Suspension Strut

Replacing front spring-strut shock absorber on right or left

The only way to establish whether or not a spring strut shock absorber needs replacing is to test it while installed with a shock tester or, while removed, on a shock absorber test unit, refer to Technical Service Bulletins.





When replacing the shock-absorber element for a McPherson strut, always ensure that the replacement unit is marked with the same code (K) as the old absorber.





Removing front wheel, refer to Wheel.
Take wires and brake hose out of holders on spring strut.
Screw in a wheel bolt and suspend wheel-bearing assembly from body with wire.





Unfasten nut.

Installation:
Wrench surface (1) on ball pin must be parallel to absorber axis.
Replace self-locking nut, install with washer.
Tightening Torque: 59 Nm





Release screws.

Installation:
Clean tapped bores in steering knuckle. Always replace micro-encapsulated bolts.
Tightening Torque: 107 Nm.





Unscrew bolt.

Installation:
Use shim on both sides.
Replace self-locking nut.
Tightening Torque: 107 Nm.





Remove nuts and take out strut shock-absorber unit.

Installation:
Replace self-locking nuts.
Tightening Torque, refer to Specifications.

Caution: M3/M Roadster: Long sheet-metal flange on thrust bearing must point in forward direction.





Clamp special tool 31 3 121 on its guide (1) in the vise.

Caution:
Each of the spring holders 31 3 123 must be secured with a screw (2).
Lay the protective inserts 31 3 128 in the spring holder 31 3 123 to prevent damage to the spring surface.





M model:
Clamp special tool 31 3 121 on its guide (1) in the vise.

Caution:
The spring holders 31 3 122 must each be secured with one screw (2).
Lay protective inserts 31 3 127 in spring holder 31 3 122 to prevent damage to spring surface.





Locate coil spring with upper and lower coil between the spring holders.

Caution:
When clamping spring coils in the upper and lower spring holder, they must be completely inserted in the recess.
Special tool 31 3 121 must never be tightened or untightened with an impact screwdriver.
The coils must not be tightened down to block position.
Only tighten down the coil springs until stress on the thrust bearing is relieved.





Caution:
Only untighten the nut if both spring coils are completely inserted in the spring holder recess! Repeat tensioning process if necessary.
Replace nut with special tool 31 3 170/210 - if necessary, replace wrench insert - unfasten and remove spring strut shock absorber.

If new coil spring is installed, observe notes (1 ... 3)!

Note 1: Release special tool 31 3 121 and remove coil spring.

Caution: The special tool must not be tightened or untightened with an impact screwdriver.

Note 2: Accommodate new coil spring with the larger end turn diameter facing downwards in special tool 31 3 121.





Note 3: Position coil spring between the spring holders so that the two spring ends (1) are approx. one turn outside the spring holders.

Caution: When clamping spring coils in the upper and lower spring holder, they must be completely inserted in the recess.
The special tool must not be tightened or untightened with an impact screwdriver.
The coils must not be tightened down to block position.





If necessary, replace rubber damper.
Auxiliary spring for standard suspension:
Distance (A) = 16 mm
Auxiliary spring for low-slung sports suspension:
Distance (A) = 8 mm
M-suspension (yellow spring-strut shock absorber) without auxiliary spring
Check rubber damper with protective tube and rings, replace if necessary.
Note installation sequence, refer to "Arrangement of spring strut shock absorber".





Ends of coil spring must be located in shoulders of spring retainers.





Replace self-locking nut and tighten with special tool 31 3 170/210 - if necessary, replace wrench socket.
Tightening Torque, refer to Specifications.





Only relieve tension on special tool until spring coils can move freely.
Under no circumstances should the special tool be extended to the extent that the spring holders make contact with the lower spring retainer, the lower coil or support bearing.
Failure to comply with this can damage the special tool and/or the spring.





Note:
If, when the coil spring is being tightened or released, the special tool fails (nut/clamping pin breaks), the coil spring can be safely released with the "emergency control".
Remove cap (1).
Actuate thread spindle (2) with hexagon socket screw key.

Caution: Only RELEASING is permitted!





Caution:
If oil was found on spring-strut shock absorber, wheel control joint must be inspected visually.
If the rubber part (1) shows signs of swelling, the wheel control joint must be replaced with a new one, refer to Ball Joint, Lower. Service and Repair