Topic: 1972 CB750 Front Brake adjustment

[callbr549]

Just now getting my 1972 CB750 out of winter storage and ready to ride. Put it away last fall, everything was running great. Today the front brake drags.  Appears the right side caliper (I think this is the "fixed" caliper) is dragging.  Looked at the Clymer manual and looks like I should be able to loosen a lock nut on the left side and unscrew a large screw from the other side of the caliper and that it should move the fixed caliper away from the disc.  I have that screw backed out really far, you can see clearance under the flat head screw head, but the caliper doesn't seem to have moved. There is a sping on this screw that looks like it should be pushing the caliper in the right direction but maybe isn't.  If I understand how this is supposed to work from looking at it, it appears there is what I would call an aluminum plate that the calipers are mounted to and that this plate (or whatever its called) is on a hinge and that maybe the hinge is frozen.

Ideas?  Need more information?

Rob

[HondaMan]

You've probably collected some moisture in the caliper from condensation over this winter, especially if it was like our 7-month long record one here. 

First thing: try pressing (hard) against the outside of the moving cliper to push the puck back in deeply. Then, use the adjuster screw you're describing to make clearance of 0.004" to 0.006" (with a feeler gage, or else 1/4 turn of the screw) between the inside puck and disc. This is the starting point. Then actuate your lever until it pumps the moving pad back out, and see if it will then release properly after you let go.

If not, you can next try bleeding the brake. About 1 time in 10, this will let the water droplets out before they corrode the piston inside and it will then work a little better.

If this fails, you probably need to replace the O-ring around the piston inside the caliper. These dry out over the years and lose their elasticity: they must grip the piston on their insides so they can pull the piston back away from the disc when the lever is released. When they get old and "wet" from moisture, the outer piston just slips through them when applied and it won't pull it back from the disc very well. This then lets the outer puck squeeze the disc, and the brake drags.