Need help diagnose disc brake issue - squeaking

[weisan]

My gravel bike is currently installed with Shimano GRX Di2, the disc brakes are stopping fine, modulation is good except one thing. When I depress the levers, no sound, the bike slows down fine, only towards to the very end coming to a complete stop, it squeaks...LOUD! What's wonrg?

[prototoast]

This is a common problem. Things I have done that have solved it for me in the past (from least to most expensive):

Make sure the rotor is spaced evenly between the brake pads.
Replace the brake pads.
Replace the rotor.
Sell the bike.

[Mikej]

Pull the pads and sand them, clean rotors with isopropyl alcohol and reassemble-

[RoosterCogset]

Isn't part of the question why there's no squeak (guessing OP's example) braking from 15 to 10mph, but braking from 5mph to 0 there is?

[thwart]

Yikes.

This could move from the Paceline to the 'I've got a problem with my disc bike' forum...

... and he ducks...

[eddief]

https://www.youtube.com/watch?v=Wewvn9VqBUw

https://www.youtube.com/watch?v=Hj9vSl2Vxns

[BagelMaster]

I currently have the exact same issue on one of my bikes. Brakes feel and sound fine. Dragging or really pulling the brakes makes no difference — the only noise is a squawk when coming to a complete halt. I had traditionally squealy brakes a couple years ago and cleaning the rotor with high % isopropyl alcohol and then sanding both the rotor and pads, then cleaning the rotor one more time for good measure seemed to alleviate the issue. It’s still chilly here so I haven’t had the time for spring maintenance yet.

[weisan]

Originally Posted by RoosterCogset

Isn't part of the question why there's no squeak (guessing OP's example) braking from 15 to 10mph, but braking from 5mph to 0 there is?

That's it. Thank you for reiterating.

[slambers3]

Originally Posted by prototoast

This is a common problem. Things I have done that have solved it for me in the past (from least to most expensive):

Make sure the rotor is spaced evenly between the brake pads.
Replace the brake pads.
Replace the rotor.
Sell the bike.

The pads and/or rotors are contaminated. I’d agree with prototoast but also offer this before replacement- When I was in the shop, we used this process to try to decontaminate, which was helpful probably half of the time.
1. Remove pads, sand sheen off with rough sandpaper until only virgin material is visible
2. Thoroughly clean rotor with speed degreaser or brake cleaner. Wipe down thoroughly and then heat the rotor with a torch working around the rotor slowly to cook off any contaminants or residue. Maybe 20-30s /rotor. Do this in a well ventilated area so you don’t have flash fire. It’s possible you may need to repeat this process.
3. Re-install, properly adjust caliper centering and carefully re-bed pads and rotors.

I’ll add since it’s GRX, when you take everything apart make sure to check and see if there’s oil weeping from the piston or seals onto the pad causing the contamination. Be very gentle with these as the pistons are easily cracked.

[Blown Reek]

Originally Posted by Mikej

Pull the pads and sand them, clean rotors with isopropyl alcohol and reassemble-

And then don't forget to bed in the brakes correctly once this is done.

However, maybe you need to face the mounts. That seems to be the go-to-around here. From what I read, almost every bike needs to be faced.

[RoosterCogset]

Originally Posted by slambers3

The pads and/or rotors are contaminated. I’d agree with prototoast but also offer this before replacement- When I was in the shop, we used this process to try to decontaminate, which was helpful probably half of the time.
1. Remove pads, sand sheen off with rough sandpaper until only virgin material is visible
2. Thoroughly clean rotor with speed degreaser or brake cleaner. Wipe down thoroughly and then heat the rotor with a torch working around the rotor slowly to cook off any contaminants or residue. Maybe 20-30s /rotor. Do this in a well ventilated area so you don’t have flash fire. It’s possible you may need to repeat this process.
3. Re-install, properly adjust caliper centering and carefully re-bed pads and rotors.

I’ll add since it’s GRX, when you take everything apart make sure to check and see if there’s oil weeping from the piston or seals onto the pad causing the contamination. Be very gentle with these as the pistons are easily cracked.

Do contaminated pads not squeal then when braking at higher speeds and only squeal when braking at low speeds -- which is original question?

I'll make up a completely guessed answer for OP.. It's like wetting your finger and running along a wine glass rim to get it to sing. Go too fast and this trick doesn't work. Something like that. :-)

[El Chaba]

Originally Posted by thwart

Yikes.

This could move from the Paceline to the 'I've got a problem with my disc bike' forum...

... and he ducks...

If one were divert forum traffic to two sub forums a disc brake problem themed one and a tubeless tire themed one the traffic here would be cut in half. I have no interest in having any equipment falling into either category, but I have to admit that I find the threads interesting in a sort of morbid, train wreck sort of a way…

[oldpotatoe]

Originally Posted by thwart

Yikes.

This could move from the Paceline to the 'I've got a problem with my disc bike' forum...

... and he ducks...

Along with 'tubeless tire setup and use'... Ah, mentioned right above..yupp

2. Thoroughly clean rotor with speed degreaser or brake cleaner. Wipe down thoroughly and then heat the rotor with a torch working around the rotor slowly to cook off any contaminants or residue.

Man 'o man, am I out of touch with current bike stuff.

I have no interest in having any equipment falling into either category, but I have to admit that I find the threads interesting in a sort of morbid, train wreck sort of a way…

I do too....for right below. Discussion forum, view and/or discuss, or not. No reason to take anything bike(toy), personally. There are far more 'don't be a follower of Ned Ludd' than disc brake or tubeless tire posts.
Luddite
Curmudgeon
retroGrouch...

[NHAero]

Originally Posted by El Chaba

If one were divert forum traffic to two sub forums a disc brake problem themed one and a tubeless tire themed one the traffic here would be cut in half. I have no interest in having any equipment falling into either category, but I have to admit that I find the threads interesting in a sort of morbid, train wreck sort of a way…

But isn't there a Retrogrouch Heaven Forum somewhere where the sub Forums are:
- Friction Shifting is Best!
- Love Those Delrin Simplex Derailleurs!
- Cottered Cranks Tips
- Rebuilding Your Freewheel
- Why More Than One Gear Anyway? Manly Men Only!

[Mikej]

Do not use brake cleaner or speed degreasers on rotors, use only a drop of dawn in water and then isopropyl alcohol and a new or known clean rag, and allow to dry before reassembling. I wouldn’t use a torch on the rotor either, I do use a propane torch on metallic pads when contamination occurs to burn out the contaminants, but that is because the pads are porous and a rotor has a solid surface, you can soak the rotor’s in IPA, then clean with a new rag.