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Front brakes locking up, need help

351c.i.d

351c.i.d

New member
Joined
Oct 7, 2005
Location
Vacaville
Moto(s)
'05 ZX6R
Hey Guys,
I just got my track bike together and took it out for a quick spin to check some things. Everything worked fine except the front brakes. After about 5 minutes of riding the lever gets really stiff and the front brakes seize up. This is the second time it's done this now. The first time they seized up to the point that the pads would not retract from the disc and the bike would not move at all. I came home and bled the brakes some and went back out and it was fine. Today the lever got really stiff again and while the pads didn't seize up, they are definitely dragging.

This bike sat for almost an entire year in my garage as I got together the parts needed to get the bike up and running. I had to pull the master cylinder off of my street bike as the old one was damaged, but the lines, pads and calipers are the parts that sat with the bike, unused for almost a year. Does anyone have any suggestions as to what to check for and what the culprit might be? Any help would be greatly appreciated. :thumbup
 
Too much brake fluid? As it heats up it can expand and lock the MC. Soak some up with the tip of a shop rag and check again.
 
Ahhh good point, I never thought of that, I'll try that here in a bit.
I'm taking apart my calipers now to take a look, so far the pistons seem to retract just fine once they're disconnected from the lines.
 
good time to split and rebuild the calipers as well as the m/c. easy stuff, not expensive, and there's no more important system on the bike imop.
 
Make sure the pistons move easily back into the calipers. If they don't, they may drag too much, creating too much heat from the friction which then causes the brake fluid to expand and make the pads grip even tighter.

Something else that might cause the same thing is if the piston in the master cylinder is not returning all the way to expose the bypass port. Make sure your master cylinder is working properly. Remove the lever, clean things up, a little grease on the pivot points and put the lever back on. You can check to see if the piston is returning properly if you have the type of MC with the resevoir attached. Remove the lids, and look at the bottom. There may or may not be a small metal clip at the bottom. This just clips on and it's purpose is to prevent small geysers of fluid from squirting up when the brakes are released. If the clip is there, remove it. Don't loose it. Don't contaminate the fluid in the resevoir. Then simply squeeze the lever and release it slowly. You should be able to see the piston move and that small hole appear, disappear, then reappear. If that looks good, put the clip back on, make sure the fluid is not too high in the resevoir and button it up.

Also, make sure the pads are right for your bike. Sometimes there are small differences in pad thickness from year to year that can produce problems like you've mentioned. If the brakes were working fine before and you haven't put new pads in, rule this one out.

Good luck.
 
All of the above is good advice, but how about checking the cheapest and most likely cause first? The brake lever is quite possibly the culprit. Go purchase a factory brake lever and swap it out.

1998 R1's were famous for these problems when the 1999-2003 brake levers were installed on them. It was difficult to tell the difference in the two levers just by looking at them, but there was just enough of a difference to lock the front brakes after a few minutes.
 
I've come across a couple of bike owners who had modified their front brake, non-stock lever, powder coat painted lever, etc. This modification caused some brake lever binding and interfered with the full release travel of the lever.

If the lever does not have full release travel it's possible that the brake line pressure is never fully relieved causing a brake binding issue or worse.
 
Good points guys, I'll definitely look.

The master cylinder, resevoir and brake lever and calipers are stock from the factory. The bike is an 05 zx6r and like I said earlier, I pulled the master cylinder from my street bike and it's never had any problems. The brake lines are steel braided goodridge and the pads are EBC's which were used on the bike just fine before I wrecked it a year ago.

I took some fluid out of the resevoir and pulled the calipers apart. I was able to push the calipers back in with only a little resistance. I've never pulled them apart so I'm not sure how easy they are supposed to go back in. I took the bike out again and sure enough, 5 minutes later the lever got uber stiff and the pads slowly locked up. I'll check the other items you guys listed above. Thanks again and keep 'em coming.
 
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Ok, so tell me if this makes any sense. I swapped over the front brake system (master cylinder, resevoir, lines, calipers, pads) from my street bike that worked just fine yesterday, and the front brakes are STILL locking up. I'm totally lost at this point. I took apart the master cylinder and checked the operation of it and it works as advertised. I've bled the system a million time and still no luck.
 
by master cylinder bleed hole, do you mean the tiny, tiny little hole on the area of the master cylinder that connects to the resevoir itself? I checked for a bleed hole on the resevoir itself and can't find anything other than the hole that feeds into the MC itself. I tore apart my MC again and check all openings and stuck one of my guitar strings through everyone one to clean them out and there were no blockages. I bled the system again and took it out and they locked up once again.
 
after letting the bike sit overnight, put the bike on a front stand and spin the front. are the brakes dragging?

if yes, check caliper misalignment? caliper bolts bent? bent / misaligned axle? brake pad alignment?

if the brakes aren't dragging, then:

check the master cylinder dust boot. sometimes those get stuck or folded weird (especially after rebuilding them or cleaning) and don't let the cylinder piston to fully return.

remove the brake lever bolt. does the master cylinder piston move at all when the lever is no longer held in place? it shouldn't.

if the brakes start out fine but then lock up once they get hot, either the master cylinder piston isn't completely opening to let hot fluid move up into the reservoir, or the small bleed hole is blocked, or there isn't enough of an air gap in the reservoir for expanded fluid to occupy.
 
Well my friend was right when he said it would probably turn out to be something stupid. After checking some other sites I went back out to the bike to check the brake light switch. Turns out the switch assemble had twisted just slightly enough to not allow the brake lever to return all the way. After I fixed that the brakes worked like a champ.

Well, at least after pulling out my hair for the past two days I've become more informed on the brake system to include breaking down the MC and calipers multiple times. Thanks again guys for all of your help!
 
351c.i.d said:
Turns out the switch assemble had twisted just slightly enough to not allow the brake lever to return all the way. After I fixed that the brakes worked like a champ.
Click to expand...

This is why it's sometimes tough to diagnose problems over the net sight unseen.

Glad you figured it out.
 
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