In this step, we will finally assemble the rear wheel brakes. This design uses the motor's rotating shell directly as a brake drum. It's certainly not best engineering practice, but these motors have large radial bearings at the ends so they can support some degree of side loading lke this. We will first mount the brake mechanism, then route the cables.Parts Required:
Brake body assemblies from Step 7
6mm Barrel Adjusters, QTY 2
4 foot brake cable with sleeve and 7mm nipple, QTY 2
1/4"-20 x 1 screw or hex head bolt, QTY 2
1/4"-20 nuts, locknut preferred. QTY 2
1/4" ID, 1/16" thick nylon washers, QTY 6
M6 x 1 nut, QTY 2
Compression spring, 1/4" to 3/8" rod diameter x 2" long, as stiff as possible
Step 32.1: Gather the parts
Bike cable cutters or cable shears
Hopefully you have collected the major brake parts listed in the BOM from a bike shop or the Internets. You will need 2 sections of cable with 2 nippled ends.
The long 1/4"-20 screws are for forming the pin joint that the brake mechanism swings upon. Using a nylon insert nut is recommend this time, since their prevailing torque (friction) means you can finely tune how sloppy the mechanism is.
I had two compression springs from a band brake accessories kit, but your hardware store should have small compression springs. The critical dimension is 2" length. The firmer the spring is, the more force the brake pedal will take to depress (But keep in mind we are still talking single-digit pounds). The coil should also fit over a 1/4" shaft - that's the outer dimension of the barrel adjusters. Otherwise, McMaster p/n 9657K387 is acceptable.Step 32.2 and 32.3: Assemble the brake bodies onto the motor mounts
Use 2 nylon washers between the brake body and the motor mounting plate's little tab, and one between the head of the screw and the brake body. There is no orientation of the screw that is preferable - pick the one which is easier for you to assemble. Tighten the nylon locknut until the mechanism can swing freely, but has very little side-to-side slop. Let's say < 1/32" is the threshold.Step 32.4 and 32.5: Cut the brake cable sleeve (just the sleeve) to length
You must have real cable shears or some other method of slicing a wound steel brake cable sleeve cleanly, like a Dremel with cutting disc. Diagonal cutters and wire cutters will not work.
Cut one 22" length of cable and one 33". These lengths are essentially all arbitrary and represent what I determined to be a good visual compromise between floppiness and a straight line. If you have a cable sleeve that is longer than 4.5-5 feet, you can just cut it in the middle somewhere approximating these lengths. A 4 foot sleeve is not sufficient to split in two.
If your bike shop gave you those little crimpable endcaps, stick one on the cut end of the cable sleeve. You may also need a nail, tiny screwdriver, or other sharp pokey thing to open up the cable passage again, after the cutting action.Step 32.6: Mount the brake cables at both ends
The shorter sleeve is for the left side and the longer is for the right. Take a barrel adjuster and put it on one end of the short sleeve.
Insert the barrel adjuster into the outer hole on the brake bodies, and thread the M6 nut onto the other side. See Figure 32.8 for the arrangement.
Take the other end of the cable and stuff it into the brake cable holder on the brake pedal mount. Do the same for the other side.Step 32.7: Slip the compression spring onto the brake cable and keep it close to the nipple
The cable has to go in loose-end first, so everything that it has to skewer has to be on it already.Step 32.8: Thread the Brake Cable through the sleeves
This step might take a little prodding because you are literally pushing a noodle, but the sleeve should prevent the cable from bunching.Step 32.9: Push the 7mm nipple into the circular slot and wedge the compression spring in between the barrel adjuster and the motor mount
Pretty self explanatory. The circular cutout on the motor mount is designed to hold the nipple end exactly. It may take some plier-pushing.Step 32.10: Pull the cable all the way through on the other end, threading it through the anchor bolts.
You might actually have done this already in conjunction with 32.8, but if you did not thread it through the cross holes in the anchor bolts, loop it back and do so. Pulling on the cable afterwards should immediately unkink the loop.Step 32.11:While keeping some tension on the cables, tighten each anchor bolt
Don't pull hard enough on the cable to start moving the mechanism on other side! Just enough such that you take up the loose slack.Keep the pedal itself butted up against the stop bolt while you do this
- that will ensure the springs keep the pedal tensed up. Tighten both bolts onto their cables, keeping your tension consistent between them.Step 32.12: Cut off the excess cable
Cut the cable off about 4" past the anchor bolt such that it's long enough to grab in the future if needed, but is not flopping everywhere. If your bike shop gave you "aglets" to crimp onto the ends, do so. This prevents stabby-cable syndrome and the ends fraying.Step 32.13: Test the brakes
Gently push on the brake pedal and observe both mechanisms for movement. They should start moving at roughly the same time. If not, then you need to adjust the tension of the lagging
side. Untighten the two M6 nuts on that side's barrel adjuster and unscrew the adjuster a little (making it stick further out of its mounting hole). Do this incrementally and stop when the movements are essentially equal.
With about 10 pounds of pressure on the pedal, the motors should be nearly impossible to turn by hand.