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Old 04-23-2015, 02:20 AM   #1
JimGregory OP
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91 RS front brake problem

While riding home in the pissing rain yesterday, I got to my exit on the highway and applied the brakes. The rear worked fine but the front didnt work at all. I squeezed harder and they popped on like a light switch! Full dive and HARD on the brakes. I nursed her the rest of the way home and the fronts were still working like a light switch. Moderate pressure did zero. Nothing. Squeeze hard and they popped on hard. Unsettling in the pouring rain I can say.
I parked it in the garage and attended to life in the house.
Now I am up for the day and wondering what in the HELL is going on? I'm pretty sure it's not the individual front calipers but it's in the MC.
Has anyone ever heard or experianced such a thing? I searched but as expected I found no referance to it.
Thanks
Jim
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Old 04-23-2015, 03:31 AM   #2
ME 109
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Perhaps the piston and seal are getting hung up in the bore somehow. Does it happen every time you apply the brake, and does it happen when stationary?
Sounds like a pull apart.
See if it happens with a caliper bleed screw loosened.
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Old 04-23-2015, 05:27 AM   #3
JimGregory OP
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Originally Posted by ME 109 View Post
Perhaps the piston and seal are getting hung up in the bore somehow. Does it happen every time you apply the brake, and does it happen when stationary?
Sounds like a pull apart.
See if it happens with a caliper bleed screw loosened.
It happened every time I hit the front brake after about 4 miles into my trip. Only on the way home yesterday, in a downpour. Never an issue before. Fluid had 2 years on it.
This morning I quickly bled out the old fluid with new. Everything seemed perfectly normal and I rode to work as if it never happened. The brakes worked great, as they always did.
Before I bled it, I had it on the center stand, lifted the front end and spun the tire. Touching the brake lever stopped the wheel spin.
Very peculiar. I have ridden this bike in the rain with no issues before. I can tell you that the brake going on HARD in the rain, and not when expected is not optimal!
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JimGregory screwed with this post 04-23-2015 at 05:43 AM
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Old 04-23-2015, 05:48 AM   #4
Beemeup
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Corrosion in the caliper/piston is all I know of that would do that. I would definitely pop them apart and lightly grease the surface of the piston with something high temp. Definitely not enough to get on the rotors.
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Old 04-23-2015, 05:58 AM   #5
Jim K in PA
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This is curious, Jim. Was the sudden deceleration accompanied by a change in handle lever angle or feedback pressure?

It almost sounds like a layer of water between the pad and rotor that got wiped and then they grabbed, but with drilled rotors this should not happen that severely.

Perhaps some water was getting into the MC/lever and being forced out under pressure? That rain was intense down here in the Poconos yesterday.
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Old 04-23-2015, 06:17 AM   #6
JimGregory OP
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I can't believe it's BOTH calipers all at once OR that it was wet rotors. It was SO on/off like a light switch.
But yes it is very curious.
With medium pressure on the handle I had zero front brakes. With hard pressure it seems like it "popped" on, to the pressure that you would expect with that much lever pressure.
And now fine.
Also once it "popped" on and I released it, it had to "pop" on again if I tried it immediately thereafter.
Perhaps I should have not bled it this morning to see if all was normal in the dry. Oh well. Guess I will find out in the next downpour.
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Old 04-23-2015, 06:24 AM   #7
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Quote:
Originally Posted by Jim K in PA View Post
It almost sounds like a layer of water between the pad and rotor that got wiped and then they grabbed, but with drilled rotors this should not happen that severely..
This is what I was thinking. Can you hear the pads riding on the rotors even without applying the lever?
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Old 04-23-2015, 06:29 AM   #8
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How old are the brake hoses? They could be breaking down inside and impeding flow of brake fluid. A lot of cases of 2000 1150 GS developing a flap inside the brake line which prevented fluid return to mc.
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Old 04-23-2015, 06:50 AM   #9
Jim K in PA
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It does seem like a system wide issue, which is why I think it might be up at the handlebar or along the primary line before the splitter. I have seen this with improperly centered proportioning valves on cars, but not on a bike!
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Old 04-23-2015, 07:00 AM   #10
JimGregory OP
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I suspected a brake hose as well. By why oh why is it perfectly normal today?
I replaced my hoses in my truck for that reason so I am very aware of it.
But usually it blocks the low pressure return flow, not the high pressure send.
I assume my hoses are original 1991 hoses. Lets say they are not older then that!
Hmm
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Old 04-23-2015, 07:03 AM   #11
Jim K in PA
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I am of the opinion it is a problem external to the brake hydraulics. Pull the master out of the handlebar mount and see if water comes out.
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Old 04-23-2015, 08:11 AM   #12
JimGregory OP
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Originally Posted by Jim K in PA View Post
I am of the opinion it is a problem external to the brake hydraulics. Pull the master out of the handlebar mount and see if water comes out.
Can this be done without disconnecting lines? I'm at work and it's hard to research it.
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Old 04-23-2015, 08:42 AM   #13
Solo Lobo
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Any chance the pads are glazed, and the rain causing very limited grip was the issue?

My R65LS acted a bike like this when the master cylinder return hole was blocked... I cleared that with a single bristle from a stainless steel brush
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Old 04-23-2015, 08:47 AM   #14
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Hold old is your fluid? Any goop or crud in the fluid (those are technical terms, right?!)?
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Old 04-23-2015, 08:50 AM   #15
JimGregory OP
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Hold old is your fluid? Any goop or crud in the fluid (those are technical terms, right?!)?
Fluid is about 5 hours old now.
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