back brake tightens when warm

It just slowly compresses causing just a slight drag at first but as it gets hotter it gets tighter.

This happens after about 10-15 minutes of driving (on a hot day) even if I don't use the brake. I assumed this is because there is moisture in the brake fluid but I am pretty sure I have bled the old fluid completely out and it still happens.

Any thoughts would be appreciated

Hello, Jim, and WELCOME to KZR forum! We're glad you're here!

As suspected, some moisture might still be in the line.

Some brakes have an adjustable rod between the foot lever and master cylinder, whereby the rod pushes against the m/c piston. If so fitted, would assure there's sufficient gap where rod enters master cylinder. Otherwise, there may be pressure by the rod against the m/c piston even when the foot lever isn't being depressed.

Might also be a clog in the tiny relief port between the piston bore and reservoir (which can cause pressure to remain in the line and keep the brake pumped up).

If not already done, would check the factory service manual for better instruction and detailed diagrams.

Good Luck!

jimimac wrote:

It just slowly compresses causing just a slight drag at first but as it gets hotter it gets tighter.

This happens after about 10-15 minutes of driving (on a hot day) even if I don't use the brake. I assumed this is because there is moisture in the brake fluid but I am pretty sure I have bled the old fluid completely out and it still happens.

Any thoughts would be appreciated

Same thing happened on my car: it was because the semi metallic pads have a positive tempco, meaning they expand as they get hotter. They were just a shade too big, and I had installed them with new rotors. I had the old rotors turned and installed them, and the slightly thinner diameter fixed it because it gave the pads enough room.

How easily does the back wheel turn when its on the center stand? Maybe the rotor is bent or warped.

Does it drag you to a stop if you keep on riding it? Mine did :laugh:

Didn't have any tools with me, so I stopped at a Dollar Store and bought a set of two pliers for $1, used the pliers to loosen the bleeder screw to relieve the pressure so I could ride it home.

Air in the lines that expanded when the drag from the brake pads heated it, and a clogged return port in the master cylinder.

Thanks for the welcome Patton. My 1983 KZ1000J does not seem to have the adjustable rod you mention. Would the clog in the tiny relief port be affected by heat? This does only happen when it gets hot. I did take the bike on a few hundred + mile drives a few months ago with no issue.

As soon as it cools down it is fine again, I actually poured water on it the other day to speed the process. I have had the current brake pads over a year with no problem before now. Don’t have a center stand but bike is easy to push when cool. I have not had it lock right up on me as I am always able to pull over when I feel it happening but it sure is tight, can’t push the bike.

Looked for KZ1000J on Kawasaki.com which listed only the Eddie Lawson Replica for KZ1000, so will venture some guess-work from there.

Here is the rear brake master cylinder rod assembly part 43010 at the bottom of the diagram.

[click on image to enlarge view] See later post for larger pic.



The next post shows the pedal shaft part 43004, to which the rod assembly presumably attaches.

If a wild guess may be forgiven :lol: ---
Perhaps the nut on part 43010 is a lock nut which could be loosened whereby the rod could be screwed further down to "shorten" it and thereby allow more gap before the rod contacts the m/c piston. Then re-tighten the locknut.

Wish I was more familar with your bike.

Good Luck!

See later post for larger pic.

Click on image for jumbo view. :woohoo:

Click on image for jumbo view. :lol:

Click on image for jumbo view.

Hey Patton

Thanks for all that, are you always so helpful?

Turns out that by bleeding the brake fluid right out of the lines and re-adding it the problem has gone away. Must of been some form of contmination in there.