Question about 1987 kawasaki GPZ 500 S - GPX 500 R
The rear brake keeps siezing up when I use it. The pistons do not appear to retract far enough back to allow the pads to be clear of the brake disc.I have taken the caliper off the bike loosened the bleed nipple and had to use a ''G'' clamp to push the brake pistons back into the caliper. Next I thoroughly cleaned off all dirt and corrosion paying attention to the two round steel rods/guides that connect the two halves of the caliper. The rods/guides have been de-rusted and polished up with emery cloth then greased with high melting point grease and have made sure that the brake pads move smoothly on these rods/guides, yet the problem still persists. I cannot think of a reason as to why the brake pistons do not retract back enough after checking the fluid level and the brake hoses are free of any kinks or acute bends. The fluid appears to be getting pumped into the caliper from the brake pedal and slave cylinder but not returning or allowing the calipers to retract when the brake is released. So the problem may be how do I check the brake pistons are able to retract properly and how do I check the slave cylinder ( located near the brake pedal and mounted behind the frame ) is working properly? Thank you for any help or suggestions.
Sounds like you need to service the caliper. Remove the piston from the caliper by pumping the brake pedal, be warned you will get brake fluid everywhere. Remove piston seals, dust and oil, you'll probably find that the grooves where they usually reside are full of 'crud' thoroughly clean the grooves, clean the seals then inspect seals for damage and replace if necessary, grease seals (high temp grease) and put back into caliper, wipe away excess grease. Inspect piston for corrosion, minor corrosion can be flatted back with 1200 grit sandpaper, if too badly corroded replace. lightly grease piston (high temp grease) and push into caliper. the piston should slide in easily by hand. Finally bleed caliper well, flush new fluid through entire system.
Posted on Mar 24, 2010
Testimonial: "Thanks for that input, I never contemplated about the crud and corrosion affecting the seals and preventing the brake pistons from moving freely. "
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Posted on Jan 02, 2017
The pistons themselves are generally the problem. The pins and guides just stop the pads from slopping about. Take pads out and caliper off and remove piston and clean out receptable. Check piston seal ring and dust (or packing) ring are not rolled, twisted or damaged. Your pads may even be worn too thin and plunger is having to push piston too far out and ring seals are not sliding on the smoother surface of piston receptable. Hope this helps. Below is a link to a typicall disc brake in exploded view form with part names.
Posted on May 17, 2010
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