February 7, 20179 yr My mate has an 07 beta rev 3 250. After half an hour or so the front brake starts to bind and gets gradually tighter until the disc is really hot. At this point the lever is tight. Any ideas? We've retracted the pistons in the calliper and dobbed them in grease and they seem fine! Where do we go from here?
February 7, 20179 yr 15 minutes ago, birdy said: Make sure you have a little free play on the brake lever. enjoy Birdy. Yes, I'd say the master cylinder piston has no gap to the lever.
February 8, 20179 yr Free play is a likely problem. It`s also possible the bolt for the lever is in a bind and every time you pull the lever it tightens the bolt. So you pull the lever and it locks in place. Very bad feeling.
February 8, 20179 yr Check the boot on the M/C between the lever and piston I saw one rusted under the clip and washer not letting the piston fully return causing the same problem of holding the pads on
February 9, 20179 yr As above. The master cylinder has a hole that allows fluid from the reservoir to replenish the system when the lever is fully let out. When you use the brake the fluid gets heated and expands. Normally not a problem as the pressure in the system is relieved every time the lever is returned to full rest and the hole is uncovered releasing the pressure into the reservoir. Some people will try to get the lever to stay closer to the bars by tightening the set screw that adjusts the lever position at rest too far. What happens is the piston in the master cylinder never returns all the way to the rest position so it never uncovers the hole to the reservoir. Pressure builds up in the brake system causing brake drag which makes more heat which builds more pressure which causes more drag.... Eventually the brake is stuck full on and the lever won't move. This can also happen if the hole to the brake reservoir gets blocked. There have been reports of cylinders with debris or misdrilled holes but I'd go for the simple solution first and check that when the lever is at rest the piston in the master cylinder is returning all the way against the circlip. Same thing happens on the clutch side though in that case it causes clutch slippage.
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