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I recently bought a new set of Tektro R539 Caliper Brakes. These brakes are nutted (non-recessed). Each brake came with one curved (concave, radiused) washer and one flat serrated washer.

photo of an uninstalled Tektro R539 bike rake highlighting that there is a serrated washer and a radiused washer

My front fork and rear brake bridge are curved on both sides with no flat surfaces. It seems I need a total of four radiused washers. I need to buy two more, and they need to be two distinct sizes as the fork and rear brake bridge are different shapes.

I've had a somewhat difficult time finding these sorts of curved washers online. I've looked into:

  • Sellers on eBay selling individual washers from vintage sets, but the ones I've found were international and kinda pricey with no sizing information included
  • An odd seller on Amazon here and there, but again, no size information
  • Fairly big names in the USA, where I'm located, like Performance Bikes and Jenson USA and had no success at all
  • Sellers from other countries than my own as well, but I'd rather not pay for international shipping if I can avoid it
  • My local bike shop had only a single curved washer in their spare parts bin and the radius/diameter seems very close, but not totally plumb
  • Local bike shops that have online stores that list wholesaler/warehouse inventory, but again, no luck
  • Modern Bike sells a set of washers, but with no information regarding what size they are.

I've tried wholesale hardware suppliers like McMaster-Carr and major hardware store chains as well. Hardware stores seem to call washers similar to these wave or spring washers, but they're not quite suitable it seems as they don't typically seem to have a flat side as needed for bike brakes.

Certainly, there are options, but I thought I should have an easier time finding a major name who would sell a variety of concave/radiused washers for bicycles. Is there a better place to search? Am I best off just buying what I can from Amazon, eBay, the few listings I can find, and just hope that some of them fit well enough?

enter image description here

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    Have you got a friend with a 3D printer?
    – Warren Burton
    Commented Mar 11, 2023 at 20:06
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    @WarrenBurton that's the seed of a good answer - want to expand that out into an answer of its own ?
    – Criggie ♦
    Commented Mar 11, 2023 at 22:10
  • @will.haley can you show us a picture of the rear of your fork where the brake bolt comes through? DOES the threaded bolt come all the way through your fork or does it end up slightly below the surface? You might have the wrong kind of nut.
    – Criggie ♦
    Commented Mar 11, 2023 at 22:14
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    @Criggie see here for a photo showing the brake bolt coming through the rear of my fork with some threads to spare. I only loosely tightened everything for the sake of the photo imgur.com/a/cHXF468 It's difficult to tell that the serrated washer in the photo hangs out over the curved surface at the rear of the fork. Also, I edited my post. The first sentence incorrectly said "I recently bought a new set of Tektro R539 Rear Caliper Brakes", but it was a matching set of front and rear calipers. Not a set of two rear.
    – Will Haley
    Commented Mar 12, 2023 at 19:21
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    @WillHaley okay thanks for that - yes I'd definitely use a radiused washer there. Good thing is you have a thick washer right there. Clamp it in a vise and start filing with a round or half-round metal file. You might be able to make initial progress using a grinder/dremel, but workholding is always a problem. Good luck !
    – Criggie ♦
    Commented Mar 12, 2023 at 22:11

3 Answers 3

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Google "Diacompe half moon washer" and you'll see a bunch of options. Diacompe is the go-to for these. They make a tight and a broad radius version and call them rear and front respectively, though in real life you use whatever matches best. Occasionally one needs to do minor reprofiling on them with a file.

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Another option is to start with a thicker washer and file it till it has the fit you want.

You can use a radius gauge to determine the curve at that location on the frame/fork. It may be possible to buy a curved endmill with the right final profile, but realistically multiple passes with a ball-nosed endmill will get you close and then hand filing to bring it to final shape.
This requires a mill and workholding gear.

There's a lot of other ways to make the profile you want, but all require workshop tools and time. Casting is another option but that also needs cleanup and finishing.

Whatever you end up doing, make sure the nut still have sufficient thread engagement.

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    You'd need a pretty thick washer to start with. V brake pads should provide a source, and if working with hand tools the spherical concave ones might save some effort
    – Chris H
    Commented Mar 12, 2023 at 8:46
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Are you sure you need two radiused washers?

The front surface is the one transmitting most of the load. The rear surface is there just to provide adequate tension for the bolt which ensures the front washer doesn't lift.

I think I would be confident using a brake with radiused washer in the front and flat washer in the rear.

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    On rounded bridges you want to use these on to prevent squishing the tube. The contact area also helps keep the mounting nut tight.
    – Nathan Knutson
    Commented Mar 11, 2023 at 23:42

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