you have an auto!I replaced the master cylinder and that seemed to help,but then it happened again! After that I was scared shitless to drive the thing. I think that I have a bad brake booster. Hope this helps somehow.:smokin: Glenn 03-24-2002, 07:42 PM Sounds like a master cylinder to me. Just throw a new one on there... :D Keith 03-24-2002, 07:53 PM Pick up a coulple of plugs to block off the line from the master. See if it will hold a firm pedal...... CRAWLR 03-24-2002, 08:51 PM It's not that air is getting into the system, the pressure is getting past the piston in the master cylinder and bleeding back into the reservoir. Although it's probably the master cylinder, another thing to consider is I had an '86 Bronco that was doing that and a master cylinder didn't cure it. Did some research and there is an anitlock valve in the system that bleeds pressure for the antilocks that was bad. Changed that and all was good. Not sure if you have antilocks or if they even did them the same way on a 91 f250 but if a new master doesn't fix it this is something to look into. SHERPA 03-25-2002, 06:25 AM Dima, it's the master going bad... I replaced the one in my 90 f-250.. --Sherpa Kevbo 03-25-2002, 07:59 AM Agree, It's either the MC or the RABS valve. There is a cover on the rear of the rabs valve. Take that off and stick a wire or allen wrench down to the piston. If the piston moves (pushes wire out) when you press the pedal, the RABS valve is leaking. If it is the MC, and it is aluminum, spring for a NEW one. (NAPA has them) It took me three rebuilds to decide that re-built aluminum cylinders don't work. Trust me, you don't want to become as good at changing them out and bleeding brake as I am. SanDiegoCJ 03-25-2002, 08:05 AM I also think it's the master cyl. Had the same symptoms on my CJ7. I replaced the master cyl. and that fixed it. FWIW, get a new master cyl., I too have had bad rebuilt ones. | |