confederateJACK

Would low disc brake fluid, in itself, cause brake to lock up/grab?

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Would Low disc brake fluid, in itself, cause a front disc brake to grab and lock up?  I have a 96 DR350 and when I bought it the guy told me that the front brake fluid was low, but I kept forgetting to buy some (Dot-4).  I've been riding the bike for almost 2 months and it's been doing great, no complaints.  But last time I rode it I did notice that the front brake wasn't as good as it normally was. Well I took it for a ride today and got about a quarter mile down the road at about 35mph and started to notice a slight surging grab on the bike, couldn't figure out why so I slowed down to pull into a driveway and as soon as I hit gravel it locked up and I tucked it and tipped over (I can't remember for sure, but I might have tried to use a little front brake as I pulled in). the front brake lever felt tight and wouldn't pull and the brake stayed locked on the wheel (not totally locked up but mostly) for just a minute or so and the disc felt slightly warm but not hot by any means. after a couple minutes it opened back up and the bike would roll freely.  So I rode back home slowly at about 5-10mph, stopping about 4 times and resting a minute or two so it would not get hot, I checked the disc every time I stopped and it barely felt a little warm to the touch but not hot and not even very warm, just slightly warm. The fluid level looks empty through the looking glass and after I got home the bike rolls free and fine.  I suspect the low brake fluid caused the brakes to grab because it didn't have enough fluid in the system to keep them open.  Does this sound like a reasonable scenario for the brake grabbing and locking up?...Low fluid alone as the culprit?  Sounds probable to me I was just looking for input. I didn't know that would happen just because of low fluid, I thought the brakes just wouldn't work if the fluid got too low.  But it seems that the fluid not only compress's the brakes but also keeps them open when you let off the lever.. is that correct?  I've owned many bikes but have never had any brake problems before with any of them and never even had low fluid in any of them before best I can recall.  Will low fluid cause this on it's own? the brake pads are fairly new (2 months old with daily use).  I just took the wheel off last week and changed the tire and while the rim was bare I put it on a rim jig and checked the rim for trueness, warping and concentricity as well as checked the disc. Everything checked out fine last week.  Low fluid was the only issue I could find with the bike, won't be able to purchase any Dot-4 until tomorrow.   I believe it would be sufficient to drain, flush, fill and bleed the brake and it should be fine after that best I can tell.  Thanks for any 2nd opinions going on the info I've given.

 

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Edited by confederateJACK

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Also the bike doesn't have any leaks of any kind that I've ever noticed or been able to find. ( no floor spots, no runny drips or slippery parts just clean dry tire-rim-brake caliper, reservoir, brake line, etc) and I've never noticed any brake fluid leaking out from anywhere and the brakes have worked perfect up until now, no noises, no rubbing, no bouncing, no grabbing, Good smooth operation, strong brakes and good lever action- good brake response- and good normal lever feel.  

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No rocks or deformation of the disk or pad? I would say three things, if a cylinder is dry enough that the piston gets stuck in the bore of the hydraulic system then yes. Or if there is air/water trapped in the line, gets hot enough to expand against the fluid and actuate the slave piston, the other option is that the system is contaminated and there is junk in the lines or something. crack the bleeder open the reservoir and see if it will drip down..if it doesn't you have a blockage somewhere.

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Low fluid would not, mis-adjusted free play of the lever and lack of caliper servicing would. Sounds like a poorly maintained bike.

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3 minutes ago, theBIGnaud said:

No rocks or deformation of the disk or pad? I would say three things, if a cylinder is dry enough that the piston gets stuck in the bore of the hydraulic system then yes. Or if there is air/water trapped in the line, gets hot enough to expand against the fluid and actuate the slave piston, the other option is that the system is contaminated and there is junk in the lines or something. crack the bleeder open the reservoir and see if it will drip down..if it doesn't you have a blockage somewhere.

Right..No rocks or deformation of disk or pad that I can see, that all looks good.  Thanks for input, i'll try your suggestion and see what happens. Appreciate the help.

 

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9 minutes ago, William1 said:

Low fluid would not, mis-adjusted free play of the lever and lack of caliper servicing would. Sounds like a poorly maintained bike.

How you came to that ignorant conclusion is beyond me. You have no idea how well my bike is maintained based on the information I gave.    Since the brakes have performed perfectly up until today this clearly rules out 'mis-adjustment' or 'freeplay' of the lever.  Much like your advice, your attitude is neither helpful nor relevant.  But i'll give you a C+ for assholishness, and, at least you tried.

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21 minutes ago, confederateJACK said:

How you came to that ignorant conclusion is beyond me. You have no idea how well my bike is maintained based on the information I gave.    Since the brakes have performed perfectly up until today this clearly rules out 'mis-adjustment' or 'freeplay' of the lever.  Much like your advice, your attitude is neither helpful nor relevant.  But i'll give you a C+ for assholishness, and, at least you tried.

So let me get this straight. You bought a 22 year old bike and the owner said it needed brake fluid. Then you rode it for 2 months without any brake maintenance, let alone adding fluid, and you're calling out someone as ignorant for trying to help you? 

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1 hour ago, confederateJACK said:

How you came to that ignorant conclusion is beyond me. You have no idea how well my bike is maintained based on the information I gave.    Since the brakes have performed perfectly up until today this clearly rules out 'mis-adjustment' or 'freeplay' of the lever.  Much like your advice, your attitude is neither helpful nor relevant.  But i'll give you a C+ for assholishness, and, at least you tried.

Great start bud, calling a moderator an &%$#@!. 

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1 hour ago, 76xtdrvr said:

So let me get this straight. You bought a 22 year old bike and the owner said it needed brake fluid. Then you rode it for 2 months without any brake maintenance, let alone adding fluid, and you're calling out someone as ignorant for trying to help you? 

if he acts like a douchbag...yeah.

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1 hour ago, confederateJACK said:

How you came to that ignorant conclusion is beyond me. You have no idea how well my bike is maintained based on the information I gave.    Since the brakes have performed perfectly up until today this clearly rules out 'mis-adjustment' or 'freeplay' of the lever.  Much like your advice, your attitude is neither helpful nor relevant.  But i'll give you a C+ for assholishness, and, at least you tried.

Sure I do. You glowingly ride with no brake fluid visible in the master cylinder and have no idea why the brake does not work properly. And yes, you can go pro with missing spokes.

 

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2 minutes ago, William1 said:

Sure I do. You glowingly ride with no brake fluid visible in the master cylinder and have no idea why the brake does not work properly. And yes, you can go pro with missing spokes.

 

You would know...You hateful old bastard

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36 minutes ago, turbo dan said:

Great start bud, calling a moderator an &%$#@!. 

Mods do not get special treatment. If I were thin skinned, I'd report the post as TT does not tolerate personal attacks in the tech or bike specific areas. Instead, I often let people 'do what they must' and let the chips fall where they may.

Brakes need fresh fluid, fresh hoses, properly lubed sliders, properly adjusted freeplay, along with good seals and proper alignment. Some people do not like these things.

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It sounds to me like the front brake caliper needs to be taken apart and at least cleaned to allow the pistons to retract properly.  It might also require new o-rings.  Brake hoses degrade with time, as do the seals and o-rings in the master cylinder.  All of this junk can cause the brake to stick.  Just my opinion.

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The brake pistons should be checked for corrosion that could also cause binding.

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This has got me thinking.  In April this year I bought a 1999 DR350SE with 4000 miles on it.  The brakes seem to be working fine in what little riding I have been able to do on the bike so far.  I'm wondering if I should just go ahead and replace the brake hoses, tear the calipers down and inspect/replace parts as necessary and re-build the master cylinders now or wait until they show some issues.

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28 minutes ago, GlennRay said:

This has got me thinking.  In April this year I bought a 1999 DR350SE with 4000 miles on it.  The brakes seem to be working fine in what little riding I have been able to do on the bike so far.  I'm wondering if I should just go ahead and replace the brake hoses, tear the calipers down and inspect/replace parts as necessary and re-build the master cylinders now or wait until they show some issues.

No, you should ignore everything until if fails, just like the original poster in this thread, and possibly crash.

' ....doh...'

OLD = REBUILD, no matter how many hours or miles it has. All things have a shelf life. Atmostphere does not preserve things, it corrodes them. Petroleum oil and grease is hydroscopic when it fails, sucking moisture into everything.  You have to take it all apart and inspect everything that has been exposed to air or sunlight. 

If you ignore this, you will damage the bike, and possibly your body.

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32 minutes ago, THE KRAN said:

No, you should ignore everything until if fails, just like the original poster in this thread, and possibly crash.

' ....doh...'

OLD = REBUILD, no matter how many hours or miles it has. All things have a shelf life. Atmostphere does not preserve things, it corrodes them. Petroleum oil and grease is hydroscopic when it fails, sucking moisture into everything.  You have to take it all apart and inspect everything that has been exposed to air or sunlight. 

If you ignore this, you will damage the bike, and possibly your body.

Well, I changed the engine oil.  I took the rear suspension apart and inspected/regreased everything.  I took the forks off and drained and replaced the fork oil.  I did all of these things because of just what you you said, I was concerned about moisture absorption.  I will be pulling the brakes apart next.

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6 minutes ago, GlennRay said:

Well, I changed the engine oil.  I took the rear suspension apart and inspected/regreased everything.  I took the forks off and drained and replaced the fork oil.  I did all of these things because of just what you you said, I was concerned about moisture absorption.  I will be pulling the brakes apart next.

Good man.  It's about the life of the bike and the life of the rider...

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Just now, THE KRAN said:

Good man.  It's about the life of the bike and the life of the rider...

The funny thing is, I did all of those other things with out thinking about it.  For some reason the brakes slipped my mind and yet the brake fluid is harder on its systems that the oil/grease is on theirs.. 

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