Disassembling and Assembling Rear Spring Strut
WM 432537 Disassembling and assembling rear spring strut
Information
Notes on repairing air-spring struts
Information
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 depressurized, 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 depressurized 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 fiber-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.
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 crosswise for mounting covers and housing.
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
1 - Residual pressure retaining valve
2 - Socket insert
- 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.
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 rear air-spring strut
Information
The components of the air spring -7- (figure shows component arrangement of rear air-spring strut), Items -2; 3; 4; 5- (figure shows rear air-spring strut), cannot be disassembled.
- Always replace the complete air spring -7- (figure shows component arrangement of rear air-spring strut)!
Rear air-spring strut
1 - Sealing ring
2 - Lid
3 - Outer guide
4 - Rolling boot
5 - Rolling piston
6 - Bellows
7 - Shock absorber
8 - Sealing ring
Component arrangement of rear air-spring strut
1 - Hexagon-head bolt
2 - Mounting saddle
3 - Hexagon nut
4 - Spring-strut mount
5 - Sealing ring
6 - Residual pressure retaining valve
7 - Air spring
8 - Rubber stop
9 - Hexagon nut
10 - Protective cap
11 - Shock absorber
12 - Sealing ring
13 - Boot/bellows
14 - Clamp
Disassembling and assembling
Disassembling spring strut
Caution:
The air-spring strut is pressurized 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 pressurized 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
2. Loosen the fastening screws on the mounting saddle.
3. Carefully remove the mounting saddle over the residual pressure retaining valve in direction of arrow.
Air-spring strut mounting saddle
4. Remove spring-strut mount with socket wrench insert 3353 and arm bracket P9630.
Removing/fitting spring-strut mount
Air-spring strut clamp
5. Remove 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).
6. Push bellows downward and secure in this position (2nd worker required!). Grasp the rolling piston and remove it upward from the shock absorber by slightly turning to the left/right.
Air-spring strut rolling piston
Rubber stop
7. When replacing the air spring, push the rubber stop -1- out of the centering device.
8. Remove boot/bellows.
9. When replacing the shock absorber, remove the cap and fit it on the new shock absorber.
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-.
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 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
Aligning the air spring
6. Align the air spring so that the residual pressure retaining valve is located close to the imaginary axis of symmetry (approx. 10° off-center) of the air-spring strut.
7. Fit bellows (large diameter up).
8. Fit spring-strut mount with socket wrench insert 3353 and arm bracket P9630.
Removing/fitting spring-strut mount
9. Fit mounting saddle and while doing so align it so that the upper arm of the bearing points to the residual pressure retaining valve.
Aligning the mounting saddle
10. Fill the 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.