Jim’s Tech Talk
By Jim Langley
Once set up well, road bike disc brakes usually just work. But, as with rim brakes, some discs can occasionally develop a rub. The usual cause is that a brake pad, or more than one, inside the brake caliper rubs on the rotor (the metal discs attached to the wheels). If you’re lucky, the rub is so minor that you don’t even notice it.
But, if you do – and especially if you can feel it or hear it when you’re riding or even walking the bike, it can drive you nuts.
Disc brakes can rub for several different reasons. A while back I gave some tips for diagnosing and fixing rubs. You can read those here.
Today, I’m sharing a tool that I think everyone who enjoys working on their own disc brake-equipped road rocket will appreciate having. It’s the Hayes Brake Pad & Rotor Alignment Tool $17.95: https://amzn.to/2pvaRbU.
This folding stainless-steel and aluminum tool is small and light so that you can even take it along on rides if you want. The aluminum body of the tool works as a brake pad spreader (once the wheel is removed), a braking power tester and a pad gap feeler gauge.
Feel ‘R Gauge for Fixing Rubbing
The best function of the tool and the reason I am recommending buying one, is its Feel ‘R Gauge Caliper Alignment Tool. It’s comprised of two side-by-side and connected stainless steel feeler gauges – the shiny piece you can see on the tool.
They’re unfolded from the tool like opening a pocket knife and then slid in between the rotor and the brake pads to act as thin shims to help center the brake caliper to stop rubbing.
These stainless gauges are so thin and flimsy (each is .25mm thick), you must handle them with care. You gently wiggle and push them into the brake, over the rotor and between it and the pads on both sides. Don’t jam/force them in or you will bend and ruin then.
I do it by holding them against the rotor and turning the rotor with the tool on it watching carefully that the feeler gauges get started right and slide into place between the brake pads and rotor.
It’s not difficult. It just requires watching what you’re doing. Also, you absolutely must keep it clean of any lube, grease or grime that could get on the rotor or pads and ruin your braking.
Now, Center the Caliper
Once the Feel ‘R Gauge is in place, all that’s needed to center the caliper is to loosen its mounting bolts (look close – only loosen the mounting bolts attaching the caliper to the frame/fork).
With the caliper bolts loose and the Hayes stainless feeler gauges in place (photo), hold on the brake you’re working on by squeezing the lever and keeping it squeezed. This will center the caliper over the rotor.
To finish the adjustment, keep holding the brake on and then tighten the bolts fixing the caliper to the frame again. Be sure to torque them, too (usually 6 – 8 Newton Meters). When you release the brake and remove the Hayes tool, the rotor rub should be gone.
I like Hayes’ rub-fixer enough that I bought several to have them in my different tool boxes and in my shop, too. I think if you’ve experienced an annoying disc rub you’ll appreciate having one, too.
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s cycling streak ended in February 2022 with a total of 10,269 consecutive daily rides (28 years, 1 month and 11 days of never missing a ride). Click to read Jim’s full bio.