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If you are trying to adjust the disc brakes, have a look at the instructions below that will help you get the most out of your Mini BMX.
Hex/Allen sizes:
- all on disc caliper are 4 mm
- Mount to frame — large eye bolt mount is 5 mm, small stabilizer hex bolt is 2.5 mm
- lever mount for handle bars is 5 mm
- Small lever adjuster (only needed for small hands!) is 2 mm.
- Wheel/axle nuts are 15 mm
1) Turn the bike upside-down. Undo the back wheel/axle bolts which will loosen the chain. Then slip the chain off the front sprocket (where the crank/pedals are). This is done by pushing the chain outwards and back-pedaling the crank. Then remove the back wheel.
2) wind the disc onto the thread on the wheel/hub, opposite side to the driver. This is self tightening due to thread direction when brakes are applied, but it pays to tighten a bit before hand to prevent it dislodging before fully tightened... Use a screwdriver or similar to lever agains the hub to prevent it coming loose first ride (reverse this to remove to change tyre). Put the screwdriver through the disc and hub and gently lever clockwise to tighten.
3) attach the caliper to the frame mount on the inside as shown. First put the larger eye bolt in (larger piece inside, hex facing out), wind in to hold in place but don’t fully tighten so you can position for the smaller stabilizer bolt. Put this in and tighten up completely. Then fully tighten the larger eye bolt to secure in place. Also on the back of the caliper there is a hex to adjust the brake pad in and out. Adjust this out so there is only around 0.5 - 1 mm of the pad visible on the disc side. This will give you some room to adjust and align the disc.
4) Put the wheel and chain back on sitting the disc inside the caliper. Ensuring the chain is the correct tightness and the wheel is aligned centre (crank should turn freely, but chain shouldn’t sag or come off easily without force). You can use the small drill holes on the frame to help centre the wheel. Once the wheel is on correctly we can adjust and tighten the caliper.
5) Align the caliper on the disc and tighten the two adjuster bolts (one top and one on bottom of caliper, top one shown in pic below). Check the caliper is semi centered on the disc so that pads each side of disc are approximately an even distance, if not slightly closer to the wheel side. You don’t need to be super fussy with this as long as it isn’t rubbing when brakes aren’t applied. Hold the caliper in place as you tighten and look that you keep clear space between the disc & caliper as you tighten. If it touches and any adjustment is needed — loosen them off again and repeat. The adjuster bolts should be tight once done, but use caution as the caliper is aluminum to keep weight down and is softer than the steel bolts, don’t over tighten.
5) Put the lever onto the handle bar right hand side (when viewed from riders position), be careful to get the bolt aligned correctly in the hole, gently wind in. The lever is also made from aluminum to keep weight down, so can thread against the harder steel bolt.
6) On the lever, align the adjusters so the openings line up as pictured below. Insert the cable into the lever as shown, pull down through the opening you’ve made then wind the adjusters in so they are tight against the lever. This allows adjustment if the cable begins to stretch over time. The small allen bolt you can see (has blue thread lock showing) can be wound in to adjust the lever inwards for small hands.
7) Insert the cable into the disc caliper as shown below, and through the clamp bolt on the arm. Pull the cable so the brake lever on the handlebars holds together, you don’t have to pull it too tight, just so the cable and tube sits in correctly at both the lever and caliper ends.
Then push the caliper lever as shown in the two shots below so the pads are nearly touching the disc (hold the cable with other hand so it slides up the cable instead of pushing it back up the tube), and tighten the cable clamp (my thumb is touching this).
If the brakes aren't tight enough, loosen the cable clamp again and push lever a little further forward with your thumb, re-tighten. Vice versa if it’s too tight and grabs the disc when brakes aren’t applied, let it slide back a few mm. Tighten, and you’re done!
If needed any minor adjustments can be done at the adjuster (silver, end of cable tube where it sits in the caliper) — but try get it adjusted at the caliper first so you have room to adjust in the future.
