Adjusting cheapo disc brakes



N

nafuk

Guest
A friends children have been bought cheapo 24" disc full-suspension
mountain bikes for Christmas.

The brakes rub slightly - when the brakes are operated the discs is
pushed over/bent slightly from the moving piston to the staionary one.

Will these wear in or is there some adjustment to the position of the
discs I can make (by adjusting the spindle)?

Thank you
 
P

Paul Boyd

Guest
nafuk said the following on 07/01/2008 15:43:
> A friends children have been bought cheapo 24" disc full-suspension
> mountain bikes for Christmas.
>
> The brakes rub slightly - when the brakes are operated the discs is
> pushed over/bent slightly from the moving piston to the staionary one.
>
> Will these wear in or is there some adjustment to the position of the
> discs I can make (by adjusting the spindle)?


You should be able to adjust both pads to be about 0.5mm away from the
disc with the brakes off. These brakes work by bending the disc towards
the stationary pad, but they shouldn't rub with the brakes off. I'm not
quite sure what spindle you're talking about adjusting though - not the
axle, surely?

Although the following link won't apply directly to you, the information
in it might be useful:
http://www.parktool.com/repair/readhowto.asp?id=124

--
Paul Boyd
http://www.paul-boyd.co.uk/
 
J

Jonathan Schneider

Guest
nafuk <[email protected]> writes:

> The brakes rub slightly - when the brakes are operated the discs is
> pushed over/bent slightly from the moving piston to the staionary one.


I have cheapish (though probably not as cheap as these) mechanical
disc brakes on my MTB where only one pad moves. It follows that the
stationary pad has to be in light contact all the time otherwise the
disc will have to bend significantly when braking and too much lever
movement will be needed.

This is what I do

1/ Clean pads and discs as necessary. Low tech cloth or even squish
paper between pads and disc and turn wheel.

2/ Use the main mounting bolts (necessary for gross adjustment) or
stationary pad adjuster (which mine has) to get the stationary pad
touching lightly.

3/ Use the cable adjusters (I have in-flight adjustable ones on the
handlebar as well as more conventional ones) to shift the moving pad
so the smallest lever movement brakes.

4/ One day the pads will really obviously need replacing and this
should be done well before metal grinds into metal and knackers the
discs.

Jon
 
D

Doki

Guest
Jonathan Schneider wrote:
> nafuk <[email protected]> writes:
>
>> The brakes rub slightly - when the brakes are operated the discs is
>> pushed over/bent slightly from the moving piston to the staionary
>> one.

>
> I have cheapish (though probably not as cheap as these) mechanical
> disc brakes on my MTB where only one pad moves. It follows that the
> stationary pad has to be in light contact all the time otherwise the
> disc will have to bend significantly when braking and too much lever
> movement will be needed.
>
> This is what I do
>
> 1/ Clean pads and discs as necessary. Low tech cloth or even squish
> paper between pads and disc and turn wheel.


IME wet and dry and car brake cleaner work well for contaminated brakes.
I've brought brakes back from shocking to perfect that way.
 
Z

Zog The Undeniable

Guest
nafuk wrote:
> A friends children have been bought cheapo 24" disc full-suspension
> mountain bikes for Christmas.
>
> The brakes rub slightly - when the brakes are operated the discs is
> pushed over/bent slightly from the moving piston to the staionary one.
>
> Will these wear in or is there some adjustment to the position of the
> discs I can make (by adjusting the spindle)?


Halfords sell shims (OK, thin washers) which move the whole caliper
inboard or outboard.
 
M

M-gineering

Guest
Zog The Undeniable wrote:
> nafuk wrote:
>> A friends children have been bought cheapo 24" disc full-suspension
>> mountain bikes for Christmas.
>>
>> The brakes rub slightly - when the brakes are operated the discs is
>> pushed over/bent slightly from the moving piston to the staionary one.
>>
>> Will these wear in or is there some adjustment to the position of the
>> discs I can make (by adjusting the spindle)?

>
> Halfords sell shims (OK, thin washers) which move the whole caliper
> inboard or outboard.


The stationary pad might have an adjuster, but i would suggest you think
twice before touching these BSO's ;)

--
/Marten

info(apestaartje)m-gineering(punt)nl
 
N

nafuk

Guest
On 7 Jan, 20:36, M-gineering <[email protected]> wrote:
> Zog The Undeniable wrote:
> > nafuk wrote:
> >> A friends children have been bought cheapo 24" disc full-suspension
> >> mountain bikes for Christmas.

>
> >> The brakes rub slightly - when the brakes are operated the discs is
> >> pushed over/bent slightly from the moving piston to the staionary one.

>
> >> Will these wear in or is there some adjustment to the position of the
> >> discs I can make (by adjusting the spindle)?

>
> > Halfords sell shims (OK, thin washers) which move the whole caliper
> > inboard or outboard.

>
> The stationary pad might have an adjuster, but i would suggest you think
> twice before touching these BSO's ;)
>
> --
> /Marten
>
> info(apestaartje)m-gineering(punt)nl


Thank you for the replies. The stationary pad does not have an
adjuster and the caliper can not be adjusted. Perhaps some shims may
help, either on the caliper or on the axle. I have set them as best as
I can. At least the kids will get a little bit of extra exercise!
 
D

Doki

Guest
"nafuk" <[email protected]> wrote in message
news:[email protected]m...
> On 7 Jan, 20:36, M-gineering <[email protected]> wrote:
>> Zog The Undeniable wrote:
>> > nafuk wrote:
>> >> A friends children have been bought cheapo 24" disc full-suspension
>> >> mountain bikes for Christmas.

>>
>> >> The brakes rub slightly - when the brakes are operated the discs is
>> >> pushed over/bent slightly from the moving piston to the staionary one.

>>
>> >> Will these wear in or is there some adjustment to the position of the
>> >> discs I can make (by adjusting the spindle)?

>>
>> > Halfords sell shims (OK, thin washers) which move the whole caliper
>> > inboard or outboard.

>>
>> The stationary pad might have an adjuster, but i would suggest you think
>> twice before touching these BSO's ;)
>>
>> --
>> /Marten
>>
>> info(apestaartje)m-gineering(punt)nl

>
> Thank you for the replies. The stationary pad does not have an
> adjuster and the caliper can not be adjusted. Perhaps some shims may
> help, either on the caliper or on the axle. I have set them as best as
> I can. At least the kids will get a little bit of extra exercise!


Surely you can loosen the caliper mounting bolts and move them about that
way? If not, ovalise the holes with a file.
 
R

Rob Morley

Guest
In article <[email protected]>, Doki
[email protected] says...

> Surely you can loosen the caliper mounting bolts and move them about that
> way? If not, ovalise the holes with a file.
>

That's not the direction that adjustment is needed.
 
S

squeaker

Guest
On 7 Jan, 15:43, nafuk <[email protected]> wrote:
> The brakes rub slightly - when the brakes are operated the discs is
> pushed over/bent slightly from the moving piston to the staionary one.
>

IME 'most' mechanical disc brakes have one moving pad (linked to the
cable actuator) and one static pad, so the disc is deflected
(slightly) when used. That said, you need to be able to adjust the
static pad as it wears (cable length does the moving one - within
reason) so that both pads are just clear of the disc. If there's no
adjuster (and the caliper can't be moved then shimming might be the
way, but I'd be wary of the pads falling out if too much is required.
Adjusting the caliper would be the other (maybe safer / easier)
approach.