More than one eager DIY bike maintenance enthusiast has fitted a new brake disc over the years, only to find that it warps in pretty short order. That’s because while it might be a bolt-off bolt-on job on newer bikes or ones that have been scrupulously maintained, a little more attention to detail is required on older bikes that have seen many miles, a lot of bad weather and a fair few spanners.
You also want to use quality replacement discs. Cheap rotors can be prone to warp, regardless of how fastidious you are when you fit them. Warped and worn discs have no place on any motorcycle, and for once we don’t remind repeating ourselves to reiterate the point that there is no room for compromise when it comes to brakes.
The front disc on my TZR-wheeled Yamaha TDR250 was probably once intended to be semi-floating but has now reached the point where it’s about to rattle off the bobbins. Fitting an EBC replacement affords us an opportunity to show some of the little tricks of the trade you need to do this job right.
Tools for the job : Heat gun. Brake cleaner. Torque wrench. Tap. Tap holder. Threadlock. Mallet. Impact driver. Nylon abrasive pad. Allen key.
Cost : A quality disc is around £70-£80. We opted for an EBC here. Disc bolts are around a quid each.
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| First of all the old disc bolts will need to come out. Make them free with the impact driver. The more observant reader might note that a previous owner has opted for disc bolts with two differently sized heads. Bodger. |
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| A hot air gun is useful on bolts that are reluctant to move. Yes, bolt and wheel are both being heated up here, but it’s less about expanding the alloy the bolt goes into and more about trying to soften the old thread lock. |
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| Despite my best efforts with a heat gun and impact driver, the hex on this one rounded out, meaning the head had to be drilled off. A squirt of PlusGas followed by the assistance of the vice grips removed the remains. |
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| Use a tap to clean corrosion and old threadlock out of the threads, so that the new bolts will be able to torque down correctly. Blow the holes out with an air duster afterwards to be completely sure they’re free of debris. |
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| To avoid warping, a brake disc must mate to a clean, smooth surface. Close inspection of the TZR wheel fitted to the TDR revealed corrosion and some spurious paint or powdercoat. All of it will have to be removed. |
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| A nylon abrasive pad, assisted by a little brake cleaner, will remove the paint and corrosion. Work it right into the edge where the centre of the disc will sit. You might want to give the bolt holes another blast of air duster when you’re done. |
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| A thorough wipe down with a workshop towel and brake cleaner will make the wheel ready to receive the new disc. A few minutes spent doing the job properly now will avoid expensive warped disc woes later on. |
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| While you’ve got the brake cleaner and shop towel out, clean off the braking surface of the new disc to remove any traces of oil, grease or protective coating used by the manufacturer to protect them in the warehouse. |
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| Apply a couple of drops of medium-strength threadlock to the new bolts prior to fitting them. Some manufacturers supply disc bolts with a blob of dried threadlock already applied. You need to do it yourself on these Yamaha ones. |
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| Working evenly on the bolts, torque them down to the settings that are specified in your trusty workshop manual – 14 lb.ft in this case. Torque the bolts in opposite pairs until the desired tightness is finally achieved. |
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| Re-fit the wheel to the bike, remembering to pump the brake pads back into contact with the disc. Correctly torque the caliper bolts, wheel spindle and pinch bolt too. You’re now ready to go and test your handiwork on the road. |