Frozen Calipers

[Mike]

I have a basic brake question.  One of my front calipers is frozen on my 76 commercial chassis.  I have two scenarios to run by you:

1. With the bleeder open and the master cylinder cover closed, I can drive the piston back into the caliper with relative ease using a large C-clamp.
2. With the bleeder closed and the master cylinder cover open, I have a very very hard time getting the piston to return.

I was under the impression (maybe falsely) that with the bleeder closed and master cylinder cover open I should be able to drive the piston back into the caliper similar to when the bleeder is open.  Is the difficulty I am experiencing in this second condition more a sign of a blocked brake line rather than a frozen caliper, or is it usually really difficult to push the brake fluid back up to the master cylinder in this manner?

Any advice would be appreciated.

[Bruce Reynolds # 18992]

Gday Mike,

If the piston can be pushed back in with a clamp, then it isnt frozen.

If it moves one way, and not the other way, then you definately have a problem with a blockage in the line, somewhere between the caliper and the M/Cylinder.

What you need to do is start undoing the fittings, one at a time, as you work your way back to the M/C, and see when it stops pushing fluid out.

What I mean is:

(1)  Okay, the bleeder screw hole is free.
(2)  Screw up the bleeder and loosen the joint in the flexible hose at the chassis mounting point and see if fluid comes out there.   If so, then that section is free.
(3)  Then, go to the next "joint" wherever it is, and it might be at the M/C.   Undo that, and see if fluid comes out there when you tighten up the clamp.

Dont forget that you have to have some fluid in the caliper to be able to perform this test, so you might have to rig up a reverse supply by installing a simple clutch M/C to the bleeder  orifice to be able to push the piston back out so you can clamp it back in again.

But, why are you trying to get fluid to the caliper with the M/C cover off?   Why not just press on the brake pedal and let the piston try and push it through.   The other thing you can do is to do the testing procedure from the M/C down to the Caliper.

Bruce,
The Tassie Devil(le),
60 CDV

[Joe Abernathy #17524]

There will be considerable more pressure with the bleeder closed than open.  The fluid will take the route of least resistance.  If the pistons press back into the caliper and the fluid level in the master rises you shouldnt have any problems.

[Sam L. Moore CLC #21210]

Sounds like the rubber section of brake line connecting to the caliper is swelled shut. To check this, simply open the bleeder screw and press the brake pedal to see if the fluid flows freely.

[Lynn 10923]

They will be a little tougher to move back with the bleeder closed as opposed to open, but they shouldnt be that tough. You may have a rubber brake hose between the body and the caliper swelled and nearly closed off. It might sound bizzare, but I had this happen to me just a couple years ago. One spring I went to take it out for its first drive. The brakes applied just fine, and wouldnt release at all. It turned out to be internally swelled brake hoses to the point where they had completely closed off. Even after three days of setting they hadnt leaked down at all. If they are the original brake hoses from 76 they need replaced anyway, just out of principle.

Lynn

[Kelly Watson]

I just replaced the front brake hoses on my 71 Eldo due to frozen calipers: The pistons would go back in using a clamp, but would not return normally. The hoses were the originals, and had delaminated internally. Time to replace them by the sounds of it ;-)