Although this guide was done for the NC30, we did exactly the same for the NSR250. The process would be more or less the same for any dual piston calipers but the calipers are the same on these two bikes, in fact some of the photos used below are from the NC, and some from the NSR.
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The front brakes on our bike were in need of attention, the pistons had lots of surface corrosion and were almost impossible to push back into the calipers, this causes the pads to rub the disks constantly heating them up and eventually warping them.
There was also sludge in the bottom of the master cylinder. Nothing less than a complete strip and rebuild would do. As well as new seals and pads it would be nice to also fit new pistons as it means less cleaning and you don’t have to worry about damaging them when you take them out, however we are trying to do this on a budget so we decided to try and salvage the existing ones.
Bike parts, as well as everything else it seems, are expensive in Australia so we ordered most of our parts from the UK. Rick Oliver is a well known resource for NC30/35 parts and conversions and even including shipping we saved considerably on Oz prices. So we ordered a set of caliper seals and a master cylinder overhaul kit (amongst other stuff) from Rick and got to work.
Overhauling brake calipers isn’t that difficult, providing you do everything in the right order and remember that if there’s any part of your bike you don’t want to cut corners with, its the brakes.
Before you take the brakes off and drain the fluid you should utilise the hydraulic pressure to get the pistons out as far as you can. Unbolt one caliper leaving the other one in place so its pistons cant move. Take out the pads and pump the lever until the pistons on the other one come out as far as they can, they will probably move unevenly so jam something between the ones that can move so the pressure is directed to the sticky ones, keep going until all the pistons are out evenly as far as they can go, but not completely or you loose your pressure – on most bikes they can’t move enough to come out anyway as long as they are out evenly. Secure these pistons by jamming something between them if you have to so they cannot move any more and then do the same with the other caliper. Once you have done this you can drain the fluid.
Now you need to split the calipers, its easier to do this with the them still bolted to the forks unless you have a vice to secure them. You need torx sockets for this. Be careful not to loose the little rubber seals at either end of the caliper.
Once they are split you can pull out the pistons, and because you used hydraulic pressure to get them most of the way out this part should be easy. CAREFULLY grab them with mole grips or something, but protect the soft pistons from the jaws with a rag or piece of cardboard. You must not score them or they may not seal properly.
If the pistons just have some surface corrosion like the ones pictured then you can just clean them up. If they are very badly corroded or scored then you should replace them, new pistons aren’t cheap but this is your brakes FFS!
Use robot pubes, I mean wire-wool, to get rid of the corrosion. Start coarse, then fine until they are clean and smooth like this:
Now use something sharp ish to get the old seals out. It doesn’t matter if you tear them as you have new ones, right?
Once they are out give the calipers a good clean. Spray brake cleaner all over and scrub out all the brake dust, pay special attention to the seal recesses. Next, give your new seals a good coating of red rubber grease, you can be excused for just using brake fluid, but why not do something properly for once in your life?
The seals should pop in easily, there should be two seals per piston. Once they are in you can gently push the pistons in, just coat with brake fluid first.
Make sure the little rubber seals (that you were careful not to loose when you split the calipers) are in place and bolt the two halves back together, torque the bolts up according to the manual, again if you don’t have a vice, wait until you bolt them back onto the forks to tighten them. Make sure you give the pad retaining pin a rub with the wire-wool to get rid of any corrosion and coat with brake grease, then put a little grease on the back (not front) of the pads.
Fit the pads and don’t forget the retaining spring.
Fit to the bike, torque the bolts, attach the brake lines with new copper washers and bleed according to the manual. If the disks have any surface corrosion get the robot pubes out again and give them a scrub, then wipe with methylated spirit and try not put your grubby finger prints on them afterwards. Cleaned and serviced the NC30 brakes provide plenty of feel and stopping power.