Disc brakes or not to brake that is the quesion

[Sie]

Recently my disc brakes have gone from bad to useless. They are extremely
spongy and however much I tighten them up it makes no difference. It doesn't
matter how much pressure I apply. Jelly would stop me more efficently. I
have already once replaced the back pads (even though they wern't worn that
much) with the same make that was already on there and although it imporved
a bit for a while. They soon got worse again. I actually swapped them back
to the old ones about 2 days ago with a little improvement!

The discs seem clean enough and I have never tried to clean them in anything
other than water.

When I first got the bike they were great and stopped you smooth and
quickly.

Also if I go no handed at anything above slow my front wheel starts to
develop a small wobble which quickly grows into a vicous one that shakes the
whole bike. Yet there are no buckles that I can see in either wheels.

Could anyone point me in the right direction?

Thanks

Sie

 

[Peter Clinch]

Sie wrote:
> Recently my disc brakes have gone from bad to useless. They are extremely
> spongy and however much I tighten them up it makes no difference. It doesn't
> matter how much pressure I apply. Jelly would stop me more efficently. I
> have already once replaced the back pads (even though they wern't worn that
> much) with the same make that was already on there and although it imporved
> a bit for a while. They soon got worse again. I actually swapped them back
> to the old ones about 2 days ago with a little improvement!

What discs on what bike? If it's a £100 gaspipe job I'd be inclined to
just dismiss it as the inevitable end of poor quality rubbish, if it's
name hydraulics on an expensive and serious bike then that would be a
different matter.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email protected] http://www.dundee.ac.uk/~pjclinch/

 

[Paul - xxx]

Sie composed the following ...
> Recently my disc brakes have gone from bad to useless. They are extremely
> spongy and however much I tighten them up it makes no difference. It
> doesn't matter how much pressure I apply. Jelly would stop me more
> efficently. I have already once replaced the back pads (even though they
> wern't worn that much) with the same make that was already on there and
> although it imporved a bit for a while. They soon got worse again. I
> actually swapped them back to the old ones about 2 days ago with a little
> improvement!

Doesn't sound like a pad problem.

If the brakes are hydraulic it sounds like they're low on fluid or have a
leak and need lines replacing and the system bleeding. If they're
mechanical it sounds like a bent, broken, movable cable holder or 'other'
problem with the cable.

> Also if I go no handed at anything above slow my front wheel starts to
> develop a small wobble which quickly grows into a vicous one that shakes
> the whole bike. Yet there are no buckles that I can see in either wheels.

Sounds like something is either too loose or too tight.

I'd check the head bearings, the front wheel bearings with the wheel off the
bike. If they have just a very small amount of play they should tighten into
the forks OK, assuming 'normal' forks, the disc rotor mounts etc .

However, you don't give enough details.

What sort of brakes, what sort of front wheel, forks, fork/wheel tightening
method etc etc


--
Paul ...
http://www.4x4prejudice.org/index.php
(8(!) Homer Rules ...
"A ****** is a ******, no matter what mode of transport they're using."

 

[MSeries]

Sie wrote:

>
> Also if I go no handed at anything above slow my front wheel starts to
> develop a small wobble which quickly grows into a vicous one that shakes the
> whole bike. Yet there are no buckles that I can see in either wheels.
>

Could be the frame out of true, thats what my problem was.

 

[Peter B]

"Sie" <[email protected]_nocrap_.com> wrote in message
news:[email protected]
> Recently my disc brakes have gone from bad to useless.

Tell us what make & type (hydraulic or cable) for specific answers.

Pete

 

[Simon Brooke]

in message <[email protected]>, Sie
('[email protected]_nocrap_.com') wrote:

> Recently my disc brakes have gone from bad to useless. They are
> extremely spongy and however much I tighten them up it makes no
> difference. It doesn't matter how much pressure I apply. Jelly would
> stop me more efficently. I have already once replaced the back pads
> (even though they wern't worn that much) with the same make that was
> already on there and although it imporved a bit for a while. They soon
> got worse again. I actually swapped them back to the old ones about 2
> days ago with a little improvement!

Are they hydraulic? If so, have you bled them? Sounds like air in the
line.

> The discs seem clean enough and I have never tried to clean them in
> anything other than water.

Try methylated spirits - gets rid of grease.

> When I first got the bike they were great and stopped you smooth and
> quickly.
>
> Also if I go no handed at anything above slow my front wheel starts to
> develop a small wobble which quickly grows into a vicous one that
> shakes the whole bike. Yet there are no buckles that I can see in
> either wheels.

That sounds like a geometry problem with the frame, not a problem with
the wheel. Could the frame or fork have got bent at all?

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Diplomacy, American: see Intelligence, Military

 

[Pete Biggs]

Sie wrote:

> Also if I go no handed at anything above slow my front wheel starts to
> develop a small wobble which quickly grows into a vicous one that
> shakes the whole bike. Yet there are no buckles that I can see in
> either wheels.

Article on "Shimmy or Speed Wobble" :

http://draco.acs.uci.edu/rbfaq/FAQ/8h.5.html

"Shimmy is not related to frame alignment or loose bearings, as is
often claimed. Shimmy results from dynamics of front wheel rotation,
mass of the handlebars, elasticity of the frame, and where the rider
contacts the bicycle."

~PB

 

[Sie]

Thanks for everyones input.

The disc system is shimano and it is not hydrolic. Similar to this one
although probably not same


http://www.shimano-europe.com/cycli...11154&pr=top_right_prodserie.phtml?psid=11154

Is it worth cleaning the disks then replacing all pads or am I wasting my
time?

I refuse to believe that they would be this bad due to poor quality as when
I first had the bike they were a sheer pleasure to use and very eifficient.


Thanks

Sie

 

[Tony W]

"Sie" <[email protected]_nocrap_.com> wrote in message
news:[email protected]
> Thanks for everyones input.
>
> The disc system is shimano and it is not hydrolic. Similar to this one
> although probably not same
>
>
>
http://www.shimano-europe.com/cycli...11154&pr=top_right_prodserie.phtml?psid=11154
>
> Is it worth cleaning the disks then replacing all pads or am I wasting my
> time?
>
> I refuse to believe that they would be this bad due to poor quality as
when
> I first had the bike they were a sheer pleasure to use and very
eifficient.

If they are 'spongey' then something is preventing the force you put onto
the brake lever being transmited to the brake blocks. In a hydraulic system
this is normally air -- which is compressible -- mixed with the fluid which
is not.

For a mechanical system it is more difficult to be sure -- but a good clean
of all the parts might reveal sometning loose, bent or broken.

Is the disc running true?

Are both blocks contacting the disc when you brake (it could be that one
side is jammed and not moving freely.

I woud suggest that it is not worth changing the pads until you have had a
good clean and look round (unless they are buggered or soaked in oil).

Have fun.

T

 

[Paul - xxx]

Sie composed the following ...
> Thanks for everyones input.
>
> The disc system is shimano and it is not hydrolic. Similar to this one
> although probably not same
>
>
> http://www.shimano-europe.com/cycli...11154&pr=top_right_prodserie.phtml?psid=11154
>
> Is it worth cleaning the disks then replacing all pads or am I wasting my
> time?

Can't hurt, but as you say they worked and now they don't, then something is
stopping them working. If a change of pads has had little effect, then you
ought to look at the complete braking system. Start at the handlebars and
work towards the brake. Check for free movement in the levers, remove the
cable and pull it by hand, it should move freely. The outer casing ought to
be able to move along the cable inner freely.

If you've used them in the rain or muddy conditions than some light oil,
three in one would do, can be dribbled down the inner cables and the outers
moved up and down to help lube the whole cable.

I'd also check the pads can move freely when the cable is pulled. Again, if
the pads don't move then there's something wrong, they should move
relatively freely, with light pressure to the cable..


--
Paul ...
http://www.4x4prejudice.org/index.php
(8(!) Homer Rules ...
"A ****** is a ******, no matter what mode of transport they're using."

 

[Simon Brooke]

in message <[email protected]>, Sie
('[email protected]_nocrap_.com') wrote:

> Thanks for everyones input.
>
> The disc system is shimano and it is not hydrolic. Similar to this one
> although probably not same
>
http://www.shimano-europe.com/cycli...11154&pr=top_right_prodserie.phtml?psid=11154
>
> Is it worth cleaning the disks then replacing all pads or am I wasting
> my time?

Yes, it's worth it as a first try. Any oil or grease contamination on a
braking surface will greatly reduce the braking efficiency, so it's
worth trying with meths to see if it makes a difference - meths isn't
very expensive.

If the disks are cable operated not hydraulic, the next thing to do is
check the cable, particularly the terminations at the ends of both
inner and outer. Also make sure the inner moves easily inside the outer
without friction - if it does not, replace the cable.

Shimano gear is on the whole OK - not the best but reliable enough. I
would be surprised if this were a quality problem.

--
[email protected] (Simon Brooke) http://www.jasmine.org.uk/~simon/

;; Semper in faecibus sumus, sole profundum variat.