Automatic adjustment
The Vectra with the 1.6-litre eight-valve engine has an automatic adjustment device on the rear drum brakes. This eliminates the need for manual adjustment. The adjustment module consists of an adjustment lever, an adjustment spring and a two-piece pressure rod, the length of which can be changed using an adjustment gear.
When braking, the pistons of the wheel brake cylinder move the shoes in the direction of the brake drum. The adjusting lever of the front brake shoe is under pre-tension due to the adjusting spring and, due to this, is constantly adjacent to the pressure rod, at the same time it engages with the saw-tooth profile of the adjusting gear.
As a result, the increasing distance between the brake shoes causes a rotational movement of the adjusting lever. As the shoes wear progressively, the rotational movement becomes large enough for the lever to engage the next tooth in the adjusting gear. The adjusting gear continues to rotate, the pressure rod lengthens. Now the brake shoes are approaching the drum again - the brake is adjusted.
Left: to adjust the brake pads, insert a screwdriver through the hole and use a pushing motion to turn the adjusting gear in the direction of the arrow until the brake pads are seated and the brake disc no longer rotates. Then turn the adjusting gear back until the brake disc rotates freely.
Right:when the brake disc is removed, the following parts are visible:
1 - adjusting device;
2 - lower return spring;
3 - pressure spring;
4 - upper return spring;
5 - expansion lock (when the handbrake is on, it presses the shoes against the drum);
6 - rear handbrake shoe.
This is how the automatic adjustment works: when the brake pedal is pressed, the brake shoes are pressed outward toward the drum. The resulting reciprocating motion of the advancing and receding bridge of the brake shoes is pulled by the adjustment lever in direction "1", rotates around the support point "2" and turns the gear on the pressure rod with the end of the blade. But this process is only carried out if there is appropriate wear on the lining. To prevent adjustment due to thermal expansion (for example, when driving downhill) brake drum, between the pressure sleeve and the pressure rod there is a heat-shrink clamp (B), which causes automatic adaptation to the gap caused by heating.
Automatic adjustment and temperature
When the brake is released, there should be a small distance between the shoes and the brake drum to allow the wheels to rotate freely. This distance should always remain with automatic adjustment. Long-term braking, for example when going down a slope, with a fully loaded vehicle can increase the temperature of the drum brakes to 350°C. Under the influence of this temperature, the increase in the diameter of the brake drum can reach 1 mm. The automatic adjustment device can perceive this as shoe wear and make adjustments with a heated, enlarged drum brake. Consequence: after the brakes have cooled, the wheels lock.
With increased thermal expansion, the adjustment must be suppressed. This is done by a so-called thermal clamp inserted into the pressure rod. The bimetallic part expands greatly under the influence of temperature and thus compensates for the change in diameter of the brake drum. The effect: the distance between the shoe and the drum remains constant and false adjustment does not occur.
Visitor comments