Weak Braking - Shimano 105

Quoted message said:

Since I exfoliated the more padded area of my anatomy on a stretch of
wet tarmac,

Sounds painful.

Quoted message said:

my rear brake has been acting up. I have a full and
unrestricted range of moment in the lever (Shimano 105) but seem
unable to apply sufficient pressure to the brake.

The brake mechanism (and pads) are fine. However, the shifter took a
knock when I fell and scraped a bit along the road.

You have either stretched that cable, or it has slipped through the nut
at the actual brake.

There is a screw on the lever where the cable exits. you need to turn
this so it move out of the lever, and this will tighten the cable.

If you need to keep adjusting this, or do not get enough adjustment from
this, you need to pull a bit of cable through the nut at the brake.

in message <[email hidden]>,

(') said:

Since I exfoliated the more padded area of my anatomy on a stretch of
wet tarmac, my rear brake has been acting up. I have a full and
unrestricted range of moment in the lever (Shimano 105) but seem
unable to apply sufficient pressure to the brake.

The brake mechanism (and pads) are fine. However, the shifter took a
knock when I fell and scraped a bit along the road. Whilst it's
scratched up a bit, there's no visible mechanical damage to the lever
and I have no problems changing gear with it.

Pulling the brake cable away from the top-tube puts a good amount of
pressure on the brakes. However, using just the lever I just can't
get enough pressure on the brakes to stop the bike. The problem must
therefore lie somewhere in the lever, or in the cable around the
lever.

I'd be very grateful for any insight. I presume I must have damaged
the gear lever, but it feels normal to use (apart from not stopping me
properly!)

Investigate everything else first, as those Shimano shift levers are not
cheap, and are not repairable - service parts are not available. I would
try changing the cable outer - the sheath - of the rear brake cable. This
will mean retaping your bars, which is a nuisance; but damage to the
sheath could produce the symptoms you describe. Also inspect all the
points on the bike where the sheath terminates - i.e. (typically) at frame
stops either end of the top tube, at the lever itself, at the brake
calliper itself.

--
[email hidden] (Simon Brooke) http://www.jasmine.org.uk/~simon/
Iraq war: it's time for regime change...
... go now, Tony, while you can still go with dignity.
[update 18 months after this .sig was written: it's still relevant]

Quoted message said:

You have either stretched that cable, or it has slipped through the nut
at the actual brake.

That's what I thought at first, but even with the cable very (i.e.
too) tight, I can't get the brake to work properly. I should have
said that in my post. The sensation is much like having an oily brake
pad (I don't) - I'm gripping hard and getting a firm response from the
lever, but it just doesn't stop the wheel from turning.

Fortunately, I got away with little more than scratches, a slightly
bent wheel and the dodgy brake. That's jolly lucky - my GPS was
doing 40 when it hit the road and turned off!

<[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Quoted message said:

You have either stretched that cable, or it has slipped through the nut
at the actual brake.

That's what I thought at first, but even with the cable very (i.e.
too) tight, I can't get the brake to work properly. I should have
said that in my post. The sensation is much like having an oily brake
pad (I don't) - I'm gripping hard and getting a firm response from the
lever, but it just doesn't stop the wheel from turning.

Mine feel like that - I assumed my brake blocks are [censored] though and/or oily.

Have you got crud in the outer tubes on the cable which is making it hard
for the cable to slide? Or - perhaps due to a bump - has the outer tubing
got a kink/sharp bend in it which the cable is struggling to pull around?
--
peter

Cheap train tickets database
http://www.petereverett.co.uk/tickets/

Email sent to this address is generally deleted upon arrival
Visit website if you want to contact me

Quoted message said:

Since I exfoliated the more padded area of my anatomy on a stretch of
wet tarmac, my rear brake has been acting up. I have a full and
unrestricted range of moment in the lever (Shimano 105) but seem
unable to apply sufficient pressure to the brake.

What happens when you pull the lever as hard as you can when not riding the
bike?

If you are not able to make the lever touch the handlebar, then there is
nothing wrong its ability to transmit force from you to the brake.

Quoted message said:

The brake mechanism (and pads) are fine. However, the shifter took a
knock when I fell and scraped a bit along the road. Whilst it's
scratched up a bit, there's no visible mechanical damage to the lever
and I have no problems changing gear with it.

Pulling the brake cable away from the top-tube puts a good amount of
pressure on the brakes.

That's no test.

Quoted message said:

However, using just the lever I just can't
get enough pressure on the brakes to stop the bike. The problem must
therefore lie somewhere in the lever, or in the cable around the
lever.

I'd be very grateful for any insight. I presume I must have damaged
the gear lever, but it feels normal to use (apart from not stopping me
properly!)

With respect, maybe the shock from the accident is causing you to /imagine/
there is something wrong with the brake lever.

Check the cable (replace if in doubt), double check the pads and brake
caliper, sand the pads, clean the rims.

~PB

Quoted message said:

Quoted message said:

You have either stretched that cable, or it has slipped through the
nut at the actual brake.

That's what I thought at first, but even with the cable very (i.e.
too) tight, I can't get the brake to work properly. I should have
said that in my post. The sensation is much like having an oily brake
pad (I don't) - I'm gripping hard and getting a firm response from the
lever, but it just doesn't stop the wheel from turning.

Then there's nothing wrong with the lever.

~PB

Pete Biggs said:

Quoted message said:

Since I exfoliated the more padded area of my anatomy on a stretch of
wet tarmac, my rear brake has been acting up. I have a full and
unrestricted range of moment in the lever (Shimano 105) but seem
unable to apply sufficient pressure to the brake.

What happens when you pull the lever as hard as you can when not riding the
bike?

If you are not able to make the lever touch the handlebar, then there is
nothing wrong its ability to transmit force from you to the brake.

Not really a kink in the cable or something trapping it preventing full
movement, maybe a broken strand.

I'm no expert, but I'd take all the inner/outers off and check them.
Then the toe of the brake to make sure it didn't get smacked and is out
of line, lastly I'd take the lever apart. But I'm no expert.

I might get someone else to have a go as well, just to verify.

Thanks for the all responses - they're very helpful.

I've already taken the bar tape off to inspect the exterior of the
cables (no visible damage or kinks) but haven't had the insides out
yet. I'll take a look tonight.

Re. pulling the brake cable at the top tube, what that shows me is
that the brake + pads are working okay. The lack of tension from the
levers is dramatic - I can put all my weight on the left lever and
still push the bike forward relatively easily, wheras pulling the
cable by hand is much more effective.

The lever itself appears to be working correctly - if I take all the
pressure off the cable it has a full range of movement, and with the
cable set correctly I can't pull the lever all the way back. However,
it is very slightly spongier than I remember it being before.

I'm beginning to think there must be an obstruction between the inner
and outer cables at their front ends. That would make sense and be a
lot cheaper to fix than a broken lever!

Thanks again!

Quoted message said:

Since I exfoliated the more padded area of my anatomy on a stretch of
wet tarmac, my rear brake has been acting up. I have a full and
unrestricted range of moment in the lever (Shimano 105) but seem
unable to apply sufficient pressure to the brake.

The brake mechanism (and pads) are fine. However, the shifter took a
knock when I fell and scraped a bit along the road. Whilst it's
scratched up a bit, there's no visible mechanical damage to the lever
and I have no problems changing gear with it.

Pulling the brake cable away from the top-tube puts a good amount of
pressure on the brakes. However, using just the lever I just can't
get enough pressure on the brakes to stop the bike. The problem must
therefore lie somewhere in the lever, or in the cable around the
lever.

I'd be very grateful for any insight. I presume I must have damaged
the gear lever, but it feels normal to use (apart from not stopping me
properly!)

undo the clampbolt at the brake and squeeze the lever, while holding the
inner cable. Movement should be smooth both ways. Look inside the
lever (it will move a bit further if you twist the lever inwards) and
check that the yoke holding the cablebarrel can move without obstruction
and isn't bent

--
/Marten

info(apestaartje)m-gineering(punt)nl

Replaced the brake cable and now it works like a charm. Thanks again
for the help!

in message <[email hidden]>,

(') said:

Replaced the brake cable and now it works like a charm. Thanks again
for the help!

Did you detect anything in the cable you removed to account for the
problem? I must admit it's an odd one!

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

:: Wisdom is better than weapons of war ::
:: Ecclesiastes 9:18 ::

Simon Brooke said:

in message <[email hidden]>,

(') said:

Replaced the brake cable and now it works like a charm. Thanks again
for the help!

Did you detect anything in the cable you removed to account for the
problem? I must admit it's an odd one!

With the *inner* cable, I can only think of either:

1) Some strands were broken or flattened & unravelled, allowing the cable
stretch.

2) It was OK but just not clamped tightly enough.

~PB

or 3) There was nothing wrong with the cable at all and actually the
braking is just as good as before really, or is better by coicidence.

~PB

Pete Biggs said:

or 3) There was nothing wrong with the cable at all and actually the
braking is just as good as before really, or is better by coicidence.

~PB

Not at all - braking hard with the new cable skids the back wheel, but
I previously could still pedal the bike forward with the brakes fully
applied.

There was nothing obviously wrong with the inner; however, I did
notice some buffed spots where it must have rubbed against the outer.
Visually, I couldn't see any problems with the outer, but it may well
be obstructed internally.

I suspect what happened was that the crash wrenched the outer cable
hard enough to deform it - either crushing or perhaps stretching the
coiled metal. Alternatively, maybe the lining of the outer had become
damaged and was obstructing the inner.

When I had the cable off the bike, the inner did seem to stick a
little in the outer - but not really very much. Perhaps the deformity
was such that it was worse when the cable was bent (i.e. up to the
handlebars).

Regardless of the cause, I'm delighted to have sorted the problem
without needing to buy a new lever!

Quoted message said:

Pete Biggs said:

or 3) There was nothing wrong with the cable at all and actually the
braking is just as good as before really, or is better by coicidence.

~PB

Not at all - braking hard with the new cable skids the back wheel, but
I previously could still pedal the bike forward with the brakes fully
applied.

There was nothing obviously wrong with the inner; however, I did
notice some buffed spots where it must have rubbed against the outer.
Visually, I couldn't see any problems with the outer, but it may well
be obstructed internally.

I suspect what happened was that the crash wrenched the outer cable
hard enough to deform it - either crushing or perhaps stretching the
coiled metal. Alternatively, maybe the lining of the outer had become
damaged and was obstructing the inner.

When I had the cable off the bike, the inner did seem to stick a
little in the outer - but not really very much. Perhaps the deformity
was such that it was worse when the cable was bent (i.e. up to the
handlebars).

Regardless of the cause, I'm delighted to have sorted the problem
without needing to buy a new lever!

If the outer was very old you could have worn a groove in the interior
liner. If this splits matters get even worse

--
/Marten

info(apestaartje)m-gineering(punt)nl