OTK Tony Kart BSD brake caliper rebuild and brake bleed

Tools required:
- 14mm spanner
- 13mm spanner
- 8mm spanner
- 4mm allen key
- 2mm allen key
- Pick, knife or and other object you're comfortable using to remove the seals.
- Gloves
- fuel line
1. Using the 13mm spanner, remove the two bolts holding the caliper to the bearing hanger and pull the caliper clear of the rotor.
2. Pump the brake pedal untill the pistons are pushed clear of the caliper, use a rag to soak excess brake fluid.
3. Use the 14mm spanner to remove both brake lines from the caliper.
4. Use the sharp object to remove the seals, be careful not to scratch or damage the inside of the caliper where the piston will sit. This could cause leaks and a loss of pedal pressure on the track.
5. Install the new seals by hand, they will snap in place easily and check they are seated fully.
6. Pour some of your chosen brake fluid into the bottle cap, with gloves hands wipe the piston and seal in a good amount of brake fluid.
7. Press the piston into the caliper untill it's fully seated. repeat for the other side. The second side was tricky so I wrapped a rag around a snapper, fed it through the caliper and used it to press the piston into the caliper with more force.
8. Seat your pads into the caliper.
9. Place the retaining pin through one side of the caliper and pad, slide the safety bush on the pin so stop the pin falling out.
10. Use the 4mm allen key/bit to fix the pin all the way through the caliper. Don't tighten it all the way up, make sure there is a bit of play either side to allow for thermal expansion. The 2mm bit is now used to tighten the grub screw on the safety bush.
11. Reverse if step 1 and 3 to mount the caliper back onto the kart.
BRAKE BLEED
12. Trace the brake line of the side you're starting on back to the master cylinder, open the lid and top with fluid.
13. On your starting side of the caliper place the 8mm spanner on the bleed nipple then place the fuel line over it.
14. Press the brake down, hold then open the bleed nipple. Air bubbles and some fluid should come out. Close the bleed nipple again and release the brake pedal.
15. Continue doing step 14 untill the fluid is clean, bubble free and don't forget to top up the master cylinder as you go.
16. Once both sides are bled and the pedal feels good, half fill the master cylinders and replace the caps.
17. Give the area a wipe down with degreaser or brake cleaner as you don't want any brake fluid sitting on your paint.
Now you're all done and ready to hit the track for a pad break in or just cut some quick times if your pads are already run in.

[@bo_bb1442]

Can I ask why the outside line has to loop around and become the inside line on the master cylinder?

[@danbloxham6133]

It won't be any specific reason just how it's worked out with the positions of the different fittings on the master and caliper.

[@Dustinboost]

Do the pistons need to be replaced for a regular rebuild if there are no problems with them or just seals?

[@danbloxham6133]

Hi Dustin just the seals mate, always check for any corrosion though and replace parts if necessary.

[@Dustinboost]

@@danbloxham6133 thanks!

[@kartaroundtheworld]

The OTK diagram shows a circlip that goes together with the seals. I didn't see this circlip in your video. Any idea what about this circlip is for ?

[@danbloxham6133]

Unsure sorry, definitely never come across circlips holding brake piston seals before.

[@kartaroundtheworld]

@@danbloxham6133 thanks anyway !

[@User85306]

The newer selfadjusting OTK Brakes have circlips (sealfadusting > pedal stroke/travel stays the same as the brake pads get worn down)
Their task is to "squeeze" the sealing ring as the piston gets pushed out, so the sealing ring holds the piston when the break-pedal is released
With those its really important that you put them in position in front of the sealing ring (they often slip back when you take out the sealing ring). Otherwise you will not be able to bleed the system propperly (respectively adjust the brake travel properly) as the piston will then always slip back, when you release the pedal.

[@kartaroundtheworld]

Thank you so much. Very helpful

[@kartaroundtheworld]

@@User85306 sorry but it is not 100% clear to me. When you say "in front" , does that mean that this circlip needs to stay in the groove closer to the brake pads, and not hitting the end of the calipers (close to the wheels of the kart), right ?