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Did boiling brake fluid lay me down?


TomS

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Don't know if this post belongs here, but being a spoiled '04 1150 RT user, I'm trying to recover from an accident on a rented 650 Kawasaki.

 

The gory details:

On the Greek island of Naxos, my rented Kawa has "mushy" back brakes when I pick it up. I take it back, they check the fluid level. It's low. Brake disk has grooves in it. Bike guy explains that a previous user has probably boiled the fluid, grooves are "normal". They top it up, brakes seem a bit better and I'm on my way with the mrs.

 

After an hour's driving in the scorching heat, a potato van with no brake lights decides to stop in the middle of the road in front of us. I step on the back brakes. Nothing. I step harder. Still nothing. Only one option left. Front brake. We slide and land hard on the asphalt scraping off skin on ankles, knees, elbows etc. Helmets protect the head, fortunately, and we break no bones, increadibly.

 

Can old boiled brake fluid cause the brakes to fail in this way when hot?

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Why would the rear brake be your first option? Rear brakes on sport bikes are there mainly as decoration. You don't really ever know when they are working or not--sort of like an engine in a Cessna 152.

 

Seriously, your first option should have been the front brake. If it was fine, you went down because of technique--not some possible problem with the rear brake.

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What laid the bike down was failure to use the front brake properly when you needed to stop. The back brake just will not slow a bike down much at all. Braking should be progressive, using BOTH brakes, with a bias towards the front of about 60/40 or 70/30.

 

Andy

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Yes, I over-simplified the story a little too much. The first braking action was a normal front/back pressure. When that felt like it didn't do what it should, was when I tested the back brake only and found no action. From then on things went wrong.

 

...and after the accident I still had almost no back brake action.

 

But I understand from your comments that the fluid is not to blame here?

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Mark Menard (Vita Rara)
But I understand from your comments that the fluid is not to blame here?

 

First, I almost never ever comment on threads like this. I feel like I'm far to wet behind the ears to comment. With that said....

 

Yes, I think you were to blame. (Please don't throw stones.)

 

With a passenger on the bike you had very little risk of a stoppy. Why you would have gone to the "back brake only" in a panic stop is completely beyond me. Why would you disengage a brake that gave evidence of working. I could see keeping the front one on, as hard as you could get it without locking the front wheel, and pumping the rear to see if you could clear it or some such. I would never let go of a brake that was working.

 

As Boffin said most of your stopping power comes from the front brake. And as David said, the rear on lighter short wheel base bikes is mostly decoration.

 

I've personally experienced a boiled rear brake on my RT while following David and company through the Dragon. I just kept working the front as hard as I could short of lockup. I think that's what you should have done, and what I would recommend in the future.

 

Now, I will admit that when I put my foot down, while at the same time using the front brake, and there was no rear brake it did play havoc with my head, but I stuck with the plan and used the front brake, and pumped the rear. The rear was dead, so I slowed my pace and road the rest of the road with just my front. As I say it did mess with my head, but it proved to me that most of the stopping power is up front, and you'd better use it when needed or it might cost you your life.

 

I'll stop rambling now. I'm glad there were no serious injuries. That's the most important part. Bikes can be replaced. People can't.

 

Take care,

 

Mark

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There are two questions here, you seem to have asked a hybrid of both of them.

 

1. Can boiled brake fluid cause the brake to fail?

2. Did that cause your accident?

 

These two statements don't make any sense together:

 

"I step on the back brakes. Nothing. I step harder. Still nothing. Only one option left. Front brake."

"The first braking action was a normal front/back pressure"

 

Some combination of those was what caused your crash, why would you Ever let up on the front brake to try and get more braking power from the rear? Or to test it? If you needed to stop the front brake is your friend.

 

So to answer 1. - yes previously boiled fluid could have introduced gases into the system and reduced braking efficiency.

2. Absolutely not, you apparently let off the front brake to use the rear then slammed the front on so hard you slid it, we have no way to analyse further because you are not giving us the whole story. However, it certainly looks like you mis-applied the brakes rather badly. Coming from the 1150RT with its stupid linked/power/ABS brakes it isn't all that surprising.

 

You need to be honest, at least with yourself, about this and properly think through what you did with the brakes and whether you practiced braking enough on a strange bike before riding on the street. Sorry to be so harsh.

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Thanks for the insight. I'm absolutely aware that (bad) braking technique is the ultimate problem here. dopeslap.gif Of course I should have been able to stop, back brake or no back brake. I had plenty of time to react. It was the 2 seconds of testing an unusual bike reaction that put us down. The comment about this confusing your head is indeed relevant to my case.

 

My point was more of a technical one: Why the bad brakes when the bike is hot, then restored brake effect when it's cold? Trying to learn something from a bad situation.

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Thanks for the insight. I'm absolutely aware that (bad) braking technique is the ultimate problem here. dopeslap.gif Of course I should have been able to stop, back brake or no back brake. I had plenty of time to react. It was the 2 seconds of testing an unusual bike reaction that put us down. The comment about this confusing your head is indeed relevant to my case.

 

My point was more of a technical one: Why the bad brakes when the bike is hot, then restored brake effect when it's cold? Trying to learn something from a bad situation.

 

First lesson is, Greek rentals are notoriously poorly maintained. Some would not have a break pedal to press - seriously. When riding a strange bike, find out what does and does not work in a controlled environment before riding off.

 

When brake fluids are very low, a top-up is not enough. There will be air/bad fluid in the system which needs to be bled out.

 

Greek rentals are dangerous.

 

So are Cypriot ones.

 

Cya, Andy

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My point was more of a technical one: Why the bad brakes when the bike is hot, then restored brake effect when it's cold? Trying to learn something from a bad situation.

 

Since nobody else has pointed this out, let me observe that bad braking technique was a major factor in this misadventure. wink.gif

 

However, in answer to your as-yet unanswered question: yes, boiling fluid can lead to no brakes. It amounts to bubbles in the system. That being said, I don't know of any fluid likely to be found in your brakes (even in Greece or Cyprus) that will boil at ambient atmospheric temperature. It takes an outside heat source, such as a dragging brake pad or shoe or a brake line laying on the exhaust.

 

Glad you weren't banged up worse.

 

Pilgrim

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DavidEBSmith

To actually answer the original question, you would only expect the brake fluid to be boiling if the bike has a dragging brake pad or the brake line is getting heated from the exhaust (as Pilgrim says), or after prolonged application of the brakes (like riding down a steep mountain grade), or doing a lot of hard braking (like at a race track). So, was your accident caused because the brake fluid was boiling? Probably not. It takes a lot of heat to boil brake fluid. Could your accident have been caused because the brake fluid had been boiled in the past, and was contaminated, ineffective, or there was air in the system? It could be a contributing factor, combined with your unfamiliarity with and unpreparedness for the braking peculiarities of a strange bike.

 

Consider that you're accustomed to riding a bike with brakes that apply extra braking power through servo power and have anti-lock protection. You get on a bike with weak manual brakes and no anti-lock. Your first instinct upon braking would be to apply the brakes with the same mild force that works on your RT, which is ineffective on the rented bike. Your instinct upon nothing happening is to apply much more braking effort, which you can do safely on your RT because it won't let you lock up the brakes, but causes a wheel lockup on the non-ABS rental bike. And I don't remember if your model RT has linked brakes, but that makes it worse, because that can get you into the habit of just hitting the front or rear, not both.

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And I don't remember if your model RT has linked brakes, but that makes it worse, because that can get you into the habit of just hitting the front or rear, not both.

This is why I still habitually apply both brakes on the K, instead of taking advantage of the system by only squeezing the front. I still ride my little Honda cruiser around, and I'd no doubt find myself in a dicey situation sooner or later if out of habit I braked that bike as if it had the K's braking system.

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Slartidbartfast
My point was more of a technical one: Why the bad brakes when the bike is hot, then restored brake effect when it's cold? Trying to learn something from a bad situation.
Ignoring the stuff everyone else has said about braking skill and technique. What probably happened to the back brake is this:

 

1. Brake fluid has not been changed in ages (if ever). Fluid has absorbed moisture from the air and the boiling point has dropped substantially.

 

2. Rear brake gets hot - either from your riding/braking style or, more likely, from the brake dragging slightly.

 

3. Brake gets hot enough to boil the brake fluid (or boil some of the water out of it). You now have a big bubble of steam in the brake system which is compressible - Hence spongy brakes with no stopping power.

 

4. Furthermore a steam bubble will cause some pressure in the system, which will make the brake drag more and heat things further. At this point, the only way to get the rear brake off is to stop and wait for it to cool (which you did) or drain the system.

 

5. Once the brakes cool off, the steam condenses and the brakes work again - Until the next time...

 

I have rented bikes with no brakes to speak of. Either you want to ride so badly, you will make allowances in your riding style or you don't want the risk and should stick to a badly maintained rental car instead smile.gif

 

My father had an entire front wheel, brakes, steering and suspension fall off one corner of his Cypriot rental car as he applied the brakes to pull over near the unguarded edge of a narrow mountain pass, with a large truck coming the other way. The rental company charged him for the damage, of course.

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