joesch

Really surprised me because my recent Tommasini Racing 80s Campy SR Front Break made a ping / pop while I was descending at about 20 and not even on the brakes. The lug nut evidently popped from the tighten pressure and I realized what happened when I saw the front break hangon over the bars.

Surprising since this was my 2nd shakedown ride. First ride was 10 miles no braking issue. Second ride at about 20 miles. Guess old lug nuts can break anytime but to sorta explode with a pop and send the brake flying over the bars.
I would think it would just crack and give out when being used, not pop off after approx 30 miles of use.

How common is this ?
Guess this is why builders should always to a few shakedown rides of longer distances.
Sure glad I was not on a steep long hill where the front break would really be necessary, like my SoCal rides.
This was flat Dallas

Check out my memory pic:

HillRider

Did the bolt break, the nut fracture or did the nut just unthread from vibration? Nutted brakes are usually fastened with a Nyloc or similar anti-vibration nut to prevent vibration loosening.

cxwrench

'Brake' not break. Your brake broke. It was your second ride on that bike and the bar tape looks that bad?

Geepig

When I strip and rebuild bikes I look at every component, and then, as you say, give them a shakedown ride.

I also recommend buying bags of typical nuts, bolts and washers and replacing as you go.

alcjphil

That was a nut, not a lug nut. Examine the bolt carefully to see if the threads are stripped. If not, replace the nut along with the appropriate washers for that brake. It is very rare for a nut to fail in the sort of use you describe unless it was either stripped or not properly tightened.

JohnDThompson 

Get a longer nut to get more thread engagement on the mounting bolt:


https://www.biketoolsetc.com/index.c...=WB-BRAKENUT19

joesch

Yes thanks for that edit correction.
The bar tape is very nice quality leather that is securely taped with double sided tape.
Do you not like how it was wrapped ?
I did not have a length that was long enough to complete one side so actually two sections for each side.

joesch

The threads are clean, no sign of stripping.
The bolt was still inserted into the fork crown and examination shows threads still look fine.

BTW, the bolt was the 19mm type shown by JohnDThompson post shows above.
I was also able to screw the bolt onto the break screw most of the 19mm length. It feels tight and I can not wiggle it.

Im still amazed it popped out and there are no signs of thread damage.

I will buy a NOS campy replacement to play it safe.

HillRider

Any signs that the bolt itself broke off? If the bolt is the same length as it was when you installed the brake I'd put a fair bit of money on the fact the nut vibrated off. A broken or fractured nut is VERY unlikely. And, yes, these are "nutted" brakes, not recessed as John showed.

joesch

Sorry I corrected my reply that you quoted above to the correct 19mm recessed nut.

Iride01 

How common is it? Probably not common enough or everyone will be checking them every ride.

Stupid things happen all the time though. Just not always the same stupid thing.

reconnaissance

I think the bar tape wrap job looks great!

AndrewJB

Please post a close-up of the bolt.
Can't really be sure from the above picture, but it looks like possibly the threads on the end of the bolt are stripped.

joesch

Dont have a picture of the recessed mounting bolt but it looked good unlike the brake screw which maybe the issue as shown below ? Difficult to picture that bolt.

Iride01 

Well that pic is showing the bolt. The other thing is a barrel nut or brake nut.

Moe Zhoost

Can't imagine that this barrel nut would just crack on its own. Perhaps you cracked it by over-tightening? But still, I'd doubt that it would launch without braking. I'd guess that your brakes were dragging enough to pull the caliper through the cracked nut.

AndrewJB

Bolt, Screw, whatever you prefer to call it Maybe its just out of focus, or the way the light is hitting the threads, but those threads just don't look right. They look like they are flat. Can you confirm if the threads are flat, or are they sharp like new threads should be?

Also is the nut the right size. Was it the original nut?

Iride01 

Now if there was some confusion on the OP's part as to what is a nut or bold and that is now cleared up. Then they should refer back to post #6
A longer nut that goes almost to the opposite internal side of the fork crown might help. If it already did, then I'd put it back on or get a new one and then see if the brake gets loose again. If it doesn't loosen, then pour some scotch until that desire to know why disappears.

joesch

Thanks for the additional questions.
It is the light hitting the threads. I checked with a magnifier rotating against the light and the threads look good.
Did the same for the mounting bolt and it looks good.
Not sure if original Campy bolt so I have ordered another not knowing what else to do other than swapping out complete brake, which I maybe forced to do if this happens again. Sure wish I had a probable cause.

joesch

I used the term "recessed mounting bolt" in my latter response above to help eliminate confusion. Using a 19mm so the solution maybe to go as long as possible, 30mm or 35mm ??

Iride01 

You have to see what fits your particular fork crown. I'd put the longest you can that allows the head of the nut to fully seat itself. If the end of the nut touches the opposite side, then you might not know if the nut is properly seated on its head. But a shorter nut that can get over at least four or five good threads of the bolt will be adequate if you know the threads of both nut and bolt are not worn or damaged.

Because I can't tell if the threads on the bolt are damaged, that is why I suggest the longest nut that fits.

cxwrench

Really? It's dirty and done backwards so it has tape securing it at the end of the drop. Wrong.

Andrew R Stewart 

I think one challenge this thread has is the use of the word "popped". It leads some to think the recessed nut cracked/broke. Did it? Post 8 states "The bolt was still inserted into the fork crown and examination shows threads still look fine." To me this reads as the nut not being damaged. So what is it? Broken nut or just a nut that loosened and unthreaded completely? Unthreading is far more likely. But this process is not a quick one. Certainly not the process that "pop" would best describe.

BTW the image of the caliper mounting/center bolt suggests some thread form flattening. This is often from a threaded fitting being stressed while loose. The nut "floats" on the bolt causing the threads to become somewhat rounded. Andy

cbrstar

I had it happen once or twice on my vintage BMX bikes bitd and it was two things. 1) I was missing the little lock washer between the nut and the spacer. As a kid I'd take the brakes off and loose it 2) Because back then I also didn't know how to align brakes properly. I didn't tighten down the nut enough because I would leave it loose so it wouldn't rub on one side of the wheel. With this being a recessed nut it's possible it's a different situation

cxwrench

Seriously...you'd have to be hugely oblivious to miss something like a caliper getting loose over time cuz it would take forever. You'd have dozens of chances to notice it.