No, this time we do not start with the often mentioned water, but with the air in the brake fluid. We are concentrating on two fundamentally different methods of venting. Let's start with the simplest: two people, one at the brake pedal and the other runs, a container with hose in the hand, under the vehicle the four wheels off.

We do not want to discuss it is absolutely necessary from the longest way to the shortest relative to the main brake cylinder. There are also manufacturers who want exactly the opposite. In any case, the compensating tank should always be well filled and best emptied as completely as possible before the first filling with new brake fluid.

Then the commands: pressure for the kick on the brake pedal with simultaneous opening of the respective ventilation screw. This should be practiced before at every screw, because it works all the worse, the older the vehicle is. So carefully set the ring wrench and look forward to trouble-free opening. Then do not tighten too hard again and continue to the next.

Because if one of the litte screws breaks off or its hexagon is rounded, the replacement of the brake cylinder is announced. Drilling and repairing the thread poses a too great risk. What happens when the venting screw breaks out in single-circuit braking at a forced braking? Remember, the braking system is highly stressed and endangered when you need it most.

So from one bleed screw to the next. There should be systems which can not be vented with this method because parts of it keep the air inside. I myself have only experienced this with a hydraulic clutch actuation. So you may also want to check for venting outside the wheel areas.

Are we satisfied with this system of ventilation? No, even if none of the described difficulties occur, and if we take care to close the vent valves while pedaling, to prevent any air from entering. No, it is the inner life of the main brake cylinder that worries us.

It has served for years or even decades. Its one or his two pistons have completed a movement that always ended at a certain point, no matter how hard the pads were worn. What does it look like there? Has the whole abrasion and other garbage been shifted, or is a small edge formed? You know rubber can even damage cast or steel in the long run.

And what happens now if the person behind the steering wheel goes over this point mercilessly? Is now metal damaging rubber? What are the consequences? Not infrequently, therefore, the cuffs are leaking after a certain time, according to the ventilation method so described. This is particularly unpleasant in the case of a primary cuff, because the leakage remains inside the main brake cylinder.

In wheel brake cylinders, e.g. In the drum brake, brake fluid expands, deposits over the linings and reduces their performance. This is noticeable, especially when you remove the drum. But with the main brake cylinder? Someone already needs to know. For a minute, the brake pedal and finally land on the floor plate or at least be sunk a little.

We have already attempted to limit the path of the pistons of the main brake cylinder by a wooden block, but then the vent becomes a seemingly endless procedure. Besides, you know, especially at the beginning not, whether both pistons really only make their usual way or one more and the other less. Conclusion: Not recommended.

Then the other method of venting: the compensation tank remains rather empty, and the new brake fluid is sent from the wheel brake cylinders via the individual bleed screws, and then fills the system to the compensation tank. Here, too, we leave open the question as to whether this has to happen in order from the longest to the shortest path.

These two videos will be missing in the book. But that does not hurt either, because you are only for a discussion basis. Is it really necessary to remove the wheels for venting? Are in the videos really emptied both chambers of the compensation tank? Is the second ventilation method really responsible without a second person? In the first video, the ventilation screw is carefully sealed, in the second, it remains open for a while. Does a vent screw really have a check valve? Are 20 or 15 pump movements per wheel really a good house number or waste? May be the first video with the control of the air bubbles is significantly better. The second video would have needed a second person.

At the last fair show visit, I was asked to thighten bolts with 100 Nm. Sorry, but afterwards it was measured 130 Nm. Since then I also use a torque wrench to tighten wheel bolts. Incidentally, a ring key should be recommended for the first loosening of the sometimes somewhat to hardly fixed bleed screws. If someone make a video, he should respect minor details.

Imprint