Adjusting Disc Brake help

diamondback_20

I bought a Diamondback mountain bike.
I'm new to disc brakes,
I decided to adjust my disc brake because the lever required more pull to slow down.
Also the I found the disc brake was squealing when braking. So I took the wheel off and took the pads out and cleaned the with Isopropyl Alcohol and took a bit of the surface of with sandpaper. But the pads back in and then put wheel on then adjusted the brake. I don't know if I am adjusting it correctly. During adjustment I spin the wheel and the disc (rotor) rubs with one of the pads only in a certain place of the rotor. Could it be that the part of the rotor is bent? Can a poor set-up cause the brake to squeal?
I have some images of the disc brake, it is a Promax Disc and pads.

supersonic

Yes, the rotor may be a bit out of alignment. See if you can spot where it is and gently bend it back (pliers in a cloth work well).

desmorrow

- you could loosen the mounting bolts for the caliper then press the brake lever to 'centre' the disc. With the lever squeezed, tighten up the bolts then release the lever and see if that helps
- in terms of the levers - some levers have a wee screw to adjust the lever position - if you move the lever away from the bar this can help. if ur not sure find out the type of brakes they are and google for a manual but some brakes don't have this
- by the looks of your picture - they arn't hydraulic - right? you should be able to adjust the pad position by using an allen key on the back of the caliper - you should be able to move the pads further away to stop rubbing or closer to get better braking.
- but if the disc is bent then you will need to straighten in - never done that myself.

diamondback_20

Yes it's a mechanical disc brake not a hydraulic.
Will give the suggested adjustments a try and see if that helps.
Thanks for replies.

diamondback_20

I still have an annoying squeal when braking, I have taken pads out, roughed up pads with sand paper and used Isopropyl on pads and rotor to clean.
Put them back in, tried again, still squealing, sprayed some muc-off disk cleaner on pads, stopped squeal for about the first mile and then the squeal was back. Maybe I need to buy new pads.

supersonic

you could loosen the mounting bolts for the caliper then press the brake lever to 'centre' the disc. With the lever squeezed, tighten up the bolts then release the lever and see if that helps

This only works with dual activated pads - this is a single pad activation, so I would not try it.

Kowalski675

supersonic wrote:

you could loosen the mounting bolts for the caliper then press the brake lever to 'centre' the disc. With the lever squeezed, tighten up the bolts then release the lever and see if that helps

This only works with dual activated pads - this is a single pad activation, so I would not try it.

Indeed. Best way I've found to get a nice short lever action on my cable Tektros is to wind the adjuster almost fully in, loosen the caliper bolts and move it so it's just clearing the disc, retighten the bolts then move the inboard pad inwards with the adjuster allen bolt.

The Rookie

Wind the static pad back, release cable tension, adjust caliper by eye to central and square and tighten bolts.

Adjust static pad in until it is just touching the disc as you spin the wheel and then back off a fraction, repeat for the moving pad (using cable clamp bolt and or tension) and you'll be sorted.