Terrible noise when feathers rear brakes

DanW82

Hi,
I've just got a Virus Nucleus 27.5 that was pre-built.
The rear brake is making a terrible juddering noise,
isn't squealing and it's not grit in the pads.

When I got the bike it was rubbing against the pads constantly so i adjusted them slightly and the wheel now turns freely.
They still made a slight noise which has gotten far worse after a few km, I've only been out 2/3 times and only done a few km each time before the brake noise is unbearable.... I haven't even used the brakes hard and hardly needed them at a in the few km I did.

Not sure if it's related but when I turn the back wheel whilst holding the bike up by the seat I can feel the bike 'bouncing' as if the wheel is turning around an oval. (Tried to include a video of this but it's difficult). Is this normal?


We also have 2 hybrids with disc brakes, I've adjusted both myself when setting them up as the discs rubbed on the pads and didn't have this issue with either of them.

I've tried basic adjustments a couple of times but doesn't solve it.

My first post here and first mountain bike since I was a teenager.

2 videos below.
One is the brake noise, the other is me turning the wheel whilst the bike is on a rack. You can see it 'bouncing'. The other bikes don't do this.

https://drive.google.com/drive/folders/19GhQ8YnyrvGNskj5gmbYS_wv_VawoVgP?usp=sharing

Any advice appreciated.

Thanks in advance
Dan

wilberforce

Have you tried bedding the pads in?
It is a bit of a painful video to watch, but you will get the idea https://www.youtube.com/watch?v=BWQxGzHQZVU

reaperactual

Could be oil or other contamination on one section of the rotor. Would get some bike brake cleaning product or iso propyl alcohol and give rotors a good clean, maybe remove pads and give them a light sanding to remove any shiny looking surface then bed them in as suggested afterwards.

reaperactual

Hold the rear wheel at the top and move from side to side and feel for play or listen for knocks. Check cassette also for play, make sure thru axle is properly tightened to correct spec or at least not loose. Try back pedalling when on the stand and feel for any resistance.

steve_sordy

In addition to what Reaper said:

Any oil or grease contamination on the discs will affect the pads, and vice versa. One hand washes the other! So you have to treat both.

In addition to cleaning the disc with iso-propyl alcohol (or disc brake cleaner, same stuff), you need to do a lot more to the pads than just sand them. I suggest the "disco inferno"! It never fails.

Disco Inferno

Remove pads and drop some iso-propyl alcohol (IPA) onto each pad, just enough for it to spread out and cover the pad area. Put the pads onto a concrete surface (I use my coal bunker). Use a gas torch (blowlamp thingy) and heat each pad surface until the corners glow red. Keep up the flame and suddenly the pads will appear to catch fire and you will get flame. Maintain the heat and then black smoke will boil off the pads. That is the contaminant burning off. Once the smoke fades, transfer the flame to the other pad.

The pads will end up with a black coating. Place some sandpaper onto a flat surface and rub each pad over the sandpaper in a circular fashion for 10-15 seconds, pausing a few times to blow off the black stuff from the sandpaper.

Refit the pads and then bed them in. Google bedding in brake pads if you don't know how to do it.

One guy that didn't have a blowlamp used the gas stove in his kitchen. It was a success, but he didn't comment on how he placated his wife at the smell and fumes when she got home.

reaperactual

Never done the 'Disco Inferno' method. Sounds like fun and would be effective at getting rid of contaminants on pads.

marcinuk

I flew through diesel puddle. Once. It did messed up my pads. Just remove them and get them very hot with gas torch. You can use over 220C but don;t let your misses see. Heat them until they stop smoking. Then pour water on them (when cold) and rub padding on padding to create paste. Then rinse with water and put them back on. DONE

Here is a short video
https://www.youtube.com/watch?v=Wewvn9VqBUw

DanW82

Cheers guys, thanks for the advice.

Unfortunately its not solved yet but I've swapped parts around and ruled a few things out.

Steps taken.
1. With IPA I cleaned up discs and pads but it didn't work, I don't have a gas torch but before getting one realised the the discs are identical to my other bike...... see point 3
2. Changed the pads.
3. Swapped the rear wheel with my other bike, the disc is identical, different size wheel but close enough that it fit nicely.

So I've swapped out the following parts and the noise remains:
1. Pads
2. Wheel
3. Disc

In doing this I removed the rear wheel and pads a few times, I noticed each time I did this the first few very light goes on the brakes was seemed ok but then started to re-occur.

So I'm now thinking about other components but it's a brand new bike that was suppose to be setup, I've not even had a proper ride on it yet. I'm just going to get into with the supplier tomorrow - I think the misses is getting frustrated I'm pissing around with it all the time and note riding the bloody thing.

I did notice when inspecting other brake components that the fluid reservoir on the brake lever has a star bolt with a slightly damaged head; as if someone has tried to tighten/loosen it with the wrong key - brakes 'responsive' though so its probably unrelated but doesn't inspire confidence.


Thanks

steve_sordy

Ref that video, he mentioned that it takes him 30 mins to "cook" the pads. I hope he was referring to when he used the oven. When I use a gas torch, I'm looking at just a few minutes. (Refer back to my previous post on the topic.)

My cues are:
# edges of pad glowing red
# flame
# black smoke
# smoke stops

It really is quick and easy

DanW82

Chain reaction have advised to take it to a bike shop and they will have for repairs under £30 and anything above they will have to approve.

reaperactual

You tried everything you could and don't think there is more you could do to sort your issues out.

Not sure the £30 will go far towards fixing costs so may need more communication with C.R.C. but they have to take responsibility as something obviously isn't right.