In every motorcycle’s life, comes a point where the brakes need to be completely overhauled.
For what ever reason from seized pistons to upgrading the system, this will need to be done to keep the performance at it’s optimum.
The reason for me doing mine was because the calipers were binding onto the brake disk, causing unnecessary heat generation and pad ware as well as the risk of the brakes locking unpredictably.
This guide is how I did mine.
This is for the right caliper, but the left is exactly the same and the rear very similar.
First thing you need to do is to remove the brake pads, you do this by removing a blanking plate (use a large slotted screw driver -
Remove the pin (anticlockwise) being careful to retain the pad anti-
Now that the pads are out, pump the brake lever once or twice to push the pistons out a bit, but make sure they don’t go so far as to start gripping the disk!
Crack open the bleed nipple with a 8mm spanner and drain the system of brake fluid, then remove the banjo bolt holding the brake line to the caliper.
To save breaking you knuckles, now is the time to get a T50 torx socket and to crack open the four bolts holding the two halves of the caliper together. Only enough to get the bolts to start turning.
Now you need to do is to remove the caliper from the bike. The caliper is held on by two 12mm bolts. Once the caliper has been removed, put the bolts back into the corresponding holes on the fork leg as to not lose these.
At this point we should now have the caliper as pictured above.
Remove the bleed nipple with the 8mm spanner and place this aside for refitting later.
Now remove the four T50 headed bolts to separate the caliper halves and place the bolts into a bath of degreaser.
You should now have the calliper in two pieces.
As shown in this picture...
What we need to do now, is remove the two rubber seals on the flat faces in the upper corners.
Next thing to do is to remove the pistons. Remember earlier when I said to pump the pistons out just after you had taken the pads out? This is where that action pays off.
If you didn’t do that, you may need to get some internal grippers to try and pull the pistons out, or try using compressed air (be careful!) in the fluid pathways, but ideally, you should have a lip of the pistons sticking proud.
Get a set of pliers and a piece of old bicycle inner-
Once they are out, put them in the bath of degreaser.
Once you have gotten both pistons out, you should have something that resembles this...
Now we need to remove the seals. Get your pointy tool, and scrape along the edge of a seal, pushing into the seem of the seal to dislodge it from it’s seat. Do this to all 4 seals.The seals nearest the top here are the dust seals, and the inner ones are the fluid seals.
Racers tend to remove the dust seals as it further reduces friction, but this requires them to be maintained to a much higher frequency!!
Now that all the seals are out, throw them away. We will be fitting new ones.
Carry out all the above on the other half of the caliper, then give them a good clean with degreaser, followed by brake cleaner.
While the two halves are drying, now is the time to get the pistons and inspect them for any damage.
Give the pistons a good clean with an old toothbrush. Gently scraping any corrosion off with a blunt edge of something.
The piston on the left is absolutely fine to be reused, the one on the right however has pitting and wear on it.
The right piston could be reused but I would not recommend it. The pitting on the piston can cause brake fade or even cause fluid to creep past the piston onto the brake pad/disk which could be fatal!
If there are any rough edges or sharp bits that can cut into the seal, rub these with a sheet of 1200 grain wet and dry paper using degreaser as a lubricant.
Once all the pistons have been cleaned, inspected for wear, or even replaced, we need to go back to the two halves of the caliper to start the rebuild.
Test fit the pistons into the calipers, making sure they slot and spin freely.
As everything is now clean and fits, we can now start to reassemble the caliper.
Place some rubber grease into the seal beds, this will assist in the life of the seal as well as allow the piston to slide in and out more freely.
There are two seals for each piston. An oil seal and a dust seal. I left out the dust seals as these calipers were being used for racing purposes only, reducing drag a little on the pistons.
For road use, I highly recommend putting dust seals in. Put dust seals in exactly the same way as the oil seals.
For road use, you would have a total of 16 seals, 4 of each type. 8 per calliper.
For race use, you would have a total of 8 seals, 4 of each type. 4 per calliper.
Get the new seals and locate them into the specific seats.
Once you have installed the new seals, remove any excess rubber grease with dry clean tissue paper.
Next, get some thin wire (I used lock wire) and go through the fluid channels to clear any rubber grease from them.
Now that all the fluid channels are clear, it is time to install the pistons.
Get the piston and smear some rubber grease around the bottom half of the skirt, this makes it easier to insert, but also prolongs the life of the seal and piston allowing to slide in and out more easily.
When you have installed the two pistons into this half of the caliper, do the same to the other half.
When you have completed both halves of the caliper, all you need to do now is to install two new O-
Some people reuse the old seals, I prefer to use new, but it’s up to you.
All that is left to do now, is to pair the two halves back together, fit the four T50 bolts back in with the aid of a little bit of copper grease, fit the bleed nipple, fit the caliper back onto the bike, fit the brake line, then bleed.
Congrats! You have just rebuilt a caliper, now go do it again for the other side and rear! :-
Guide written and phographed by Harley Godzisz. 2011