Disc Brake Gives Out

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doug
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Disc Brake Gives Out

Postby doug » Tue Sep 27, 2011 2:37 pm

I am a 30+ year rider with over 100k two wheel statute miles under my belt, and 29k+ km on three wheels :D. I am a graduate of both the Motorcycle Safety Foundation Rider Courses and the Ohio Dept. of Public Safety motorcycle course (a MSF course clone), and I have had only two, relatively low speed, unplanned dismounts in my career; neither involving an impact with another vehicle or stationary roadside object. I attribute my good fortune in no small part to the fact that early on I was trained to use both front and rear brakes to their best advantage. If you have formal training (which I HIGHLY recommend), you know how the stopping power is proportioned, front versus rear brakes, and the proper braking technique to use during high and low speed manuevering. No boasting intended, I am just saying I know how to use the brakes.

I love to take trips with my Ural in the very beautiful Appalachain Mountains. Since taking delivery of my rig in October of 2007, I have made 8, 1000-2500 km tours in the mountains with a good sized adult in the chair and a good amount of gear in the trunk and/or strapped on the luggage rack. On two trips, heavy park road tourist traffic has led to long, slow, steep mountain descents that have resulted in the front brake giving out. Moments before giving out, I could feel the brake pads begin to seriously drag and not release. Then, the lever pulls back to the grip with zero fluid back pressure despite repeated "pumping" attempts with the lever. Fortunately, my speed on these descents has been low enough that I have been able to control the rig with a downshift and serious pressure on the rear brakes. Pulling off the road and cooling off the brake disc caliper with drinking water that I usually carry on board has returned the brake to normal operating condition. After the first episode, I theorized the brake fluid was boiling and I changed to a dot 4 fluid (higher boiling temp than dot 3) but the problem reoccured. On fast descents, this has not been an issue and I suspect the air flowing past the caliper is stripping enough heat away to keep the caliper below a critical temperature reached during the slow descents.

My old BMW R100RT has a curb weight of just over 500 lbs wet and has twin discs up front. The Ural has a wet weight North of 750 lbs and has just the one so it may be undersized for the weight of the vehicle and it may just be something I have to live with.

Any similar experience amongst the fold?

Best Regards,
Doug
Last edited by doug on Fri Aug 10, 2012 5:12 pm, edited 1 time in total.
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Re: Disc Brake Gives Out

Postby elliotf » Tue Sep 27, 2011 2:59 pm

This is a problem with high altitude and overheating brakes. This is out of a BMW manual:
"Serious Considerations – As stated before, boiling temperature increases as pressure is applied. If the brake fluid in your BMW motorcycle has enough water in it to boil at normal air pressure (1atm at sea level, less here in Salt Lake City!), and if you use your brakes aggressively, you may generate enough heat to exceed the wet boiling point. The brake system pressure may make the boiling point high enough to stop the boiling. But, when you release the brake lever, the pressure goes back down to about 1 atm. At that pressure the brake fluid could begin to boil. Then the next time you try to apply the brake, the boiling fluid will cause you not to have any brakes! This could really be a problem, particularly if you are coming down a mountain pass at high speeds with a full load and a passenger and need to slow down for that next turn!! We cannot emphasize too strongly the importance of flushing your brake fluid annually."

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Re: Disc Brake Gives Out

Postby cdscoot » Tue Sep 27, 2011 3:45 pm

Hmmm. Good point!
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Re: Disc Brake Gives Out

Postby doug » Tue Sep 27, 2011 5:57 pm

elliotf wrote:This is a problem with high altitude and overheating brakes. This is out of a BMW manual:
"Serious Considerations – As stated before, boiling temperature increases as pressure is applied. If the brake fluid in your BMW motorcycle has enough water in it to boil at normal air pressure (1atm at sea level, less here in Salt Lake City!), and if you use your brakes aggressively, you may generate enough heat to exceed the wet boiling point. The brake system pressure may make the boiling point high enough to stop the boiling. But, when you release the brake lever, the pressure goes back down to about 1 atm. At that pressure the brake fluid could begin to boil. Then the next time you try to apply the brake, the boiling fluid will cause you not to have any brakes! This could really be a problem, particularly if you are coming down a mountain pass at high speeds with a full load and a passenger and need to slow down for that next turn!! We cannot emphasize too strongly the importance of flushing your brake fluid annually."


Good post. The description affirms my suspicions about the boiling fluid. Thanks! I did change out the brake fluid before the last outage so I don't think it is a moisture issue. Makes me think that the brake is borderline or marginally undersize with regard to its surface area for the weight of the rig. The one brake caliper/rotor is having to dissipate the heat generated by stopping 50% more weight than what the two similar size on my BMW are having to dissipate off and the surface area is just not there to do it. The heat accumulates and the fluid boils. I think dot 4 boils at about 350 F at 1 atm.
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Re: Disc Brake Gives Out

Postby Dwight » Tue Sep 27, 2011 7:40 pm

Hey Doug,

I experienced the same thing as you did on a ride on the Blue Ridge Parkway last year. Scared the heck out of me.

I've been told that the best technique to use on long downgrades is to keep it in the lower gears and don't break in small, gentle amounts. Instead, grab a real handful of brake to slow down a lot, quickly -- and then let loose so the brakes can cool down some before you grab the next handful.

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Re: Disc Brake Gives Out

Postby cdscoot » Tue Sep 27, 2011 7:41 pm

I wonder if you could put another disc on the other side? Or you could go back to a drum? :lol:
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Re: Disc Brake Gives Out

Postby mgtibb » Tue Sep 27, 2011 8:04 pm

Dwight wrote:Hey Doug,

I've been told that the best technique to use on long downgrades is to keep it in the lower gears and don't break in small, gentle amounts. Instead, grab a real handful of brake to slow down a lot, quickly -- and then let loose so the brakes can cool down some before you grab the next handful.

Dwight


Dwight is right. This is the correct way to brake when descending long grades. Sorry, but if your overheating the brakes then your doing it wrong.
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Re: Disc Brake Gives Out

Postby BinDerSmokDat » Tue Sep 27, 2011 10:04 pm

When the wife and I did Delaware Water Gap this spring there were some long twisty steep downhill sections of road (well relatively long and steep for NJ :D ).
They required some attention to keep the fully loaded rig +2 riders from entering corners faster than is prudent.
I knew the front disc would be overworked, so I used the appropriate gear, with some engine braking and the rear brakes to provide trailing braking.

It worked very well, and the front disc was only needed at the bottom of the hills when it was necessary to come to a complete stop.
I experienced no brake overheating and the front disc stopped the rig very easily.
Also my pads and fluid were less than a year old, so that is another factor to consider.

If I were having trouble overheating the front brake, I'd...

1. Chalk/adjust the drum brakes, make sure they are optimal.
2. Change brake fluid, flushing the line with some plenty of fluid to guarantee there is no moisture lurking anywhere.
3. Check pads.
4. Choose a gear that matches desired road speed to reasonable RPM's with minimal braking input.

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Re: Disc Brake Gives Out

Postby doug » Wed Sep 28, 2011 10:10 am

Thanks for all the feedback. My rear brakes have both been "chalked" and work very well and I put new front pads on before BURP this summer. The problem I faced both times I experienced the failures (and the reason it has not occurred more than twice in my 29,000+ km experience with the rig) was that I had a long line of cagers in front and behind me dictating the speed of the descent, which was significantly slower than I would normally go. If you ride your rig through the Great Smokey Mountain National Park in the summer/fall, you will experience this; the park roads can be very CROWDED and during the episode last week, construction had the traffic packed in tight strings making the normal congestion even worse. When the road is open and I am able to determine my own rate of descent (If you ask Niteblues, he has followed me on the Blue Ridge Parkway and will vouch for how well I brake/drift/and sling the rig through the turns), I never "ride" the brakes. I tried to stay off the front brake as much as possible and use the transmission and rear brake, but because of the very awkward speed dictated by the traffic hemming me in and the tall space between first and second gear, there wasn't much else that could be done. I can promise you I made every effort to stay off the brake for extended periods but you can only get so close to the bumper in front of you and the engine and rear brakes just weren't enough.
Last edited by doug on Wed Sep 28, 2011 11:35 am, edited 2 times in total.
In the stable:
2007 Ural Patrol: 35,000+ km, Winner of the highly coveted "Cleanest Ural" award at CRAP 2011 & 2012
1988 BMW R100RT (owned since new)
2012 Honda Goldwing

Previous Steeds: 1987 BMW K75S, 1979 Kawasaki KE 250, 1982 Honda MB-5

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Re: Disc Brake Gives Out

Postby Niteblues » Wed Sep 28, 2011 10:30 am

Yes, I concur with your assessment of how you ride. You certainly don't overuse the brakes!

Your weight calculations are off a bit though. 750lbs is the dry weight of the rig. Add 200lbs for the driver, 150 for the passenger and you're already way over 1000lbs. Since you had on riding gear and helmets and some gas in the tank and oil in the engine and the tool roll in the trunk and all the camping gear and a cooler with Baltika and ice, now how much do you think it all weighs?

But I have never had any issues with my front brake- even when descending Mt Washington in NH. First gear was too slow and second gear was like a runaway bike on it's way straight to the bottom! I heavily mashed the front and back brakes every 100 feet or so to bring the rig back to a more comfortable pucker factor. Sometimes the front brake would go all the way to the handlebar, but that was mostly due to needing a bit more fluid in there and a good bleeding which I hadn't done. Ever.
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Re: Disc Brake Gives Out

Postby elliotf » Wed Sep 28, 2011 12:06 pm

You could try Dot 5.1 brake fluid. (Not dot 5 as it is not compatable with dot 4). "DOT 5.1 fluids are simply DOT 4-type fluids which meet DOT 5 performance requirements. Because of this, they typically can be mixed with DOT 3 or DOT 4 fluids without concern. In some circles, they are even referred to as ‘DOT 4 Plus’ or ‘Super DOT 4’ fluids " It will raise the boiling point".

Here is a like to a good read on brake fluids:
http://www.stoptech.com/tech_info/wp_br ... d_1a.shtml

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Re: Disc Brake Gives Out

Postby BinDerSmokDat » Thu Sep 29, 2011 10:20 am

doug wrote:The problem I faced both times I experienced the failures...was that I had a long line of cagers in front and behind me dictating the speed of the descent, which was significantly slower than I would normally go.


Thanks for the clarification. I missed your reference to traffic in the original post.

The suggestion to use DOT 5.1 is probably the best one.
If gearing/rear brake isn't enough and you are still overheating the front,
you might just have to accept the fact that you are at the limits of your Ural.
Pull over, open a beer and let the brakes cool off/traffic die down.

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Re: Disc Brake Gives Out

Postby BinDerSmokDat » Thu Sep 29, 2011 10:30 am

Here is something interesting...I was reading up on DOT 5.1 and found this...

DOT 4 Dry Boiling Point 446º F "Wet" Boiling Point 311º F

Brake fluid is considered "wet" when it absorbs 3% water by volume of the system.
So given how poorly everything else on a Ural seals, I'd bet enough moisture is accumulated to diminish maximum performance in the conditions Doug was experiencing.

http://www.afcoracing.com/tech_pages/fluid.shtml

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Re: Disc Brake Gives Out

Postby bokad » Thu Jul 12, 2012 5:59 am

+1. My front brake gave out yesterday in similar conditions.
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Re: Disc Brake Gives Out

Postby a1930ford » Thu Jul 12, 2012 6:18 am

:lurker:
Last edited by a1930ford on Fri Sep 28, 2012 5:23 am, edited 1 time in total.
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