The front brake started to squeal on my '78 a few hundred miles after I installed new aftermarket pads. It seems Yamaha was aware of the squeal issue because they took a couple steps to eliminate it. First was an anti-squeal caliper clip. This is nothing more than the original type clip with little squares of rubber glued inside .....
I don't think these are available from Yamaha anymore but would be simple enough to make. Just glue some little rubber squares cut from an old inner tube or something inside the clip you have. But, pull both your clips and inspect them. Note that the one with the rubber, the "anti-squeal" clip, should be installed in the forward spot. Maybe you have one but it was incorrectly placed in the rear spot.
The second step Yamaha took was to install shims behind the pads, #12 and #13 in the drawing below .....
On mine, doing the first step, installing the rubber padded clip, didn't help, but it's so simple to do, I would try it. Doing the second step, installing the shims behind the pads, is what fixed mine. As far as I know, none of these parts are available anymore. I scrounged mine from spare later calipers I had.
I don't think these are available from Yamaha anymore but would be simple enough to make. Just glue some little rubber squares cut from an old inner tube or something inside the clip you have. But, pull both your clips and inspect them. Note that the one with the rubber, the "anti-squeal" clip, should be installed in the forward spot. Maybe you have one but it was incorrectly placed in the rear spot.
The second step Yamaha took was to install shims behind the pads, #12 and #13 in the drawing below .....
On mine, doing the first step, installing the rubber padded clip, didn't help, but it's so simple to do, I would try it. Doing the second step, installing the shims behind the pads, is what fixed mine. As far as I know, none of these parts are available anymore. I scrounged mine from spare later calipers I had.