The Mechanic
Guest
Having read quite a few of your posts concerning 'warped discs' etc. I thought that some useful and reasonably easy to carry out checks would be useful to anyone eho is fairly DIY mechanically competent.
You will need plenty of light, a measurement device such as a steel ruler, vernier caliper, dial test indicator; these last two offer the ability to be far more accurate in any readings/measurements obtained.
Bike should be on the main stand, paddock stand or blocks so that either the front wheel or rear are clear of the ground.
Squeeze the front brake lever a few times and operate the rear brake a few stabs as well, chack to see if the wheels rotate easily without too much binding. It is entirely normal for the pads to just rub slightly, when the bkie is moving centrifugal force and the brake caliper piston seal (returning to its normal shape....not under the influence of hydraulic pressure) will tend to pull/throw the pads away very slightly from the disc. Thats the reason why it is so important to keep the pistons and seals clean.
Now you are familiar with the general feel of the brakes as they are at present you can proceed to the next stage.
Decide which end you want to do first, prepare the machine so that the wheel you have chosen is a couple of inches clear of the ground. Rotate the wheel by hand and just observe the rim and tyre to make sure they are not ovalised, wobbling or doing anything they shouldn't be.
Now if you are working on the front wedge some rag into the brake lever so that you or someone alse does not inadvertently operate it, alternatively put something under the rear brake pedal or on top to prevent same.
Remove (for the front wheel) both sets of pads keep them in order so that they are fitted back into the same position in the caliper (same side of the disc). The rear brake will be attended to in the same manner but obviously only one set of pads will be removed.
Again with rotate the wheel by hand, it should spin considerably more easily than before giving consideration to speedo drive, oil seal friction, and for the rear a degree of added friction due to the transmisssion.
We are now concentrating our attention around the disc and brake caliper region. Observe the gap either side of the brake caliper whilst rotating the wheel, note any wobble if it appears to you observable to the naked eye in the disc....this is serious.
Take hold of the wheel top and bottom and (preferably with someone staedying the bike test the wheel bearings for sideways movement....there should be NO discernable movement. Do this for both wheels when convenient.
If all is ok, we will now start to carry out measurements.
Take your chosen measuring device and carefully measure the distance between the brake disc and a fixed reference point on the brake caliper body ( I would suggest the outer flat edge where the pad slides into the caliper as this is identical on both sides of the caliper). Now note down the measurement and then rotate the wheel through 1/4 revolution and measure again, repeat until you have at least four readings/measuerments.
Now repeat the operation on the opposite disc, noting down the readings.
Don't panic if you get wildly differing readings...calm down and double check the measurements again.
I do not have B*W's specifications for brake disc run-out, suffice it to say that there should be NO discernable difference between your readings at any stage.
WHAT TO DO IF YOU HAVE A SUSPECTED WARPED DISC:
Assuming the warranty has expired or you want to prove a point then follow the next steps.
Unbolt the brake disc from the wheel hub and make sure that the mounting area is free from burrs or raised (pulled) threads, what this means is that the hub/disc mating surface is totally smooth. You don't need to remove the whee to do this on the front.
Rotate the disc around one or two mounting holes and then refix using a torque wrench to finally tighten the mounting bolts. Do these bolts up evenly and work diagonally so that the disc can seat down evenly if you tighten the bolts like going round a clock face you will most certainly 'load' the disc.
Time for a cuppa....or something stronger!
Right, rested.....good, now for the next stage.
Measure each brake pad, they should all be the same in pad thickness. You may if you wish gently rub the braking surface of the pad with emery cloth placed over a perfectly flat surface, this will remove any bedding in marks and will affect your braking until the pad has bedded in again. The reason for this exercise is to enable you to make both pads give the same thickness measurement.
Apply a 'thin' coating of either Copa-Slip or high melting point grease, to the pad metal backing and the edges of the metal backing that contact the caliper. Refit the pads WITHOUT the retainers to BOTH sides and apply the brake lever a few times.
Slacken the caliper to fork leg mounting bolts ( one to two complete turns of the bolts) Now apply the brake again and you should still be able to move the caliper very slightly up and down as though trying to move the caliper in the same direction as the wheel. If this is not possible the caliper is out of alignment with the disc, you may need to add small shims between the caliper and fork leg mounting points or the caliper mounting faces may need to be reduced slightly. If this sounds complicated let me assure you it isn't and its something any professional thats worth their salt would do as a matter of course. You've come this far don't give up now!
Another area to check is the wheel spindle to wheel spacer clamping effect. In other words is the wheel spindle pulling the forks to far together and forcing the calipers out of true alignment with the brake discs.
Warning you cannot do this next bit on a bike with single sided (slider type calipers). With the brake calipers tightened to the fork mountings, slacken the wheel spindle and see if the wheel spins any freer than before. If it does then the wheel spindle is pulling the forks out of true aligment, creating binding brakes and uneven loading of the discs which will cause warping sooner than later.
The remedy is to fit slightly longer spacers or use a shim or two, on the other hand it is entirely possible for this scenario to be reversed and the fork/wheel spacers could be forcing the legs outward creating the same effect.
Try getting someone to hold the brake on whilst the wheel spindle is tightened and then see what effect that has.
Finally the brake calipers need to be serviced for cleansing. To do this remove the pad on one side of the caliper only, GENTLY apply the brake lever a SMALL amount and the piston will move in towards the disc. Thoroughly clean the exposed part of the piston and then smear either rubber grease or as I have used to great effect a small amount of 'o'-ring chain lube with a small paint brush. Ease the piston back in just sufficient to allow the brake pad to be reinserted. CARE wrap some rag around the master cylinder just in case you force the piton back too far, there shouldn't be any leakage from the reservoir, but just in case.
Now double check everything that you have disturbed, ensure the brake pad locating pins and security devices are fitted back correctly, all brake caliper bolts are correctly tightened and the wheel spindle (if disturbed) is tightened to the correct torque setting.
Now roll the bike back and forth working the brakes on and off to ensure they are SAFE. Go for a ride.......
Obviuosly I'm relying on your common sense here so if you still have a warped disc it will need to be sorted with B*W or your dealer etc.
Good luck in your quest, and if you do all of the above its entirely at your own risk, I accept no responsibility whatsoever. But you'll notice that your brakes are probably alot better than they were.
WARNING WARNING if you have ABS brakes please be very careful not to damage the SENSOR / PICK-UP or its wire.
Good luck, this took me longer to type out than it did to actually do the work explained.
You will need plenty of light, a measurement device such as a steel ruler, vernier caliper, dial test indicator; these last two offer the ability to be far more accurate in any readings/measurements obtained.
Bike should be on the main stand, paddock stand or blocks so that either the front wheel or rear are clear of the ground.
Squeeze the front brake lever a few times and operate the rear brake a few stabs as well, chack to see if the wheels rotate easily without too much binding. It is entirely normal for the pads to just rub slightly, when the bkie is moving centrifugal force and the brake caliper piston seal (returning to its normal shape....not under the influence of hydraulic pressure) will tend to pull/throw the pads away very slightly from the disc. Thats the reason why it is so important to keep the pistons and seals clean.
Now you are familiar with the general feel of the brakes as they are at present you can proceed to the next stage.
Decide which end you want to do first, prepare the machine so that the wheel you have chosen is a couple of inches clear of the ground. Rotate the wheel by hand and just observe the rim and tyre to make sure they are not ovalised, wobbling or doing anything they shouldn't be.
Now if you are working on the front wedge some rag into the brake lever so that you or someone alse does not inadvertently operate it, alternatively put something under the rear brake pedal or on top to prevent same.
Remove (for the front wheel) both sets of pads keep them in order so that they are fitted back into the same position in the caliper (same side of the disc). The rear brake will be attended to in the same manner but obviously only one set of pads will be removed.
Again with rotate the wheel by hand, it should spin considerably more easily than before giving consideration to speedo drive, oil seal friction, and for the rear a degree of added friction due to the transmisssion.
We are now concentrating our attention around the disc and brake caliper region. Observe the gap either side of the brake caliper whilst rotating the wheel, note any wobble if it appears to you observable to the naked eye in the disc....this is serious.
Take hold of the wheel top and bottom and (preferably with someone staedying the bike test the wheel bearings for sideways movement....there should be NO discernable movement. Do this for both wheels when convenient.
If all is ok, we will now start to carry out measurements.
Take your chosen measuring device and carefully measure the distance between the brake disc and a fixed reference point on the brake caliper body ( I would suggest the outer flat edge where the pad slides into the caliper as this is identical on both sides of the caliper). Now note down the measurement and then rotate the wheel through 1/4 revolution and measure again, repeat until you have at least four readings/measuerments.
Now repeat the operation on the opposite disc, noting down the readings.
Don't panic if you get wildly differing readings...calm down and double check the measurements again.
I do not have B*W's specifications for brake disc run-out, suffice it to say that there should be NO discernable difference between your readings at any stage.
WHAT TO DO IF YOU HAVE A SUSPECTED WARPED DISC:
Assuming the warranty has expired or you want to prove a point then follow the next steps.
Unbolt the brake disc from the wheel hub and make sure that the mounting area is free from burrs or raised (pulled) threads, what this means is that the hub/disc mating surface is totally smooth. You don't need to remove the whee to do this on the front.
Rotate the disc around one or two mounting holes and then refix using a torque wrench to finally tighten the mounting bolts. Do these bolts up evenly and work diagonally so that the disc can seat down evenly if you tighten the bolts like going round a clock face you will most certainly 'load' the disc.
Time for a cuppa....or something stronger!
Right, rested.....good, now for the next stage.
Measure each brake pad, they should all be the same in pad thickness. You may if you wish gently rub the braking surface of the pad with emery cloth placed over a perfectly flat surface, this will remove any bedding in marks and will affect your braking until the pad has bedded in again. The reason for this exercise is to enable you to make both pads give the same thickness measurement.
Apply a 'thin' coating of either Copa-Slip or high melting point grease, to the pad metal backing and the edges of the metal backing that contact the caliper. Refit the pads WITHOUT the retainers to BOTH sides and apply the brake lever a few times.
Slacken the caliper to fork leg mounting bolts ( one to two complete turns of the bolts) Now apply the brake again and you should still be able to move the caliper very slightly up and down as though trying to move the caliper in the same direction as the wheel. If this is not possible the caliper is out of alignment with the disc, you may need to add small shims between the caliper and fork leg mounting points or the caliper mounting faces may need to be reduced slightly. If this sounds complicated let me assure you it isn't and its something any professional thats worth their salt would do as a matter of course. You've come this far don't give up now!
Another area to check is the wheel spindle to wheel spacer clamping effect. In other words is the wheel spindle pulling the forks to far together and forcing the calipers out of true alignment with the brake discs.
Warning you cannot do this next bit on a bike with single sided (slider type calipers). With the brake calipers tightened to the fork mountings, slacken the wheel spindle and see if the wheel spins any freer than before. If it does then the wheel spindle is pulling the forks out of true aligment, creating binding brakes and uneven loading of the discs which will cause warping sooner than later.
The remedy is to fit slightly longer spacers or use a shim or two, on the other hand it is entirely possible for this scenario to be reversed and the fork/wheel spacers could be forcing the legs outward creating the same effect.
Try getting someone to hold the brake on whilst the wheel spindle is tightened and then see what effect that has.
Finally the brake calipers need to be serviced for cleansing. To do this remove the pad on one side of the caliper only, GENTLY apply the brake lever a SMALL amount and the piston will move in towards the disc. Thoroughly clean the exposed part of the piston and then smear either rubber grease or as I have used to great effect a small amount of 'o'-ring chain lube with a small paint brush. Ease the piston back in just sufficient to allow the brake pad to be reinserted. CARE wrap some rag around the master cylinder just in case you force the piton back too far, there shouldn't be any leakage from the reservoir, but just in case.
Now double check everything that you have disturbed, ensure the brake pad locating pins and security devices are fitted back correctly, all brake caliper bolts are correctly tightened and the wheel spindle (if disturbed) is tightened to the correct torque setting.
Now roll the bike back and forth working the brakes on and off to ensure they are SAFE. Go for a ride.......
Obviuosly I'm relying on your common sense here so if you still have a warped disc it will need to be sorted with B*W or your dealer etc.
Good luck in your quest, and if you do all of the above its entirely at your own risk, I accept no responsibility whatsoever. But you'll notice that your brakes are probably alot better than they were.
WARNING WARNING if you have ABS brakes please be very careful not to damage the SENSOR / PICK-UP or its wire.
Good luck, this took me longer to type out than it did to actually do the work explained.
