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Pelican Technical Article:

Rear Coil Springs Replacement

Kerry Jonsson

Time:

3 hours3 hrs

Tab:

$400

Talent:

***

Tools:

13mm, 16mm, 10mm, 22mm wrenches

Applicable Models:

Mercedes-Benz R129 (1990-02)

Parts Required:

Rear coil spring

Hot Tip:

Use a jack and a pry bar to move the lower control arm into position for installation

Performance Gain:

Restore normal ride height or install lowering springs

Complementary Modification:

Replace shock absorbers if necessary

Your suspension system is there to absorb road irregularities. On the W129 chassis there's a spring mounted at each corner of the suspension to support the weight of the car. The springs will compress and allow the suspension to move upward and isolate the impact from the body of the car. Springs immediately want to return to their normal shape and will slam back into the ground as it uncoils. It is the job of the shock absorber to slow down the spring's reaction and slowly return the suspension to the ground. This keeps the tire in contact with the road and promotes more traction while driving over bumpy roads. As a performance upgrade you can also install lowering springs. This will lower the ride height of the car and still maintain the ability to absorb road irregularities without bottoming out. A car with a lower ride height can corner at higher speeds because of the lower center of gravity. So if your are interested in a performance upgrade this is definitely a good modification to make.

Lift and support the rear axle of the vehicle. You do not have to remove the tires to perform this job but it does make access much easier since you may not have access to an automotive lift. See our tech article on jacking and supporting your vehicle and removing the front tires. Always wear safety glasses when you're working underneath the car.

The procedure to replace the rear coil spring is the same for both the left and right side. In these pictures I am working on the left side. Keep in mind all the steps apply to both sides. It is recommended you replace both sides at the same time to keep your handling neutral.

Remember your car may have been serviced before and parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts I give may be different from what you have so be prepared with different size sockets and wrenches.

ThisPicture illustrates the underneath the left side of the car looking at the lower control arm and subframe.
Figure 1

ThisPicture illustrates the underneath the left side of the car looking at the lower control arm and subframe. Locate the hydraulic roll bar sensor (green arrow).

Unplug the electrical connection to the hydraulic roll bar sensor by pressing the wire retainer (green arrow) and pulling the connector straight off the sensor.
Figure 2

Unplug the electrical connection to the hydraulic roll bar sensor by pressing the wire retainer (green arrow) and pulling the connector straight off the sensor. See the following steps for detailed information.

Push the metal retainer to unlock the electrical connector.
Figure 3

Push the metal retainer to unlock the electrical connector.

Unplug the electrical connector from the hydraulic roll bar sensor.
Figure 4

Unplug the electrical connector from the hydraulic roll bar sensor. Then, remove the 10mm fastener (green arrow).

Remove the hydraulic roll bar sensor from the car.
Figure 5

Remove the hydraulic roll bar sensor from the car.

Remove the brake pad wear sensor harness from the lower control arm mount.
Figure 6

Remove the brake pad wear sensor harness from the lower control arm mount. Unclip it from the plastic mounts. You do not have to remove the brake caliper and brake rotor to do this job. I have done so for photographic purposes.

Remove the brake pad wear sensor harness from the second lower control arm mount (green arrow).
Figure 7

Remove the brake pad wear sensor harness from the second lower control arm mount (green arrow).

Remove the 10mm fastener that holds on the lower control arm lower plastic cover.
Figure 8

Remove the 10mm fastener that holds on the lower control arm lower plastic cover. See the next photo for a view from below of the fastener.

ThisPicture illustrates looking up at the lower control arm from underneath.
Figure 9

ThisPicture illustrates looking up at the lower control arm from underneath. Remove the 10mm fastener (green arrow).

Remove the lower plastic cover from the lower control arm by pulling it away from the control arm.
Figure 10

Remove the lower plastic cover from the lower control arm by pulling it away from the control arm.

Place a jack under the lower control arm (red arrow).
Figure 11

Place a jack under the lower control arm (red arrow). Remove the 16mm nut (green arrow) for the shock absorber lower mounting bolt. Do not remove the bolt yet. Remove the 13mm fasteners (yellow arrow) for the sway bar link lower mount.

Temporarily remove the jack from under the control arm.
Figure 12

Temporarily remove the jack from under the control arm. This is to give you enough room to break the lower control arm bolt loose. Do not remove the lower control arm bolt with the jack removed, just break it free. Loosen the 22mm fastener for the lower control arm to spindle mount. Once loose, place the jack under the lower control arm again.

With the jack under the lower control arm, remove the shock (red arrow) bolt from the mounting hole (yellow arrow).
Figure 13

With the jack under the lower control arm, remove the shock (red arrow) bolt from the mounting hole (yellow arrow). The shock will compress upward when the bolt is removed. Then pull the fastener out of the lower control arm mounting hole (green arrow).

Slowly lower the jack until you take all of the tension off of the rear coil spring.
Figure 14

Slowly lower the jack until you take all of the tension off of the rear coil spring. Be careful, as the spring in under a great deal of tension. Be sure to work slowly.

With the lower control arm all the way down, remove the coil spring from the upper perch.
Figure 15

With the lower control arm all the way down, remove the coil spring from the upper perch.

When fitting in the new coil spring remember to make sure the end of the rear coil spring (green arrow) fits into its groove (yellow arrow) in the lower control arm before assembly.
Figure 16

When fitting in the new coil spring remember to make sure the end of the rear coil spring (green arrow) fits into its groove (yellow arrow) in the lower control arm before assembly. Installation is the reverse of the removal steps. Fit the spring in the upper perch and make sure the bottom of the spring ends in the groove for it in the lower control arm. Jack up the lower control arm to hold the spring in place. Line up the mounting holes for the spindle and the lower control arm then install the fasteners. Continue to jack up the lower control arm and install the rear sway bar link lower mount and rear shock absorber lower mount. Install the lower control arm cover and the hydraulic roll bar sensor on the lower control arm. Plug in the hydraulic roll bar sensor and route the wiring for the brake pad wear sensor harness. Lower the car and roll it forward and backwards a few feet. Use a tape measure to measure between the ground and the highest point of the wheel well and verify both left and right sides of the vehicle have the same ride height.

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