Howdy all,

Quick question, I've noticed this week my rear brake seems to be dragging on the disc. In a couple of left hand corners I can hear it scraping along the disc-it has that metallic sound when the calipers are just grabbing the disc.  How do I measure the 'float' or in essence how much free play should the pads have on the disc surface?

FWIW i'm doing a 8000km serivce this weekend and will use some brake/disc cleaner around the caliper assembly to see if it loosens up any gunk that may be restricting the caliper pistons from retracting like they should.  I generally use the front brake on the majority of riding, just use the back for tucking the bike (helps pull the bike into the corner-I obviously don't brake hard enough to lock the brake and skid) into sharper corners or coming to a quicker full stop at intersections if needed.

Cheers in advance for advice on the rear brake drag issue.

IE

 

I'm not an expert, but I think disk brake pads inherently 'rub' on the rotor, but only marginally. it's just part of the design. There's no 'spring' mechanism or whatever to pull the pads away from the rotor, as you probably know. The release of pressure on the pads allows the disk to 'push' the pads away just enough to cause minimal drag, hence minimal scraping sound...

You could be right about gunk not allowing the pads to freely release, but personally I've never had that problem.

Sometimes it's an indication of low fluid

Depending on how often the caliper gets washed and with what, Maybe the lube on the slider pins has dried up/gone hard/ contaminated. you may have to relube these pins. Failing that, the caliper assy may need a new seal kit installed if the seals have gone hard or again contaminated. How old is it, and if it is still under warranty, take it back and get them to suss it.
They do have a anti rattle plate that puts pressure on the pads, but it is not designed to keep the pads off the disc.

1st check disc with a straight edge too make sure the disc is flat ,  clean out the old brake fluid & flush out & bleed  push the pistons back as far as they will go in & out a few times too clean there path as well then bleed proper , 

Take your foot off it?

 Thaks all for replies.

@Colstah, your thoughts were along those I had.

@Crowy, I checked the fluid, it's well within the limits.

@Kiwidave, I couldn't see any stop adjuster near/around the pedal lever, although I did check to make sure it wasn't binding.

@FLHuTCHU, thanks for your excellent advice, I checked brakes over agagin.

@DR56, cheers, the disc is straight.

@IRON, ha ha, I assume your taking the piss.  That's as funny as your DIO chicken roaster!!

I serviced and cleaned the bike on the weekend.  Only took it for a quick ride to help remove the water.  I did use a liberal amount of brake cleaner around the disc surface and pad area.

Prior to cleaning the bike, I was only hearing it at slower speeds (less wind/bike noise etc, around 40/50km) after having used the rear brake.  I was thinking it was taking longer for the pistons to retract than the front ones which I have never heard the pads scrape on the disc.  I also use an open face helmet and find I can hear more of what's going on around me than the full face helmet.

Past experience riding dirt bikes led me to think the pistons wern't working as they should.  Comments received refer to this and why it could be happening.  Usually it's gunk, road grime etc.  In rare cases the piston seals can dry/harden which in turn hold the piston from retracting as it should.  Similar to the comments made by others.

Anyway, it's a new week, the bike is cleaned and ready to roll.  I'll be listening to see if it makes any difference.  BTW the front brake is an upgraded XR1200 caliper while the rear is the std part for the Iron.

Cheers all for excellent advice.

IE

 

 

 

hahah yeah! nothing like a turkey bang! hope you have it sorted.

 Just a quick update, after spraying the rear brake caliper with brake degreaser and cleaning the bike, I don't seem to hear the rear brake drag like the previous week.  So i'm putting the noise down to some gunk around the pistons and this may have been binding the system up a little.

In effect it's all good now.

EXCEPT I had a "V IN ERR" code come up on the bike.  It's one of those new combo units. Checked the HD Forums USA site and found the way to clear it is to remove the main fuse, wait, then reinstall.  Turns out the advice is good I have the speedo reading again as it should. 

Cheers

IE