Brake Caliper Mounts

A project log for SECApocalypse

Yamaha XJ750 "SECA" with adjustable Hossack front end and Mad Max style

sebwierssebwiers 05/29/2016 at 05:580 Comments

I knew eventually I'd have to get around to mounting front brakes, and with most of the other fabrication work done, it was time to take on this task. Since I was doing new mounts, I figured I'd pick up some improved brakes, and took the gamble of buying to cheap Yamaha "Blue Dot" R6 brakes on Ebay. The pads don't cover my whole rotor (the old mono-pot was a wider pad,) but that's OK, and the otherwise fit my rotors pretty well.

Most importantly, they don't hit the spokes, although the wheel clearance is VERY thin when spaced for my rotors! The photo shows the very narrow space the spokes pass through. It looks scary, but that's how cast / machined aluminum wheels tend to be - simple thin disks with cut-outs.

To get the positioning right, I took four key measurements with the brake caliper in place:

This gave me the dimensions I needed to lay out a pair of tabs that would put the brake pads in proper relation to the swept portion of rotor. Below is the result of that layout work, tacked in place. My rotor is made for a single pot brake, so the brake track is only 80% covered by the new brake, but the new brakes are correctly aligned on the outer part of the rotor, and the pads do not go past the edge (or even within 1/8" of it) at any point.

To ensure the mounts were in the right location and (mostly) aligned, I used a fairly crude jig. The task of the jig was to get the lower bolt hole the right distance from the axle, and keep the mounts as close to aligned and centered as possible. The tabs themselves provided alignment for the upper bolt hole.

Once they were tacked down, I fully welded the tabs. I "stitch welded" (using multiple short spots of weld) rather doing this all in one run, to minimize distortion.

Despite these efforts, I had no expectation the brake tabs would be exactly perpendicular to the axle. Welding also left weld bead in areas I needed to be flat and smooth for the brake / bolt heads to sit properly. The solution was to clamp the halves of the fork in the mill and square up the caliper mount brake faces, get rid of weld bead where needed, and cut away the "bridge" that aligned the two tabs during weld assembly. Machining after welding is often necessary where parts joined with welds need precision alignments / spacings. I also took this opportunity to add some (more) decorative cutting on the fork tips and bridge (also removing a tiny bit of unsprung mass).

And here's what the bike looks like (from the front) now: