bike repair gone wrong

kingoffifa

well..

helped a lad yesterday fix a puncture on a disc brake (hydraulic) .

now the brakes squeal like the proverbial pig.

both front and back.

any idea what i did wrong? could it just be dirt on the rotors?

any suggestions would be great - dont have these types of brakes myself.

all we did was take the wheels off and put them back on again.

Pinch Flat

kingoffifa wrote: »

well..

helped a lad yesterday fix a puncture on a disc brake (hydraulic) .

now the brakes squeal like the proverbial pig.

both front and back.

any idea what i did wrong? could it just be dirt on the rotors?

any suggestions would be great - dont have these types of brakes myself.

all we did was take the wheels off and put them back on again.

Check the wheel is seated correctly. Plenty of guides on the interweb - http://www.bikeradar.com/gear/article/how-to-align-your-disc-brake-calipers-32591/

Guys at bike radar are pretty good

kingoffifa

will do. thanks for link.

disco1

You need to reset the calipers.......take both wheels out...used a blunt screw driver or butter knife and put detween the disc pads and gently add pressure to widen the gap careful not to damage pads...this resets the pads.
Pop wheels back on job done.

seamus

You need to be careful with disc brakes that you don't get any contaminants on the rotor. These will transfer to the pad, causing uneven grip of the pad against the rotor, which causes vibration and this familiar squeal you hear.

This often happens if you liberally spray lube on the bike and manage to soak the rotors, but can also happen if you're just doing routine work like changing a tube and manhandle the rotor with dirty hands.

Aside from checking the simple stuff like the wheel being in place properly and the skewers being tight enough, there are plenty of guides online for cleaning the rotors & pads.

inc21

Clean the discs with alcohol when you have tried all the above and the squeal is still there.

JBokeh

Could be anything from the R/H and L/H getting swapped and are not bedded into the grooves on that side of the disc,A few hard decelerations from about 30 - 40 km/h will bed them,but don't come to a complete stop,and do them in rapid succession so the disc gets hot,let it cool a bit and chuck some water over it,and repeat a couple more times,the braking should get better every time.

Could also be that there was a bit of brake fluid got onto the pads,get some brake cleaner from a motor factors in aerosol form,take the pads out,spray them liberally with the cleaner,allowing it to run out of the pad. If they are sintered pads you can heat them on and off for 3 second intervals with a blow torch,until they stop smoking,and it helps burn the oil out of the pads,but only with the sintered pads and not the resin ones. I've done this with mine quite a lot of times because they're pretty rare and expensive,so I just clean them off. Give them a rub with sandpaper or a file,spray the disc with brake cleaner and whack them in and go through the bedding process again.

However if they are avid brakes they tend to squeal like a mofo and it is hard to stop it,I had them before and tried all sorts of tricks with sticky tapes and glue to shut them up and nothing was a permanent fix.

LagunaSeca

disco1 wrote: »

You need to reset the calipers.......take both wheels out...used a blunt screw driver or butter knife and put detween the disc pads and gently add pressure to widen the gap careful not to damage pads...this resets the pads.
Pop wheels back on job done.

Step 1 as above. Put a thin rag/bit of old t-shirt etc. around the screw driver or knife to avoid damaging the pads.

Step 2. Put the wheel back on and tighten up. Loosen the 2 allen key bolts that connect the brake caliper to the fork. Apply the brake lever and keep it applied while you re-tighten the allen bolts. Once done release the brake lever and the caliper/pads should be centred.