TOPIC:

Hey there folks. I'm once again in desperate need of your assistance. 

Since rebuilding my '78 KZ1000, I've had issues with the rear brake locking up on me. It happened twice early on. I pulled apart the master cylinder, and the relief port was plugged. I fixed that, and it worked fine for a little over 1000kms, but it happened to me again last night, while on the highway. I got off as quick as I could and cracked the bleeder. The fluid was boiling, and she was smoking enough that a concerned citizen turned around to offer me the fire extinguisher out of his truck. 

Today I was pulling apart the rear brake caliper to try to diagnose what happened. I had one heck of a time pulling the codder pins out as the space between the caliper body and the outside pad was nearly non existent. Basically, the outside pad was edged tight between the body of the caliper and the brake rotor. 

In order to remove that outside pad, I had to loosen up the axle to make enough room for the pad to slip out. 

I then noticed that entire caliper is off center from the rotor, as if I were missing a spacer on the axle between the hub and caliper. I've checked the parts schematic umpteen times, and I'm certain there's no part that I'm missing in the assembly. What could cause this, and how do I fix it?
 

If you look closely at your second pic it seems that the caliper is on an angle, the disc is hard up against the top of the caliper but has some clearance at the bottom, I'd say your caliper mount is bent....  That would have resulted in dragging the right pad and explains the excessive heat....

I'm pretty sure it just looks that way in the photo? Here's some other angles. 

 

Nevermind. I understand what you were saying now. I'll look into that. 

wrote:

Nevermind. I understand what you were saying now. I'll look into that. 

I should have used arrows....!!   

Yes, Its the same both front and back of the caliper , that's what led me to believe the mount is slightly bent, there's really nothing else it could be.....

Your rotor could also be cone-shaped from heating of the outer edge.
Place a straight edge across the diameter to check flatness.

You just have to figure out why it happened.

From Kevin Cameron's Sportbike Performance Handbook

I think 750 R1 is on it... I thought the same looking at the pictures. If it’s not bent the look at the weld mount on the swing arm. Or the stay arm. Ether could be bent. I think the hole in the bracket where the axle passes would be oval. 

I think the rotor is warped. Whether or not that's the cause or effect remains to be seen. Going to pull the wheel off tomorrow to confirm. If it is, I think there's a machine shop in town that may be able to flatten it. I guess that will depend how bad it is. Don't really want to have to buy a new rotor right now, because I don't think I could handle not replacing the front one at the same time. 

If you have  correct mounting and spacers in place?
Plain and simple! One of your pistons or both are seizing after it gets hot!
Common on cars and trucks all the time! Same thing! Caliper is hanging up from a seized piston!
I would be searching eBay for a rear caliper. Buy the "Brake Crafter" rebuild kit. With the new stainless steel pistons! Do it right. Then it will be safe and fixed for a long time! I've taken a few brakes apart in my time!

I did order the kit from brake crafters with the new pistons. Seems like the right thing to do after boiling it regardless, but look back at the photos. The rotor is rubbing on the caliper itself, not the piston. 

wrote:

If you have  correct mounting and spacers in place?
Plain and simple! One of your pistons or both are seizing after it gets hot!
Common on cars and trucks all the time! Same thing! Caliper is hanging up from a seized piston!
I would be searching eBay for a rear caliper. Buy the "Brake Crafter" rebuild kit. With the new stainless steel pistons! Do it right. Then it will be safe and fixed for a long time! I've taken a few brakes apart in my time!

The spacers have nothing to do with it, even if he did have the wrong ones, the caliper would not be on an angle, just closer to one side than the other, the pictures clearly show the caliper angled toward the disc. I agree with the heat seizure

Kaylinator, I wouldn't be surprised one bit to see a warped disc after the amount of heat that went through it, personally, I'd junk the disc and caliper and get new {second hand} ones that are straight, there should be a few around the forum waiting for a new home........ Just use a steel ruler on the disc on the bike, you'll soon see if its warped.

I would double-check the entire system. From master cylinder, hose, on back to the rotor.
Check the brake fluid for debris. You mentioned that your relief port was clogged. Not that this is it, but your brake hose, if it's old, could be disintegrating internally. Leaving bits to get stuck within the relief port.
It could be almost anything. Just check over the entire system.