433037 Disassembling and Assembling Front Spring Strut
WM 433037 Disassembling and assembling front spring strut
Tools
Information
Notes on repairing air-spring struts
As of a mileage of 200,000 Km it is recommended that the air springs be replaced per axle if there is damage to one air spring.
If the shock absorbers leak, the complete air spring strut is to be replaced. The oil of the shock absorber can damage the roller.
When depressurised, the air spring must not be twisted. There is the danger that the roller in the inside of the air spring will be damaged by bending or folding and thus significantly reduce the running time.
Air-spring strut
1. Before loosening the air lines in the installed state, check if the rolling boot is still filled with the residual pressure of approx. 3 bar. To do this, press on the rolling boot of the air spring with your thumb. The rolling boot must give perceptible resistance. If no significant resistance can be felt, the air spring is depressurised and must be replaced along with the residual pressure retaining valve.
Checking the air bellows
The greatest possible care and cleanliness, as well as perfect tools are important requirements for carrying out perfect repairs on air-spring struts. The general and basic rules of safety apply. These are specifically listed here again for repairing air-spring struts.
- Thoroughly clean the connection points and their surroundings before loosening them.
- Do not use fibre-shedding cloths.
- Do not take spare parts out of the packaging until right before installation.
- Only use lubricants that have part numbers.
- Carefully cover open components or close them if the repair work will not be carried out immediately.
- Do not use an impact bolter.
- Observe correct tightening torques. => 43 Tightening torques
Residual pressure retaining valve
WARNING
Vehicle is lowered when air line is loosened
- Risk of squashing
-> When loosening the residual pressure retaining valve, raise the vehicle on a lifting platform.
-> Only leave the vehicle on the lifting platform until a new residual pressure retaining valve is installed and the air-spring strut is filled.
The residual pressure retaining valve may only be replaced if:
Removing/fitting residual pressure retaining valve
- it was damaged during removal and installation,
- it was damaged while disassembling and assembling the air-spring strut,
- the sealing ring is faulty,
- it does not allow any more air to come out (valve jammed).
If the residual pressure retaining valve is jammed, the vehicle must be lifted for replacement on the platform lift and the wheels must be allowed to turn freely. It must not be compressed with an empty rolling boot.
Gaskets, sealing rings and bellows
Always replace sealing rings and bellows.
After removing gaskets, examine the contact surfaces on housings for burrs and damage.
Always loosen and tighten screws or nuts in diagonally opposite sequence for mounting covers and housing.
Tools and materials
Tools for repairing air-spring struts
Torque wrench 2-10 Nm (1.5-7.5 ftlb.)
Torque wrench 60-100 Nm (44-74 ftlb.)
Socket-wrench insert 3353
Brace P 9630
Socket insert T10158/1
Information
Overview of front air-spring strut
Information
The components of the air spring -7- (figure shows component arrangement of front air-spring strut), Items -2, 3, 4, 5- (figure shows front air-spring strut), cannot be disassembled.
- Always replace the complete air spring -7- (figure shows component arrangement of front air-spring strut).
Front air-spring strut
Component arrangement of front air-spring strut
Disassembling and assembling
Disassembling spring strut
CAUTION
The air-spring strut is pressurised with approx. 3 bar residual pressure. Never us an impact bolter to loosen the fastening screws. Do not bend over the mounting saddle during disassembly.
- Risk of injury from the pressurised air-spring strut when loosening the screws.
-> Always unscrew the screws on the mounting saddle by one turn only, on alternating sides. During disassembly, allow the air to escape by tilting the mounting saddle slightly.
1. Clamp the air-spring strut on the lower mounting point (use aluminium protective jaws -A- .).
Lower mounting point for air-spring strut
2. Loosen the fastening screws on the mounting saddle and carefully remove the mounting saddle.
3. Remove spring-strut mount with socket wrench insert 3353 and arm bracket P 9630.
Removing/fitting spring-strut mount
4. Remove clamp.
Air-spring strut clamp
Information
When replacing the air spring, always replace the boot/bellows.
If the rolling piston slips out of the outer guide during disassembly, it must be correctly positioned again when assembling.
- When sliding in the rolling piston, the roller must lie evenly between the outer guide and rolling piston (roll fold).
5. Push bellows downward and secure in this position (2nd worker required.). Grasp rolling piston -1- and remove it upward from the shock absorber by turning slightly to the left/right.
Air-spring strut rolling piston
6. When replacing the air spring, push the rubber stop -1- out of the centering device.
Rubber stop
7. Remove boot/bellows.
8. When replacing the shock absorber, remove the wheel acceleration sensor -1- and fit it on the new shock absorber.
Wheel acceleration sensor
Assembling spring strut
Information
When replacing the air spring, always replace the boot/bellows.
If the rolling piston slips out of the outer guide during disassembly, it must be correctly positioned again.
- When sliding in the rolling piston, the roller must lie evenly between the outer guide and rolling piston (roll fold).
If the shock absorber is not replaced, the sealing ring must be replaced.
- Make sure that everything remains absolutely clean. The smallest impurities can cause leakages.
- Clean the contact surfaces of the sealing rings with a lint-free cloth.
- Lightly grease sealing rings with Syntheso Glep 1 (ET No. 000.043.204.68).
1. Replace sealing ring on shock absorber -Arrow- (figure shows rear shock absorber).
Shock absorber sealing ring
2. Pull boot/bellows completely over the collar of the shock absorber, so that it engages (small diameter downward, 2nd worker required).
3. Fit rubber stop (small diameter downward).
4. Position the air spring on the shock absorber. Grasp the rolling piston and push it downward by turning it slightly to the left and right. If the rolling piston has slipped out of the outer guide, it must be pushed back in again while forming a circumferential uniform roll fold on the rolling boot -Arrows-.
Roll fold
5. Clean the surfaces -2- on the mounting saddle and on the air spring with a lint-free cloth. Replace sealing ring -1- on the air spring.
Sealing ring
Information
To align the air spring, carefully turn the rolling piston in order to not damage the roller.
6. Fit and align the air spring. While doing so, the residual pressure retaining valve -1- must be located exactly at the imaginary axis of symmetry -Arrow- of the air-spring strut. The residual pressure retaining valve must be facing in the opposite direction to the CDC valve.
Residual pressure retaining valve
7. Fit bellows at the top.
8. Fit spring-strut mount using socket wrench insert 3353 and arm bracket P9630.
Removing/fitting spring-strut mount
9. Fit mounting saddle -Screws A- and align it so that the upper arm of the bearing -B- points to the residual pressure retaining valve.
Fitting mounting saddle
10. Align the air spring again so that the residual pressure retaining valve is located exactly at the axis of symmetry -Arrow- of the air-spring strut.
Aligning the mounting saddle
11. Fill the air-spring strut. => 4301 Filling specification for air-spring strut
Checking the air-spring strut
Checking for leaks
1. Dip the filled air-spring strut completely into a water bath.
Information
Before fitting the air-spring strut in the vehicle, carefully blow out and dry all electrical connections and the residual pressure retaining valve with compressed air.
2. There must be no air bubbles rising in the water bath. If no air bubbles can be seen, the air-spring strut can be fitted in the vehicle.
3. If air bubbles appear in the water bath, the air-spring strut must be disassembled again. Replace all sealing rings again. Check the residual pressure retaining valve again visually.
4. Repeat the leak test in the water bath.