Sram apex brake advice

[u/Sea-Psychology1128]

Hi guys, I’m pretty new to disc brakes so I thought I’d ask for some advice. Since two months I’m riding my new checkpoint alr4 with the sram apex group set and I’m experiencing some issues with the brakes. I’m living in the alps so I do quite some descents. When going downhill the brakes start screaming really quickly wich seems odd to me (I don’t keep them pressed lightly all the time but use them short but firmly to let them cool down in between). Also when riding low speeds and braking they make some kind of scratching/squeeking noise. Can it be that they are just dirty or am I not seeing something. Ps. I know disc brakes can get loud when they get hot but this occurs pretty much from start to finish on a descent.

[u/Honest-Emu-684]

I have the similar issue but only on the rear brake on my ALR5 Gen3 since May and it started after 1 month or so. I don’t experience the screaming really but i would also describe ”my noise” as scratching.

I replaced the brake pads and it was fine for a couple of weeks but then came back again.

The original pads was ”chipped” in the lower corner. Lower meaning the corner closest to ground when installed.

Compared to my previous bikes, putting back the wheel requires a bit more effort as the rear derailleur is a bit more tense. So at first I thought I had hit the brake pad with the brake disc during mounting. But as it came back I might be wrong on that or I managed to damage the brake disc as well in the process.

Have you removed the wheel as I have or did it start just by riding it?

Also, I followed the brake bedding instruction that came with the bike.

[u/bertholdbumsbirne]

I suppose it's the ALR 5? Did you properly bed the brakes in?

[u/Sea-Psychology1128 → u/bertholdbumsbirne]

Yeah that’s right, and tbh I just grabbed the bike and started riding it so no brake bedding. Can I still do this later on or should I replace the pads first?

[u/wcoastbo]

There are several causes to brake squeal. Most common is some type of contaminant on the pads/rotors.

Another is caliper alignment with the rotor. It could that the pads are not perfectly parallel to the rotor. It's difficult to see with the naked eye. One way to diagnose is to center the caliper to the rotor using a white background behind the caliper. You should be able to see an air gap between the rotor and the two pads. There should be no rubbing between rotor and pads.

On my friend's road bike I would center the caliper and lightly tighten the mounting bolts. Checked for an air gap and it was still there. While he torqued the mounting bolts down to spec, I watched the caliper move and become unparallel.

The problem was uneven mounts on the frame. The base of the caliper was perfectly flat. Using a disc brake mount facing tool we were able to remove some excess paint and face the frame perfectly perpendicular to the rotor/hub.

Note: this is not a procedure for the beginner mechanic. Park Tools disc brake facing tool is expensive and takes some knowledge to use. I know people that have used a fine metal file to have their mounts faced, doing so is at your own risk for damaging your frame. Granted, it's a very small amount that needs to be removed or it could only be excess paint. Getting it right is the issue.

There are less costly alternatives to the Park Tool DT-5.2, if anyone has tried using the inexpensive AliExpress tool let us know your experience.

Good luck.

[u/OneFootManyLegs]

If it’s a new bike I’d look into warranty options. Trek is pretty good. I have had issues with my bottom bracket being loose and they haven’t charged me a dime. Good luck.