On a typical modern, 1000cc motorcycle that can easily amount to around half a ton of bulk to haul up. Don't forget all that energy doesn't just go away either. In this case, it's turned into heat, heat which mainly the brake discs (but also the brake pads, calipers and disc carriers) have to somehow dispose of. Whether your brake discs are worn-out, warped or bent, or you're after improved braking performance, lighter weight or just like new looks, you'll not go far wrong with a set of new aftermarket brake discs.
There's no better weight to lose than un-sprung weight. Your suspension will have an easier time, and even better, less rotating mass equals less gyroscopic effect, so your motorcycle will be easier to change direction too.
The patterns cut into the brake discs are not just for show either. More venting will improve heat dissipation and therefore reduce brake fade. As with all things brake related, take care and do everything properly with the correct tools. A bad job with brakes can have catastrophic consequences.
Things we need to replace our brake discs are a nice bowl of hot soapy water to clean up the calipers. Also useful for washing away any spilled brake fluid before it destroys paintwork.
Torque wrench – best not to guess when tightening calipers and disc bolts. Get the settings from a service manual of from the brake disc install manual.
Decent selection of rags – there's lots of much flying about in your brakes. Some clean lint-free rag for final wipes too.
Spanners might be needed for loosening your wheel spindles.
Thread lock is essential for disc mounting bolts, and well worth using on caliper bolts too. Get the right color (strength) for the job.
Old toothbrush is great for cleaning out caliper recesses.
- Check that your discs and pads (if you're fitting new brake pads) are the correct fitment for your motorcycle. Get your motorcycle on stands. If it's at all unstable on the stands, crack off tight nuts and bolts with the motorcycle on the side stand, and strap the motorcycle to your workbench. Failing that, cable tie the rear stand to the swing arm. Remove front wheel.
- Remove brake disc retaining bolts. Make sure you have a decent fitting tool as these can be tight and be coated with the thickest thread lock known to man. Have the wheel upright, and use your leg as a 'brake', undoing the bolts towards you. Remove the disc from the hub.
- To stop your brand new brake discs going rusty, they are often coated with an anti corrosion agent. Get a clean rag and some brake cleaner and give the discs a good but serious cleaning. Clean the mating face on the hub, and the disc retaining bolts.
- Fit the brake discs to the wheel hubs giving the discs a turn back and forth to make sure there's no dirt or grit between the mating surfaces. Put a dab of thread lock on the bolts, then nip them up in a star pattern, i.e. top, bottom, move round one bolt and repeat. Now torque the bolts using the same pattern as you did to nip the bolts. As a final check work round them clockwise.
- Work on one caliper at a time, remove the old pads, get a bowl of hot soapy water and a toothbrush and give the caliper a thorough clean. Carefully pump the pistons out a little, and evenly, just until you can see a clean portion of them while keeping an eye on the fluid level in the reservoir. If you're on your own, use an old pad and an elastic band (to retain it) to stop the pistons in the second caliper popping out.
- Get your toothbrush and clean the pistons thoroughly, concentrating especially on the bits your can't see, and checking for corrosion, pitting or damage. The pistons should all move reasonably freely. If they don't, you'll (at least) need to work them in and out a few times with some proper brake seal grease being careful that the other pistons don't pop out.
- You're now ready to refit the front wheel and calipers. Make sure any spacers are fitted, then slide the wheel into place. The spindle should slip into place easily with the wheel supported. Reverse the removal process leaving the spindle clamp bolts loose 'till the motorcycle is off the front stand. Give the fork a quick bounce to make sure they re not twisted, then tighten the clamp bolts. Obviously you'll be using a torque wrench where applicable, right?
- Now give the brakes a good pump and check the brake fluid level. You may need to remove some fluid if the reservoir has been topped up with worn pads, but while you're there, now is as good a time as any to give the brake system a bleed though and change to braided brake lines.