I recently replaced a MC and rear wheel cylinders on my sons '77 F100 and now the front calipers bind after driving about a mile. Loosening either the bleeder screw or line on either caliper releases hydraulic pressure and the calipers retract from the rotor(unlock). I'm suspecting the proportioning valve. How do I check it out? And if it needs replacing are there any pitfalls to watch for. Thanks.
Dan

 

being you changed the M/C and now you have a problem,I'd look at the M/C push rod as being too "long" and not allowing the M/C piston to fully return against the snap ring.The push rod is adjustable in length by screwing in the male portion back into the female portion once removed from the booster.The trick is to get it where the push rod is not touching the M/C piston while everything is bolted up,but, very close to it.Also verify the M/C piston itself is fully returning to the snap ring, i have seen remans that bind up all on there own.
Phillip

 

Appreciate you response. We checked the pushrod length which checked ok, and we even returned one MC suspecting a possible bad unit, but with the replacement the brakes have the same symptoms. After the pressure is releived the pedal feels fine for about a mile, then you can feel the pedal stiffen to the point of locking the front calipers. Any other ideas? Thanks.
Dan

 

Whew, I'm stumped now ! This may be a long shot but I think it may be the booster itself.Let's suppose the internal air check valve, the one for the atmospheric air,is leaking or not closing off,allowing the vacuum to gradually pull the brake pedal down or even pulsate a little, effectively applying the brakes for you ? Can you actually see the pedal height decrease as you are sitting still w/ the engine running? As a reminder, you only have to apply the M/C about a 1/8" to block off the fluid return hole in the resevoir,causing no release problems, but then again, bad rubber hoses will do the same.
Phillip

 

Dan, Try what Phil suggested and turn the rod in a couple of rounds and see what happens. I was having a problem when I first converted to power disks. There was just enough friction for the disks pads to get hot and swell onto the rotor. and finally the front tires were sliding. Disconecting the mc form the booster is simple and no bleeding to do afterwards. Try it and let us know.


John

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

This is a long shot since the problem seemed to start immediately after changing the MC but I had a truck that had sat for a long time when I bought it, I was having the same problems. It turned out to be the rubber brake lines at the wheels. They would let fluid into the brakes but prevented the shoes from retracting.

Trail Rider

 

Hopefully I'll have some time tomorrow to try as you suggested. I'll post the results. Thanks.
Dan

 

>Hopefully I'll have some time tomorrow to
>try as you suggested. I'll
>post the results. Thanks. Dan
>

First thing I rechecked was the problem. The MC had about .100" preload. Backed it off and everything works correctly. Thanks for all the advice. Now, if you ever need someone to star in the sequel to Dumb and Dumber you'll know who to suggest.
Thanks again.
Dan

 

Dan you can't qualify, first of all, you seeked wisdom from the most astout group of problem solvers in the world. You took council and fixed your problem. Seems to me just to be a little oversite on your part. Now if you had argued this for a couple of weeks, you could have been in the running. [img]/dcforum/Images/happy.gif[/img]



John

66 F100s
In the still cool hours of the night, you can hear chevys rusting away.

 

I have seen the above mentioned complaint caused by bad hoses on two different occasions. One was on a "Chxxy" Motorhome and it warped the rotor it got so hot.