Front Brake

[Melena]

I just had a new front tire put on and now that I've put the wheel back on I notice a slight drag on the disc that I hadn't noticed before.   What is strange, to me anyway, is that I hear the brake brushing the disc at only one place.  The sound is at only one place around the whole circumference of the disc.   Oh, and they are Brembo calipers.

What do you think about this?  Is it something to be concerned about?

[airhead]

Unfortunately Mel, it sounds like the disc may be warped or bent. Perhaps they were a bit ham fisted when they mounted the wheel, who knows. Only one way to find out and that employs a dial gauge with someone who knows how to use it.
All discs can drag to some extent, it's the nature of disc brakes, but if it starts to do it in only one spot, especially if pumping at the lever is experienced, time to do something. Some can live with very slight pumping, but it does affect braking performance and efficiency to some degree.

Bill.....................;-)

[Justin B.]

Can't really add much to what Bill said except that I consider it more of an "annoyance" when it's very slight.  I guess it couldn't hurt do lossen, rotate, and re-torque the rotor...

[Melena]

Okay.  Thanks guys.  It's not much of a drag at all, and there is no pumping at the lever.  I've got some other ideas to try too.  I could easily try loosening, rotating and re-torqueing the rotor too.  

Been in touch with John Falconer and he suggested a simple thing to try - before tightening up the pinch bolts on the front axle to bounce the front forks up and down without applying the front brake.  Then go for a ride and and use the brakes hard.  

I'll try the simplest stuff first.  

It could be that this has dragging has been there and I never noticed it before.  Every time I look at the bike I'm learning something new about it that I'd never noticed before.  I guess that's a good thing.  

[Justin B.]

I'm not sure what the spec is for runout on the disc but even .001 could be noticed in this manner.  I don't think you need to worry about it if you can't "feel" anything through the lever.  I warped a front rotor so bad on an old MGB I had that it felt like the brake pedal would oscillate a 1/4 inch or so when applying the brakes but they still stopped...

[thrang]

You probably already checked this but make sure there isn't any crap built up between the piston and break pad. It only takes a little bulit up to get the pad slightly off line and causes a horrid squeaking and a drag on the disk.

[Melena]

Thanks thrang.  Actually, I haven't checked that yet.   It's too dark now, but I'll probably take the cover off tomorrow after work and take a look.  I'll try to clean it up as much as I can without taking it apart.   I think they will be okay for awhile.  They worked well just a few weeks ago.

[drewboid]

One other thing to check is that the wheel bearings are properly pre-loaded.  too little preload and the wheel will rock slightly - too much and the bearings wear too fast.  Put the bike on the centerstand with the front wheel off the ground - see if there is play in the bearing.  Try loosining the axel nut until you feel the play and then tighten until it goes away.  

YMMV - just a suggestion.
Drew