I need help, poor brakes!!
07-13-2009, 06:50 PM
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I need help, poor brakes!!
OK, I'm new here and I hope that someone can help me! I ecently purchased a 1984 F150 2WD LB Explorer model with 302 and auto in it. When I bought the truck it had really soft brakes. Fluid dripping from brake line running to right rear drum and "whooshing" noise from power booster. I found a leaking rear line which I replaced. Still no brakes to speak of.
Next I bled the rear brakes. Still nothing. I next bled the front left, then had to replace the front right caliper (bleeder frozen in place). Still no brakes.
Next I replaced the booster. Now I had no resistance at all. I pulled the master cylinder back off the booster, and adjusted the MC actuating rod to 3/8" from the spline on the rod (which is where the old booster rod was). Gone was the "whooshing" noise but still had zero pedal at all.
Off came the MC again and I adjusted the rod all the way out. Now I have brakes that require a ton of pressure and the back brakes lock up. The front brakes don't seem to work at all. I spun both front tires by hand while having my son bot pump the brakes and hold the brakes.
When he begins to pump the brakes, the front wheels would stop very breifly, then spin again (pressure to spin wheels was applied constant).It's as if the front calipers begin to work, then go away completely.
I'm at wits end now and the onl;y thing I can think of that could still be at fault would be the proportioning valve or the MC.
HELP!!!!!
JT
jonspider1991@gmail.com
Next I bled the rear brakes. Still nothing. I next bled the front left, then had to replace the front right caliper (bleeder frozen in place). Still no brakes.
Next I replaced the booster. Now I had no resistance at all. I pulled the master cylinder back off the booster, and adjusted the MC actuating rod to 3/8" from the spline on the rod (which is where the old booster rod was). Gone was the "whooshing" noise but still had zero pedal at all.
Off came the MC again and I adjusted the rod all the way out. Now I have brakes that require a ton of pressure and the back brakes lock up. The front brakes don't seem to work at all. I spun both front tires by hand while having my son bot pump the brakes and hold the brakes.
When he begins to pump the brakes, the front wheels would stop very breifly, then spin again (pressure to spin wheels was applied constant).It's as if the front calipers begin to work, then go away completely.
I'm at wits end now and the onl;y thing I can think of that could still be at fault would be the proportioning valve or the MC.
HELP!!!!!
JT
jonspider1991@gmail.com
07-13-2009, 07:06 PM
#2
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Hello and welcome to the forum. We need to back up for my clarification, not necessarily your error. The brake booster rod cannot touch the master cylinder piston. Clearance is needed there or the MC piston will not retract enough to exposed the internal ports to replenish itself of fluid as pads wear. Need to carefully follow booster instructions or measure from mating surface of cylinder to botton of piston. This dimension needs to be slightly greater than the exposed rod of the booster. Its great that you have your son as an assistant, great times in a boys life "helping Dad with the truck". Remember mine well, dad was a great assistant. 
Recheck this and just try gravity bleeding one cylinder at a time. If they won't bleed by gravity the adjustment for the booster rod is incorrect.
Recheck this and just try gravity bleeding one cylinder at a time. If they won't bleed by gravity the adjustment for the booster rod is incorrect.
07-14-2009, 05:57 AM
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Thanks Bill!!!!
Bill thanks for the advice! I replaced the master cylinder at 9pm last night and readjusted the booster rod back to where it was upon removing the bad boster (3/8" from the spline or knurled portion where the rod threads in) and like magic I have perfect brakes now! I don't think they've ever worked this well! Thanks again for the encouragement & support!
This feeling of accomplishment is why I do al the work on my own vehicles!
This feeling of accomplishment is why I do al the work on my own vehicles!
07-25-2009, 11:13 PM
#4
Senior Member
Yeah I have seen plenty of bad Master Cylinders, there are allot of groups that consider this normal because it is common. Usually they will not leak and if do will leak into the brake booster. One common problem is that when stepping on the brakes the pedal will creep down usually if this happens pumping the brakes will not help much.
