rear brake issues

[mike g]

had a slight problem with rear brake, wondered if anyone has any ideas?
bike has ABS and BMW HP rearsets. I don't use the rear much.
anyway when i got the bike there was several inches of pedal movement before the brake came on. I adjusted the slack out so maybe 5- 10mm of free movement all seemed ok until I rode down to brands (about 15 miles) when found the brake was jamming on - I don't think i'd touched it. so backed off adjuster so wheel free - lots of free play. went out again and ok for about 5 miles then after 10 more, same problem. so backed off adjuster some more, maybe inch of free play and it's been ok since.
front brakes are fine and am slick mode most of time so should be delinked. checked the system out; fluid is new, the caliper was clean and free moving, disc runout is less than 0.02mm. the brake pads had some chunks out - not sure if that was cause or effect, so cleaned them up and put them back. not got round to trying to adjust again or put the new pads in, but i can't think whats causing it (bike had about 11,000 miles on it). brake works ok but don't really like that amount of free travel

 

[babarr46]

It sounds like air trapped in the rear circuit, it happens & is a bitch to bleed out to as you need a pressure bleeder. It's happend A few times to me, starts as a spongy rear brake & goes after a few pumps..... Do not adjust the free play as when the fluid expands so does the air!!

 

[andy1970]

i've got a 2014 abs model and when you first ride the bike at low speed i cover the rear brake and find you have loads of play in the lever/no rear brake until the abs/traction control lights go out and then the lever jumps up/goes firm and the brake is "normal".always thought it was normal for the bike and a quirk of the abs system.

 

[r25sti]

do we have rear brakes.

 

[RickS1K]

do we have rear brakes.

Ha ha, that's what I've always thought... I have always found my rear brake to be exactly as the OP described. In the beginning I used to try and stop the bike (from low speeds) with the back brake only, and just got used to that being too much effort/worry, although it reassured me that the brake did work to some extent.

When the dealer recently changed the back brake, it was exactly the same. Kinda assumed from this that that's how it should be - on the rare occasions I have gone to use the rear I've always assumed that it has made me feel better rather than having actually done anything to the speed/balance of the bike.... the only other effect it has had on me is to condition me to use the back brake less on my other bike (which doesn't have integrated brakes), which is a habit I'd prefer to unlearn!

Rick

 

[soofsayer]

My back brake works fine. Some play in it but it does scrub off some speed.

 

[mike g]

thanks for the comments - might see if I can borrow mates pressure bleeder see if it makes any difference. (think I will have a good read of the service CD as not done ABS before).

does anyone else think the HP rearsets are a bit naff not having any adjustment for lever height? Instructions suggest moving the peg so it's suits the lever!

It's a good job we don't use theback much!

 

[r25sti]

I think the hp rearsets look naff,they don't match in colour or design.i bought the lightech ones there much nicer.

 

[mike g]

just got round to RTFM and it suggests pressure bleeding followed by good old manual bleeding to make sure it's worked! also suggests 2.5mm (+/-0.5mm) feeler guage is inserted between lever and stop when you adjust the free play on the actuating rod free play, might check that later and see what happens.

 

[mike g]

checked free play @ 2mm so it's not that. try bleeding at the weekend, if that don't work new pads I suppose.

 

[Marcus81]

They do have a fair amount of travel in them before anything happens but excess free play and sponginess could indicate air in the system, as for the brake locking on when a brake master cylinder is in the off position (brake not applied) there is free path for the fluid between the reservoir and the calliper, as you ride there will be a small amount if heat generated from the disc rubbing the pads, as the pads expand the piston moves back displacing fluid to the reservoir, if you adjust too much free play out you close the path from the top of the master cylinder to the reservoir, as the calliper pistons try to move back the fluid has nowhere to go so the pads get hotter and hotter increasing in size until the brake jams on.

 

[mike g]

bled them, one bubble, no difference, new set of sbs pads, much better (still pretty crap!) funny the old ones weren't all that worn, maybe they didn't like being cooked.
whilst playing around I got the abs lights out and checked if front brake worked rear, it didn't seem to;in slick or rain mode with it running on paddock stand - all very strange? but i think that's it for me now