How to check and change your brake discs     

Find the fault

The first thing to do before taking bits apart, is finding the fault – if there is one, of course. During fitness tests, for instance, many bikes show brake disc problems on the rollers, so we know that we can change them. Another sign of a warped brake includes the feeling of the lever almost pushing back against your braking fingers, as the disc curvature pushes the pads back as it completes a cycle.

Identifying the issue

Now we think we’ve found a fault, it’s time to identify the issue. Even if a disc is warped by less than 1mm it will make a massive difference, so we put a dial gauge on the disc and spin the wheel. If it pushes the pin and gives a reading of movement (more than the service limit, usually around 0.3mm), the discs need to be changed. Never just change one though, always do both.

Whip the calipers off

When changing brake discs, it’s always important to change the pads as well, so both items wear in properly and are at their optimum. We’ll cover the pads separately as that’s a whole different ball game, but it’s always easiest to get them done first. Some bikes, like this Suzuki, have R clips holding the pads in, so while the caliper is still loosely on the machine, get the pin out. Take the caliper bolts out now and rest them with a bungee cord (or something similar) out of the way – the best way is to cling them on to the handlebars, or the mirrors.

Get those pads out

While the calipers are hanging free, swap the pads over. It’s always best to use the same brand of pad and disc, but it doesn’t matter so much. Here it will vary from caliper to caliper, but slot them out as per the machine.

Insert the new pads

Push the new pads in through the same method the others came out; they should just click in nicely. Make sure they’re in securely, and if necessary pushed apart slightly further so it’s easy to fit them on to the new disc, which may be slightly thicker. Do this by gently prising with a flathead screwdriver, taking care not to damage the pads.

Drop the wheel out

Now the calipers are out and the pads have been taken care of, it’s time to get down to business and get the wheel out. If it hasn’t been changed in a while, be careful as it may be pretty stiff, so gently undo the pinch-bolts on the bottom of the forks before undoing the spindle and wriggling it out. If you’re using a small fork stand, you may find you need to loosen the mudguard if necessary – don’t sweat though, as you should only need to do two, or four on the fork legs to work enough space. Once you’ve done this, pull the wheel out and free of the bike, and lay it down on an old tyre. By doing this you’re keeping the rim and the discs safe and off the ground.

Loosen the disc bolts

Now you have the wheel on the deck and resting on the spare tyre, the next port of call is removing the disc bolts. This is the hardest part of the job as if you’ve had a set of discs from standard, they may have never been touched since they left the factory; and on a lot of bikes, the bolts can almost feel like they’re made of cheese! My little secret here is using ‘EZ Grip’, which is a little magic bottle of friction drops. A little application of this stuff on the end of the tool, means that when it’s put into the bolt it will grip like sandpaper, and turn the bolt rather than rounding it off. This is the biggest risk of this section here, so take your time, and if necessary use a breaker bar – and even a gentle tap and a bit of heat if they’re really tight. I wouldn’t recommend that though, and definitely don’t be doing it on new bikes as there is a spacer between the disc and the rim on a lot of new machines (like the R1), which you don’t want to damage, bend or loose. Once you’ve loosened the bolts, the disc should come out nice and easy.

Scour the surface

With the old disc now separate from the rim, it’s time to give the mating surface some TLC; careful cleaning where the disc has been sitting. Remember, if you’re removing the discs to powder coat or paint the wheels, make sure you cover this little section up – even a layer of paint can knock the discs slightly out of alignment. The best tool to use here is a scotch brite pad, with a firm toothbrush to finish – don’t use any harsh wire brushes, or sandpaper. Without being too rough, gently get rid of the dirt, grime, and any crap that’s lodged itself in – if it’s really bad, take it to a skimming company to be done, but just make sure they don’t skim away the metal.

Sort the bolts and thread

Now, most new discs won’t actually come with new disc bolts, so you have two choices: either buy a new set (always try and use a reputable brand, like Probolt), or clean up the original bolts and use them. If they aren’t too battered I’ll always use the original bolts, but before sticking them back in, it’s always worth giving them and the thread in the wheel a nice clean-up. The easiest way to do this is getting another scotch brite pad, sticking the bolts in a drill, and giving them a quick whizz! It will clean the bolts up again to look like new, and help take any of the old thread-lock that’s remaining. After this, it’s worth cleaning the threads up as well; a tap works perfectly, and you’ll be looking at roughly an M8 x 1.25, but always use a size checker to be sure. Get the tap, stick it in the driver and get those threads nice and tidy.

Line up the new disc

With the bolts and threads looking like new again, it’s time to get your new disc out the box and lined it up nicely. If you have the right disc, it should line up exactly to where the bolts are. If it doesn’t, you’ve got the wrong one and you’ll need to change it.

Get those bolts back in

Make sure you don’t jump the gun here, as just before you re-install the new bolts on your shiny new disc, make sure you’ve stuck some thread-lock in the threads. Get it as far down the thread as you can, as you don’t want the bolts jumping out on you mid ride! From here, loosely insert every bolt into the wheel, and gently nip them up. It’s best to go round in a star shape here from corner to corner when tightening, and make sure you check out the manual for the correct torque setting. Usually it will sit somewhere between 22 and 25Nm, but it’s always best to make sure. Once all the bolts are secured, give the wheel a clean with some blue roll and brake cleaner to wipe away any excess bits or Loctite that might have escaped.

Repeat!

You’ve done one side...it’s time to flip the wheel over and do it all over! Make sure the steps are the same, and don’t get too complacent, especially when removing the disc bolts.

Insert the wheel

With both new brake discs installed and the wheel cleaned up, it’s time to get it back in the bike. Line it up in between the forks and get the axle back through. Make sure it’s torqued up properly, and if undone, that the pinch bolts underneath the fork legs have been tightened.

Bolt the calipers With the wheel now set up properly, it’s time to re-install the calipers, which have already been fitted with new pads. Make sure the calipers are bolted on properly, and once again check your manual for the correct torque settings – these ones came in at about 39Nm.

Pump the brake

With the wheel back in and the calipers bolted on properly, give the front wheel a spin and pump the front brake lever. This gets the fluid from the master cylinder down into the calipers, and will mean that you have braking power as soon as you need it.

Take it easy!

With new pads and discs on the bike, it’s vital that you run them in properly. For the first 30km or so, they might feel slightly vague as they wear in nicely. So be patient if they don’t have the same bite for the first few rides. Also, make sure you break them in smoothly as well with lots of gentle braking, rather than infrequently grabbing big handfuls.

Choosing The Right Discs

It’s all very well and good having a quick bike, but if your brakes are a bit pants, you’re going to have a tough time stuffing your mates. This is why it’s always important to get the very best brake discs you can – although OEM discs are great nowadays, there’s a whole range of aftermarket rotors that will turn your brake lever into an anchor. One thing to note is, if you’re going for an aftermarket set, always go for a reputable brand: EBC, Brembo, PFM, etc. Unknown discs might work out to be incredibly cheap, but chances are they’ll last half as long and won’t give you the same amount of stopping power. There are also different types, materials and weights which offer different benefits. The main thing you’ll see when purchasing a set is the different types. If you’ve got fixed discs which are mainly made from one material, they are best for the road. If that isn’t enough for you there are also floating and semi-floating discs which allow the rotor to heat up and expand – which are much better for use on track, rather than on the road.

Health Warning!

Unless you are 100% sure of what you are doing, do NOT try this at home. Correctly fitted brake discs are essential to your riding safety and if you don’t feel confident and competent to carry out the advice in this feature, do not attempt it. Seek further advice from a specialist or take your bike to an accredited garage to get the work carried out professionally. It’s better to be safe than sorry.