Front Brakes Binding

6 replies to this topic
  • ShakaZulu

Posted December 03, 2004 - 04:46 AM


Hi Guys this is my 1st post. What's the best way to test if my pistons in the master cylinder are sticking. I bled the system last night and put the wheel back on but after all the air is out and the brake lever is working the front wheel is really tight to turn. It's a 98 WR 400

ShakaZulu :cry:

  • 5valve

Posted December 03, 2004 - 07:18 AM


dont know of any test, but they arent hard to remove, clean, reinstall and bleed (again)
remove the cylinder and pads and keep pressing the lever, till the pistons fall out
if one of the two is coming out faster, block it, and keep on pressing the brake, till they both drop out

  • MathProf

Posted December 03, 2004 - 09:44 AM


I was doing some end of year lubing of bearings and found that my front wheel bearing was bound up pretty good. If you haven't pulled the wheel lately you may want to take a look. :cry:

I did a 60 mile snow ride the weekend before and blame that for packing grit into the bearing. I check the bearing everytime I re-tire, which is once a month.

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  • ShakaZulu

Posted December 03, 2004 - 10:49 AM


Thanks will do it now :cry:

  • ShakaZulu

Posted December 03, 2004 - 10:50 AM


Thanks for your input. I have a new wheel bearing so it should not be that. Happy riding :cry:

  • Indy_WR450

Posted December 03, 2004 - 12:32 PM


You can feel if the pistons are binding when you apply and release your brakes and spin your front wheel by hand while it is on a stand off the ground.
If the drag is more than usual you will feel it and you may even get a humming sound from your caliper when your pistons are binding in the caliper and there is some brake pressure pulses vibrating thru the sticky pistons.

  • Hamish

Posted December 03, 2004 - 02:09 PM


it will almost always be the pistons in the caliper, not the master cylinder.
Remove the caliper and pads. GENTLY pump the brake lever as you are watching the pistons. One piston will start to move. Only let it move out about 3mm. Then clamp or wedge that piston so it can't move anymore. Continue pumping GENTLY, so that the 2nd piston moves out by about 3mm. Check that the fluid in the master cylinder hasnt run dry. You may find this piston is tight and doesnt want to move. If this is the case it's tome for some new piston seals and a good overhaul of the caliper. If all is well, clean the exposed area of the pistons (very important) and push the pistons back inside the caliper and reassemble. If you do find that you need replace the seals, make sure you clean in the bottom of the seal grooves very well, as this is what generally causes piston binding. Replace the pistons aswell if they are scratched or damaged.


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