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back brake tightens when warm
- jimimac
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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
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- Patton
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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!
1973 Z1
KZ900 LTD
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- bountyhunter
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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.
1979 KZ-750 Twin
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- edd
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- steell
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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.
KD9JUR
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- jimimac
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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.
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- Patton
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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!
1973 Z1
KZ900 LTD
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- Patton
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1973 Z1
KZ900 LTD
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- Patton
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- Posts: 18640
- Thank you received: 2098
1973 Z1
KZ900 LTD
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- Patton
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- Posts: 18640
- Thank you received: 2098
1973 Z1
KZ900 LTD
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- Patton
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- Posts: 18640
- Thank you received: 2098
1973 Z1
KZ900 LTD
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- jimimac
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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.
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