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Rear Multi-Link Suspension Arm Removal
 
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Pelican Technical Article:

Rear Multi-Link Suspension Arm Removal

Tom Morr

Time:

5 hours5 hrs

Tab:

$180

Talent:

***

Tools:

Ratchet/socket set, combination wrenches, M12 triple-square bit, torque wrench, coil spring compressor

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Suspension control arms

Hot Tip:

Use the special spring compressor if removing the lower control arm

Performance Gain:

Improved ride and handling, longer tire life

Complementary Modification:

Replace any cracked bushings and leaky shock absorbers

A mushy-riding suspension that tends to wander indicates that the bushings are wearing out. As the rubber bushings crack, caster and camber can exceed factory specifications.

Bad bushings can be replaced individually. (Please see the separate how-to on the procedure.) However, some R170 SLK owners might find it easier to swap in new control arm assemblies that already have the bushings pre-installed. Although the rear multi-link arms rarely go bad themselves unless they're crunched in an accident, replacement units are readily available. They're also somewhat affordable. Pelican Parts' prices range from $18 for an OE-spec camber strut to $104 for a new lower control arm.

The R170 SLK (and several other Mercedes-Benz cars) uses a 5-link rear suspension: five arms connect the knuckle/wheel carrier to the car's rear subframe. Here are some of the arms' details, using a pre-facelift 2000 SLK230 Kompressor as an example.

Camber Strut

This arm connects to the top of the knuckle.

Torque: 70 Nm at the knuckle (40 Nm if the bolt is an M10); 70 Nm, then an extra 45 degrees at the subframe

Tension Arm

If it's possible for a knuckle to have a shoulder, this arm attaches to that boss--directly below the camber strut.

Torque: 70 Nm, then an extra 45 degrees (both ends)

Tie Rod/Track Rod

The tie rod's pivoting end at the knuckle eventually wears out. The rod's inboard end has an eccentric bolt, allowing the rear tires' toe-in to be adjusted. Mark the bolt before removing it. Install the replacement tie rod with the same orientation so alignment won't be totally out of line. If retaining the existing rod, a tie rod end puller might be required. Our project car's tie rod end slipped out of the knuckle with no puller required. A pickle fork can also be used to separate the tie rod end from the knuckle. However, this usually damages the tie rod's rubber boot, effectively giving it a death sentence.

Torque: 70 Nm, then an extra 45 degrees at the subframe; 25 Nm (M10x1) or 30 Nm (M10x1.5) at the knuckle

Torque Strut

This is the arm that attaches to the bottom of the knuckle, across from the main lower control arm/spring link.

Torque: 70 Nm, then an extra 45 degrees (both ends)

Lower Control Arm/Spring Link/Dog Bone

Although some owners successfully use a floor jack to gradually lower the control arm until the coil spring topples out, the safe and reliable way is with an application-specific spring compressor. Generic outside-the-spring compressors likely won't fit on the R170's rear suspension; the inside-the-spring "pancake" tool is designed specifically for the job. Coil springs can be lethal, and removing the lower control arm is better left to a professional if the proper spring compressor isn't available.

Torque: 70 Nm, then an extra 45 degrees at the subframe; 120 Nm, then an extra 45 degrees at the knuckle; 55 Nm for the lower shock absorber bolt

In general, remove and replace the arms one at a time, unless the knuckle needs to be relieved or removed in order to replace an axle shaft or a wheel bearing. (Please refer to those articles for details.) Normally, the inboard/frame bolt is undone first. The knuckle end is unbolted next. Reverse the process to install the new link arm.

For final fastener torqueing, the suspension should be jacked up until the rear axle shaft is parallel to the ground. (Be careful not to jack the car off of the jack stands.) This should restore rear wheel alignment somewhat. Professional alignment is recommended after replacing rear arms, especially if new tie rods are installed.

Preliminary steps include raising the car and securing it on jack stands.
Figure 1

Preliminary steps include raising the car and securing it on jack stands. Remove the rear cross brace, or one of its T50 Torx bolts so that the brace can be pivoted out of the way. If the lower control arm/spring link is being removed, take off the 10mm bolt (arrow) on either side that secures the plastic cover to the arm. Then unclip and remove the cover.

The axle shaft, emergency brake, and backing plate were removed for other articles, making the link arms more visible.
Figure 2

The axle shaft, emergency brake, and backing plate were removed for other articles, making the link arms more visible. The arms that comprise the 5-link rear suspension: camber strut (yellow arrow), tension arm (purple arrow), tie rod/track rod (red arrow), torque strut (blue arrow), and lower control arm/spring link (green arrow).

Note the orientation of the bolts before removing them.
Figure 3

Note the orientation of the bolts before removing them. Or, take photos for reference during re-assembly. Many of the knuckle bolts take an M12 (12mm) triple-square/12-point bit, which often must be ordered in advance if it isn't already in hand. (Normal parts stores don't stock it.) Many of the nuts take a 19mm wrench or socket.

Remove the arms' inboard bolts first.
Figure 4

Remove the arms' inboard bolts first. They're generally harder to access, but they come out quicker when the outboard end is still stabilized by the knuckle.

With the exception of the lower control arm, our project car's other arms all have bolts that take an M12 triple-square bit.
Figure 5

With the exception of the lower control arm, our project car's other arms all have bolts that take an M12 triple-square bit.

The tension arm is relatively affordable.
Figure 6

The tension arm is relatively affordable. Some owners opt to replace the links arms instead of spending time replacing old bushings.

The tie rod/track rod uses an eccentric bolt to set the toe-in.
Figure 7

The tie rod/track rod uses an eccentric bolt to set the toe-in. Mark its orientation (arrow) before removing the tie rod.

Replacement tie-rod ends are available, but most owners opt to replace the entire arm instead of pressing in a new end.
Figure 8

Replacement tie-rod ends are available, but most owners opt to replace the entire arm instead of pressing in a new end. A 17mm wrench (arrow) is used to remove the tie rod end's nut at the knuckle. The tie rod often separates from the knuckle with a gentle tap. If not and the tie rod is going to be retained, use a tie-rod end puller. If the boot is cracked or damaged, replace the tie rod.

The torque strut attaches to the bottom of the knuckle, similar to the other arms.
Figure 9

The torque strut attaches to the bottom of the knuckle, similar to the other arms.

To remove the lower control arm/spring link/dog bone, the arm must be unbolted from the knuckle.
Figure 10

To remove the lower control arm/spring link/dog bone, the arm must be unbolted from the knuckle.

Before unbolting the shock absorber from the lower control arm, compress the coil spring using the special tool (arrow).
Figure 11

Before unbolting the shock absorber from the lower control arm, compress the coil spring using the special tool (arrow). (Please see the coil-removal article for details.) If the shock's bolt doesn't remove easily, use a floor jack under the control arm to relieve the load. The jack will also be needed to line up the holes during re-installation.

Once the shock's lower mount is free, the control arm can be pushed down.
Figure 12

Once the shock's lower mount is free, the control arm can be pushed down. The compressed coil spring can then be lifted out.

One bolt secures the lower control arm to the subframe.
Figure 13

One bolt secures the lower control arm to the subframe. (The axle shaft and other components have been removed here for other articles.)

Replacement lower control arms are available.
Figure 14

Replacement lower control arms are available. However, replacing the bushing (red arrow) in the existing arm is more cost-effective, assuming the arm hasn't been damaged. Take the opportunity to clean out the coil pocket (green arrow) to minimize squeaks. Replacing the coil isolators can also absorb suspension sounds.

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