Re: Disc brakes won't release

On 10 Sep 2005 13:16:01 -0700, mdevour@xxxxxxxxxx wrote:

>Front disc brakes on a '70's vintage Dodge van won't release except
>when I put a c-clamp across the caliper. Once the pedal is pushed,
>they're locked on again.
>It's been parked for over 10 years. I'm resurrecting it long enough to
>drive it to the local salvage yard or charity lot, so I'm not looking
>to put a lot of anything into it.
>I cleaned up the caliper sliding surfaces. The shoes were new when it
>was parked. I ground the thin layer of rust off the discs with an
>abrasive wheel in a drill. The bearings are fine.
>Power steering, 6 cyl, manual 3-speed, Tradesman 110 model.
>Is this a problem in the master cylinder? Do the calipers need to be
>rebuilt? What else might it be?
>What is *supposed* to retract the pads, anyway?
>Mike D.

Calipers need to be replaced, is my bet. What causes them to return is
the drag on the seals when the pistons are pushed out. Lay a rubber
band on a table, and gently move your finger slightly over the upward
edge. What you see is basically what the seal in the caliper does, it
"leans over". A good seal will try to return to the straight position,
dragging the piston back with it.

However, don't count on that being the end of it. You may be in need
of new flex lines, The problem could also exist in the master cylinder
or the proportioning valve. A basic test would be to crack the bleeder
when the front brakes are "hung". If the brakes release, you are
looking at more than calipers.

I'd bet on the calipers, personally. But I'd be prepared for more.

Whatever you do, don't block off the front lines, and attempt to drive
it with only rear brakes. You would have only about 30% of your
braking power. Not to mention that if an emergency occurred, and you
had to apply the brakes hard, you might as well have no brakes. With
the weight shifting to the front end, the rear wheels would tend to
lock, and the best that you could hope for is not to get it sideways
before you hit something.

Moving a car anywhere without proper brakes is extremely stupid, and
suggesting anyone do so is a sure sign of some severe mental handicap.