Disc brakes won't release

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?
Thanks,
Mike D.
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snipped-for-privacy@eskimo.com wrote:

Why not take the money you will spend in getting the brakes fixed and pay to have it towed. My guess is that if you get the calipers working you will find other problems with the brakes to fix before you can safely drive that van. If you are going to donate it for a tax deduction then donate it as is.
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John S. wrote:

Those are options, John, but one of the motivations here is to get the thing out of hear soon. The charity places will tow it, but may take over a month to get around to it.
Paying to have it towed will be a lot more than I would spend on refurbing the calipers, so long as I do the work myself. *If* that's where the problem is. That's why I'm asking.
I hope that explains things.
Thanks,
Mike
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snipped-for-privacy@eskimo.com wrote:

Just be prepared to find other problems with the brake system even if you replace the frozen front calipers with Pep Boys refurbs. The master cylinder and rear brakes may suddenly start leaking from all the rust and crud that will undoubtedly be stirred up.
I've not had a lot of luck with home refurbing of calipers, but the kits are not all that much so give it a try. The worst result is that the refurb doesn't work, you are out some $$ and have to wait 30 days.

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snipped-for-privacy@eskimo.com wrote:

This answer is based on experience with a 1970 Plymount Valiant with disk brakes which I once owned.
The disk brake pistons have developed rust blisters, impeding free motion. You can't see the blisters because they are inside the calipers. The fix is to rebuild the calipers with new pistons or replace the calipers. Been there, done that, paid those dues!
Daniel B. Martin
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Let me respond to all of your posts here:
Daniel B. Martin wrote:

Thanks Dan. That sounds likeliest, while keeping everyone else's comments in mind.
John S.,
I hear you, and I don't expect miracles. I'm pretty cynical about my chances, actually, but I'm holding out for cheapness! <grin>
My next experiment will be to remove the inboard brake pads, temporarily reinstall the calipers, and apply the brakes to extend the cylinders. I'll then push them back in with a C-clamp, then repeat a time or two more.
My hope is the brake fluid will get into the dry parts of the cylinder and lubricate enough (and break up the rust enough) that they'll retract again. I don't care if it's not a permanent fix, obviously.
If that doesn't work, I'll probably investigate a tow-bar, which is something I had *not* thought of before. For *that* suggestion, thank you Ted! I'll pass on the idea of running with just the rear brakes, though. <grin> Not that it couldn't work, but it's a little riskier than I like.
To all, thanks for your comments. I'll work on it and let you know how it turns out!
Mike D.
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snipped-for-privacy@eskimo.com wrote:

Disk brakes don't have retraction springs like drum brakes. The pads always "float", almost touching the disk surface. The only forces which retract the disk brakes are axial runout of the disk and the elasticity of the caliper seals. Those seals are like O-rings but they are square in cross section rather than round. They are captive in machined recesses in the caliper body and bear against the piston. They are what keep the hydraulic brake fluid inside the caliper.
Daniel B. Martin
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this is what you do. get the calipers pushed back in disconect the brake lines and plug the lines ? or take the pads off put a clamp around the caliper and bolt it back on and go ? you will still have back brakes to stop ?
since your only going to the bone yard ???
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The pads don't retract, in the sense that drum brakes do. The caliper piston can move back into the bore a bit due to slight runout of the disc, but there is no retraction mechanism nor any need for it. The pads should not bind against the rotor, however.
Problems in the piston and seal area can make the pads ride too tightly, as can the slides.
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all of the previous comments are on the mark - another possibility: the flex lines can collapse internally restricing fluid release
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On 10 Sep 2005 13:16:01 -0700, snipped-for-privacy@eskimo.com wrote:

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.
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wrote:

No, not so! The trick is to make sure to have the same stopping distance as when you have the front brakes.
I'm too lazy to do the math but assumimg your right and that his back brakes will give him 30% of the stopping distance all he needs to do is drive 30% of the speed limit and he will have the same stopping distance. Obviously the traffic behind him won't care for this so he will need to do this late at night, when there's little traffic. And since the vehicle's been sitting for 10 years hopefully he doesen't live in a state that has mandatory insurance because going down a road marked 45Mph at a max speed of 13Mph is sure to attract attention from the local police.
Another way to do it would be to rent (or build) a tow bar, assuming he has a trailer hitch on a working car. He would need an assistant to ride in the van and push on the van's brakes to make the brake light go on when he brakes.
Ted
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