My disc brakes aren't working after I cleaned them

[Anthony MTB]

So my front disc brakes were squealing a bit, so I got some isopropyl and cleaned the rotor and pads. When I put the wheel back on, the squealing had stopped but the brake is not working properly. Even if I clamp the brakes really hard the wheel still moves if you push it. Has anyone got any solutions?

[Sprockets]

Something I've done in the past 

Ride your bike in the parking lot, pedaling while holding the brake in to warm up the disc and pads. Spray some clean water over the pads and again pedal with brake in to get it nice and hot again. Repeat this a couple times and see what happens. If your pads are contaminated, you could try holding a flame onto them to burn some contaminant off. But make sure to remove them from your brake caliper before doing this. 

[The Ouzo]

similar to what Sprocket has suggested

get a little speed (20-25km/h) and then slam on the brake in question, only release just before you come to a stop, repeat.

basically like you're bedding in the brake again.

[openmind]

Before you do the above things, take the pads out and rub them smooth and clean on some medium grit sandpaper. Don't use alcohol on the pads, only the rotors. Works for me every time. 

[MORNE]

Your disks basically work because when you apply the brakes, a small amount of material from the brake pad is deposited onto the rotors, creating a friction layer. When you clean them, you remove that layer.
 

So yes, when you bed them in initially / from new…you are basically trying to get pad material on them. As mentioned already, this is why water helps when bedding in a new/clean rotor…it makes a bit of a ‘paste’ which settles into the irregular braking surface better. They’ll be noisy for about 4-5 hard pulls but you’ll feel the power increase exponentially. 

Edited January 24 by MORNE

[love2fly]

On 1/24/2025 at 11:35 AM, MORNE said:

Your disks basically work because when you apply the brakes, a small amount of material from the brake pad is deposited onto the rotors, creating a friction layer. When you clean them, you remove that layer.
 

So yes, when you bed them in initially / from new…you are basically trying to get pad material on them. As mentioned already, this is why water helps when bedding in a new/clean rotor…it makes a bit of a ‘paste’ which settles into the irregular braking surface better. They’ll be noisy for about 4-5 hard pulls but you’ll feel the power increase exponentially. 

Yip. Once you get Stiction of the material, you get Friction.....or something like that and it helps braking performance. It applies to racing car brakes with carbon discs as well.

Edited Saturday at 02:23 PM by love2fly

[Anthony MTB]

Thanks I did everything and it helped a lot my brakes are working fine now😊

[The Ouzo]

17 hours ago, love2fly said:

Yip. Once you get Stiction of the material, you get Friction.....or something like that. It applies to racing car brakes with carbon discs as well.

you see, I was taught in the automotive world many many eons ago that hot discs and water are a recipe for warped / cracked discs.

So when I see water being poured on bicycle discs or hear of advice to do so I get the hibby jibbies 

[MORNE]

2 hours ago, The Ouzo said:

you see, I was taught in the automotive world many many eons ago that hot discs and water are a recipe for warped / cracked discs.

So when I see water being poured on bicycle discs or hear of advice to do so I get the hibby jibbies 

Many (or not so many) ‘eons’ ago brake pads in cars contained asbestos too, but hey, they worked great except for the increased heat generation and uneven wear patterns, oh..and the cancer dust. This meant discs warped way easier due to the huge temp deltas. 

Surely then you must know that discs wont warp by being briefly splashed by a small amount of water? Like say…in the rain…or what about driving through a large puddle. 

Hell, there were f1 teams using this trick in the 80s to cool brakes,  exploiting a loophole in the regulations by adding water to the brake cooling system during a race, effectively making the car lighter through the race.

On a bicycle, excess heat will glaze the pads and or boil the fluid way before warping the disc anyway. You are more likely to warp n bicycle rotor in a crash or by bumping it into stuff.

On the topic of using water to bed in brakes…you are literally just using a squirt of water on the brake pads/caliper like you would when you wet sand something. You arent cooling anything to the point of a 100*C temp swing.

I get roadies are a bit late to the disc brake party, but these are all tried and tested methods to break in pads/discs on mountain bikes. Imagine warping a rotor every time you rode in the rain or through some puddles. I wouldn't trust a ham fisted car mechanic to work on a bicycle that costs more than most the cars they work either 😅

Edited Saturday at 12:40 PM by MORNE