Brakes: Disc brakes draqgging

[rkimmell]

1963 Cruiser l/f caliper will not release the hydraulic preasure from the outter piston. If I crack the bleeder, there is preasure. If I crack the line into the caliper, it has no preasure. The piston moves freely in the bore, new hoses, blew out the steel lines, and adjusted the master cyl. push rod. The right side releases o.k.
There are three holes in the piston. I don't know what they are for.
Any suggestions?
Thanks,
Rich

[63 R2 Hawk]

Did it just suddenly start doing that, or have you done some recent brake work? One possibility might be that the caliper isn't properly centered. The Dunlop calipers aren't self centering and require shims to center them when they were installed in the factory. Could be the calipers were removed and the shims weren't reinstalled in their original positions. Something to check......

[(S)]

These have pretty small travel, and small , complicated tubing and valving to them. You probably have some rust or crud inside, and only a small amount of pressure going 'in' and none going back 'out' Try bleeding all 4 calipers to get the crud out. It is likely that one cylinder is already toast.

Kits and new cylinders are an item I stock here and most other vendors also have them.

[(S)]

Good point, but it sounded to me like the car was already driving? He did not say.....

[StudeRich]

/Cut/The piston moves freely in the bore, new hoses, blew out the steel lines, and adjusted the master cyl. push rod. The right side releases o.k.
There are three holes in the piston. I don't know what they are for. Any suggestions?Thanks,Rich

I have never seen the Pistons "move freely" in the bore. They require quite a bit of force to move them through their very short travel due to the center rod and the drag on a good Piston seal. Are there fresh seals in there?

I have to wonder about the master Cylinder push rod adjustment. If the rod is from a Single Cylinder Power Disc brake Car, it should not need adjustment.

The three holes in the Piston do not go all the way though, so no problem. They all are made that way.

[64V-K7]

The pistons ride on a guide pin, which is anchored to the cylinder. When the brakes are applied,
the travel is very slight and is almost entirely facilitated by a small spring, captured at the base of the
guide pin. This spring also acts to retract the pads when the brakes are released. If the guide
pin gets damaged while in the rebuild process, by prying the piston out, instead of blowing
them out with air pressure, then you can have the same problem you describe.

[rkimmell]

I dont know about the shims. Please tell me more about them.
Thanks

[rkimmell]

I did not see any spring in the caliper. Please
tell me more about them.
Thanks

[hausdok]

I did not see any spring in the caliper. Please
tell me more about them.
Thanks

http://www.studebaker-info.org/tech/...ems/dunlop.jpg

[tbirdtbird]

As StudeRich suggested, check the master Cylinder push rod adjustment. takes 15 secs. Using your hand gently depress the pedal. It should move down about 1/4" to 3/8" with no resistance at all. Meaning during that travel the pushrod has not yet contacted the MC piston

[Andy R.]

I dont know about the shims. Please tell me more about them.
Thanks

The shims fit between the caliper and the mounting bracket to center the caliper on the rotor. If off center, one of the pads will drag on the rotor.