...from twin-pivot brake. Or any old redundant Shimano front brake I can cannibalize. I want to convert a DA 7800 rear brake to nut-fit. (AK rear bolt is too short.)
Go to ya local B&Q centre - you should find what you are looking for! They sell parts by the thousands or singly
Do you have both brakes, and you're fitting them to a non-recessed frame by any chance?
If so, what I've found is the simplest way is to swap the brakes round and use the front brake on the rear so the bolt is long enough. Then drill the rear hole on the fork and use a longer (recessed style) nut that can reach the threaded part of the shorter rear bolt.
Ah yes. That is intelligent, Alex. I have several internal nuts of various lengths and may not need to do any surgery on the (modern) front fork. This astuce had not occurred to me — thanks for suggesting!
I'm not totally sure that @AlexD's suggestion is on the money. It depends how long the bolt on the old rear brake is, but it's not ideal to have the sleeve nut and pivot bolt meeting so far forward. SJS sell the original pivot bolts and from the look of them you could do a proper conversion with the JTek bolt and stick with the nut-fitting. Spa also do a version of the same thing in stainless.
What's the issue with that, out of interest? Surely if there's enough engaged thread it's as secure as the usual recessed bolt? Assuming the nut you use isn't made of cheese, of course.
I had no idea that these were available to retail customers. I looked up the part number in the Shimano db but thought it unlikely Madison would supply an individual customer with so small an item. Oddly, I did have exactly the part I needed — from an RX-100 brake! — in my spares box for years but must have cleared it out.
I'll try Alex's suggestion and if that doesn't work, ffm's, and report back! Thanks for the help fellers.
It's probably fine, but it's a bit close to the shonky solution that some people apply of fitting a rear brake to the front and then fitting a nut onto the tiny pivot bolt inside the steerer up against the inside of its front face. This is a bit ropey because it doesn't provide enough resistance to the brake being levered up or down. If you use a long sleeve nut on a short bolt then their interface is quite a long way forward so they may have to deal with greater bending forces than if the bolt is the correct length and the interface is at the back of the steerer (plus you usually get more threads engaged that way).
Each of you is right in your own way! As @ffm says, the bending moment on the pivot bolt of a rear brake installed on the front is not ideal. The bolt should properly extend a good way into the fork crown, where it can be captured by plenty of thread in the recessed nut. In my case the fork crown is narrow from front to rear, and by chopping down a long recessed nut to exactly the right length, I was able to make it span the full distance, capturing the 6–7mm of available thread on the pivot. So the @AlexD solution was the one I adopted.
I did try to dismantle the rear brake so as to replace the pivot bolt but gave up because the threaded collar was seized on and yes I did undo the 2mm grub screw first!
Oh yes, thanks to @531slx for selling me the brakes!
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