Itermittant braking with disk brakes.

[RMARSHP]

Hi. Just bought a new Pedelec mountain bike over the internet. All is working well apart from the disk brakes that have a severe case of ABS. Hard braking is DIABOLICAL, intermittantly grabbing and fading. I had the bike safety checked when I got it and mentioned the brakes but although tighter, the problem is still there, on both front and back wheels and with the motor switched off. Could it be as simple as something greasy on the disks or rims, or might there be another answer?

 

[Smokin Joe]

Warped rotors.

Lay them on a flat surface to check and if that is the case replace.

 

[lpretro1]

More likely contaminated pads than warped rotors - they are grabbing & releasing as the slippy bit is encountered. Fit new pads, bed in and they will be fine

 

[Globalti]

Juddering and a loud squawk as the bike rolls to a stop are classic signs of brakes contaminated with oil or brake fluid. Clean the rotors with IPA or glass cleaner and put the pads in the dishwasher.

 

[Drago]

Surely not? The road boys have been telling us that discs are the Second Coming, the drawback free saviour of us all.

 

[Andywinds]

I've had this with dirty pads before. In the end I removed rotors and cleaned them up and fitted new pads. I think for now I am happy with my rim brakes on the road bike because of this. Warped rotors, how often does this happen, had MTB for years with rotors and never had a warped one.

 

[Globalti]

Warped rotors can be straightened by bending judiciously with a padded spanner.

 

[RMARSHP]

Thanks to all for your advice. Pretty sure the rotors are running true, so I think you're all right when you point to contamination. I'll get cleaning and report back. Thanks again.

 

[bykeshed]

Contaminated pads/discs, possible cheap pads not bedded properly.

Properly cleaning pads and rotors should sort it - properly clean doesn't mean just wipe over, this'll make it worse. Automotive brake cleaner sprayed onto a clean cloth for the rotors, clean several times spraying onto a clean bit of cloth each time. Pads just need to be rubbed lightly on very fine sandpaper in circular motions for a few seconds. The pads may need bedding in properly again.