This page is based on my own bike, a GPZ900r A8 model, this model utilises twin opposing piston callipers and floating discs. These may not be the same as on your bike, but the principal is the same. You pull the lever, hydraulic fluid is forced through the lines into the calliper body, which in turn pushes the piston out thus grabbing the brake disc. On here I shall describe the procedure that I use to totally dismantle the calliper and rebuild it.

What you will need:

-A sealed supply of correct specification brake fluid, in the case of most bikes DOT 4. Ensure that the supply is in a sealed container, not just with a lid on, but a factory seal (usually a foil seal), this is because brake fluid will absorb moisture which will boil in the system rendering your brakes inoperable.

-A plentiful supply of clean rags.

-A basic tool kit which includes screwdrivers, spanners, circlip pliers a length of tubing and a clean container.

-Plenty of patients and time (you NEED to get this right, it's your life on the line).

-To aid part identification, see this half calliper diagram

To Dismantle The Calliper

1. Remove the brake line guide on the forks.

2. Remove the two bolts which attach the calliper to the fork. Be careful not to let the calliper hang from the line as this may put to much strain on the line.

3. Repeat this on the other fork.

4. Remove the two screws from the plate at the rear of the calliper and withdraw the from the calliper.

5. Remove the "R" pin that retains the brake pad bar in the calliper. Carefully remove the pads and place them somewhere clean.

6. Remove the four piston insulators (plastic bits) from the pistons.

7. Slowly pump the brake lever to push out the pistons from the calliper. It is important to get all four pistons to come out of their bores at the same time, this is done by holding the ones that are furthest out whilst the other catch up. I find that using a piece of wood or several pieces of something like hard board put in place of the pads helps me to get this as near to being right as possible.

8. When all pistons are as far out as you can get them without actually being out, remove your packing from between them and pump the brake lever to free one of them. At this point you will lose pressure at the brake lever, you will also start to leak fluid from the piston bore from which the piston came, CLEAN IT UP.

9. Remove the banjo bolt that connects the brake line to the calliper, again at this point you will lose brake fluid so BE CAREFUL, place the end of the brake line into a container to avoid the fluid coming out all over your shiny paintwork.

10. When you have removed the brake line from the calliper and secured the end in a container, tip the calliper up at various angles to empty most of the brake fluid out.

11. Now remove the four allen bolts which connect both halves of the calliper together.

12. Separate the two halves of the calliper and remove the two seals from the oil ports - although these will probably fall out as you separate the calliper.

13. Take one half of the calliper and remove the pistons, inevitably one or both of them will not come out by hand. To remove the pistons if/when this occurs is quite simple if there is a handy second person about. To remove them you will need a foot pump and a cable tie. Place the foot pump on one of the oil ports, on the other one place your finger or thumb, get you friend to depress the foot pump whilst you excerpt pressure on the oil passage and the foot pump, quite considerable force is needed to prevent air escaping. When one of the pistons comes out, put it back in, but not too far, then tie a cable tie around the calliper and piston and repeat the operation until the second piston comes out. If the half of the calliper you are doing also has the port where the brake line fits, you will obviously need to apply another finger or thumb to seal it.

14. Using a suitable tool - I usually use an instrument screwdriver - begin to remove the dust and oil seals from the calliper ports. Do not try to re-use these seals, it is false economy and you will end up going through this procedure again.

15. When all the seals have been removed, carefully clean all the dirt and corrosion from the insides of the piston ports. Pay particular attention to where the seals fit, try and get right into the corners, but be very careful not to damage the piston bore.

To Rebuild The Calliper

16. Once you have done this to both callipers, it is time to start re-building them. Take a deep breath and buy some new seals, not cheap when you are replacing all of them, but what price do you put on your own life? Ensure that the internal bores of the calliper are clean, I usually rinse them out with some old (but unused) brake fluid.

17. Before you fit the seals, cover them in brake fluid, this applies to both the oil seal and the dust seal. Then, very carefully, seat them in their respective recesses within the bores.

18. When all four seals are in place, cover the outer walls and base of the piston in brake fluid. Carefully push the pistons into their bores, make sure they go in square and not at an angle.

19. Repeat this for the other half of the piston.

20. With one half of the calliper on a firm surface, place the two small round seals in the oil ports, then carefully address the remaining half of the calliper and mate the two together.

21. Using finger pressure only, fit the four allen bolts into the calliper body. Then carefully tighten them to the "recommended torque".

22. As the bleed nipples are renowned for causing problems, this is an ideal opportunity to fit new ones.

23. Re-fit the insulators.

24. Taking care not to contaminate the pad friction pads, apply some high temperature grease to the back of the pads.

25. Grease the pad retaining bar with calliper grease and re-fit the pads into the calliper, making sure that when you re-fit the "R" pin that the "closed" end is facing forwards.

26. Re-fit the calliper body to the fork leg and torque the two bolts to the required torque.

27. Using two new copper washers, re-attach the brake line with the banjo bolt, one washer fits each side of the brake line fitting.

28. Repeat the above for the other calliper.

29. Remove the two retaining screws from the master cylinder and carefully remove the lid, remove the inner dust seal, this may or may not come away with the lid, if not take it out. At the risk of boring you to tears, watch out for splashes or drips of fluid, see em', wipe em' up.

30 Attach your length of tubing to the bleed nipple, the other end should be in your "clean" container. For a container, I find that one of those 2 litre plastic milk bottles with a hole in the lid is great.

31. Pour some fluid into the master cylinder reservoir, about two thirds should be OK. Then, start pulling that lever, I find it rewarding in the early stages to pull the lever in just a small amount (about a quarter), this way the air will escape into the cylinder and you get to see the bubbles.

32. After a while, you will see fluid start to climb the tube. Close the bleed nipple.

33. Make sure that you have sufficient fluid in the reservoir, then pump the lever until you feel some pressure. When this pressure is felt, hold the lever in, undo the bleed nipple so that the pressure is released then quickly tighten it again.

34. Repeat number 32 until all the air has been pumped out of the system, as I said earlier, this WILL take hours so don't promise your beloved to take her out.

I have heard different methods that people use to lessen the need for this, but by far the most widely used would be to fill the reservoir with brake fluid, then tie the brake lever to the bar and leave it overnight. This may or may not work, I have never tried it, but lots of people swear by it.

35. Ensure that the fluid level is OK, then re-fit the dust cover and top to the master cylinder

36. Before you go and test the bike on the road, try the brakes out on your drive/path/garden. Just to make sure nothing is going to drop off. When you eventually take it out on the road, be careful, you could have missed something or contaminated the pads, so GO EASY.