2000 R1150 GS Rear Brake temporary failure

[delhonrock]

I've descended 800 vertical feet in 1.5 miles at a walking pace, dragging the rear brake and feathering the front brake with the clutch in. With out any notice, the rear brake is gone...the pedal pushes to the bottom of it's throw... no rear brake. I stop. The caliper is very hot. It cools and resumes normal operation.

Actually I coasted to the bottom of this hill using only the front brake at a snails pace. When reaching the bottom, the caliper was cool to the touch and the brake felt normal.

What was that about?

ABS, non integrated, ABS instrument lights operating normally, brake pads near wear limit, no brake fluid leak.

Thanks
Michael

[Mr. Frank]

When was the last time the rear brake fluid was flushed?

[PacWestGS]

Michael, I don't want to sound harsh but,

It's not meant to be used that way, and that's a dangerous way to get to the bottom of a steep hill (sounds like a dirt one). You boiled the brake fluid in the caliper by over using it. Check to see how much is left in the reservoir and bleed the air out of the system before riding again.

You should be using the front brake and engine to control speed and a combination of the clutch and rear brake to control speed and direction. If the hill is as you say very steep you can switch your engine off (leave the power on) and use the dead engine as a brake with the clutch and front brake. Either way it should always be in gear, first or second. The clutch can take more abuse than the rear brake caliper and the front brakes are what stop a motorcycle even in the dirt.

HTH
Don't forget to bleed the brake system of any air that might be trapped in there now. Or you might get a nasty surprize at an unsuspecting moment.

Russ

[bluwing]

Sounds identical to my experience in the Bighorns last summer.
My fix was new Dot 4 in the system to get rid of the old fluid that could not handle the heat.
I put speed bleeders on so I can have fresh fluid often.
I'm not sure how to control a fully loaded GS down hill with out cookin' something.
You either risk a front wheel slide out, a toasted clutch or boiled back brake.
I guess that's what makes them more fun off road than a little dirt bike.
(that an the sweat...knowing the cost of things you break if you dump it).
Bluwing

[delhonrock]

Harsh? No problem. The bike and I are used to it.
Fluid's changed, good to go.

Thanks for the tip, SFDOC! Engine off, power on.

Thanks, you all are great!
Michael

[j-budimlya]

Michael, I don't want to sound harsh but,

It's not meant to be used that way, and that's a dangerous way to get to the bottom of a steep hill (sounds like a dirt one). You boiled the brake fluid in the caliper by over using it. Check to see how much is left in the reservoir and bleed the air out of the system before riding again.

You should be using the front brake and engine to control speed and a combination of the clutch and rear brake to control speed and direction. If the hill is as you say very steep you can switch your engine off (leave the power on) and use the dead engine as a brake with the clutch and front brake. Either way it should always be in gear, first or second. The clutch can take more abuse than the rear brake caliper and the front brakes are what stop a motorcycle even in the dirt.

HTH
Don't forget to bleed the brake system of any air that might be trapped in there now. Or you might get a nasty surprize at an unsuspecting moment.

Russ

You did not actually "boil" the brake fluid, but you boiled the water that had been absorbed by the old brake fluid.....and it boils at about 212 degrees....less in the mountains....

this is the reason for flushing the brake fluid out....to get rid of the absorbed water in the fluid...in addition, the water causes corrosion in the calipers.....and this as you might imagine is not good either.....

[soffiler]

You did not actually "boil" the brake fluid, but you boiled the water that had been absorbed by the old brake fluid.....and it boils at about 212 degrees....less in the mountains....

What I infer from the above is that as soon as the brake fluid reaches 212F (at sea level, less in the mountains) some boiling begins. Thus you're screwed at 212F. Not true. In fact it is the brake fluid mixture boiling - the water is absorbed in the mixture, no longer separately available to boil at 212F. Think of antifreeze mixed with water, and how this changes the boiling point of the mixture relative to pure water. The water component of an antifreeze mixture does not begin boiling at 212F either.

Brake fluid boiling point degrades with water absorption in a manner similar to that shown in the following chart (which is admittedly for DOT 3; the DOT 4 used in our machines will follow a similar curve)

http://www.aa1car.com/library/bfluid.htm

[j-budimlya]

What I infer from the above is that as soon as the brake fluid reaches 212F (at sea level, less in the mountains) some boiling begins. Thus you're screwed at 212F. Not true. In fact it is the brake fluid mixture boiling - the water is absorbed in the mixture, no longer separately available to boil at 212F. Think of antifreeze mixed with water, and how this changes the boiling point of the mixture relative to pure water. The water component of an antifreeze mixture does not begin boiling at 212F either.

Brake fluid boiling point degrades with water absorption in a manner similar to that shown in the following chart (which is admittedly for DOT 3; the DOT 4 used in our machines will follow a similar curve)

http://www.aa1car.com/library/bfluid.htm

this means we are dealing with a true solution....and the boiling point is only slowly reduced......that must be why the Park Rangers....test your auto brake temperature when decending the road fromt he tp of Pikes Peak....they do not test motorcylces.....

[PacWestGS]

.....that must be why the Park Rangers....test your auto brake temperature when decending the road fromt he tp of Pikes Peak....they do not test motorcylces.....

I remember that from my recent trip. I think it would be more so that bikes have manual transmissions and most cars have automatic ones that most people just use "P" "R" & "D" and wouldn't even know what 1-2 & 3 are to be used for. Even if they put up signs that say use low gear for next xx miles. I followed cages down the hill that had the brakes on all the way down. While I shifting between 3rd and 1st and only braking as needed to slow before a shift or after passing said cages to the bottom of the mountain. The Park Ranger's have probably never had a bike crash because the brakes failed.

I'm sure that had I put the bike in high gear or neutral and rolled down the brakes would not have lasted a very long time and the rear would go first just because of it tiny size.

Michael - another thing (as I read in your original post) is that you said your pads are near the end. This would transfer the heat directly and quicker to the caliper piston because the steel backing can't absorb and dissipate the heat like the compounds in the brake pads. So what may have not been an issue before, became one this time.

As far as water content in brake fluid, I don't know about that. Oil and water don't mix they remain separate properties and compress at a different rate.

Doc

[soffiler]

...As far as water content in brake fluid, I don't know about that. Oil and water don't mix they remain separate properties and compress at a different rate...

Doc - are you trying to relate the properties of brake fluid with oil? Um, if so, ah, don't. They are VERY different fluids.

[PacWestGS]

Doc - are you trying to relate the properties of brake fluid with oil? Um, if so, ah, don't. They are VERY different fluids.

Hehehe, NO - I knew as soon as I hit the send button that someone would tell me the difference between a silicones based product and a petrolatum oil. Far as I know silicone resists water better than oil, but what do I know? I don’t… :doh

Some are mineral based, some are silicon based, and some are complete manmade synthetics. Some deteriorate rubber, some don't, some have a higher boiling point than others, and some need to be changed very frequently to reduce corrosion. What may be best for one application may be worse for others. I know to use what the manufacture has recommended and to replace it every two-years for best performance.

Maybe we could start another “Oil Thread” what is the best “Brake Fluid” to use for a specific purpose and bike? Hehehe :nyah

Doc :wave

[Mr. Frank]

Brake fluid is hygroscopic. It attracts and absorbs water. The more water in the brake fluid, the lower the boiling point. Steam doesn't work the brakes very well. Periodic replacement of the brake fluid removes the water. This property of brake fluid is a good thing because it keeps water from hiding in out of the way places and corroding the system.

[PacWestGS]

Brake fluid is hygroscopic. It attracts and absorbs water. The more water in the brake fluid, the lower the boiling point. Steam doesn't work the brakes very well. Periodic replacement of the brake fluid removes the water. This property of brake fluid is a good thing because it keeps water from hiding in out of the way places and corroding the system.

Thanks to both you and Steve, I have learned or re-learned something today. By doing some basic research insted of reliving my past (which was a very long time ago) I have learned something about brake fluid that I didn't know.

I love this place!!! :clap

I know why somethings happen, but I don't always understand what makes it happen. :banghead

You guys are great! :nod

Doc

[PUDGYPAINTGUY]

Aparently the fluid deteriorates faster than one can imagine too. I just had mine in for the fluids to be changed in the clutch and brakes and wow what a difference, I had to change the pressure on the pedal and lever now that I apply. I guess the recommendation for more frequent changes has more merit than I gave to it originally.

[soffiler]

Brake fluid is hygroscopic. It attracts and absorbs water. The more water in the brake fluid, the lower the boiling point. Steam doesn't work the brakes very well. Periodic replacement of the brake fluid removes the water. This property of brake fluid is a good thing because it keeps water from hiding in out of the way places and corroding the system.

YES! And it is exactly the reason NOT to use DOT 5 silicone-based brake fluid. DOT 5 does NOT absorb water. Thus water stays separated and is laying in wait to boil and/or corrode whatever it is in contact with. It's a very handy property of the conventional brake fluids (DOT 3, DOT 4, DOT 5.1) that they absorb water... so you can get it out periodically.