help with disc brakes

[Kooner]

Hello,

I just bought a 2004 GT I-Drive 2.0 bike and I believe there is
something wrong with the front rotor. This bike has mechanical disc
breaks.
The brake pads rub the rotor ever so slightly in the same spot as the
wheel rotates. I spent a few hours adjusting the whole brake assembly
but, the pad still rubs. I can see a slight wobble in the front rotor
as is spins. I took the bike back to where I bought it. The bike
mechanic agreed the rotor was slightly warped so he bent/flexed it a
little with his hands! The rotor wobbles less but, the pad still rubs.
The rear pad and rotor is perfect. I mean, there is a hair of a gap
between the rotor and pads and there is absolutely no rubbing on the
rear rotor. So, my questions are:

1. Is there a flatness or wobble specs for bike rotors?
2. Is in normal for the front pads to rub? What if the bike is
turning?
3. What is the annoying vibration sound coming from the front
rotor/pad assembly when I'm riding? Is it something to do with the
floating or sliding caliper?
4. What else can I do or try?

Any help would be appreciated.

Kooner

 

[Kinky Cowboy]

On 24 Mar 2005 23:10:17 -0800, "Kooner" <[email protected]> wrote:

>Hello,
>but, the pad still rubs. I can see a slight wobble in the front rotor
>as is spins.
>Kooner

If you can see the wobble, the rotor is too warped. Take it back to
the shop and insist on getting a new rotor. Warped rotors can
contribute to brake judder, which is an annoyance you shouldn't have
to put up with on a new bike.


Kinky Cowboy*

*Batteries not included
May contain traces of nuts
Your milage may vary

 

[David]

"Kooner" <[email protected]> wrote in message news:[email protected]...
>
> 1. Is there a flatness or wobble specs for bike rotors?

Rotors have runout specs. Yours likely exceeds the spec.

 

[daveornee]

Hello,

I just bought a 2004 GT I-Drive 2.0 bike and I believe there is
something wrong with the front rotor. This bike has mechanical disc
breaks.
The brake pads rub the rotor ever so slightly in the same spot as the
wheel rotates. I spent a few hours adjusting the whole brake assembly
but, the pad still rubs. I can see a slight wobble in the front rotor
as is spins. I took the bike back to where I bought it. The bike
mechanic agreed the rotor was slightly warped so he bent/flexed it a
little with his hands! The rotor wobbles less but, the pad still rubs.
The rear pad and rotor is perfect. I mean, there is a hair of a gap
between the rotor and pads and there is absolutely no rubbing on the
rear rotor. So, my questions are:

1. Is there a flatness or wobble specs for bike rotors?
2. Is in normal for the front pads to rub? What if the bike is
turning?
3. What is the annoying vibration sound coming from the front
rotor/pad assembly when I'm riding? Is it something to do with the
floating or sliding caliper?
4. What else can I do or try?

Any help would be appreciated.

Kooner

Clearance between pads and rotor is in the range of 0.6 to 0.8 mm (depending of manufacturer). You should be able to set the pads to that clearance and not have any rotor touching. If the rotor touches anywhere through it's rotation it is out of specification.
Ask your shop for a replacement.

 

[Jose Rizal]

Kooner:

> 1. Is there a flatness or wobble specs for bike rotors?

Probably, but these won't be to the nanometer.

> 2. Is in normal for the front pads to rub?

No, unless the pad is much too close to the rotor.

> What if the bike is
> turning?

What if it is?

> 3. What is the annoying vibration sound coming from the front
> rotor/pad assembly when I'm riding? Is it something to do with the
> floating or sliding caliper?

Might just be the rubbing you're experiencing. If you're hearing the
noise while braking, the sound is of the rotor holes going past the
clamped pads.

> 4. What else can I do or try?

Rotors are easily trued; no need to go to the LBS. Turn the wheel and
mark the spot where the rotor is rubbing on the pad. Get an adjustable
wrench and clamp it on the rub spot, and gently(!) bend the rotor away
from the rub. Trial and error will show you the appropriate amount of
bending on the rotor to eliminate rub.
>
> Any help would be appreciated.

Rotors will get out of true at some stage, especially when you use the
brakes for prolonged periods and the rotor gets quite hot.

 

[Kooner]

Jose Rizal wrote:

> Kooner:
>
> > 1. Is there a flatness or wobble specs for bike rotors?
>
> Probably, but these won't be to the nanometer.
>
> > 2. Is in normal for the front pads to rub?
>
> No, unless the pad is much too close to the rotor.
>
> > What if the bike is
> > turning?
>
> What if it is?


> When I'm riding the bike and making a sharp left or right turn, I can
hear a med to high pitch vibrating sound. It's always there when I make
a sharp turn. The front wheel is not vertical during a sharp turn so,
I'm thinking that the rotor or pad assembly is shifting a fraction of a
millimeter?

Kooner

 

[CEarly]

"Kooner" <[email protected]> wrote in message
news:[email protected]...
> Jose Rizal wrote:
>
>> Kooner:
>>
>> > 1. Is there a flatness or wobble specs for bike rotors?
>>
>> Probably, but these won't be to the nanometer.
>>
>> > 2. Is in normal for the front pads to rub?
>>
>> No, unless the pad is much too close to the rotor.
>>
>> > What if the bike is
>> > turning?
>>
>> What if it is?
>
>
>> When I'm riding the bike and making a sharp left or right turn, I can
> hear a med to high pitch vibrating sound. It's always there when I make
> a sharp turn. The front wheel is not vertical during a sharp turn so,
> I'm thinking that the rotor or pad assembly is shifting a fraction of a
> millimeter?
>
> Kooner
>

Hub bearing properly adjusted?

 

[Jose Rizal]

Kooner:

> Jose Rizal wrote:
>
> > Kooner:

> > > What if the bike is
> > > turning?
> >
> > What if it is?
>
>
> When I'm riding the bike and making a sharp left or right turn, I can
> hear a med to high pitch vibrating sound. It's always there when I make
> a sharp turn. The front wheel is not vertical during a sharp turn so,
> I'm thinking that the rotor or pad assembly is shifting a fraction of a
> millimeter?

If you have a suspension fork, it's probably due to one of the legs
compressing just a little more than the other at the turn, which tilts
the hub axis relative to the dropouts, which will then move the rotor
closer to one of the brake pads. The pads also do not return to the
same positions after use, because they have some play and the retaining
springs are not strong enough to keep them pressed flat against the
calipers when not in use.

You can increase the gap between your rotor and pads, and bend the
retaining clips to provide more force to the pads against the calipers,
to eliminate the slight rubbing at turns.

 

[Tom Sherman]

Kooner ? wrote:

> ...
> 2. Is in normal for the front pads to rub? What if the bike is
> turning?...

Bicycles do not produce significant lateral loading on the wheels while
turning, so this should not cause brake rub.

Trikes on the other hand impose lateral loads on the wheels while
turning, and a slight ringing indicating very minor rubbing of the disc
from one pad is not uncommon.

--
Tom Sherman - Earth (Downstate Illinois, North of Forgottonia)

 

[Phil, Squid-in-Training]

Tom Sherman wrote:
> Kooner ? wrote:
>
>> ...
>> 2. Is in normal for the front pads to rub? What if the bike is
>> turning?...
>
> Bicycles do not produce significant lateral loading on the wheels
> while turning, so this should not cause brake rub.

If you're swaying the bike from side to side while powering out of the
saddle, it does and it should.
--
Phil, Squid-in-Training