By: Ron Milam
I am sure every one is thoroughly sick of hearing about oily exhaust pipes and horrid things like that, so this month lets talk a little about brakes. Brakes are probably one of the most troublesome systems on a trials motorcycle. I bet if you asked 10 of your friends if they were satisfied with their brakes, 9 would say no. This is despite the fact that they are riding a fairly new $5500 motorcycle. What is it that makes brakes such a source of grief?
I have a few things that came to mind. First, trials bike brakes are shrimpy. They are only a small notch above bicycle brakes. This is partly a price we pay for light weight. Second, the actuation systems (brake pedals for true trials bike dummies) of many bikes are poorly laid out. The main purpose of the rear brake pedal on a Beta Techno is to minimize any mechanical advantage between your right foot and the rear caliper. If you are a GasGas or other owner, don’t snicker. Yours is probably not that much better. Third, the brakes are generally full of mud and other unhealthy stuff. Fourth, we demand an awful lot of those tiny units. You expect them to lock up easily when you want to hop or nose wheelie, but you don’t want them to lock up when you get sloppy with their application. Generally, the brakes on a new bike work pretty well. It is only after a few days of use in bad conditions that you notice the loss of stopping power. I am going to list a few things that I have learned about brakes. Maybe you already know all of these. If so, you may skip over to the classified ads. If not, some of the things may improve your brakes. Those of you who know me, know that I ride a much fiddled with ’96 Beta. Soon after I got it, I discovered that most owners of Betas don’t like their brakes. I now have a 4 piston caliper on the front and a rear rotor which is 38mm larger than stock. I now love my brakes whether wet or dry. You can make yours work well too, with a little work.
You should make sure that your rotors are not bent or warped and that your calipers are in alignment with the rotors. If you see a rotor flexing as the brake is applied, that is a sign of possible misalignment. Uneven pad wear can also be a sign. This is normally caused by bent caliper mounting bracket or by the wheel being out of alignment ( especially on the rear). If you are new to trials, you may wander why brake rotors are mounted loosely to the hubs. This serves 2 purposes. It allows the system to compensate slightly for misalignment. It also keeps you from getting killed. This is always a nice thing. If you hit something with your front wheel and flex your forks, the caliper is momentarily knocked out of alignment with the front rotor. This happens because the caliper is mounted to the fork leg and the rotor is mounted to the wheel hub. If the rotor did not float a little bit, it would push the pistons back into the caliper. You would not know anything was amiss until you grabbed for some front brake and the lever pulled all the way to the grip. If you were to think quickly and release the lever and pull it again, you would find everything normal again. Some people find the looseness of a floating rotor disconcerting, but it is definitely worth the aggravation. Side to side play is all that is needed. If your rotor rocks front to back, you can tighten it up by replacing the bushings and or mounting screws.
Running pads that are excessively worn can also cause problems. Some calipers are prone to piston sticking if the pads are too thin. This is because the pistons must extend so far that they become cocked in their bores. Also, rear brakes can experience special problems if the pads are too thin. Rear brake pedals often do not have sufficient travel to both actuate the caliper and also to allow the piston to uncover the charge port of the mastercylinder. Ever notice the reservoir and hose connected to the middle of your rear mastercylinder? This allows enough additional fluid into the high pressure side of the system to make up for the fact that your pistons are hanging out farther because of pad wear. When you release the pedal it must allow the mastercylinder piston to return far enough to uncover the little hole in the cylinder where the hose is connected. If you have your pedal adjusted too low, the piston can’t retract far enough and no additional fluid can get in. You won’t notice the problem until one of those muddy, brake ruining events that cause rapid pad wear. You will find the pedal going lower and lower until finally it bottoms out on the skid plate just when you need it most. The only advice I can give you here is to pay attention to this possibility. Bikes vary in this regard. You may never see the problem or it may plague you. If you have ever thought about putting shims in behind worn pads, I can say from experience that this works fine and can save a lot of money.
I guess the little running joke about the no name column is over. This happened as I was looking at my bookshelf. I just hope no one reports me to that computer book company that prints books on all subjects ( except trials bikes ) by the same name. Next month we will finish up on brakes so you have 30 days to order parts and buy fluid.
-Ron