This is a subject like many others where you can find varying opinions and instructions on how to go about setting up and adjusting mechanical disc brakes. I only have and use Avid BB7 brakes. I started off with Avid BB5 brakes which I would not wish on my worst enemy as the saying goes. They are junk in my opinion. They required almost constant daily adjustment which got old quick. The BB7 is a far superior brake and well worth the additional expense over the BB5 brakes. The main difference between the two besides the brake pads is that the BB5 brake only has one adjustment knob for the brake pad … that is, only one side can be adjusted. The other side is stationary. The BB7 has adjustment knobs on both sides making it much easier to get proper adjustment initially. And once adjusted the BB7 seems to remain in proper adjustment for quite some time. If you have the BB5 brakes you are on your own as I won’t waste my time trying to instruct how to adjust them as they aren’t worth the time and effort involved. My advice is to upgrade to the BB7s. Anyway, I am not going to link to the instructions of others here, but rather I am simply going to share how I go about setting up and adjusting the brakes.
To start out it is important that the rotors run true. If they are bent or damaged they need to be repaired or replaced. There is a special tool to use to straighten a bent rotor, but if one lacks this tool an adjustable wrench can be used if the bend is only near the outer part of the disc. If it is further inward toward the center of the disc an adjustable wrench won’t do. I have a Park Tool straightener, but there are other brands available.
If the rotor is straight and true you can move onto the setup of the brake. Basically by setup I mean positioning the brake caliper and brake pads properly on the rotor. Again, not everybody goes about this the same way, but I am only sharing how I do it and it has worked great for me. Ideally it would be best to do all this with the rider of the trike seated on the trike so that the effect of the rider’s weight is taken into consideration as I am sure things would change a little just like the toe in measurement sometimes changes when the rider is seated on the trike. This is especially true if the rider is heavy. I have never done that myself as it would be difficult if one is by themself to sit in the seat and perform this procedure.
It is most important that the caliper be positioned correctly so that the rotor is centered and parallel to the brake pads. Otherwise it is likely that the brake will rub and make noise, especially when cornering. Also the brakes won’t work as well as they could and the brake pads will wear uneven.
The mounting bolts have special washers which are dished and cupped so that they fit together and “adjust” to the positioning of the caliper over the rotor.
The procedure I use to align the caliper and brake pads on the rotor is simply to leave the mounting bolts loose so that the caliper can move freely.
I then sort of wiggle the caliper around while I turn the brake pad adjustments (red plastic knobs) in so that they tighten against the rotor and center the caliper over the rotor. I initially wiggle the caliper around a bit just to ensure it is freely moving while the brake pads are being adjusted in. Turning these adjustment knobs can tighten the brake pads sufficiently to hold against the rotor aligning it properly. I then carefully tighten the mounting bolts being careful not to move the caliper in the process. An alternative way of doing this is to tighten the brake pad adjustment knobs only partially so that squeezing the brake lever will tighten the brake pads on down against the rotor. Holding the brake lever on (or using some means of holding it on) I then tighten the mounting bolts carefully. Now with the caliper and brake pads aligned the brake pads can be adjusted properly.
Here is a video about centering hydraulic disc brakes which is pretty much the same process as mechanical disc brakes with the exception of having to push the pistons back out..
When adjusting the brake pads I simply back them off just enough initially so that they don’t rub when the wheel is spun. I then pull the brake lever to see how it feels. If it is too tight I loosen one of both of the brake pads a bit more. I also look down at the brake pads to see what the gap is looking like as I want to be sure both pads are evenly spaced out from the rotor. One should try to keep the gap between the brake pad and rotor the same on both sides so that when the brake is applied both brake pads make contact at the same time and not be forcing the rotor over to one side. It should remain straight and not flex (be forced) sideways.
Keep in mind that when cornering hard there is some flex in the wheel and often times some rubbing will occur between the brake pads and the rotor. If this is bothersome the brake pads can be further adjusted out if needed.
Keep in mind that if a wheel is removed or realigned (adjusting the spokes) or a rotor is removed and then reinstalled or a new rotor is installed the caliper and brake pads may need to be realigned. That is what happened to my trike recently. I adjusted the spokes realigning the wheels which resulted in the need to reposition the caliper and brake pads. Once I did that my brakes worked much better. Obviously having properly working brakes is most important. They will help us …
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