Home | Contact Us | FAQ | Search & Site Map | Link to Us
Sign In | Join | Other 45 Sites in Network
HomeAnnouncements
Discussion Groups
By Brand
BMWChevroletDodgeFordGMHondaLexusMercedes-BenzNissanPeugeotToyotaVolkswagenOther Brands
By Topic
4x4 CarsRVsDrivingMaintenance & RepairCar AudioCollectible Cars
Country Specific
Australian ForumsUK Forums
ArticlesAuto InsuranceBuyingCars & TechnologyMaintenanceMiscellaneousSafety
DMV Resources
Related Topics
MotorcyclesBoatsMore Topics ...

Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / September 2005

Tip: Looking for answers? Try searching our database.

Disc brakes won't release

Thread view: 
Enable EMail Alerts  Start New Thread
Thread rating: 
mdevour@eskimo.com - 10 Sep 2005 21:16 GMT
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.
John S. - 10 Sep 2005 21:32 GMT
> 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,
[quoted text clipped - 18 lines]
>
> Mike D.

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.
mdevour@eskimo.com - 10 Sep 2005 21:58 GMT
> 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.

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
John S. - 11 Sep 2005 00:24 GMT
> > 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
[quoted text clipped - 9 lines]
> refurbing the calipers, so long as I do the work myself. *If* that's
> where the problem is. That's why I'm asking.

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.

> I hope that explains things.
>
> Thanks,
>
> Mike
Daniel B. Martin - 10 Sep 2005 21:42 GMT
> Front disc brakes on a '70's vintage Dodge van won't release...

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
mdevour@eskimo.com - 12 Sep 2005 17:58 GMT
Let me respond to all of your posts here:

> The disk brake pistons have developed rust blisters, impeding free
> motion.  ... The fix is to rebuild the calipers with new pistons or
> replace the calipers.

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.
Daniel B. Martin - 10 Sep 2005 21:49 GMT
> What is *supposed* to retract the pads, anyway?

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
tudysmuck@yahoo.com - 11 Sep 2005 06:15 GMT
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 ???
HLS@nospam.nix - 11 Sep 2005 14:43 GMT
> What is *supposed* to retract the pads, anyway?
>
> Thanks,
>
> Mike D.

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.
nospampls2002@yahoo.com - 11 Sep 2005 15:14 GMT
all of the previous comments are on the mark - another possibility: the
flex lines can collapse internally restricing fluid release
Raymond J. Henry - 12 Sep 2005 05:13 GMT
>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,
[quoted text clipped - 18 lines]
>
>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.
Ted Mittelstaedt - 12 Sep 2005 10:15 GMT
> >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,
[quoted text clipped - 44 lines]
> Moving a car anywhere without proper brakes is extremely stupid, and
> suggesting anyone do so is a sure sign of some severe mental handicap.

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
tudysmuck@yahoo.com - 12 Sep 2005 20:37 GMT
Hey f.ck you a.s hole  RAY the guy just want's to get it to the bone
yard  AND DOES NOT WANT TO PUT NO $$$ INTO IT    ---DID YOU READ THE
POST AND UNDERSTAND YOU FUCKIN  COCKROACH    LIKE HE IS GOING TO BE
DRIVING 50 MPH  TO THE BONE YARD !!!!!!!!!!!!  A MEAR 15  MPH IS JUST
FINE

11. Raymond J. Henry   Sep 11, 9:13 pm     show options

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.

Reply
 
Sign In
Join
My Latest Posts
My Monitored Threads
My Blog
My Photo Gallery
My Profile
My Homepage

Start New Thread
Enable EMail Alerts
Rate this Thread



©2008 Advenet LLC   Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.