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Sep 5th 2018, 06:27 AM   #1
 curve addict's Avatar
 
  Apr 2016
  Des Moines, WA

  ...1987 Yamaha FZR1000...
Brake locks while riding; the likely suspect...

I just shared this on Didley's post. I thought I should share it here too.

In my years of working on bikes, and those four-wheeled things, I've learned this:

In a bike (or car) that's been running, the most common cause of brake lock up is a clogged equalizer port in the master cylinder. There are two holes in the bottom of the master cylinder reservoir. If your bike has remote reservoirs, these holes are under that plastic elbow.

When the brake lever is fully released, the tiny port opens to allow the fluid pressure from the calipers to return to atmospheric. This creates slack, so to speak.

If you can only see one port, then the tiny port is clogged. (If the fluid is too dirty to look through, assume it's clogged) As the fluid in the calipers heat up, the calipers close and eventually clamp down on the rotor.

The ideal fix is a disassembly and thorough cleaning and rebuilding, or replacing, the unit. A quick fix is to gently work a very fine wire into that port and push the sediment plug through. Then get home and fix it correctly.

A roadside remedy is to crack open one of the caliper bleed bolts to release the brake (and close it). Stay off the brake or it may lock again and get to a safe spot to effect a repair.

Note: This symptom can also be caused by a master cylinder piston that is not fully retracting as it should.
Rusty Nail, DGA, mars and 1 others like this.

Edited by curve addict on Sep 6th 2018 at 07:20 AM Reason: clarification
Sep 5th 2018, 10:28 AM   #2
 mars's Avatar
 
  Jan 2016
  McMinnville, OR

  CB160RR, CB550, SportClassic
I too replied to the other thread but it's worth mentioning here as well:

Be sure to take precautions when using wire to try to clear the return port, as the built up pressure can cause brake fluid to squirt everywhere when it lets go.

Also, FWIW, I've been having this issue lately and I read that another cause of this sort of thing can be aging brake lines, where the plastic starts to come off in strips that act like a check valve, allowing fluid to pass one direction but not the other.
Sep 6th 2018, 05:11 AM   #3
 
  Mar 2018
  Gig Harbor

  2008 BMW R1200GS Adventure
I appreciate you both sharing.

I think my primary issue was the age of the fluid. It had broken down to the point that there were murky white-yellow globs at the bottom of the reservoir. I caught this at the very end last night and I almost disregarded the change in shade as the aged plastic of the reservoir body. Swished it around with the bleeder hose and it all started floating around.

Cleaned it out. Glad I didn't miss that. I really don't feel like doing this again unless I've planned for it.
Sep 6th 2018, 07:12 AM   #4
 curve addict's Avatar
 
  Apr 2016
  Des Moines, WA

  ...1987 Yamaha FZR1000...
Yes, that's very common in old fluid. As often as not, a used bike will come to you with the original brake fluid still inside. Changing the fluid every two years will prevent this issue, as well as flush some of the sediments out; tiny rubber and metal bits resulting from normal wear and tear.
Sep 6th 2018, 11:20 AM   #5
 
  Mar 2018
  Gig Harbor

  2008 BMW R1200GS Adventure
Good to know. I washed it off when I got to work and dried it off as best I could.

Went out and checked a little bit ago. Didn’t notice any more fluid. Played with the brake a bit, but it’s still looking good.
Sep 6th 2018, 05:28 PM   #6
 Sentinel's Avatar
 
  Jun 2016
  Poor Tortured

  2015 Kawasaki Concours 14 - The Origame Sea-Dragon
i am doing mine when it gets too cold to ride this year.
i had some brake work done a few years ago by an honest mechanic.
he told me if people flushed their brakes like the manual says he'd be out of brake work.
Sep 7th 2018, 05:20 AM   #7
 
  Mar 2018
  Gig Harbor

  2008 BMW R1200GS Adventure
Everything is working fine. Brakes felt a little softer this morning, so I’m going to bleed them again this weekend.
Sep 7th 2018, 08:16 PM   #8
 Rock Dodger's Avatar
 
  Feb 2016
  Washington

Quote:
Originally Posted by curve addict
Yes, that's very common in old fluid. As often as not, a used bike will come to you with the original brake fluid still inside. Changing the fluid every two years will prevent this issue, as well as flush some of the sediments out; tiny rubber and metal bits resulting from normal wear and tear.
Yes!
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