PSA: Tektro R559 brake bolt thread size
 

Just when you think you know what to do, someone throws you a manufacturing curveball: Tektro has changed the internal thread size on their R559 calipers.

https://cimg3.ibsrv.net/gimg/bikefor...2e88981166.jpg

Up till now, the larger thread that fits into the brake pivot arm on these has been 7mm. This standard is shared with the Campagnolo and Dia-Compe calipers referenced here, along with the Jtek Engineering nutted replacement bolt, and a number of knockoff or no-brand dual pivots out there.

This particular R559 varies from that by using an 8mm shaft and hardware - the locknut and bushings are all designed for the larger bolt.

Following is the earlier 7mm bolt with 8mm hardware sitting loose on it:

https://cimg3.ibsrv.net/gimg/bikefor...2d9f9e0b58.jpg

This nut isn't supposed to slide down that far:

https://cimg4.ibsrv.net/gimg/bikefor...9d20195779.jpg

Conveniently, you can check this without disassembling the whole caliper: The locknut shown above is the one that holds the return spring at the back of the dual pivot. You can loosen the spring and easily remove it to check whether it is marked "M8" on the reverse side.

https://cimg0.ibsrv.net/gimg/bikefor...45d911a43b.jpg

Granted, I'm aware this probably won't affect too many people, seeing as the R559 is now available anywhere with nutted hardware. In my particular case, I was bucking the trend by trying to convert it from a nutted front to a recessed rear - go figure.

Just wanted to document this lest someone else fall into the same trap.

-Kurt