Front brake locking on by itself?

[Danny]

I was recently on a long ride with lots of steep decents and found I was regularly getting a loud vibrating sound from my front wheel which was like a brake locking on even though I wasn't touching the brake lever. . I also only got the sound when I was going above 17 mph. Often this started if I hit a small bump in the road and usually went on for about 30 seconds or until I hit another minor bump.

As this was mostly happening when I was going down quite steep and technical descents I was reluctant to lean over too much to try and work out if it was really caused by my brakes locking on somehow or was the result of something else vibrating or rubbing.

I was riding a Cannondale Synapse with a Shimano 105 groupset.

Any ideas about what could have caused this?

 

[Webbo2]

I was recently on a long ride with lots of steep decents and found I was regularly getting a loud vibrating sound from my front wheel which was like a brake locking on even though I wasn't touching the brake lever. . I also only got the sound when I was going above 17 mph. Often this started if I hit a small bump in the road and usually went on for about 30 seconds or until I hit another minor bump.

As this was mostly happening when I was going down quite steep and technical descents I was reluctant to lean over too much to try and work out if it was really caused by my brakes locking on somehow or was the result of something else vibrating or rubbing.

I was riding a Cannondale Synapse with a Shimano 105 groupset.

Any ideas about what could have caused this?

Have you checked whether your front wheel is fastened tight.

 

[Danny]

Have you checked whether your front wheel is fastened tight.

Well it was fastened as tight as it normally is. By which I mean you feel some obvious resistance when you close the quick release lever but not so tight that you really have to push on it to get it closed.

 

[ColinJ]

Can you pull the top of the wheel sideways?

I have had wheels with lateral movement due to hub problems .

Is the wheel true?

 

[figbat]

Disc or rim brakes? Hydraulic or cable?

 

[Ian H]

Disc or rim brakes? Hydraulic or cable?

The fundamental first question.

 

[gbb]

For me, I'd inspect the front wheel and spin it, feeling and listening really carefully for any breakdown in the bearings. I've had BB bearings lock under pressure, usually the cheaper cageless type where one ball can effectively grind against the next, it almost locks them up. Never had it on a wheel though...
If all.ok, move on to the next theory.

 

[Danny]

Disc or rim brakes? Hydraulic or cable?

Rim breaks

 

[Ian H]

Take the wheel out and check the fork blades are solid and the dropouts are securely attached. If you've fitted a larger tyre, check you have more than paper-thin clearance at the crown. Then check the wheel turns freely, there is no play in the bearings. If there's a mudguard then ensure that's properly fitted. Are the brake blocks/shoes tight? Is the brake caliper secure? No front luggage interfering with the brake cable? Etc.

 

[Danny]

Can you pull the top of the wheel sideways?

I have had wheels with lateral movement due to hub problems .

Is the wheel true?

Some belated responses to some of the detailed questions as we were away over the weekend so I didn't have access to my bike...

I can't pull the wheel sideways and I would say that the wheel is about 99% true.

 

[Danny]

For me, I'd inspect the front wheel and spin it, feeling and listening really carefully for any breakdown in the bearings. I've had BB bearings lock under pressure, usually the cheaper cageless type where one ball can effectively grind against the next, it almost locks them up. Never had it on a wheel though...
If all.ok, move on to the next theory.

I've tried spinning the wheel and can't hear or feel any grunginess in the bearings. However it is not really replicating descending at speed with my weight on the drops or break hoods so it could be hehaving differently under pressure.

 

[Danny]

Take the wheel out and check the fork blades are solid and the dropouts are securely attached. If you've fitted a larger tyre, check you have more than paper-thin clearance at the crown. Then check the wheel turns freely, there is no play in the bearings. If there's a mudguard then ensure that's properly fitted. Are the brake blocks/shoes tight? Is the brake caliper secure? No front luggage interfering with the brake cable? Etc.

There's no obvious problems with the carbon fork blades or dropouts.

I'm using the same size tyres that came with the bike. It's a road bike with no room for mudguards or luggage.

 

[Webbo2]

Did the whole bike vibrate or just the front wheel.
Have you experienced a speed wobble on any bike before. If so was it anything like what happened.

 

[figbat]

Is the brake caliper bolt tight? The one that affixes it to the fork.

 

[Danny]

Did the whole bike vibrate or just the front wheel.
Have you experienced a speed wobble on any bike before. If so was it anything like what happened.

Just the front wheel as far as I could tell. Because I was descending quite fast on some tricky wet roads I didn‘t want to lean over too much to try and work out what was going on.