21 Oct 2017

20th October 2017. More on my Tektro R725.


Friday 20th 53F, 12C, very dark overcast with distant mist. More rain promised as the trees move gently back and forth to the wind. Walked to the village and back.

The previous 'chapter' was getting a bit long so I have divided it here.

Another hour, or rather three, spent on the Tektro front brake pivot in and out of fine drizzle. I finally managed to free the pivot by holding the rear bridge firmly but gently in the grooved, plywood jaws of a B&D workbench. Then used an adjustable spanner on the brake block arm to gradually increase the distance it would rock back and forth. The brake is now usable but I'll keep adding oil to help it free up further. I wasn't able to get the arm off the pivot for a proper clean. And doubted my ability to get the return spring back on by the time I had rescued it from the nearest treetop or hedge!

It may be the regular winter salting on the roads has crept in unnoticed and corroded the steel pipe of the pivot. Hard chrome treatment was used way back at the beginning of the last century in some industries but not even now for modern cycle accessories it seems. Treat this verbiage as a reminder to check and oil your own brakes and their pivots. Do it now but keep the oil off the rims and blocks!

After repeated attempts I realised that the Tektro rear brake was rocking back and forth on its round nut. Doing so no matter how much I tightened it. There was nothing else for it but to rough out an inverted-U, packing piece of the same shape as the rear bridge to clear the tyre. So I quickly chain drilled some scrap aluminum by eye and then used an angle grinder for a quick and dirty shaping.

A hole was required for the Tektro's rear, hex socket head, 13mm diameter nut. Fortunately I had a 14mm drill for a clearance hole and used the slowest speed of my large pillar drill. My machine vice safely avoided too many lost limbs.

A washer was also required to provide a flat bed for the Tektro nut on the back of the fork crown. Then it needed two 10mm holes spaced at 40mm to clear the Tektro's rear projections. Finally the brake was fixed immovably and I could align the brake blocks to the new position. I may tidy up its appearance once I have proven the alloy packing to work as well as I hope.

Tektro's rear nut is an oddity and you really should check your rear brake for rocking if you are using paired Tektro R725s on your trike. Or a hidden R725 behind the fork crown on your legally roadworthy, track bike. A special model of the R725 is needed with a much deeper stirrup/bridge. [see image] You'll also need a properly and accurately drilled fork crown. This is definitely not a job for a borrowed Black & Decker on your Carbon fixie!

A rocking brake mechanism will either cut a groove in the tyre bead with the errant brake blocks. Or wear away the paint inside the brake track of the rim. I've had both problems without a clue as to why it was happening, until now. The brake blocks always looked well aligned when the trike was standing still. Grr?

Click on any image for an enlargement.


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