 Disc Brake
kfz-tech.de/PDB22
Of course, the basic advantages of disc brakes should first be mentioned. Compared to the drum brake, it has a larger area exposed to the surrounding air, so it can release its heat better. It has almost no self-
reinforcement, so it is less prone to pulling crooked. Compared to the rather massive drums on trucks, the disc brake is even lighter.
With commercial vehicles, time in the workshop is twice as expensive because the loss of use is added to the cost of repairs. Any reduction in maintenance work is therefore a blessing for the forwarding company. The disc
brake saves a lot of money here.
For example, changing the pads is significantly shorter than with drum brakes, and there is no need for extensive rework, such as machining the pads on the mounted brake shoes and possibly unscrewing the drums. The
working hours for pad and disc changes have been reduced even further in recent years. For example, it would be advantageous to have a positive connection between the hub and the disc, as can be seen in the picture
below.
kfz-tech.de/PDB23
But there is also another reason for this type of connection. A brake disc with an attached pot (pictured at the top) warps much more unfavorably when heated than one that is separated from it. Less heat is also transferred
here. Basically, truck brake discs are at least internally ventilated.
This is how the skills add up. In addition to better dosability and less fading there is less weight. The attached diaphragm cylinder together with the mechanical transmission of power always looks a bit bombastic, but
depending on the design, different directions of expansion are possible. And to make maintenance easier, there is a longer difference in the service life of the pad and disc compared to the drum brake in trucks than in cars.
The more axles are equipped with disc brakes, the more these advantages come to the foreground. Below you can see a disc brake with a spring accumulator, as can be easily seen from the long screw for mechanically
releasing the brake. It also becomes even clearer here that all disc brakes on trucks work on the principle of floating calipers. A second membrane cylinder between the rim and disc or with a corresponding deflection
mechanism would also be difficult to imagine.
| Replacing the brake discs |
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First remove the membrane cylinder. Then the retaining clips for the brake pads and the brake caliper carrier. Either you loosen all the inner screws and then lift off the wheel mount and brake disc with two people, or you
screw in two bolts instead of two opposite screws, which you can use to do this on your own without causing damage.
With driven rear axles, one meets the full-floating axle. Special requirements must be observed here, otherwise the repair will take significantly longer. Instead of a series of screws, a central nut is possible on BPW axles, for
example.
kfz-tech.de/PDB25
Then, or better already yet, knock out the wheel bolts beforehand. Damage doesn't matter because new ones are used anyway. Of course, cleanliness must be ensured before installing the new brake disc. The two
remaining stud bolts make it easier to re-introduce the wheel mount with brake disc.
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The inner pads and saddle are not moved directly, but rather via a lever system. The covering is moved from behind in two places using special partially integrated pressure pieces (picture below). This is done by two
punches with an automatic adjustment device which are connected to each other by a chain and a so-called bridge with the lever coming from the membrane cylinder. Mechanical reinforcement is also possible here.
Unlike in cars, the brake caliper usually accesses the disc from above. Although there is a wear indicator embedded in the brake pads, instead of a simple warning when a certain degree of wear is reached, a continuous
display using a potentiometer is also possible.
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| Here is another disc brake with external planets that is more difficult to install . . . |
kfz-tech.de/PDB28
| Ceramic brakes instead of the usual cast iron brakes are also possible on trucks . . . |
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It's unbelievable what temperatures the normal brake disc can withstand. There are pad manufacturers who guarantee (limited) functionality even at disc temperatures of more than 1000°C. It is also amazing that cracks in
truck brake discs that are not continuous up to a certain extent do not have to be repaired by replacing the discs.
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