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7-1
BRAKE SYSTEM
OVERVIEW
BRAKE CALIPER OVERVIEW
Overview ........................................................... page 7-1
Caliper assembly ................................................ page 7-3
Brake pads - removal & installation .................... page 7-4
Removing brake caliper assembly ....................... page 7-5
Master cylinder overview ................................... page 7-9
Master cylinder removal ................................... page 7-10
Brake pedal ...................................................... page 7-13
Brake fluid level inspection .............................. page 7-14
Brake fluid change............................................ page 7-14
Bench bleeding master cylinder........................ page 7-15
Bleeding the brake system ................................ page 7-17
Brake troubleshooting....................................... page 7-18
Drum brake system overview ........................... page 7-19
Drum brake parts identification ........................ page 7-20
Changing brake shoes....................................... page 7-21
Drum brake adjustments................................... page 7-27
The disc brake system used on J&J go-karts is a simple, one-circuit design using an oversized master cylinder (for extra
reservoir capacity). Brake lines are covered with a braided, stainless steel outer covering for additional strength and
durability; these special lines are made at J&J for this application. It is not recommended to substitute other types of
brake lines on J&J go-karts.
The caliper assemblies are a dual-piston (one piston per side, applying equal pressure to brake pads), very simple
system with only two moving parts (the pistons).
Brake Pads: two pads (one on each side) are pushed against the disc via hydraulic pressure behind the caliper pistons.
The material is organic and chosen for the speeds and rigors of concession go-kart use.
Brake Disc: a simple, 1/4” steel disc with two holes provide access to the caliper mounting bolts.
The J&J/FPX brake caliper is a dual-piston design. The pistons travel in the machined bore of each caliper half. A
simple, square-edge seal retains the fluid and suspends the machined piston in the caliper bore. As the diagram shows,
fluid pressure on the piston forces the brake pads against the disc during braking operation. The seal provides a small
amount of rebound when the pressure is released, thus, the brake pads are allowed clearance to prevent dragging on
the brake disc when the brakes are released.
CALIPER REBUILD
With the brake pads removed, slide a piece of 1/4” plywood (cut to the width of the brake pads) between the two
pistons. Use a rubber-tipped air nozzle to gently blow air into the brake fluid fitting of the caliper. This will cause the
pistons to pop out against the plywood surface. Unbolt the two Allen-head cap screws and separate the two halves. Be
aware that between the two halves is an o-ring seal. This o-ring is to seal the fluid passage between the two halves. If
the o-ring is missing and/or damaged, the brake caliper will leak fluid out between the two halves. Remove the caliper
pistons. The piston bores may be pitted or rough; this is not usually a problem unless the seal groove is damaged.
When replacing the piston seal, carefully install the seal into the groove of the caliper bore. Make sure the seal is not
twisted and fits nicely into the groove. Use a brake assembly lube (such as Wilwood 290-11087) on the piston and seal
surface to make the procedure of piston installation easy. Screw the two caliper halves (with o-ring seal) together and
torque the Allen-head cap screws to 29 ft.lbs.
NOTE: The piston is finely machined steel, and any rust spot or other damage to the seal surface means the part must
be replaced. The piston can be cleaned using a “Scotch Bright”-type material. Use “Brake Clean” to clean all parts;
avoid using water-based or oil-based cleaners.
Piston travel
Piston
Seal groove
Caliper half
Caliper bore
Piston seal
O-ring seal