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Replacing front brake - worst case scenario - need urgent help

Old 03-18-16, 08:28 PM
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jnbrown
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Replacing front brake - worst case scenario - need urgent help

I am installing a Shimano BR-7800 Dura Ace front brake and while torquing the the barrel nut to the recommend value 8 N-m it snapped. So half of it is inside fork threaded onto the brake bolt so I can't get it out. Can I disassemble the brake from the front? There is a small allen screw on the knurled nut just behind the brake. Thanks for any advise.

Panic is partly over, I got the broken part out by jamming a screwdriver into the hollow center - whew!
But now I need a new mounting nut and it needs to be 27mm long. Not sure a local shop will have this.
Found something on e-bay

https://www.ebay.com/itm/Shimano-Cali...gAAOSw~otWezLs

We may have to ride with jus the rear brake tomorrow, the ride is mostly flat and on bike paths so hopefully will be ok.

Last edited by jnbrown; 03-18-16 at 08:59 PM.
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Old 03-18-16, 09:42 PM
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Personally I'd skip the ride rather than not have a front brake. Most of your braking is from the front and if there is a situation that you needed to do an emergency stop and only skidded on your rear wheel, may not be able to avoid whatever you needed to not hit.

Most bike shops should have that part in stock. Buy one and have them install it for you. 8Nm sounds like a pretty high torque value, but never looked it up myself.
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Old 03-18-16, 09:53 PM
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I will be scouring local shops tomorrow morning but I am not that hopeful as 27mm is not very common. Most forks have a deep recess to use a standard length bolt which I believe is 10mm. Our Alpha Q fork does not have a recess.
i also thought 8 N-m was high but Shimano specifies 8 - 10.
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Old 03-19-16, 05:20 PM
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Most things on a bike are maximum torque. You need to tighten to the point the part is snug and holds, not exceeding the torque spec.

It's not uncommon to brake bolts tightening them past where they're snug to hit a torque spec.

Your brake isn't going to fly off because you didn't hit a precise torque spec, but as you found out it can break if you tighten to a number, regardless of how firm iit is in reality
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Old 03-19-16, 07:12 PM
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I usually "borrow" whatever parts I need from another bike in the stable or pull one from the parts bin. If you don't have spares, ask the shop what they have in their take-off / cast-away parts bin.
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Old 03-19-16, 11:00 PM
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Originally Posted by jnbrown View Post
We may have to ride with jus the rear brake tomorrow, the ride is mostly flat and on bike paths so hopefully will be ok.
PLEASE don't ride with just a rear brake. Your stopping distances will be more than twice as long, and no matter where you ride, you never know when you will need every bit of braking you can get.
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Old 03-19-16, 11:21 PM
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Originally Posted by jnbrown View Post
I will be scouring local shops tomorrow morning but I am not that hopeful as 27mm is not very common. Most forks have a deep recess to use a standard length bolt which I believe is 10mm. Our Alpha Q fork does not have a recess.
i also thought 8 N-m was high but Shimano specifies 8 - 10.
This is the problem with using torque wrenches and blindly following a spec.

Shimano makes the brake, and sets 8-10 torque spec based on the strength of the bolt. However they didn't make the nut.

Had you not had a spec and torque wrench, you'd have properly tightened it using hand feel and judgement guided by experience and gone to sleep early to be ready for your ride tomorrow.
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Old 03-20-16, 05:41 AM
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Toronto Cycles also has recessed nuts in a variety of sizes in Titanium.
Titanium Recessed Brake Nut,, Titanium Dura Ace, Aluminum Caliper

Does the nut have to be exactly 27mm? That would seem to be awfully close tolerances. I would think you could go a couple mm longer or shorter without problems.

At least with Titanium, Aluminum, or Stainless nuts, you should be able to grind them down if necessary.
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Old 03-20-16, 12:44 PM
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Went to my favorite shop in the morning and they had plenty.
I don't think the torque spec was at fault although I do agree sometimes they are higher than needed.
The old nut that broke was pretty rusted and I think that is why it broke, good thing it didn't happen on the road as it could have ripped the brake off and into the wheel.
The whole thing started because I put new brake pads on and since the Mavic brake I had doesn't have a quick release was unable to remove the front wheel from the bike with air the the tire. I used have a quick release on my Campy shifter but changed to SRAM a while back. So I was installing a new Dura Ace brake and whole thing just snowballed from there. Anyway problem solved, and we had a nice ride even though we got a late start.

Last edited by jnbrown; 03-20-16 at 12:48 PM.
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Old 03-23-16, 03:14 PM
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Glad it all worked out.
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Old 03-23-16, 05:05 PM
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Originally Posted by FBinNY View Post
Originally Posted by jnbrown View Post
I will be scouring local shops tomorrow morning but I am not that hopeful as 27mm is not very common. Most forks have a deep recess to use a standard length bolt which I believe is 10mm. Our Alpha Q fork does not have a recess.
i also thought 8 N-m was high but Shimano specifies 8 - 10.
This is the problem with using torque wrenches and blindly following a spec.

Shimano makes the brake, and sets 8-10 torque spec based on the strength of the bolt. However they didn't make the nut.

Had you not had a spec and torque wrench, you'd have properly tightened it using hand feel and judgement guided by experience and gone to sleep early to be ready for your ride tomorrow.
+1
Valuable tool, particularly as you develop feel, but not to be blindly followed
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