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.
Ride total: 9,452
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 streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.
Save the money. Loosen the caliper mounting bolts, squeeze the lever ensuring the pads are tight against the rotor then as you keep tension on the brake lever slowly tighten the caliper mounting bolts. If you tighten the bolts too quickly it may cause the caliper to move, so as the bolt snugs go slowly. Been doing this for decades with nary a squeal, Unless of course your rotor is bent.
This! I have also been doing this for years.
Save your money.
Cheers
Looks like a useful tool but a folded business card works, too.
The metal slide cover on an old 3.5 floppy disc does the same.
Also, I have cut strips from a thin plastic card (thinner than a credit card). Seems to work well.
Thanks for the feedback and tips, guys. In our previous article on disc brake rubbing, which is linked to early in this latest story, the business card trick is shown.
Centering the caliper without a shim tool like the one from Hayes or a business card will work if you’re lucky, Ken – which you obviously have been (congrats!). But, it doesn’t always work with all rubs. That’s where a shim tool like this comes in handy. The Hayes tool is easier to slip into place than a business card and easier to remove, too, but the card will work nicely, too.
Using a metal slide cover off an old 3.5 floppy is a clever idea and I’m even old enough to have a few of those lying around still 😉 Thanks Bobby!
Thanks for the added tips!
Jim Langley
Usually when a rub is persistent I’ll shine a light through the caliper and line it up manually. If it continues I’ll just replace the rotor. I think someone many years ago made varying size shims to mount behind the rotor to help with machining irregularities. I’ve not wrenched at shop in years so I may be a bit out of touch with the latest techniques and parts available. Thanks for the reply and best to you.