A lot of users of vehicles were thinking, for sure not only once, about the level of difficulty of braking blocks replacement. Not only single person stated that it is simple, not complicated action and does not require special tools. Few skilled moves and our vehicle can be equipped with new set of braking blocks. Is it for sure? Do these actions influence on our safety? In fact, looking from observer’s perspective, braking blocks replacement may seem to be prosaic. However, if we look closer, these actions bear huge responsibility for our and passengers safety.
Together with the responsibility, the knowledge on the latest braking systems operations must be taken into account. Presently, in passenger vehicles two braking systems are recognized: disc and drum. Front axis is the most often equipped with drum system, and rear one depending on the vehicle weight and engine power, disc or drum. In this paper we will focus on disc systems. Every disc brake consists of the following elements:
These three basic elements decides on the vehicle stop. Obviously, to provide proper functioning, braking fluid must be provided from hydraulic pump trough flexible and fixed braking cables for every caliper.
Operation of disc brake is as follows. At the moment of pressing the brake pedal, braking fluid pressure is generated and is directed to braking caliper. Braking fluid causes relocation of a caliper small piston towards a block causing the contact with braking disc. As in vehicles floating calipers are used most often (with one small piston on one side of a disc and slidingly mounted body of a caliper) the force that makes small piston move influences on the caliper body causing its moving in opposite direction to advancing small piston. Moving caliper body, on opposite side of a small piston is equipped with characteristic “guides" pressing second braking block to the disc. Such operations of the clamp counteracts to creating forces and moments bending braking disc.
In some vehicles, with sport nature most often, fixe clamps are used, where it is tightened to the element of a vehicle suspension. The clamps are equipped with at least one pair of small pistons located on both sides of braking disc. The operation of this clamp is a bit different as while pressing the brake pedal, both small pistons shall press down blocks to braking disc. In this case, the clamp body does not move because it is inflexibly connected with a vehicle suspension. Undoubtly, the advantage of this system is increase in the braking efficiency trough rise of the force pressing a block to a disc, and intensifying the efficiency of braking system. The system is not free from defects. The most important defect is the difference in forces of a friction of clamp small pistons, and it causes uneven pressing down of blocks to braking disc and, as an effect, it create forces and moments that bends the disc.
Having the knowledge about the construction, type and operations, we can describe proper method of braking blocks replacement considering nuances of its construction. When are vehicle is protected we start to disassembly the wheel. After its disassembly we make preliminary inspection of braking system condition. We verify the condition of braking disc, assessing its working surface as far as corrugation and unevenness is considered, we verify if any disc cracks on working area and mounting area are present. Afterwards, we verify braking clamp paying attention to all leaks of braking fluid.
After preliminary inspections, we disassembly braking clamp (in floating clamp version), unscrewing screws mounting the body to yoke. In some structures, screws are guides of clamp body at the same time. After the clamp disassembly, removing braking blocks and verifying it under the cladding thickness and its condition is possible.
It can be assumed that at this moment mounting new blocks is sufficient, tighten clamp and it is done, but nothing more incorrect. When blocks are dismounted, cleaning the surface after the cooperation of blocks and clamp yoke is necessary. The surface are contaminated because of, not only the dust after braking, but also these are contamination arising out of a roadway. The surfaces can be cleaned with a wire brush, and surfaces of adhering of a block to the shackle shall be leveled with a file. It shall allow to free movement of a block without its wedging. In some types of braking systems, the surface of a cooperation of blocks and shackle are lined with special elements made of stainless sheet. These elements shall be cleaned thoroughly and from fixture places in a shackle corrosion shall be removed.
Guides of clamp body removed shall be previously cleaned, not forgetting about clearing mounting openings in a clamp body. Avoiding this place can be a reason of a clamp blocking and a Wheel warming up, and as an effect it leads to bearing, clamp seals damage and excessive wear of blocks. The guides shall be greased with special agent for clamps.
When all cooperating surfaces are cleaned, we start to work with a clamp. Prior to pressing a small piston to a clamp body, it is necessary to apply small amount of grease into clamps under a anti-dust cover of a small piston. It will decrease a friction and protect anti-corrosion protection of the surfaces.
Afterwards, we force a small piston into a body with special tool. After this action, the level of braking fluid in an equalizing tank under hydraulic pump shall be verified. If the level is too high, excessive amount of fluid shall be transferred to a tank with old fluid with a syringe.
Prior to the assembly of new braking blocks, clearing external surface of braking disc radiator is welcomed. On the surface, dirt and first of all corrosion products accumulates. These products and dirt can be a reason of loud operation of braking system, and it decreases the comfort of a vehicle use. The cleaning is carries out with sharpened and hard tool, pressing its finishing to the surface of disc radiator and blocking its movement, by supporting it on a clamp shackle. Afterwards, we clean the surface by manual rotation of a disc.
When all elements are cleaned, we can start to final assembly of new braking blocks. The assembly works shall be started from placing blocks in a shackle. Afterwards, we apply a braking clamp and tighten it to the shackle. On threaded surface of a screw mounting a clamp to the shackle (if it is not an equipment of blocks set) we apply firstly a glue to screw connections. When all blocks are replaced, we cannot forget about verifying the braking pedal position. Thus, we get in the vehicle and press braking pedal few times to eliminate clearance in braking clamps.
The replacement of braking blocks in fixed clamps seems slightly different. Referring to movable clamp shortage, disassembly of braking blocks is carried out by dismounting blocks guides. When guides are removed, blocks can be dismounted, it is removed perpendicularly to the wheel axis. All activities connected with cleaning braking system are analogical and rigorously necessary. When clamps and discs are cleaned, it is possible to assembly new braking blocks. When we consider this version of a clamp, replacement of a set of blocks and mounting elements is necessary. It is available irrespective of blocks set.
We have just come to an end of seemingly simple action. We remember that despite simplicity of works, the replacement of braking blocks bear huge responsibility for the safety of our clients. We shall make efforts to do the replacement observing all rules of vehicle repairs principles.