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no modulation on my cable disks.. help?

NoodooNoodoo Posts: 214
edited June 2007 in MTB workshop & tech
Recently, my front Tectro Io cable disk brake has started playing up.
there is no modulation with it any more, it is either all or nothing... it's been fine for months before this.

for example,
If I lift the front wheel and spin it, then gingerly, slowly pull the brake lever, the pads eventually bite VERY suddenly and stop the wheel. there is no slowing of the wheel, it just *STOPS*.

It's like the pads and disc are coated in contact adhesive... as soon as the pads touch the disc, the wheel stops dead.

I've not made any major adjustments to the brakes, there is about a paper thickness gap between each pad and the disc and the disc is not warped.

I took the pads out and checked the wear with a micrometer and the pads don't appear to be miles off scew or anything. There is a .013" difference between wear on the leading and trailing ends of the pads, so it has been fractionally out of line at some point i guess.
I tried swapping the pads over (inboard to outboard) and that made no difference, so i'm not convinced that this .013" wear difference is an issue.

The caliper is tight to it's mounts, but the pads appear to shift very slightly within their 'pistons' when braking. I think the amout of movement is normal though because it's about the same movement as on a set of Tektro hydraulics and a set of Hayes Soles.

when riding, the problem manifests itself in the form of an extremely easy to lock up front wheel, which is getting a bit dangerous on the really steep stuff.
It doesn't stop in exactly the same manner as when there is no weight on the wheel, but anything more than very light finger pressure once the pads have bitten in and it will lock the wheel even when i'm riding it.

The pads have got loads of meat left on them, the disc is fine, the disc to hub mounts are fine and everything is securely bolted together and free from wobbles...

So, has anyone got any advice/info/clues, anecdotal/factual or otherwise?
I'm all out of ideas as to what is causing it.

Saracen Mantra with Marzocchi MX Pro ETA's, 24-7 Silverstar pedals... and a map holder.

Saracen Mantra with Marzocchi MX Pro ETA\'s, 24-7 Silverstar pedals... and a map holder.


  • haroexoneharoexone Posts: 165
    does the lever get closer to the bar than it used to?
  • mongooseTE17mongooseTE17 Posts: 328
    Whats the bite point in the lever? Are the pads glazed? if so give them a light rub with a bit of sandpaper.

    My Elite!
  • mmm_piemmm_pie Posts: 1,934
    Had this on my chucker a couple of years ago- after being very on/off, the brakes will just get stiffer and stiffer and eventually the lever will be very difficult to pull at all.

    It can be solved temporarily with a lubricant on the joints (obviously not getting it on the pads or disc) and down the cables but after a while you might just have to scrap them.

    The trouble with this kind of equipment is that its only designed to work for a while, so say if you tried out a bike with it on, it would work fine in a shop and for a few months.

    If its still under warranty you could try and get a new brake.

    not working :(
    <blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by haleybunny</i>

    Sometimes it overheats. You have to make sure it's in a ventilated place all the time.
    <hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
  • mongooseTE17mongooseTE17 Posts: 328
    Also when were the cables (inners and outers) last changed? They can easily fill up with mud and censored and give you poor modulation.

    My Elite!
  • joshlebjoshleb Posts: 623
    The cables could have stretched, that could affect modulation, but not 100% sure

    <b><center>Got My Vans On But They Look Like Sneakers</center></b>
  • wwjjttwwjjtt Posts: 204
    the calipers need to be serviced. go to lbs if you can't do it yourself.

    never grow up..... just find a bigger playground!

    stinky custom ->

    not so custom stinky->
  • NoodooNoodoo Posts: 214
    I've sorted it.

    Within the calliper are 3 ball bearings, each placed in a groove which curves around the centre of the calliper piston. Each groove gets shallower towards it's end.
    The idea being that the piston rotates when you pull the brake lever. The piston moves outwards due to the ball bearings rolling towards the shallower end of the groove.

    The problem that I had was caused by one of the bearings having fallen out of it's groove and into one of the other grooves; so I had 1 bearing in one of the grooves, no bearing in another groove and 2 bearings in the final groove. This was causing the piston to sit at a slight angle and to be unstable.
    What was happening when I pulled the brake lever was that the pad was making contact with the disc and then the piston was rocking on its unstable platform and grabbing the disc, stopping it immediately.

    So, there we have it. I hope that makes sense.

    Saracen Mantra with Marzocchi MX Pro ETA\'s, 24-7 Silverstar pedals... and a map holder.
  • Who meWho me Posts: 493
    Modulation on cable disc brakes? Is this possible? Thought that was the main benefit of hydros?
  • NoodooNoodoo Posts: 214
    in fairness, they're not bad when they're working right.
    obviously, hydraulics put more of the power frm your finders into stopping you, but other than this problem i've had, I can't fault their operation.

    Saracen Mantra with Marzocchi MX Pro ETA\'s, 24-7 Silverstar pedals... and a map holder.
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