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The brake setting up can be decomposed in 3 main blocks, based on the placement of the blocks in the kart. The first element is composed by pedal and by small bar or cable connected to it, which pulls another bar which operates the pump. The second element is composed by the pump, located close to the tank. The third element is composed by all back parts: supports, diskbrakes, pads and small pistons. The functioning is quite easy. When
the pedal is pressed, a small rigid bar (linked to the pedal) is
tightened, and this bar pushes another small bar put above the pump
(picture in the middle) until the end of the plastic coverage. With
this mechanism the oil is pushed inside the pipe going out the pump,
and then it is divided into 2 parts: one for each small piston.
In fact the oil, which has been compressed, pushes against a small
piston (not visible in the picture, but the outline can be glimpsed,
which is the cylindrical protuberance where the pipe arrives); then
the small piston pushes a pad (directly connected from the piston
side) against the brake’s disks. It happens for both pads.
The friction between pads and the disk causes a big deceleration
of the axle and as a consequence, a decrease of the angular speed;
the final result will be the kart slowing down.
Connected to the pedal, besides the small bar, there should be a security cable, which links the pedal to the pump. This allows the braking even if the bar had to break. The security cable is compulsory during races. The brake pump includes a block parallelepiped shaped, a front rubber coverage, a small bar put above (which is used to press and push the oil), and a back exit, where the oil flows. The pump has to be well fixed to the kart. Notice the screw darker than the others: it’s that one to be unscrewed and to eventually insert the oil when the old oil has to be eliminated or when, whatever the reason, fresh air enters in the brake setting up. It’s actually impossible the pump breaks down since its simplicity, but it could happen the joint (between the pump and the cable) become for example too slackened. The other important element is the back brake unit. We can see two big supports, well connected to the chassis. To these supports some pads are connected thanks to screws; these screws have the peculiarity of having a spring to recall the pads after a brake. Regarding pads, they are made of Carbon-Kevlar, material which should make pads thermally stable and fireproof; they are very hard (for example in comparison with the disk), but they can be consumed very fast: it implies the pads have to be often replaced; they are more consumed than the disk. In addition to this, the material used causes a friction bigger than the contact between iron and iron. It’s quite complex to explain, but you can immediately understand it if you see the brake unit. In these supports, the small pistons are inserted and they have the task of pushing the pads against the disk. The disk is detached from the unit just described and it turns together with the axle, strongly fixed to it thanks to a compass, in the same way the sprocket is connected. The best disk is the lightest one, since in this way it makes less heavy the kart during the acceleration phase and it has less inertia during brake. At the same time the best disk is also the disk thermally very stable and which can cool down very fast. These two aspects are partially in contrast one to the other and for this reason a good arrangement has to be found. An excellent solution is the self-ventilated disk (which is not the disk in the picture): instead of being a unique disk, it composed by 2 disks linked through some sleepers which leave a lot of space in the middle, so that a lot of air can flow and the disk can be very fast cooled down. There are also setting ups a bit
different than the one I described, but this one is the only I have
a direct and personal experience. For example there are setting
ups with only mobile pliers (and maybe the other is semi-mobile),
setting ups with different kinds of pumps, setting ups with 2 back
disks or, in 125 category, with 4 disks. Even if, considering everything
together, they are not so different than the setting up described
here. So it’s possible your brake setting up has 2 pumps.
The whole brake setting up has a cost which could vary between 200 and 450 euro, depending on materials used, on brand, on functions, etc…. Brake setting up is very often sold together with the chassis and that is why they are usually of the same brand; some firms don’t provide chassis and brake, so there are brands just focus exclusively on brake (like Brembo). Motorquality is another firm which produces only brake and in particular its business is producing supports. Let’s now analyze its several parts, which parts have to be repaired, replaced or thrown away; so we have to recognize those symptoms which indicate something is not working properly, and in this case you should see the “maintenance” section for the repairs actions. The pedal. The brake rod is actually indestructible, but it can be very easily twisted in case of crashes (accidents or heavy objects falls on it). The replacement is quite cheap since the part is mechanically simple. Sometimes this rod allows a slight regulation: if it’s pushed ahead, it pushes the pedal and it brings the pads near the disk (this thing is very useful when the race is quite long). Sometimes this regulation is quite easy, other times more difficult and it could even be not possible at all; or the setting up has a clearance auto-recover or you cannot regulate the distance in the described way. Anyhow this possibility is for small and slight regulations, for the most important and basic ones you have to act on the pads spacer (we will see them later). The pump. You have to act on the pump in order of clearing out the setting up when you need it, or better when the small pistons push the pads against the disk in a too weak way (with the consequence of having not enough power during brake) or when the setting up behaves in an irregular way. Supports for the back setting up part. I don’t believe they can have specific problems, you just have to check if they are well fixed to the chassis (screws well tightened) and well strong between them (in fact you probably noticed they are 2 supports fixed through 2 screws and not a single one, almost like the semicarters). The small pistons [number 4] are generally parts which do not require particular replacements and they don’t give you particular problems. The brake pads [2] are subjected to wearing, depending on how much they are used. They last a lot, and you can use them really until their end (with a very slight decrease in performance). In fact, on a total of 15 mm of thickness, 3-4 are useless, while all the rest can be exploited. And, another positive aspect, a couple or a series of pads costs about 20/25 euro (depending on the brand and on the model of the brake setting up). So, if you look at all costs you have to consider for your kart, the pad’s one is the least considerable. When the race starts to be “too long” you have to act setting the spacer between small pistons and pads, in such a way to get these last ones closer to the disk brake; we will see how to do that in the “maintenance” section. The cost of these spacer is very exiguous; in the market you can find spacer of 0,5 - 1 e 2 mm, and they have a shape very similar (almost the same) to the pad’s one. Other pieces: cables (or sheathes, [above the n.1]) where the oil flows, some screws of several dimensions [7, 6, 1], welding screws [8] and other. All these parts are very cheap, difficult to break, and very easily available. The disk brake. This is another long-lasting
part: if everything is normal, you never have to replace it. Its
replacement could happen based on your needs: some people consider
a small buckling or a scratch very relevant, while for most of the
karters, even if the disk is consumed, it can be still used. It’s
very important to keep it clean and without rust, since rust could
change the friction coefficient, at least until first brakes which
would clean it but which would ruin it. It’s absolutely necessary
its replacement when it breaks or when there’s a deep scratch
where there are screws which connect it to the axle. There are normal
disk brakes, auto-ventilated, holed, etc.. and the price is anyhow
quite expansive: almost more than 100 euro.
Considering that all brake setting ups are different one from the other, even if differencies are not so big, the following explanation comes from the experience I had from my kart brake system. 1) Recovering the right pads run
through spacers. Bought the necessary and suitable spacers for your pad (if you want you could try to build them by yourself, even if it’s advisable only in case you cannot find the right ones in the market), the operation is quite easy and fast: it could take not more than 30 minutes. On the other hand, it’s quite easy loosing calm and self control, in particular if the number of spacers you have to put between the pad and the small piston is quite big. Remember, during the operation, not to touch the brake pedal: in fact some air could enter in to the system and then you could be obliged to clear it out. So there are some allen screws [marked with n.1] with some springs which are used to allow the pad coming back. Keys to unscrew these screws are the only ones really indispensable; in addition to these ones, what is very necessary are the keys to slacken two supports [8], in order of having more space and so more comfort to insert the pads. Usually, there’s also a long small screw bolt, used as a security part and able to keep the pads in the right position (not visible in the picture since is put in the front part): you should also have keys to unscrew that one too. There are two methods to do this operation, depending on the spacers type you have to insert and on the brake setting up. The first method consists of unscrewing completely the 4 screws with the spring [1] (method I personally prefer), the second one is unscrewing the screws on the top part and just slackening the screws on the bottom part. The advantage of this method is in the reassembling phase, where you could take several minutes in trying to fix the pad to the first screw, not hitting the centre of the pad hole. The following action (which could also be executed in advance) is unscrewing the long security screw, being very careful (if you unscrewed all screws) the pads and the old spacers don’t fall down. Now you can remove the pads and reassemble them together with the spacers (if for example you have few) or leave the pads there and insert (pushing a bit) spacers between the pad and the small piston (which should be at its place, [4]). Once executing this operation on one pad, it’s better screwing both the screws, being very careful to hit the centre of the hole and not to strongly tighten completely one screw before and the other one later, but tightening a bit one screw and then the other one (alternating the action). On the other hand you could risk to ruin the filament of the pad. It could be a problem screwing it, if the springs push back: with one hand you should keep the pad still, in order of having both holes (where the screw is inserted) on the same line (the first hole is the chassis’s one) and with the other hand putting the screw, and pushing strongly with the allen key. If the problem is keeping everything stable and still, you could insert again the long screw in order of performing the operation (without screwing) and at the end remove it once again to act on the other pad. Now, you have to execute the operation for the other pad, and so you have to screw the security screw and fix again two supports, tightening the screw.
Once you’ve done all these things, you have to strongly screw all screws: you should easily understand when they are tightened enough; in fact they should do a slight “click” and become suddenly very hard: that is the point you have to stop tightening. Do not wait for a very clear and sharp “click”. A remark just to conclude: each person
has the right to set the distance between pads as he/she prefers,
but generally it’s better having a very short run to be able
to modulate (from the early beginning) the brake – in fact
with a long run you need to realize in advance when the pad hits
the disk and then you can concentrate on the brake itself. Also
remember to keep two pads in a distance from the disk not too much
off balance in one side (al least having both small pistons mobile);
on the other hand the kart would brake more in one side than in
the other, and you could have an anomalous disk wear and a lost
of brake power. Finally, it’s very important pads do not touch
the disk when you are braking: in addition of slowing down the kart
(in particular during accelerations), the disk would warm a lot,
causing a decrease in brake performance and, if the disk reaches
a very high temperature, you could even have a fire (it’s
unlikely but possible….). 2) Setting up clearing In addition to the tool we’ve just talked about, you will need an allen key to unscrew the screw put on the pump and even the one to unscrew the screws where the cables end in the back part [6]. So you have to unscrew the screw on the pump. In case you are using the second method, you should incline the kart of a quite high angle, in order of having the pump higher than the back brake system; in case of the other method you can leave the kart at its place. Now just insert the oil (special for brake setting up) in the small hole and push the brake. It would be better unscrewing, but not completely, the small allens where the girdles ends (they should be 2, the already mentioned [6]), so that the oil can exit together with the air. In addition to this, you always have to mind, when you fit in the oil keeping the brake pedal pushed, that there’s an abundant quantity of oil, so that the air cannot enter. The operation can be considered concluded when the oil will stop going down and during the brake it will just go out from the hole. Attention: the oil will incline to go out, but when there’s still space (air), after a minute it will go down, on the other hand it will never go down. Now, always keeping the kart inclined for security reasons (the oil could go out), close the pump screw and then the back ones you’ve before slackened. Now, on the track, you should notice an improvement in the brake setting up functioning. 3) Exhaust oil change This operation has to be done when the oil is in the brake system for a certain time (almost 1 year) and it has become of a dark colour, almost black. As a first thing you have to empty the brake setting up in the most complete way, removing the old oil; then you have to add the new oil, in the same way you did for the clearing (point n.2). For the first operation it should be enough unscrewing the back screws (maybe removing them at all) and then start braking for a while. 4) Brake setting up removal If, whatever the reason, you have
to dismantle the brake system, as a first thing you have to divide
2 semi-blocks [screws 8], then detach these ones from the chassis
[screws 7], remove the small security screw bolt and finally remove
the girdles coming from the small piston. Now you should be able
to remove everything without any particular problem, if necessary
dividing or dismantling some parts which cannot allow you to dismantle
everything.
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