Monday Maintenance: Fitting your discs - Bike Magic

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Monday Maintenance: Fitting your discs

Stopping in a box

Now you’ve chosen your disc brakes it’s time to fit them to your bike. We’re dealing with basic simple installation with a complete pre-assembled system here. If you’ve got a separate hose and lever set up like Shimano XT or need to unplug the hose for trimming or mounting then we’ll deal with that next week, when we’ll also cover bleeding your disc brakes.

Fitting the rotor
Mr Rotovator

The first step is bolting the rotor onto the hub. Make sure you grease the bolts and threads but be very careful not to get any grease on the braking surface itself.

Tighten all six bolts finger tight and then tighten them properly in an opposed order – ie one side then the other rather than round in a circle – to keep the rotor centred and reduce the chance of bolts shaking loose. Give a final check round for tightness and you’re ready to roll.

Holy rotating anchors Batman!

Now fit the front wheel to the bike, making sure it rests straight in the dropouts. If in doubt stand it on the floor and release and close the QR skewer. It’s also worth switching the skewer so that the lever is on the opposite side to the disc so you don’t burn your fingers trying to undo it.

Caliper fitting

Before you start pulling off V-brakes make sure the caliper is fitted. Otherwise you won’t be able to ride to the shop and sort out any problems, so leave everything where it is until you have to move it.

Checking first can help as a spacing guide.

Before you start pulling bolts and washers off, just slide the caliper onto the rotor to see which of the various thickness spacers you’re likely to need.

Then it’s case of trial and error adding and removing the washers until you get a smooth running fit. If you’re lucky they’ll pop straight on, but if the mount is mis-aligned or you’ve got a long 4 pot caliper to squeeze the rotor through you might need to do a bit of gentle filing of the disc tabs to even things out.

If you’re struggling to see the gap between disc and rotor slip a piece of white paper behind the caliper to act as backdrop as you squint through.

Lever fitting
Levers are much nicer than the photo.

Then it’s up to the far end of the hose to whip off the now redundant V-brake lever and stick on your shiny new disc brake lever. All the usual rules about tightening bar clamps enough to keep them in place but not enough to stop them moving in a crash apply as does checking for clearances on shifters and setting correct lever reach before you set out.

Now simply secure the hose to stop if flappping and catching – but making sure the bars and suspension can still move freely – and protecting the frame with patches anywhere the hose is likely to rub.

Now whip off the V-brakes and stick them in that special shoe box of things you’re keeping just in case, but will actually never use.

First ride tips

Although disc brakes are generally far more powerful than V’s you have to wait for them to bed in to get that power so take the first ride very gently.Although anything oily or greasy will spell death to any hope of braking power, coating the discs with wet mud or even Coca Cola can speed up the bedding in process. Another technique is just to ride along with them dragging slightly to help heat them up and burn them into readiness.Although we’ve said braking might be poor at first bedding can occur very suddenly halfway through a ride, so always err on the side of caution and pull the lever gently rather than grabbing a handful.

If you find the rotor rubbing for any reason we suggest you wait till you get home before adjusting as it’s all too easy to lose washers if you start mucking about at the trailside.

Now we’ve got you rolling we’ll be dealing with some of the problems that can occur when fitting and fettling disc brakes and calmly guiding you through them. Be warned though it might be worth recruiting an extra pair of hands in advance.


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