The auxiliary brake consists of an actuator and two actuating mechanisms installed in the joint of the exhaust system silencer intake pipes.
The auxiliary brake mechanism (Fig. 2) includes a housing 3, a flap 11, a shaft 13 and a lever 4.
When the brake is not engaged, the mechanism flap is positioned along the flow of exhaust gases and the axis of the intake pipes.
The brake mechanism control is pneumatic, consisting of a valve (Fig. 3), three pneumatic cylinders, and the pipelines connecting them.
When the valve button is pressed, compressed air is supplied through the pipelines to two pneumatic cylinders (cylinder diameter 35 mm and piston stroke 65 mm — Fig. 4), whose pistons position the mechanism flaps perpendicular to the exhaust gas flow.
Simultaneously, compressed air is supplied to the 30×25 pneumatic cylinder (Fig. 5) mounted on the fuel injection pump cover, which cuts off the fuel supply.
The auxiliary brake mechanisms 23 (Fig. 6) are attached by bolts 2 to the flanges at the joint of the intake pipes 3 and 22 of the exhaust system silencer.
The same bolts attach the brackets 6 for mounting the pneumatic cylinders 7 to the flanges.
The auxiliary brake control valve is fixed to the cab front panel, and its button is located to the left of the clutch pedal.
The auxiliary brake assemblies are removed and partially or completely disassembled when malfunctions are detected, such as jamming of the flap shaft in the housing bushes, wear of pneumatic cylinder parts, loosening of the bolts securing the mechanisms to the intake pipes, etc.
Removal and disassembly of the auxiliary brake
During removal, unscrew the nut 18 of the ball pin 19 and disconnect the end piece 15 from the lever 5.
Remove the split pins and unscrew the nut 8 of the pin 11, remove the washer and the pneumatic cylinder 7 as an assembly. Unscrew the lock nuts and nuts of the four bolts 2, remove them, remove the bracket 6, gaskets 1 and the mechanism 23 as an assembly.
To remove the fuel cut-off pneumatic cylinder, remove the split pins of the pins connecting the cylinder to the bracket and the lug on the cylinder rod to the fuel injection pump lever, remove the cylinder as an assembly.
When removing the valve, unscrew the nuts and disconnect the pipelines from it.
Unscrew the nut securing the valve to the cab floor panel and remove it. The auxiliary brake parts, being in an exhaust gas environment, partially corrode, and the gaps between them become clogged with soot particles; therefore, to facilitate disassembly, the auxiliary brake should be soaked for a day in kerosene or diesel fuel.
During mechanism disassembly, file off the rivet head 2 (see Fig. 1) and, using a 4 mm diameter punch, remove it from the shaft and flap.
Secure the auxiliary brake mechanism by the lever 4 in a vice and, by turning the housing 3, remove it from the shaft 13.
Remove the flap 11 from the housing.
Remove the cover 9 from the housing and remove the spring 8, washer 7 and retaining ring 6 from it. Unscrew the nut 10 of the tie bolt 5 and remove the lever 4 and key 15 from the shaft 13.
Using a 3.5 mm diameter punch, drive the pins 1 and 12 out of the housing and remove the bushes 14.
The bush from a blind hole in the housing can be removed by a hydraulic method (Fig. 164) using consistent grease.
The flap axis can be used as a rod.
When disassembling the 35×65 pneumatic cylinder of the mechanism drive, it must be clamped in a vice by the cover 5 (Fig. 161) and unscrew the body 2, remove the sealing ring 3.
Extend the piston bottom 6 from the cylinder by 10–15 mm and secure it, loosen the lock nut 14 (see Fig. 6).
Unscrew the end piece 15 and the lock nut.
Remove from the cylinder the piston 6 (see Fig. 4) assembled with the rod 1 and the springs 8 and 10.
Remove the limiter 9 from the rod 1, and the seal 7 from the piston. If necessary, disassemble the end piece.
Before disassembling the 30×25 fuel cut-off cylinder, unscrew the nut and disconnect the stop lug from the rod.
Then clamp the lower part of the cylinder 8 (see Fig. 5) in a vice, unscrew the cover 2 and remove the piston 5 assembled with the rod 9 and the spring 6.
Remove the seal 4 from the piston, and the limiter 7 from the rod.
When disassembling the valve (see Fig. 3), clamp its lower part in a vice.
Disconnect the lower part of the boot 7 from the bush 6.
Remove the thrust ring 11 into the gap formed.
Pull the button 8 and remove from the body the pusher 9 assembled with the boot 7, the bush 6, the sealing rings 5, 10 and 14 and the spring plate 4.
Remove the spring 13 from the body.
Reposition the valve in the vice to access the lower part of the valve.
Remove the thrust ring 1, remove the valve guide 17 and the sealing ring 18 from the body.
Remove from the guide 17 the inlet valve 15 with its stem 16 and the valve spring.
Remove from the pusher 9 the sealing rings 10, 14, the plate 4, the thrust ring 12 and the bush 6.
The parts of the pneumatic cylinders, mechanisms and valve must be washed in petrol, then dried and carefully inspected.
The gaskets between the flanges of the intake pipes and the auxiliary brake mechanisms must not have tears, delaminations or other damage.
Tears, deep scratches, hardening and permanent deformation, as well as other damage to rubber parts are not allowed.
The data for checking the parts of the auxiliary brake mechanism and pneumatic cylinders are given in Table 1.
Table 1
Bush. Inner diameter:
- - nominal size - 14+0.050 mm;
- - permissible size - 14.10 mm
Flap shaft. Outer diameter:
- - nominal size - 14-0.060 mm;
- - permissible size - 13.80 mm
Ball pin. Diameter of spherical surface:
- - nominal size - 12-0.120 mm;
- - permissible size - 11.75 mm
End piece of the auxiliary brake actuator rod. Diameter of hole for ball pin:
- - nominal size - 12+0.160 mm;
- - permissible size - 12.25 mm
Assemble the auxiliary brake units and install them on the vehicle in the reverse order of disassembly and removal from the vehicle.
The following requirements must be observed:
- - the flap shaft must rotate freely in the bushes without jamming. Lubrication of the shaft and bushes is strictly prohibited;
- - lubricate the end piece 15 (see Fig. 6) and the ball pin 19 with a thin layer of graphite grease;
- - lubricate with a thin layer of CIATIM-221 lubricant: for the auxiliary brake control valve, the pusher 9 (see Fig. 3) assembled with the sealing rings, the bush 6 and the body 2 at the point of contact with the rod; for the pneumatic cylinders, the piston assembled with the sealing ring, the rod and the cylinder.
After assembly, check the pneumatic cylinders for tightness under an air pressure of 5.3 kgf/cm².
Detect air leakage points with soap emulsion, which should be removed after checking.
During the check, also measure the rod stroke, which should be 65 mm for the 35×65 pneumatic cylinders and 25 mm for the 30×25 pneumatic cylinder.
The rods must return to their initial position without jamming under the action of the springs.
When installing the auxiliary brake mechanism on the vehicle, adjust the screwing length of the rod «Л» (see Fig. 6) so that when the pneumatic cylinder piston is in the uppermost position, the key 4 is positioned along the axis of the intake pipes. The mechanism flap will then be fully open.
Also check the tightness of the bolts securing the intake pipes of the exhaust system, and if necessary, tighten the bolts securing the intake pipes to the engine exhaust pipelines.
