Frame/wheel flex and disc brake problem

Hello,

I have some problems with my rear disc brake:
When the rear is not weighted, the wheel+rotor spins freely and the distance
between pads and rotor is evenly ditributed. However, when I sit on my bike
it touches the inside pad (note that I weigh 68 kg....).

At first it was driving me crazy (re-adjusting the caliper+pads numerous
times), but now I have identified the problem, and am very close to finding
the cause:
1) frame flex (Specialized Stumpjumper FSR comp 2003)
2) wheel flex (Shimano deore disc+Mavic X221 rims, not so good anyway,
looking for upgrade with DT swiss component wheels)
3) skewer flex? (Shimano deore, already ordered XTR skewers)

Note that the distance the rotor moves (when you put weight on the bike) is
very small (+/- 0.2 mm) but deadly when using discs.
I hope the cause can be found in 2) and 3) (will try with some other wheels
at the LBS) but I am afraid that it might be cause nr 1)
When the rear wheel is weighted it should bend in a way that the rotor
touches the outer pad (if that was the cause) right?

Anyway, have some of you experienced similar problems?

Thanks,
Caspar

(PS: now I have the pads adjusted so that they are free when I sit on the
bike.... and drag when you just spin the wheel)

Caspar Lugtmeier & Eva Skotarczak wrote:
Hello,

I have some problems with my rear disc brake:
When the rear is not weighted, the wheel+rotor spins freely and the distance
between pads and rotor is evenly ditributed. However, when I sit on my bike
it touches the inside pad (note that I weigh 68 kg....).

At first it was driving me crazy (re-adjusting the caliper+pads numerous
times), but now I have identified the problem, and am very close to finding
the cause:
1) frame flex (Specialized Stumpjumper FSR comp 2003)
2) wheel flex (Shimano deore disc+Mavic X221 rims, not so good anyway,
looking for upgrade with DT swiss component wheels)
3) skewer flex? (Shimano deore, already ordered XTR skewers)

Note that the distance the rotor moves (when you put weight on the bike) is
very small (+/- 0.2 mm) but deadly when using discs.
I hope the cause can be found in 2) and 3) (will try with some other wheels
at the LBS) but I am afraid that it might be cause nr 1)
When the rear wheel is weighted it should bend in a way that the rotor
touches the outer pad (if that was the cause) right?

Anyway, have some of you experienced similar problems?

Thanks,
Caspar

(PS: now I have the pads adjusted so that they are free when I sit on the
bike.... and drag when you just spin the wheel)









The first thing I would look for is a broken axle. If you have enough
frame flex to cause the drag, I would look very carefully for cracks.

Miles

Yes, that's what I tought too, I have already checked that (and the
tightness of the freehub bolt).

Thanks,
Caspar

"miles todd" schreef in bericht
...


Caspar Lugtmeier & Eva Skotarczak wrote:
Hello,

I have some problems with my rear disc brake:
When the rear is not weighted, the wheel+rotor spins freely and the
distance
between pads and rotor is evenly ditributed. However, when I sit on my
bike
it touches the inside pad (note that I weigh 68 kg....).

At first it was driving me crazy (re-adjusting the caliper+pads numerous
times), but now I have identified the problem, and am very close to
finding
the cause:
1) frame flex (Specialized Stumpjumper FSR comp 2003)
2) wheel flex (Shimano deore disc+Mavic X221 rims, not so good anyway,
looking for upgrade with DT swiss component wheels)
3) skewer flex? (Shimano deore, already ordered XTR skewers)

Note that the distance the rotor moves (when you put weight on the bike)
is
very small (+/- 0.2 mm) but deadly when using discs.
I hope the cause can be found in 2) and 3) (will try with some other
wheels
at the LBS) but I am afraid that it might be cause nr 1)
When the rear wheel is weighted it should bend in a way that the rotor
touches the outer pad (if that was the cause) right?

Anyway, have some of you experienced similar problems?

Thanks,
Caspar

(PS: now I have the pads adjusted so that they are free when I sit on
the
bike.... and drag when you just spin the wheel)









The first thing I would look for is a broken axle. If you have enough
frame flex to cause the drag, I would look very carefully for cracks.

Miles

4) FSR rear end bearngs have play in them, replace. (688RS)

That's a good one. If it's not the wheel/skewer I will do this.
Thanks,
Caspar

"Caspar Lugtmeier & Eva Skotarczak" wrote in message
...
snip
Note that the distance the rotor moves (when you put weight on the bike)
is
very small (+/- 0.2 mm) but deadly when using discs.

I know that the manual probably states that 0.2-0.4mm is the recommended
clearance. In reality and in practice I have found it to be more like
0.5mm. I think that 0.2mm is wishful thinking.
--
Westie

The disc brakes are Magura Louise's, model 2004. And no, it is not wishful
thinking but measured... (using a tool).
I would much more prefer a distance of 0.5 mm !! (obviously)

Caspar

"Westie" schreef in bericht
...
"Caspar Lugtmeier & Eva Skotarczak" wrote in
message
...
snip
Note that the distance the rotor moves (when you put weight on the bike)
is
very small (+/- 0.2 mm) but deadly when using discs.

I know that the manual probably states that 0.2-0.4mm is the recommended
clearance. In reality and in practice I have found it to be more like
0.5mm. I think that 0.2mm is wishful thinking.
--
Westie