Problem with Avid 7 BB Discs

[arallsopp]

Howdo.

Went out for a training ride on the SMGTe this morning (aborted 10 miles in due to incredible amounts of ice on the road. After my second tumble, I turned around....)

Been having an issue with the front disc brake, and thought I'd spend the time out of the saddle to fix it. Its working pretty much fine at the moment (annoyingly) but with hope that someone can diagnose the issue, here's what it does:

Occassionally, without any input from me, it grabs the rotor. Holds it about 50%. If I try to brake, it doesn't let me move the lever more than half way. After a couple of goes, it'll free up and give me full range again.
There's never anything visible caught in it, but that's exactly what it feels like.

When I get home after a long ride, I notice the front rotor pretty much always squeaks if I move the bike backward. Sometimes, after it stands for a minute, the front brake seems to even be on, with the front wheel locked in place. Seems to go away if I pull the lever on though...

I was wondering if it could be a cable fraying or sticking in the sleeve, but it never happened before I switched my front wheel out to put a SON hub in, so I suspect its something to do with the position of the new disc compared to the old one.

Got about 1500 miles on this bike at the moment. Any thoughts as to how to make the next 1500 as trouble free?

Cheers

 

[Steve Austin]

Could be a couple of things
1. sticky pistons
2. calliper needs centring again
3. needs new pads
4. cable stiction/or it needs bleeding

all easy to fix. I would bet money on sticky pistons. Mine do the same thing routinely

 

[arallsopp]

If I said they were cable operated mechanicals, would that change your bet?
I'll try re-centring the callipers, as I understand that bit.

How to solve a sticky piston though? Do I even have pistons?

Arallsopp is deeply not a technical boy

 

[byegad]

Sounds cable related to me (A BB5 user).

 

[jpembroke]

You don't have an issue with the cable being pulled when you steer, do you? Just wondering if the brake has been set up with not enough cable/outer. This could cause pulling when you steer sharply.

Either way, changing the cable and the outer is the first port of call, IMO. Also worth removing and refitting the pads. Be careful with that spring though.