Front Brake locks up after sitting in hot sun - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 11 (permalink) Old 09-10-2008, 02:34 PM Thread Starter
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Front Brake locks up after sitting in hot sun

Ok, this is a new problem with the '93 750 Vulcan with 10K. The front brake locks up after it sits out in the parking lot all day. Sometimes I can get on it a ride several yards or mikes before it just makes me stop cold. If it can put me in a embarassing or awkard situation it seems to chooses those times to bring me to a stop.
To get home I let a little fluid out of the one or both front calipers. This solves the problem until the next day. I came home and try to bleed them but they are fine. I even ordered Speedbleeders for both calipers. They are pretty cool little items and seem to work fine. But I still have had the problem a few times. To avoid the problem I've learned to gently test the front brake before leaving, if it feels very tight (no lever movemnet) I try not to use the front brake on the ride home. If they are tight when I get home and I just don't feel like messing with it they seem fine the next morning all the way to work even if I use the front brake.
Does anyone have some advice? Could it be a sticking caliper?
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post #2 of 11 (permalink) Old 09-10-2008, 02:52 PM
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A sticking caliper, or the master cylinder holes are plugged or possibly brake lines collapsing.
I'd guess you need to drain and clean everything.
Ya don't want to NOT have the use of the front brakes. That's almost 80% of the stopping power!!

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post #3 of 11 (permalink) Old 09-10-2008, 03:43 PM
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Hyper's right! You need to change the fluid and clean the calipers and that should fix the prob.

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post #4 of 11 (permalink) Old 09-10-2008, 07:30 PM
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Is the resevoir overfilled and the fluid has no expansion room? If so as soon as you open the brake lever minutely the fluid could push pressure to the caliper.

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post #5 of 11 (permalink) Old 09-10-2008, 07:37 PM
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I believe the master cylinder is the problem. Clean and rebuild it.

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post #6 of 11 (permalink) Old 09-10-2008, 08:39 PM
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Originally Posted by rckmtn View Post
Is the resevoir overfilled and the fluid has no expansion room? If so as soon as you open the brake lever minutely the fluid could push pressure to the caliper.
I would do the check resevoir for overfill first, cause I'm lazy and don't like to spend money...
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post #7 of 11 (permalink) Old 09-10-2008, 09:40 PM
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Have you ever changed the brake lines? Those are "wear" items and are supposed to be replaced every 4 or 5 years. I wouldn't think that'd be the most likely culprit but if other things don't get you going, you might look in to it. Sometimes a little "flap" of brake line can sort of act like a valve.
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post #8 of 11 (permalink) Old 09-10-2008, 11:56 PM
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You definitely need to rebuild or replace the master cylinder.I know from sad experience and two broken thumbs.Your symptoms sound exactly like mine before they finally locked up and flipped me off my bike at 30 mph. Most embarasing.
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post #9 of 11 (permalink) Old 09-11-2008, 12:53 AM Thread Starter
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I've only had the bike a few months so I am assuming the brake lines are originals. I have had different levels in the master cylinder and it doesn't seem to make much difference in it. The problem kind of builds up over a few minutes or especiallu if I use the front brake without thinking. Everyones ones advise makes sense and could not hurt to remove the calipers for a good going over and new lines and replace or rebuild the master cylindder. I have the fear that it would lock up fast and toss me, so far it has come on gradually. I just realize I am adding more throttle for less speed, pull over a bleed the barke and it is good to go. But it has happened at the worst of times, so it needs attention asap.
Thanks for everyones response, this is a very good resource for a newbie.
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post #10 of 11 (permalink) Old 10-05-2008, 08:00 PM
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I'm probably a month late, but I had this problem and it's the master cylinder. Mine was the pin hole in the bottom of the MC, it was clogged and wouldn't release pressure. Cleaned it and good to go. Oh yeah, I also replaced all hoses, union bolts, rebuilt calipers (new pistons, seals), and rebuilt the MC. All needed to be done, bike hadn't been riden for 10 years. The pinhole was my my problem in the end, I bet it's yours. Change the fluid too, speed bleeders are awesome!

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