RACING CAR BRAKES (WITH CAST IRON DISCS)
The capacity of the reservoir must be such that when the brake fluid is between the MIN and MAX levels the volume is at least equal to the one required by the brake pistons stroke in case of maximum pad and rotor wears.
Mounting of the reservoir
a. Use the pipe fittings and the washers (in copper or in rubber) suggested by the supplier of the reservoir.
b. In order to avoid any vacuum inside the reservoir, as a consequence of the brake fluid level lowering, it is always necessary to have a hole diam. 1 mm in the reservoir cap, independently from the presence of the bellows diaphragm in the reservoir.
Choice of the master cylinder
a. The master cylinder diameter must be chosen in function of the type of calipers which have to be fed, of the brake pedal ratio and of the max pressure we want to obtain: every variation of the master cylinder diameter involves an increase or a decrease of the master cylinder area of about 15%.
b. The rubber boot, between the push rod and the hydraulic part, must always be assembled.
BRAKE PEDAL MECHANISM (SYSTEM CONTROLLED BY 2 MASTER CYLINDERS)
a. The brake pedal mechanism must be designed and manufactured in order to allow a complete stroke of both master cylinders. In case of systems where the strokes of the two master cylinders are very different from each other, it is necessary that the rod connecting the two push rods is at the appropriate angle.
b. For a more linear functioning of the brake pedal/master-cylinder mechanism, it is important that the distance between the pedal fulcrum and the push rods is equal or greater than 40 mm (see Fig. 1a).
c. Furthermore, it is also important that in the rest position, the rod axle is placed back of 10 – 12mm compared to the fulcrum axle.
d. Check that in the rest position the rod connecting the two push rods is perpendicular to both push rods.
e. Check that between the joints of the rod connecting the two push rods and the pedal there is a clearance of at least 1 mm each side, in order to allow the eventual inclination of the rod compared to the push rods axle (see Fig. 1b).
a. The caliper fixing to the upright can be carried out with bolts or with gauged stud bolts and nut; this system allows a more rigid fixing and it is recommended for all the applications on calipers with the radial fixing.
b. Mount the caliper onto the knuckle such that the arrow marked on the inner half-caliper corresponds to the forward direction of rotation of the brake disc (the disc must enter the caliper through the side corresponding to the smaller piston and exit through the other side corresponding to the larger piston).
c. The caliper must be mounted in a symmetrical position with respect to the disc centre line: the difference between dimensions “a” and “b” must be 0,6 mm MAX (see fig. 2).
a≠b: 0,6 mm MAX
d. The disc and pads protrusion must be 0,3 mm MAX (see Fig. 3 and Fig. 4).
e. Check that in no working condition, pads touch the disc fixing bell or the upright.
f. Assembly and disassembly of the pads must occur without any force; the pads radial and lateral clearance inside the caliper must be 0,2 mm MIN; with the pistons in backward position, the clearance between them and the back plate must be 0,5 mm MIN (see Fig. 5).
g. The clearance between disc outer circumference and caliper bridge must be 2 mm MIN, with a difference between the two sides of 0.4 mm MAX (see Fig. 6).
h. The M 10×1 bleed screws tightening must be carried out with a torque of 12 – 16 Nm. Apply thermal tape on the external half-caliper in order to monitor operating temperature. These can be supplied by BREMBO under part number R 02.5168.10/25.
Choice of tubing
a. Where it is possible, we recommend the use of steel rigid pipes, since they do not increase brake fluid displacement.
b. In case flexible brake hoses are used, it is necessary to use the Teflon type with braided steel sheath.
c. The hoses internal diameter must be 2.5 or 3 mm; the brake fluid displacement of 1 meter of these hoses is 0.2 cm MAX (for the type having internal diameter 2.5 mm), and 0.3 cm MAX (for the type having internal diameter 3 mm) at the pressure of 70 bar; hoses with a smaller diameter restrict fluid flow, while hoses with a bigger diameter would considerably increase the brake fluid displacement of the system.
a. Pipe fittings must be tightened to the prescribed torque.
b. The pipe fittings seal must be sealed with annealed aluminium or copper seals; these seals can be used only once.
c. Check that tubes are not squashed or pinched and that they are not subjected to high temperatures (close to the engine, exhaust pipes, etc.)
a. Use only high boiling point DOT 3 or DOT 4 brake fluids.
b. Use only brake fluid from a new and sealed container.
c. Change brake fluid before each race.
a. Use of liquids other than brake fluids will damage the brake system components.
b. Since the brake fluid is hygroscopic, we have to consider that in presence of high humidity, the boiling point can be considerably lowered; in these cases the brake fluid has to be replaced daily.
BRAKING SYSTEM BLEEDING
a. In the case of a braking system controlled by two parallel master cylinders operated by a rod, bleed one front and one rear caliper, in order to allow both master cylinders a complete stroke.
b. Every time the pedal is back, let master cylinder refill simultaneously for at least 2 seconds before pushing the pedal.
c. When the bleeding is finished, keep in pressure for at least 10 seconds, checking that there aren’t any leakages.
d. Refill the reservoirs.
After running a few kilometres, proceed with the following inspections:
a. Wheels must rotate freely without any residual torque.
b. There must be no contact between disc and caliper.
c. No pulsations must be felt on the pedal, otherwise identify which disc causes the problem and check again the disc/bell and bell/hub assemblies.
For the discs and pads burnishing, it is necessary to follow the running-in procedure related to the friction material used; it is however necessary to ensure that during the first kilometres, low pressure applications are carried out for short times in order to allow the bedding of all the pad surface on the disc. Only later you will be able to proceed to the real running in which will end when every pad has reached the best working condition. The running in procedure (bedding of the disc/pads coupling surfaces) must also be carried out when already run-in or used pads are used. Only after the running in is performed, it is possible to take full advantage of the braking system braking capacity.
BRAKING SYSTEM FINAL INSPECTIONS
a. There must not be any interference between disc and caliper.
b. The max temperature reached by the calipers must be lower than 180°C (inspection to be carried out through the thermo tapes applied on the calipers).
c. Check the working temperature of the discs, verifying the changes occurred to the thermal paints applied on the external diameter of the discs.
If the braking system performance is not considered satisfactory, it is necessary to reduce the discs ventilation. Furthermore a rapid quick cooling could increase the risk of cracks on the discs. If discs reach high temperature, it is necessary to improve the cooling. A high working temperature of the discs causes a decay of the braking power and excessively high temperatures in the brake calipers.
BRAKING SYSTEM BALANCING
The braking system has to be chosen in function of the vehicle characteristics; it is very important that the max braking power is equally distributed between the front and the rear axles; when the braking system is correctly balanced, the working temperatures of the front and rear brakes must be similar. It is possible to adjust brake balance between the front and rear axles through the adjustment rod, but only for variations up to 10% MAX: in fact the pedal force must be always applied in the vicinity of the centre of the adjusting rod in order to obtain a good efficiency of the brake pedal mechanism. If the system isn’t balanced even after adjusting, causes must be searched somewhere else: master cylinders diameter, caliper type, disc diameter etc. In any case, before replacing any components, it is necessary to make sure that the combination of components works correctly. A good general rule to obtain a good efficiency is however to have as similar as possible the master cylinders loads and strokes.
INSPECTION OF THE BRAKING SYSTEM AFTER USE
After every race, it is necessary to proceed with the following inspections and interventions:
Verify that there are no leakages from the various components, connections, or fittings. If a leak is found on one of the fittings, either increase the tightening torque, or replace the defective component.
Check carefully the disc braking surfaces. The disc can’t be used again if:
– on the braking surfaces there are cracks having length higher than 5 mm; in case the crack begins from the external or internal diameter, even if the length is shorter, the disc must be replaced (see Fig. 8).
– It has a wear of 1 mm compared to the new thickness (0,5 mm on both sides);
– The braking surfaces show scorings, which can damage the correct pad/disc contact.
a. Check that the external half calipers connecting pipes are not bent or dented, caused i.e. by the entrance of stones between the wheel and the caliper; in case of damage, overhaul the caliper.
b. Check the max temperatures reached by the caliper, checking the thermo tapes applied on the internal half caliper:
c. if a temperature of 180°C is reached, we recommend the overhauling of the caliper or to replace the seals;
d. If a temperature of 210°C is reached (max value of temperature the caliper can stand for short periods), it is absolutely necessary to overhaul immediately the caliper and search the causes of the overheating, since under these conditions the correct operation of the brake isn’t guaranteed anymore.
Pads wear inspection
Pads should not have a friction material thickness lower than 2 mm MIN; if the pads are excessively worn, they must be changed.
Pads must not show excessively anomalous or uneven wears; the following must be checked:
a. Pad tangential taper wear difference must not exceed 1 mm MAX, bearing in mind that the direction of wears of the same caliper must be according to what shown on the Fig.9.
b. Pad radial taper wear difference must not exceed 1 mm MAX, bearing in mind that the direction of wears of the same caliper must be according to what shown on the Fig.10.
Defective or excessively worn pads must be changed.
Back plate deformation
Back plate flatness error must not exceed 0.2 mm MAX (see Fig. 11); – in case of excessive back plate flatness error, the pads must be changed
Overhauling and replacement
– Master Cylinder
These must be overhauled after 5000 km MAX of running, or when problems arise;
They must be overhauled after 5000 km max of running, or when problems arise, or if the temperatures go above those shown through the thermo tapes applied on the calipers.
a. The external cleaning of the master cylinder and calipers must be carried out with noncorrosive agents and anyway not with solvents, gasoline or similar, since these products could damage rubber components (seals and dust boots).
b. During warehousing protect the inlet and outlet holes of the master cylinder and of the calipers with the appropriate caps.
c. Half-caliper union bolts cannot be re-screwed, or carry out modifications to the calipers.
d. Replacement of components with non-BREMBO parts is not permitted.
e. BREMBO recommends the overhauling of its products through its own authorized personnel; therefore BREMBO doesn’t take the responsibility for overhauling carried out by someone else.