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How to fit a rear brake to a front carbon fork

How to fit a rear brake to a front carbon fork

So here’s an age old conundrum that nobody seems to have solved. Or at least nobody seems to have put on the internet. I have a very funky Kurve CNC machined rear brake caliper and an equally funky carbon fork on a fixed wheel bike. This always seems to happen as you generally have to buy nice brakes in pairs, someone fits the front one to a fixie or single speed bike and there’s an overload of unloved rear brakes floating around. Hence how I got mine.

Notice that the pivot bolt that sticks out of the back of brake on the left is very short as it’s designed to go through a small rear chainstay, not a chunky fork. One solution is to replace the pivot bolt with a longer one but these aren’t available for the Kurve brakes (they are available for some Shimano brakes though). Another solution is to use a longer recessed bolt to bridge the gap. I’ve had to use a super-long 30mm recessed bolt just to attach a normal front brake, so I’d need at least a 50-60mm recessed bolt… and these don’t exist.

So my solution was to make one. I thought I’d share the process just in case it helps you out of a sticky situation too.

First, this is what happens in a normal front fork…

Now this is what happens when you use a rear brake with short pivot bolt… it doesn’t work!

Even using an ultr long recessed bolt doesn’t work…

So I need to make a longer bolt somehow. I’m also keen to keep the ‘recessed’ bolt feature, as it’s not only neater but is how the fork was designed to accommodate a brake bolt. I could try and surface mount a bolt but this may end up damaging the carbon fork’s outer shell. So you’re going to need some kit…

So first thing to measure stuff. Insert the brake into the front of the fork and hold it in place. Insert a spare bolt or allen key into the rear of the fork until it comes into contact with the brake pivot bolt. Make a mark on the allen key where it exits the back of the fork. If your fork has a recess (like mine) then mark where the allen key first exits the fork, niot where it finally emerges from the recess itself. Obviously, this is how far in the pivot bolt is inside the fork, or to put it another way, how long a custom recessed bolt shaft would have to be to just touch the brake pivot bolt but not screw onto it. Mine was about 40mm. Now add 10mm to this measurement to allow for a good overlap with the pivot bolt when it’s screwed in. I.e. now a total of 50mm.

So now we need to get some recessed bolts to use as parts. Seeing as my fork seems to be very wide, I got hold of two 30mm recessed bolts from my local bike shop. I’m a “known person” so I got them for free but expect to pay about £3 each. Put it this way, there’s a 35mm titanium one for $7 Toronto Cycles or a 30mm steel one at SJS Cycles for £6.99.

So I need to make a bolt 50mm long so I can do that with a 20mm recessed bolt and 20mm of the threaded tube from the other bolt. So next thing to do is to use a hacksaw to chop 20mm off the threaded tube part of the long recessed bolt. File it as flat as possible and offer up the ‘unchopped’ end to the end of the existing recessed bolt, so you have a nice, clean interface between them. Now we need a way of joining them together…

You’ll also need to chop the threaded bit off the normal bolt. Again, measure it so that it’s long enough to fit entirely within the normal recessed bolt and has enough extra thread to screw into the threaded tube… but short enough to leave that 10mm or so of the threaded tube free at the end. Use s file to flatten the end of the bolt and remove any rough metal. Then carefully cut a slot about 3mm deep into the end with a hacksaw. It doesn’t have to be too neat but it does pay to be as accurate as you can. That’s it for the manual labour.

Now add some strong metal adhesive / epoxy glue (I used Araldite Rapid Steel) to the threaded shaft and screw it into the normal recessed bolt. Be sure to clean the thready first mind as any grease will stop the glue holding. Use a flat headed screwdriver in the slot you cut to tighten it. Then screw on the threaded tube to  the rest of the shat that sticks out (again, with glue). Leave to set for at least 24 hours (or whatever your glue instructions suggest.)

Now you should be ready to rumble. If all goes well and you have measured everything relatively well, it should just work like a normal recessed bolt, only a really long one! Thus…

Finally, don’t forget to swap over the brake pads as they are directional and because you’ve flipped the brake, the left pad will now be on the right and vice versa.

Now there’s no excuse not to use all those rear brakes cluttering up Ebay!

1 comment

  • Smart idea, love the solution.

    By the way I was told one (not sure if it’s true but it makes sense) that the reason you can’t use V brakes on a road bike is that, on a caliper brake the force is going through a strong part of the fork (the yoke) whereas all the force on V brakes go through the actual arms of the fork themselves, and if you’ve got carbons then they’ll shear since they’re not designed for sideways stress, only longitudinal.

    Anyway just my random QI comments, and disclaimed as usual by the fact that a bloke in a pub told me so it could be all completely wrong, but it makes sense in that V brakes are much better than calipers and probably with little additional weight (if any)

    Kaz

    p.s. Say hi to the tribe from HK!