Disk (or Disc) Brakes and Bicycles: How to Go From Soft and Squishy to “Holy Crap!” (Even With Mechanical [Cable] Brakes).
I was told, when I purchased my tandem, that the calipers we had were meant for a flat-bar bike and that we might have to swap them for road calipers should the need arise. They were squishy, but they worked well enough that I was never afraid of riding the bike with my wife on it… and I’m about six times more careful with my best friend, wife, partner and Rear Admiral on the back of the bike than I am solo.
On the other hand, it took a second to stop the bike properly and I really didn’t like that, so this past weekend, I took to figuring them out to see if I could improve on what I had.
First things first: Your Rotors
If your rotors are wobbled (and many are – mine were) and if you’re going to keep them quiet while you ride, you have to open the calipers which makes the brakes squishy. Sometimes it’s really tricky the angle you have to be at to see where you have a wobble so I’m going to give a photo at a very tight angle to hopefully illustrate what you should be looking at to see if your rotor is straight.
In the photos above, it’s difficult to get the camera in exactly the right location to pick up the two gaps on either sides of the pads – trust me, they’re there.
You have to pay attention to which way the rotor needs to be bent to straighten it out by looking for light between the brake pads and the rotor. If everything seems to be straight, then you see a wobble to the outside, you bend that exact part of the rotor in. Opposite that if it wobbles in, bend it out. Use an adjustable crescent wrench or a special rotor tool to gently bend the rotor in or out as needed. The rotor should be dead straight when you’re done or this won’t work.
Now, assuming the calipers are properly aligned, you have two adjustments for a mechanical set of brakes once they’re centered. The cable tension/barrel adjuster and the inboard/outboard adjustment at the back of the caliper (or front with a set screw depending on the model of caliper – mine are on the back (toward the spokes). The cable tension sets the outboard pad for my calipers. Once the rotors are straight, look between the brake pads and set the cable tension with the barrel adjuster so you’ve got just a few hairs worth of space between the rotor and the outside pad. Then, turn the dial (or set screw with an Allen key) on the back so there’s just a few hairs’ space between the inboard pad and the rotor.
Give the wheel a spin. If it rubs anywhere, you’ll hear it. Get yourself in a position where you can see the wobble and figure out where the rotor is bent and straighten it. Once it’s perfectly straight, give it a spin and test the brakes. If the pads are relatively clean, it should be quite stout compared to what you had. If not, tighten down the barrel adjuster or the back set screw/dial to get it even tighter.
If done right, there should be a world of difference betwixt what you started out with and what you ended with. The key is patience. Straightening the rotors is a bit of a tedious process.