97 Kawasaki Prairie 400 front brakes locking up
 

So one day just riding along i noticed my speed decreasing significantly, i let off the throttle an then bike came to a screeching hault. I had to open the bleeder valve to release them. From that point on every time i rode i had to periodically bleed the brakes a couple times a ride. The strange thing is, it would happen even when i hadn’t engaged the brakes recently.

Finally this last time it happened i bled them, an some shot at my hand, it was hot. I rode maybe another half mile trying to get home and it happened again. When i opened the bleeder it spewed out burning hot and sizzling, i couldn’t even close the bleeder until it stopped. After getting it back home without brakes, i filled the reservoir with dot3 as it calls for, the brake lever pumps but with no resistance but fluid will run out the bleeder. I’m going to inspect my pads and clean the master cylinder. But what would be causing this issue?

The master cyl is not releasing fluid back into the reservoir, so fluid expands with the heat of the brakes and puts the brakes on, so the brakes heat up more and put themselves on harder. Make sure pitons and sliders on calipers are free, but main thing is to rebuild the master cylinder, making sure the one way valve (if it has one) is working and the piston springs right back to the circlip in the cylinder.

Also pull off the hose(s) and check for restriction/proper flow. They can swell shut on the inside but look fine from the outside.

Ok thanks, I’ll work on taking it apart this weekend then give y’all an update.

How old is the brake fluid? If it has moisture it will expand when hot, creating more heat as the brake pads grab rotor, more expansion, etc until brakes are grabbing so hard the rotor doesnt move.

I would also check the caliper piston & seals because they could be gunked up which causes piston to not fully release, causing heat, and if the fluid has moisture the process starts again.

If you are not sure the fluid is fresh and there are no air bubbles, I would start with replacing fluid first.

I finally got some time to work on the problem. Took the master cylinder off, cleaned it up, blew air through it. And took brake lines off an blew through them. Have it back together now and bled the brakes. Didn’t get time to go on a test drive, but seems the master cylinder had some crap clogging it up. Will post the result in a few hours when i get back to it

Everything seemed good, drove it around for about 8miles. Braked to a stop multiple times, and had no issues. So thinks it’s solved, thanks again.

So do you think it was moisture in the fluid, or stuck calipers?
I had the same issue with my prairie when I got it. It only had 5 hours on it at 8 years old. I ended up just riding it fast, and it put a little wear on the pads, and my problems went away, but I may go and change the fluid, just becasue.

OPs problem was the master cylinder. When the master cylinder piston is in the off position, fluid can run from the hoses into the reservoir, sticky calipers, old fluid, doesn't matter if the fluid can get out of the pipe, into the reservoir as it expands. Sticky calipers don't help as the brakes get hot because the pads don't come off slightly after you let go of the lever. This is, easy to check, put brakes on, release lever, push bike forwards,and see if wheel rolls easily afterwards. That was probably your problem, as the fault went off with use.