Road Bike, Cycling Forums banner
1 - 20 of 37 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter · #1 ·
Does anyone have an idea why the front brake on a dura ace brifter would lock up when going over a bump in the road?
Here's the scoop. I recently bought a new road bike, a Gunnar Roadie with a full dura ace set up. I bought the frame and components from the LBS and had them assemble it. The components were a take off from a new bike, supposedly never ridden, they look new. The frame is brand spankin' new.
I was on a group ride, cruising along about 20 mph or so when I hit a bump in the road. My front brake locked up and put me over the bars. No apparent damage to my bike but the front brake was locked up solid. When I got home, after a trip to the ER, I pulled the bike out of the van the brake was still locked up. I moved the shifter and squeezed the brake and then the brake worked fine.
I'm going to be off the bike for a while, but now I question the shifter and what recourse I have. The bike only has 160 miles on it.

-Mark
 

·
RoadBikeRider
Joined
·
1,053 Posts
Are you saying that you never even applied the brake? Or are you sayin' that you applied the brake and then it locked up? I don't see how the brakes would lock up just riding over a bump. Maybe you have a defective/sticky mechanism? Not sure what sort of liability there might be? Might want to talk to an attorney if it is mechanical failure.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #3 ·
I never applied the brakes, I was riding on the hoods, hit the bump and I was airborn. The bump was nothing out of the ordinary, it wasn't even a pothole, just a small dip and rise in the asphalt. I think it's a defect.
 

·
Registered
Joined
·
21,831 Posts
Lockjaw

Marko Polo said:
I never applied the brakes, I was riding on the hoods, hit the bump and I was airborn. The bump was nothing out of the ordinary, it wasn't even a pothole, just a small dip and rise in the asphalt. I think it's a defect.
Please explain in more detail. For example, were the pads clinched on the rim and the cable slack, or was the cable taught and the lever slack? Is it possible the pads are adjusted to "high" and they grabbed the tire? What did you do to free up the brakes? Have you been able to detect any stickiness in the lever action? Can you reproduce the lockup?

It is rather hard to envision how a defect in the levers could spontaneously apply enough force to the brakes to put you over the bars. Where would that force come from? What you experienced sounds a lot more like picking up some road debris and having it jam between the tire and fork.
 

·
Registered
Joined
·
60 Posts
Since you hit a bump while on the hoods at the same time the brake locked the most likely cause would be the shift lever sliding down on the bars, the cable tightens as the lever moves down and the housing holds tight under the bar tape. Doesn't take much movement if the brakes are set tight. More common on carbon bars with a slick finish but if the lever wasn't tight enough and/or an odd placement this can happen on an alum bar too. When you moved the shifter the tension was released and the brake opened, probably nothing wrong with the shifter or brake. There's most likely a good mark on the bar from the clamp nut-inspect it.

At our shop we put carbon assembly paste under all bar clamps (carbon or alum bars) to give some extra grip and torque to spec. And check the spec for both the bar and clamp-you be surpised the varience in min and max spec for bars and shifters out there. Some bars have a max torque below the min spec of the shifter.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #6 ·
Kerry, when I picked my bike up off the road the brakes were locked up tight on the rim, the wheel wouldn't move and if memory serves the lever was tight. When I dropped my bike off at my house I pulled it out of the van and the brake was still locked. My front deraillieur was in the big ring but the chain was off, I shifted to the small ring and put the chain on and squeezed the brakes and they were fine. I'll admit I didn't do any real troubleshooting as I was in some pain. Tomorrow I'll go back over to my house and take a better look and see if I can recreate the problem.

Cosmo, I do have carbon bars, so I'll check for lever movement/marks.

I've built a few mountain bikes, all single speeds, and fixies in the past but this is my first "real" roadbike that's why I had the LBS build it up.

thanks for the info
 

·
Registered
Joined
·
3,431 Posts
cosmo333 said:
Since you hit a bump while on the hoods at the same time the brake locked the most likely cause would be the shift lever sliding down on the bars, the cable tightens as the lever moves down and the housing holds tight under the bar tape. Doesn't take much movement if the brakes are set tight. More common on carbon bars with a slick finish but if the lever wasn't tight enough and/or an odd placement this can happen on an alum bar too. When you moved the shifter the tension was released and the brake opened, probably nothing wrong with the shifter or brake. There's most likely a good mark on the bar from the clamp nut-inspect it.

At our shop we put carbon assembly paste under all bar clamps (carbon or alum bars) to give some extra grip and torque to spec. And check the spec for both the bar and clamp-you be surpised the varience in min and max spec for bars and shifters out there. Some bars have a max torque below the min spec of the shifter.
Could it also be the bar clamp on the stem? It's a fairly common mistake to undertighten those, and when you hit a bump with weight on the brifters, the bars will rotate downward.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #10 ·
Ok, I have looked at the bike. Both shifters are scraped up as expected. It looks as though the rear assembly stayed in place, maybe pushed up a bit. The front assembly definitely moved, down. I moved the thing up, down, in and out and the brakes work fine. I cannot get the problem to show up.

I guess my main concern is more for piece of mind. Is this going to happen again? I don't really understand how it's possible to go from apparently functioning well to locked up tight without doing anything other than hitting a bump in the road.

I ride about 3500-4000 miles a year on the trails and the road and have not had a road crash until now. I could see if it was something obvious, like a huge pothole or a sewer grate, or even tangling with another rider but a bump in the road? come on I live in Wisconsin, after this winter and spring the roads are crap, there is no such thing as a smooth road.
 

·
Registered
Joined
·
5,555 Posts
Marko Polo said:
Ok, I have looked at the bike. Both shifters are scraped up as expected. It looks as though the rear assembly stayed in place, maybe pushed up a bit. The front assembly definitely moved, down. I moved the thing up, down, in and out and the brakes work fine. I cannot get the problem to show up.
What do you mean by "assembly"? The brifter? If so, it sounds like what Cosmo described above--did you understand what he was talking about? I'm gonna refrain from a huge anti-carbon rant, but you need to make sure the brifters will stay in one place.
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #12 ·
Yes, I mean the brifters. If I understand Cosmo, shouldn't I be able to recreate the brake lockup by moving the brifter one way or the other? I have tried moving the brifters around every which way and if I move them 15 or 20 degrees outward from straight I see the brakes tighten up a little bit. What I experienced was a total lockup of the brakes. No matter how I move the brifters I cannot get the brakes to lock the way they did, not even to the point of the pads touching the rim.

The bump I went over, I would equate the force to the equivilent of popping a wheelie maybe 3 inches high.
 

·
Back from the dead
Joined
·
20,800 Posts
Do you KNOW that your brakes locked up, causing the crash, or are you making the ASSUMPTION that because you found them locked up AFTER the crash, they must have locked up to CAUSE the crash. Because those are totally different things.

It would not be unusual to find your wheel doesn't turn after a crash for a variety of reasons. This could be because the brakes are locked up, perhaps due to the cable housing slipping out of a cable stop somewhere. But that doesn't mean that is what caused the crash.
 

·
Registered
Joined
·
13 Posts
Something must be missing. The calipers are held open by a spring. If the brake pads
( with no debris under them ) are "clamped" to the rim so tightly as to cause the effect you described, there had to be tension on the cable substantially greater than the opening force of the spring. It appears that the bump, however minor, was enough to allow the brifter to slide down the bars driven by your body weight on the hoods. I'm simply trying to clarify what others have said. The brifter is simply a lever and a cable. IMHO it can't fail the way it has appered to.
 

·
Registered
Joined
·
284 Posts
bar tape on or off

When trying to duplicate it, the bar tape has to be on and tight. That's what causes the brakes to tighten when the brifters shift. The tape holds the casing and the brifter sliding forward pulls the brake cable.

When I was getting new bars set up right, it happened to me. I thought I had them set right and taped the bars. Then when I rode, they needed to be a bit lower. I loosened the clamp and slid the brifter down and forward a slight bit. Tightened it back up. re-mounted and started to pedal. Nothing. Brakes locked from the forward movement. The good news is that no one saw me do a tip over before got got my cleats out !!
 

·
Registered
Joined
·
13 Posts
Discussion Starter · #16 ·
Mohair, the brakes locked up to cause the crash. Usually when I see a bump I kind of unweight the bike to float over it. I unweighted and the next thing I knew I was slammed over the bars, no nose wheelie or anything. The bike just flipped over.
 

·
Shirtcocker
Joined
·
60,886 Posts
Marko Polo said:
Mohair, the brakes locked up to cause the crash. Usually when I see a bump I kind of unweight the bike to float over it. I unweighted and the next thing I knew I was slammed over the bars, no nose wheelie or anything. The bike just flipped over.
you sure a stick or rock didn't get caught in your wheel? I really can't see how a brake could spontaneously lock up without the brifter being depressed or something getting stuck in the brake.
 

·
Registered
Joined
·
1,350 Posts
cosmo333 said:
Since you hit a bump while on the hoods at the same time the brake locked the most likely cause would be the shift lever sliding down on the bars, the cable tightens as the lever moves down and the housing holds tight under the bar tape.
Ding, ding, ding!!

He wins the prize. The shop didn't tighten the levers tight enough.
 

·
RoadBikeRider
Joined
·
1,053 Posts
I have also seen wheels lock up after a crash because the calipers are knocked off center. This will cause one brake pad to rub the rim. Maybe the levers slid down during the impact causing you to go over the bars and it locked up during the impact by the calipers being knocked out of alignment??????
 
1 - 20 of 37 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top