Considering the increase in this "squeaky brake" syndrome, I wonder...can all of you who are reading this, who also have squeak, tell us which brand of brake pad you are using? I have a suspicion...this bike went through this whole scenario in the 1980s, when asbestos was outlawed, and it was a while before some non-squeak pads appeared, and they were not as cheap as the squeaky ones. Now, with so much junk being made in China, those noisy ones may be back, under various re-labellers...
I also replaced my pads this Spring with some new "generic" ones that I got from an eBay store for $10, as I was out of $$ at the time, for lack of a job then. They have turned out to be VERY squeaky, and no form of (the usual) pad modifications will stop it. The surface of the pads has melted ever so slightly and crystallized the next portion of the pad that will contact the disc, and this is the source of the noise. Severe sanding to remove the glass also removes about 5000 miles of wear depth, and only stops it for a month of commuting (about 1000 miles or so). It is definitely the pad material.
BTW, for reference: here's the operating mechanism of the 750 disc: The clearance between the stationary (inside) pad and disc should be set at about .006" by using the above-pictured adjuster screw and locknut. After about 1,000 miles on new pads, set this again (this was part of Honda's "dealer tuneup" at the 1000 mile mark on these bikes). After that, whenever the moving pad is pressed to the disc, the square cross-section O-ring in the caliper deforms a bit rhombic (it has a reach range of .012"), and the spring force of this O-ring pulls the caliper piston back when the pressure is released. This is unlike many cars, where the disc pushes the pads back, because the thin stainless steel disc of these bikes (and many bikes, for that matter) would warp quickly if the disc had to generate the constant heat of pushing back the puck. (Cars, starting around 1985 or so, adopted this same mechanism, to improve fuel mileage by reducing the disc drag, and to make lighter brakes).
Our aging calipers need some attention to restore this performance, as you will likely find the outside edges of the caliper piston to be something less than smooth: more like corroded. This causes immediate damage to a new O-ring (and old ones, too) that make the ring unable to pull back on the piston. Then, when the push is applied, the piston slips through the O-ring, and cannot pull itself back. In fact, it remains pushing on the puck, with noisy results and drag.
So, what to do? Disassemble the caliper, clean and smooth (don't polish to shiny) the piston's edges. You will see where this O-ring action started, then as the years went by, it has left its mark along the piston as witness marks. You will also likely see that the years of brake fluid absorbing moisture from the air has resulted in corrosion around the back edges of this piston, which is the part that has torn up the O-ring now. Also, the alkaline soap in the high-PSI carwashes will corrode the areas where it enters, like around the puck side of this piston, and the brake puck and caliper's housing. Clean it all.
Finally, take a brake cylinder hone (use the 3-stone, short stone variety) and hone the inside of the caliper where the piston lives, just enough to smooth out the irregularities you will find there. Smooth the outside of the piston with 400 grit, then 1000 grit, emery paper (wet sanding will help). This will reduce further corrosion later. Clean everything well, wet with brake fluid, and reassemble, using a new O-ring. Wipe a SMALL amount of brake grease or anti-seize around the outside of the new brake puck, and make sure it does not bind in the caliper as it moves in & out.
I just bought some new O-rings and caliper pistons, too: they are still available. I have some calipers that were too far gone to be reused on the Hondaman Specials I'm building, so I bought new parts for them, instead. On my own 750, I have used the above-outlined process twice in it's 130,000+ mile-long life (and a few others, not mine), with perfect results. It takes some time, but heck, it's winter, so...
