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Offline Keenconsumer

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  • Bike: 2019 Z900
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Sticking back brake
on: August 01, 2020, 07:09:25 AM
2019 Z900 1,700 kms (1,000 miles) from new. 

No problems after riding for a few hours over and fast straights.  After refuelling it was sluggish through the gears.  Pulled over after about 2km to find the back brake was binding, and the disc was hotter than Jennifer Aniston.  Waited for it to cool, rode 2km home, no problem.  Put the bike up on paddock stands - no binding at the caliper piston, no sticking at the lever, pads are good, disc is true, hydraulics all good.  Dealer inspected it, didn't find a fault.

Riding since then the back disc is warm but the front discs cool, despite only using the back brake at low speed in traffic.  No obvious fault.     :084:

Anybody else had this problem?  Any suggestions? :440:
Last Edit: August 01, 2020, 07:12:18 AM by Keenconsumer
The advantage of the rain is that, if you have a quick bike, there's no advantage.
Barry Sheene

Offline Tudtran

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Re: Sticking back brake
Reply #1 on: August 01, 2020, 08:11:39 AM
Maybe a rock got stuck?
Happened to me last year on a dirt road. My rear brake wasnt stuck but it was squeaking.

Offline JohnCW

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Re: Sticking back brake
Reply #2 on: August 01, 2020, 10:57:57 AM
*Originally Posted by Keenconsumer [+]
Pulled over after about 2km to find the back brake was binding, and the disc was hotter than Jennifer Aniston. 

Mind if I ask how you determined the back disc was binding on the side of the road.  Might add some insight.

Offline 3alfa3

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Re: Sticking back brake
Reply #3 on: August 01, 2020, 11:05:14 AM
Clean:
Pads pin (check if its smooth, or there are markings on it where pads glide). Put pin in el. drill and with fine grit sandpaper clean pin
Brake piston

Check if caliper guide pins moves freely, if not, clean them and relube with high temperature silicone grease

Check if brake pedal returns freely.
Last Edit: August 01, 2020, 11:10:00 AM by 3alfa3

Offline Keenconsumer

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Re: Sticking back brake
Reply #4 on: August 01, 2020, 09:12:45 PM
Thanks for the replies. 
@Tudran - yeah, I thought that too.  Last year a small pebble wedged itself between the engine and cable on my Z1000 and jammed the clutch.  Couldn't find anything when I first stopped on the Z900, but that may have caused the problem, so fiddling around at the roadside got rid of the blockage? 
@JohnCW - my mate was following me and said the brake light was on the whole time from leaving the petrol station until stopping.  I ride balls of feet on pegs, so it wasn't accidental activation.  Brake light hasn't come on before or since without the brakes being intentionally applied.
@3alfa3 - good idea, will do. 

Paranoia means I check during every ride - even with minimal use the back discs always seems to be warmer than the front, but maybe that's normal.  Problem seems to have gone away, but this sort of random glitch brings back bad memories of owning a Ducati  :012: 
Last Edit: August 01, 2020, 09:14:01 PM by Keenconsumer
The advantage of the rain is that, if you have a quick bike, there's no advantage.
Barry Sheene

Offline JohnCW

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Re: Sticking back brake
Reply #5 on: August 02, 2020, 02:21:44 AM
*Originally Posted by Keenconsumer [+]
Thanks for the replies. 
@Tudran - yeah, I thought that too.  Last year a small pebble wedged itself between the engine and cable on my Z1000 and jammed the clutch.  Couldn't find anything when I first stopped on the Z900, but that may have caused the problem, so fiddling around at the roadside got rid of the blockage? 
@JohnCW - my mate was following me and said the brake light was on the whole time from leaving the petrol station until stopping.  I ride balls of feet on pegs, so it wasn't accidental activation.  Brake light hasn't come on before or since without the brakes being intentionally applied.
@3alfa3 - good idea, will do. 

Paranoia means I check during every ride - even with minimal use the back discs always seems to be warmer than the front, but maybe that's normal.  Problem seems to have gone away, but this sort of random glitch brings back bad memories of owning a Ducati  :012:

Based upon the description you've given, I'd do two things.  Check you have appropriate clearance between the pedal push rod and master cylinder in the fully released position (you should be able to feel this by pushing the pedal slowly down by hand, about 1/2" - 3/4" at the pedal end.  If that's ok, I'd give the whole system a REALLY good flush out by bleeding about a liter brake fluid (cheap enough) through it.  Why?  Because the only other reason I can think of for the pedal failing to return (keeping the light on) is a bit of junk in the fluid blocking the master cylinder return port.  Even if bleeding doesn't flush it right out it'll push it way down the line where it won't cause any problem.

My rear rotor (not a Z900) is always WAY hotter than my front disks.  I think its just a function of the relative size of each brake.  We put a lot more pressure on that small rear rotor via a relatively long brake pedal that we think compared to the relatively short front lever on big front calipers/rotors.   I go through about 3 sets of rear pads to each set of front pads.  If someone has told you not to use the rear brake, ask them why a MotoGP bike has one, or the Ducati GP bike even has a thumb operated rear brake so it can be used cranked right over on the right side when they can't get their foot on the pedal such is the extreme lean angle.
Last Edit: August 02, 2020, 02:22:26 AM by JohnCW

Offline Keenconsumer

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Re: Sticking back brake
Reply #6 on: August 02, 2020, 09:23:10 AM
That makes a lot of sense, thanks.

I've checked it out as suggested (no problem) so on to a thorough flush and clean.  Meanwhile there's still no recurrence of the original problem.

( :455: but sort of relevant) On a wee test ride today I got talking to a guy riding an MV F3.  Apparently the F3 rear brake going soggy after a couple of weeks has been a known fault for a while, but nobody at the Castiglioni Research Centre can or will resolve it; latest theory is that the master cylinder ionises the brake fluid over a short period, adversely affecting the properties of the braking fluid...
...and we're back to weird random Ducati type issues.

Cheers
The advantage of the rain is that, if you have a quick bike, there's no advantage.
Barry Sheene

Offline RobZ900

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Re: Sticking back brake
Reply #7 on: Yesterday at 12:28:42 AM
Have a look through my photos. I had a problem with my rear calliper due to the slide pins. Kawasaki decided not to bother putting any grease (or very little) on the pins. That coupled with brake dust and general road grime meant the calliper wasnt able to move. The result was the pad on the piston side wore almost all the way down to the backing plate while the inner pad was like new. Took the calliper off, cleaned everything up and actually greased the slide pins with rubber grease. Replaced the pads and good as new. I now make a point of doing this twice a year to avoid a repeat of the problem.
Motorcyclist - noun (moh-ter-sahy-klist)
: a person willing to take a container full of flammable liquid, place it on top of a hot, moving engine and then put the whole lot between their legs!