Disk brake squealing after bike shop changed my pads. Is it enough reason to ask them to re-service (for free)?

Question

I recently took my bike to the shop, since it started making a weird metal on metal (not squeal, just hard brushing sound). After checking it out they saw that the back brake pads were really (REALLY) worn down, so they changed them.

Now my bike is doing a really loud screechy sound when I use the back brakes, and the bike doesn't even stop that fast, I remember my back brakes being pretty strong, completely stopping the back wheel even if I was going fast (of course, if I was going fast it would drift a little.. but the wheel was locked). Now it's making this loud sound and just kind of slowing me down slowly, but not fully breaking.

I didn't know if this was normal.. but after reading a few question here like this, it seems like it is definitely not. (Fixing noisy V brakes)

Is this a legitimate reason to take the bike back to the shop and tell them there is something wrong with their work?

Thanks!

Answer 1

I tend to run into the same scenario when I replace my own brake pads on my bike's TRP Spyre mechanical disc brakes. TRP is Tektro's high-end division, and I use Shimano B01S resin pads or anything similarly shaped (TRP says pads for Shimano BR-M515/M575 calipers will fit).

The cause of the squealing in my experience is the lack of proper bed-in. Disc brakes (even on cars) work best when there is enough of the brake pad's friction material deposited onto the face of the rotor. When you change and install new brake pads, this synergy is lost. The rotors still have the "memory" of the old brake pad material on their faces, with very tiny imperfections that don't line up with the surface of the new pads, and this is what gives the high-pitched squealing. When you bed in new pads to the rotors, you're effectively scrubbing off the old friction material while replacing it with that of the new pads'.

To bed-in new brake pads, find a flat surface or downhill incline where you can build up a bit of speed. Accelerate to about 10 miles an hour, then pull on the levers - smoothly but powerfully - to an almost complete stop. Keep repeating this over and over. With enough cycles you will notice the squealing become less audible.

Some people even resort to sanding of the rotor faces and fresh pads with 100-grit and 220-grit sandpaper in order to get the old friction material off and quicken the whole bed-in process. Be careful handling the brake rotor, though - best to use gloves for this job as skin oils can easily contaminate a rotor.

Brake pads will also naturally bed-in by themselves, but you will have to bear with the screeching that whole time.

Answer 2

This isn't necessarily unusual for fresh disc pads.

Give it a solid 20 miles. Then if you still have problems coming to a stop, take it to the shop and have them look at it. Even still, it's not necessarily something wrong with their work. It might be, if they were clumsy and didn't align things properly or left oil on the pads. But a little noise isn't enough to convict them.

Answer 3

I'm assuming Avid BB7 style brakes and not hydraulic. I wouldn't bring the bike back. If you are using skewers on your hub, remember that any slight mis-alignment of the wheel in the dropouts will affect brake disk squeal. Because the skewers are so easy to reset, as well as its pretty easy to turn the red adjustment knobs on the brakes you might discover this is something you want to understand how to 'adjust' yourself. With skewers on the axles and BB7 style brakes no tools required. You will have to understand the 1/3 alignment rule for that style brake.

If you have hydraulic brakes, and a non-adjust axle mount system that's a different story. Please do bring the bike back to the shop. It would be safer to have a pro look at the system to ensure everything is correct.

On the other hand, if you wanted the shop to teach you a thing or two about BB7 adjustment (1/3 alignment rule) and skewer use (how tight is should it be?), most shops would be happy to help you.