MR BRIDGES

THE THING ABOUT BRAKES, APART FROM THE FACT THAT THEY’RE FAIRLY ESSENTIAL, IS THAT THEY PROVIDE A LOT OF OPPORTUNITY FOR MAKING PUNS, WHICH IS SOMETHING I THINK I SHOULD AVOID HERE AS WE COULD ALL DO WITH A BREAK.

– THE

GURU IMPARTS MORE OF HIS KNOWLEDGE OF MECHANICS

Most motorcycles these days have perfectly adequate brakes, and any shortfall in performance’s usually down to a lack of maintenance rather than any design flaws, and fitting ‘better’ brakes won’t remove the need for maintenance. On older machines where the brakes aren’t up to the standard we’re now used to, fitting a master-cylinder with a smaller bore than the original can make a worthwhile improvement without involving anything more complicated than normal hand tools. Bear in mind though that it’s the area of the piston, rather than the diameter, that’s doing the work, and a 14mm bore has an area of 153.958sq.mm, and a 13mm bore has an area of 132.7495sq.mm – a drop of around 14% which is a fairly substantial change, and leads to a reasonable increase in brake fluid pressure. It’s a fairly common mod on XS650s, and my old single disc XS650 was fitted with a 13mm Magura master-cylinder which made a lot of difference to the braking, and improved the feel.

If you’re thinking of improving the brakes on something of that era, then a master-cylinder swap is a good place to start. This brings me to the KLR, and its lack of a front brake. To go back to the beginning, when I was lowering the whole thing I wanted to use a smaller diameter front rim than the 21” it came equipped with and, to that

end, I fitted a 19” Cagiva wheel that I had lying around. That meant there wasn’t a mechanical speedo drive any more, and the disc on the Cagiva wheel was about 10mm larger in diameter than the Kawasaki one, and sat further away from the fork leg (Fig.1), which meant that the caliper wouldn’t fit. Okay, so this could’ve all been avoided by getting a 19” rim laced to the Kawasaki hub, but that would’ve meant spending money and I’m not very good at that so it was time to make an adapter bracket to move the caliper away from the spindle, and in towards the disc.

Having to move the caliper significantly inboard was fortunate as that left room for the adapter bracket. With the caliper sat on the disc, the gap between its mountings and the lugs on the fork leg was 5mm (Fig.2) and, since I had some 5mm steel plate, I could make the bracket out of that. The caliper mounting bracket’s also made out of 5mm thick steel, which’d tend to suggest that a piece of 5mm plate would be up to the job.

To do this by drawing it out I would’ve measured from the centre of the spindle to the centre of each of the holes in the mounting lugs, and then measured them centre-tocentre, giving me three sides of a triangle. Then, I’d’ve taken the same measurements for the caliper with it sat in the right place on the disc, giving me two triangles that shared a common point (the spindle centre) that I could superimpose on each other, and rotate them until there was room for everything. Rather than draw it though, I used a more empirical approach, and started by measuring the hole centres for the caliper (Fig.3). Since accuracy was important, and everything was Japanese, I measured it in metric because, chances are, if the ruler says 55mm then the holes’re exactly 55mm apart. That’s 2 11/64 of an inch, and you’re already about 5 thou out if you measure it in imperial.

Armed with a measurement, I slipped the caliper on to the edge of the steel plate, and marked where the holes landed with a felt pen (Fig.4). Then I centre-punched one of the marks, and set my calipers to 55mm, then put one leg of the calipers in the centre-punch, drew an arc with them, and measured the distance between the centre pop and the line, and adjusted the calipers to correct the distance.

Once I was happy that they were set at exactly the right distance, I scribed a mark on the second felt pen mark (Fig.5), set the centrepunch on it, and lightly tapped the punch with a hammer. Getting an accurate punch mark can be tricky but, by making a very light mark, then it’s possible to move the mark by angling the punch, and striking it harder this time. (Having the calipers set to the distance you require also makes starting again relatively painless.)

With the hole locations centre punched, I drilled them with a pilot drill (Fig.6) before moving on to the correct size drill. I chose a 10.2mm drill (Fig.7) so that I had clearance on the bolts, but everything wasn’t going to flop around while the bolts were loose (Fig.8) although, as most drill bits make slightly oversize holes, a 10mm one’d probably’ve worked.

At this point the 5mm plate needed sculpting to clear the caliper body, so I took off just enough material to clear the body with a flap disc on the grinder (Fig.9). With the caliper bolted to the plate, I offered it up to the disc to get a rough idea of what I was going to have to cut off (Fig.10), and used the jig-saw to cut the material down to a more manageable size (Fig.11). That let me get the caliper in something like the right place to mark the holes for the mounting lugs. Before doing that, I taped some thick wire to the disc to space the caliper off the edge (Fig.12), checking from the other side of the disc to see that the pads were sweeping the right part of the disc (Fig.13).

At this point it’s helpful to have an assistant hold the caliper while you mark the positions of the mounting holes on to the bracket, so you can safely assume that the picture of me marking the holes with one hand (Fig.14) while taking a photo with the other was faked. Since the mounting holes were originally meant for bolting the caliper too, it followed that they were the same distance apart as the caliper holes, so I’d set the calipers to one side so that they were still adjusted to the correct measurement. When marking out the holes, I first centre-popped the one nearest the wheel spindle, then scribed an arc with the calipers before drilling that hole to 10.2 mm. This allowed me to position the plate, and the caliper, on the forks and re-mark the second mounting

hole as a bit of insurance against having made an error due to the lack of assistance (see Fig.14).

Once I was happy that the last hole was in the right place, I centre-popped it, and drilled it out to size before trimming the bracket to its finished size. Placing washers under the heads of some bolts placed in the holes’s a useful guide when marking out the finished shape (Fig.15). As luck would have it, there was sufficient clearance between the adapter bracket and the disc to get a nut in there (Fig.16), which saved me from having to machine anything, and a rummage through the bolt drawer produced a couple of 10mm bolts with shanks long enough to protrude from the mounting lugs and into the adapter bracket once the threads’d been cut down to length (Fig.17), but I’m going to have to go online and find the fine thread bolts for the caliper, which means I’ll have spent some money after all.

With the bracket bolted in place (Fig.18), the caliper sits behind it, and bolts in place quite happily (Fig.19), and I think that’s pretty much all the major lumps sorted out on this (Fig.20), and just a few bits and pieces to track down. Anyone got a YDS7 petrol cap?

MR. BRIDGES