Front brake locking up!!

Okay, I am a noobie, so sorry for posting a topic this soon, but I ran into an issue last night and figured you all could possibly provide some insight!

I ride a ’78 KZ650 with the dual front disc brakes. I was riding last night, and it started to feel funny, it was making a rhythmic squeak coming from the front wheel. Within 5 minutes of riding the front brake completely locked up. (I assume from overheating?) The lever was in the extended position (not pushed in) and wouldn’t go anywhere. The brakes were fully on and the bike wasn’t moving. I released the pressure valve, and it cleared everything up and worked perfectly after that.

The reason for the post is I am confused as to why this would happen in the first place? I just bought this bike on Monday. I am thinking I need to change the brake fluid, but is there anything else I should be looking into? Possibly one of the hydraulic pistons isn’t firing in line? Etc etc.

Thanks a ton in advance! Picture of my bike:

hey nice 650 and welcome.....so i also think that is a weird one....it would be great to know if both were sticking on on only one(my bet is one )- piston in one of the calipers has junk built up around where it receeds back itno the caliper to release pressure on
the disk after braking......i would wait and see what guys here think ...and dont worry about posting probs thats what brings us together here and helps someone in the same boat later.....i think if you pull the calpers and let the fluid psi out that you can clean
with brake cleaner and a toothbrush
around the pushing side of each ones piston and also lube with grease the two "carrier" bolts that bolt the caliper together (not the mounting bolts)also tighten the mounts good with lock washers on install,i just almost died when i spaced it last week on a bolt:woohoo:
and slide em back in also sand some glaze off the pads while you got em off and when you reassemble
get a bleeder kit for 10 bucks from harbor freight or just use 2-14 inch vertical tubes and really feed some fluid out while bleeding tapping stuff and wiggleing lines ect.each time...some times the piston on a caliper cant go back from crudd....but wait and see what folks here think first...my way takes an hour at best...peace and welcome...craig

You could have air in the line(s). Try bleeding your brakes.

thanks for the input so far, guys! I think it was the left side (as you are sitting on the bike) that initially locked up. I will try bleeding this weekend. I figure maybe that's a good idea anyway since I don't know how the previous owner treated the bike.

I would check the back of the left fork, if it has an oily sheen it might be leaking from your left caliper, a good indication of brake problems.. If the caliper needs to be fixed its actually pretty easy, the only thing you need is patience in bleeding them when you reinstall, took mine a few days after bleeding to firm up.

I have the same rig and just pulled apart the brakes recently. It seems the brake pad that seats on the caliper is really only held in loosely and if worn to thin might fall between the rotor and bracket causing a lockup. Or you pad might be separating from the backer and folding over causing the same thing..

Best bet would be to remove the caliper in question and have a look.. I found it easier to put the calipers back on the bike after fiddling with em if you take the top off your master cylinder and use a blunt object to push the piston in and allow more space for placement.

Good luck..

I had one of the rubber brake lines on the front of my camaro go bad and it wouldnt let the brake fluid back out of the caliper. Anybody ever had that happpen on a bike.
Tom

thomas ed wrote: "I had one of the rubber brake lines on the front of my camaro go bad and it wouldnt let the brake fluid back out of the caliper."

Never on a bike, but it happened to me on a '79 Caprice.

I'd check inside the master cylinder for the two small holes that are designed to move brake fluid from and back to the master cylinder after braking pressure is created.

Take a toothpick and see if either of them are pluged(you might have to remove the small piston that is moved by the brake lever). I'd check the seals on the piston and the condition of the piston on the brake caliper(s).

Be careful as brake fluid makes a great paint stripper!!

There are two holes between reservoir and bore.

The larger hole feeds fluid into the bore.

The small hole, sometimes difficult to see, relieves pressure from the bore and line when brake handlebar lever is released.

The small hole might be blocked and thereby unable to relieve brake line pressure, resulting as if brake remains applied after releasing handlebar lever, so brakes over-heat and pads lock up against the disc.

I would check out the small hole.

Good Luck!

Patton wrote:

There are two holes between reservoir and bore.

The larger hole feeds fluid into the bore.

The small hole, sometimes difficult to see, relieves pressure from the bore and line when brake handlebar lever is released.

The small hole might be blocked and thereby unable to relieve brake line pressure, resulting as if brake remains applied after releasing handlebar lever, so brakes over-heat and pads lock up against the disc.

I would check out the small hole.

Good Luck!

wow this sounds a lot like the culprit. Thanks again everyone. I am going to delve into this issue over the weekend and I will report back!

Ive seen people overfill the front master cyl before riding and once you start riding the heat expands the fluid and applies the front brakes and locks them up.

mariozappa wrote:

You could have air in the line(s). Try bleeding your brakes.

That was my guess. gas expands when it gets hot.