Figure 269. Front brake mechanism design: 1 - Brake caliper bracket (bolted to the front axle); 2 - inner shoe with retaining spring; 3 - guide pin, 25 Nm; 4 - plug; 5 - brake pad wear sensor with wire; 6 — caliper cylinder; 7 - spring; 8 - outer shoe
Figure 270. Position of the brake caliper with the wheel removed
Figure 269 shows the brake caliper components. For the appearance and position of the caliper after removing the wheel, see. in Figure 270. Although the removal process is considered here from one side, the pads must be changed as a set:
- if old pads are installed, they should be marked according to the installation side and position when removed (external, internal);
- with the engine off, press the brake pedal several times to relieve the vacuum in the system;
- unscrew the brake fluid reservoir cap;
- loosen the wheel bolts, place the front of the car on supports and remove the wheels;
Figure 271. Removing the spring (7 in figure 269) using a screwdriver: 1 - lid; 2 - wire plug; 3 — bleed nipple
- disconnect the brake pad wear sensor wire. To do this, remove the cover and pull out the plug (figure 271);
- using a screwdriver, remove the connecting spring 7 (see figure 269) between the caliper and the caliper bracket;
Figure 272. Brake caliper mounting bolts (shown by arrows)
- on the back side of the caliper, use a screwdriver to remove the plugs from the mounting bolts and unscrew them with a hex key. You will need a straight Allen key that fits into the socket head. A bent hexagon is not suitable, since the bolts must be tightened to a certain torque during installation. After unscrewing the bolts shown in the figure 272, remove the caliper cylinder. Hang the cylinder on a wire from the front axle so that it does not hang on the brake hose;
Figure 273. External shoe
- remove the brake pad from the caliper side, the outer pad remains on the caliper bracket and is removed from the brake disc side (figure 273). If the brake pad linings are worn to a thickness of 3.5 mm or less or are oily, the pads should be replaced as a set. Although the brake pads are allowed to wear down to a thickness of 2 mm, the warning light in the instrument cluster lights up at a value of 3.5 mm. Always replace both pads, even if one of them is not worn. If the pads are very worn, the piston may seize. In this case, you should send the caliper for repair. For security reasons, this work is not described here;
- repairs are also necessary if the mudguard in the cylinder body is damaged. The brake pad wear sensor must be replaced if the contact plate insulation or any other part of it, including the wire, is damaged;
Article was obtained from the portal MercedesMan.ru
Figure 274. Determining brake disc wear
- check the surface of the brake discs and clean them thoroughly before installing new pads. Measure the thickness of the disc as shown in the figure 274. It may need to be replaced or polished.
When installing the pads, the following operations must be performed:
- clean the contact surface under the brake pads in the caliper;
- pump out some brake fluid from the master cylinder reservoir as described above;
Figure 275. Recessing the brake caliper piston before installing the pads
- press the piston into the cylinder. For this purpose, the clamp shown in the figure is used 275;
Figure 276. Inner shoe
- install the shoe with the spring into the caliper cylinder as shown in the figure 276, and press in the direction of the arrow;
- insert the outer shoe into the mounting locations of the caliper bracket so that it occupies the position shown in the figure 273;
- insert the second pad into the caliper bracket;
Figure 277. Tightening the caliper mounting bolts
- carefully position the cylinder body over the pads and screw the mounting bolts through the pads into the caliper bracket. Wrap them with a hexagon as shown in the picture 277, torque 25-28 Nm. The hexagon shape must match the one shown in the figure so that a torque wrench can be installed on it;
- after tightening the bolts, put the caps on them;
- insert the spring into the caliper and bracket;
- twist the wear sensor wire into a spiral and connect it to the caliper contact. Install the plug connection cover;
- press the brake pedal hard several times to get the pads to fit onto the disc;
- if necessary, add brake fluid to the reservoir;
- install the wheels, lower the vehicle and tighten the wheel bolts to 160–180 N·m;
- after installation, press the brake pedal several times until its normal travel is established. If this is not done, the brakes may not work during the first test while driving. If the pedal "fails", check the tightness of the system. During the first kilometers after installing new pads, do not brake too sharply. To properly work in the brakes, you should brake several times from 80 km/h to 40 km/h while smoothly pressing the pedal. After each braking, you should wait a little so that the brakes do not overheat.