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brake system



brake pads

basics of brake modification

Powerful car must have adequate brakes, so upgrading the brakes is a must for a car with an extra muscle. There are two main objectives when upgrading brakes; increase of friction and reduce of high temperature fade.

Fading is caused by overheating of the brake pads. Fading is dangerous because it can lead to boiling of the brake fluid. When the brake fluid has been boiling, air bubbles are created in the brake lines. Next time you press the brake pedal you are compressing air bubbles instead of moving brake fluid so you don't have any brakes. Fading can be reduced by improving the cooling on the brake components. The first thing to do is feed cold air to the discs and pads, but prevent rain from going the same route. Another way of cooling the brakes is use of ventilated discs. A ventilated disc is essentially 2 discs put closely together but with enough room between them for air to flow through. In order for ventilated discs to work at their best a cold air feed is required. Additional procedures can be taken to emprove brake action even more; drilling and slotting.

drilled rotors

Cross drilling involves drilling rows of holes through the friction surfaces of the rotor. There are two main reasons for such an action, more efective cooling and higher surface friction. The cooler your rotors are the better your stopping distances are. The holes in the rotor are drilled in a pattern that enhances the air flow at the same time not affecting the structural integrity of the rotor. The holes are also commonly labelled "cooling holes" because of the improvements they make in this area.

When the friction surfaces of a rotor are smooth and flat, there is no means of escape for the gasses and dust which build up between pad and rotor. This is not a huge problem in normal driving conditions, but is an important consideration in high-performance applications. These contaminants tend to "wedge up" and reduce braking performance. The bigger the pads and the higher the braking temperatures, the more likely the problem. The drill holes - which are sometimes called "gas relief openings" - provide an exit route for the dust and gas. Better cooling means less fade during repeated heavy brake applications.

Lastly, the holes help dissipate water when driving in poor weather.

There's another thing worth noting: after the rotors have been put into service, a close inspection may reveal tiny surface cracks around the holes. Some people might feel that this indicates a problem, or even necessitates rotor replacement. It's not the case - small surface fractures are common with cross-drilled rotors due to the increased localised stresses. Large cracks, of the type which cause pedal pulsation, are a different matter. These are usually the result of abuse or poor maintenance and are no more likely to appear in cross-drilled and slotted rotors than in normal discs.

slotted rotors

Slotting involves milling a series of shallow grooves from the centre of the disc to the edge. This treatment should increase the bite of the pads to stop the car more quickly. The process doesn't involve removing as much metal as cross-drilling, so it doesn't result in as great a weight saving. However, slotting is even more effective than cross-drilling in combating the problem known as "out-gassing". This happens at very high braking temperatures, when bonding agents used in allmost all serial brake pads produce a gaseous products. Under extreme conditions, this gas can create a pneumatic cushion between pad and rotor, giving a driver a normal pedal feel but reducing the amount of friction being generated. The slots let away this gas and restore full contact. Slotted discs also tends to even out the wear across the brake pad surface and clean of the brake dust.

But remember that slotted disc have a smaller affective surface for braking then ordinary discs. Direction of grooves is not relevant for their action.

The drilled rotors develop stress cracks if heated quickly. Instead, slotted-only rotors are not so prone to this effect. It is claimed that there is no performance loss due to the missing holes, which are basically a cosmetic addition, with the slots providing virtually all the benefit over standard rotors.

Drilled and/or slotted rotors will deliver better braking performance than conventional discs, but the difference could not be termed as dramatic, since main advantages are notable only in extreme contitions. They offer what could be termed a "small but significant improvement".

There's no intrinsic reason.

brake pads

Compared to a conventional racing pad with a coefficient of friction of 0.31, the TMS Racing coefficient is 0.458. This higher coefficient of friction gives the driver a lower pedal effort and more braking torque (i.e. shorter stopping distance). An added feature of the TMS Racing compound is that while the coefficient of friction is high, excessive rotor wear is not a problem because the coefficient of friction remains stable across the temperature range of the pad. With some carbon compounds, the coefficient of friction goes up with temperature, thereby causing excessive rotor wear. The ceramic insulator is molded into the compound during production and is placed between the backing plate and friction material.

Coefficient of friction 0.458

Fading can also be reduced by fitting brake pads or shoes with a harder material. A disadvantage of using harder material is that the brakes need some heat in them to work properly. This means that after a driving a long distance without using the brakes, the first time the brakes are pressed, they are not very effective.

Terry also suggested I also try the Carbon fibre brake pads also as they would enhance the drilled rotors.

actual GS modifications

Serial GS brake system is a good platform to begin with , it-s equipped with four disk brakes regardless of a model.

Ventilated discs can be found on the Citroen Axel. These discs and calipers will fit straight onto all Ami Super/GS(A) gearboxes. The Axel brakes use common red DOT brake fluid, so adaptation to green hydraulic LHM must be done. Fortunatelly this can be done easilly; Axel's calipers need to be rebuild with GSA rubber seals.