Play in Dura Ace brake caliper

[Francesco Devittori]

Hi all,

it has been a long time I don't post here, but I remember many
outstanding mechanics here, so maybe someone can help me solve this
problem.

I have a front Dura Ace 7800 brake caliper that has some play around
the pivot (the one that goes through the fork). It looks like the
brake "floats" around that pivot, so I cannot keep it aligned. It
stays "almost" aligned just because the housing keeps it in place, but
it doesn't look right.
If I grab the whole caliper with my hand, I can easily rotate it side-
by-side (about half a centimeter).
When I open the brake (with the "quick release" plastic lever), the
caliper opens on on side but since the housing is pushing it down, it
ends up badly misaligned.

I noticed that the thin washer that sits just behind the brake body
(before the "strange" thick spacer that goes against the fork) has
some play, i.e. I can rotate it with the finger. The rear brake, which
is working fine, does not have this play.

Maybe it's just something to thighten, but I don't know where to
look...
I hope my explanation was not too confused!

Does anybody have any idea or suggestion? I have some races coming and
a brake almost touching the rim is the last thing you want to think
about...

Thanks!

Frenk

 

[Lou Holtman]

Francesco Devittori wrote:
> Hi all,
>
> it has been a long time I don't post here, but I remember many
> outstanding mechanics here, so maybe someone can help me solve this
> problem.
>
> I have a front Dura Ace 7800 brake caliper that has some play around
> the pivot (the one that goes through the fork). It looks like the
> brake "floats" around that pivot, so I cannot keep it aligned. It
> stays "almost" aligned just because the housing keeps it in place, but
> it doesn't look right.
> If I grab the whole caliper with my hand, I can easily rotate it side-
> by-side (about half a centimeter).
> When I open the brake (with the "quick release" plastic lever), the
> caliper opens on on side but since the housing is pushing it down, it
> ends up badly misaligned.
>
> I noticed that the thin washer that sits just behind the brake body
> (before the "strange" thick spacer that goes against the fork) has
> some play, i.e. I can rotate it with the finger. The rear brake, which
> is working fine, does not have this play.
>
> Maybe it's just something to thighten, but I don't know where to
> look...
> I hope my explanation was not too confused!
>
> Does anybody have any idea or suggestion? I have some races coming and
> a brake almost touching the rim is the last thing you want to think
> about...
>
> Thanks!
>
> Frenk
>


It is a little confusing, but do you have the right nut length? Maybe it
is bottoming out before it clamps the caliper against the fork. Is this
a new installation?

Lou
--
Posted by news://news.nb.nu (http://www.nb.nu)

 

[Francesco Devittori]

On Jul 26, 10:01 pm, Lou Holtman <[email protected]> wrote:
> Francesco Devittori wrote:
> > Hi all,
>
> > it has been a long time I don't post here, but I remember many
> > outstanding mechanics here, so maybe someone can help me solve this
> > problem.
>
> > I have a front Dura Ace 7800 brake caliper that has some play around
> > the pivot (the one that goes through the fork). It looks like the
> > brake "floats" around that pivot, so I cannot keep it aligned. It
> > stays "almost" aligned just because the housing keeps it in place, but
> > it doesn't look right.
> > If I grab the whole caliper with my hand, I can easily rotate it side-
> > by-side (about half a centimeter).
> > When I open the brake (with the "quick release" plastic lever), the
> > caliper opens on on side but since the housing is pushing it down, it
> > ends up badly misaligned.
>
> > I noticed that the thin washer that sits just behind the brake body
> > (before the "strange" thick spacer that goes against the fork) has
> > some play, i.e. I can rotate it with the finger. The rear brake, which
> > is working fine, does not have this play.
>
> > Maybe it's just something to thighten, but I don't know where to
> > look...
> > I hope my explanation was not too confused!
>
> > Does anybody have any idea or suggestion? I have some races coming and
> > a brake almost touching the rim is the last thing you want to think
> > about...
>
> > Thanks!
>
> > Frenk
>
> It is a little confusing, but do you have the right nut length? Maybe it
> is bottoming out before it clamps the caliper against the fork. Is this
> a new installation?
>
> Lou

In fact the fork is new, but the caliper is used (looks fine though).
I think the nut is the correct length, as it was supplied with the
fork. Also with the caliper removed from the fork, I can still see
that the washer can move. In the rear caliper the washer is thight
even when the brake is not installed.

Here a picture: http://img67.imageshack.us/img67/9430/dabrakezm4.jpg ,
when the caliper is installed, if I grab it and move it side-by-side,
the "spacer" stays in place, thight to the fork (that's why I think
the nut is ok), but the washer has some slight space to move..

I don't know if now it's a bit more clear...

 

[Calvin Jones]

It is likely that is not a washer but the locknut for the pivot
adjustment. One arm is adjusted by taking it off the bike. See this
at
http://www.parktool.com/repair/readhowto.asp?id=20

 

[A Muzi]

Francesco Devittori wrote:
> it has been a long time I don't post here, but I remember many
> outstanding mechanics here, so maybe someone can help me solve this
> problem.
>
> I have a front Dura Ace 7800 brake caliper that has some play around
> the pivot (the one that goes through the fork). It looks like the
> brake "floats" around that pivot, so I cannot keep it aligned. It
> stays "almost" aligned just because the housing keeps it in place, but
> it doesn't look right.
> If I grab the whole caliper with my hand, I can easily rotate it side-
> by-side (about half a centimeter).
> When I open the brake (with the "quick release" plastic lever), the
> caliper opens on on side but since the housing is pushing it down, it
> ends up badly misaligned.
>
> I noticed that the thin washer that sits just behind the brake body
> (before the "strange" thick spacer that goes against the fork) has
> some play, i.e. I can rotate it with the finger. The rear brake, which
> is working fine, does not have this play.
>
> Maybe it's just something to thighten, but I don't know where to
> look...
> I hope my explanation was not too confused!
>
> Does anybody have any idea or suggestion? I have some races coming and
> a brake almost touching the rim is the last thing you want to think
> about...

5mm key on the back of your fork tightens the brake to the fork.

Slip your fingers aside the tire on both sides before doing _anything_
to your brake. Is that wheel centered in the fork ? Do check first.
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

 

[Francesco Devittori]

On Jul 26, 11:16 pm, Calvin Jones <[email protected]> wrote:
> It is likely that is not a washer but the locknut for the pivot
> adjustment. One arm is adjusted by taking it off the bike. See this
> athttp://www.parktool.com/repair/readhowto.asp?id=20

I think this is the answer, I need to adjust the locknut. I will try
soon. I didn't realize that the Parktool website had so detailed
instructions, thanks for the hint.
I'm surprised shimano does not have a service manual for their brakes.
(they just provide the exploded view and the basic installation
sheet).

As I'm finally understanding how the caliper works, I have a couple of
questions more:
- what's the function of the small bolt that goes inside the locknut?
Is it to keep the locknut in place once adjusted?
- what's the function of the similar small bolt that goes inside the
bridge (under the bridge)?
Parktool's website calls it "setscrew" and shows a shimano brake that
has it under the bridge, and a campy one that has it inside the
locknut. However from what I can tell the BR-7800 has both...

Thanks for the great help!

Frenk