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Rear Coil Spring Shock Replacement
 
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Pelican Technical Article:

Rear Coil Spring Shock Replacement

Tom Morr

Time:

2.5 hours per side

Tab:

$75 to $222

Talent:

**

Tools:

Heavy-Duty Spring Compressor (BM-924-0231), floor jack, jack stands, adjustable wrench, ratchet and extensions, 10mm socket, 19mm socket, 17mm wrench, 16mm wrench and socket, T50 Torx

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

New shocks and or springs and related mounting hardware

Hot Tip:

Take your time when compressing the springs. Plan on repositioning the compression plates and the telescoping rod one or more times.

Performance Gain:

Better ride and handling

Complementary Modification:

Replace front shocks and springs

Because the bulk of the R170's weight is on the front suspension, the front shocks and springs normally wear faster than the corresponding rear components. However, some SLK owners decided to replace all four corners at the same time, sometimes opting to upgrade to high-performance aftermarket components when swapping out tired shocks and springs.

Regardless of whether the new parts are OE-spec replacements or aftermarket upgrades, the process is similar. Aftermarket lowering springs can actually be slightly easier to install, since they don't require as much space between the upper tower and axle pad as stock-height coils.

Replacing suspension components isn't difficult. However, it can be dangerous if the proper procedures and tools aren't used. If you don't feel comfortable working with coil springs, paying someone to do the job might be prudent. Coil springs can do significant damage if they aren't properly compressed.

Overall, rear spring/shock removal and replacement is similar to the front (see that article for additional details). Shocks tend to wear out faster than springs. Over time, shocks' internal seals crack, allowing the oil to leak. Also, the shocks' high-pressure gas de-pressurizes with age. A noticeable decrease in bump-absorption/general decline in ride quality is an indicator of deficient shocks. Oil on the shock bodies is another sign that they need to be replaced.

Although generally more durable than shocks, springs settle over time. Occasionally, they even crack. More often, though, the rubber isolators that serve as buffers between the upper coils and the shock towers deteriorate, creating squeaks. The springs must be removed to replace the isolators, so this is an opportune time to add fresh coils.

Tips: The first step is to remove the roll over switch from the center of the rear axle if your case has it. (The 2000 SLK 230 shown here doesn't). Ideally, shocks and struts should be replaced in pairs: both sides of the axle. This helps keep side-to-side tire wear even. Bumpy roads destroy shocks faster than smooth ones, but typical shock life is five to seven years or 50,000 miles. The Mercedes-Benz manual/Workshop Information System (WIS) recommends replacing the shock piston's self-locking (nylock) retaining nuts as opposed to reusing them. Replace the shock's rubber mounting eyes if they show visible signs of rot or cracks. The shocks' upper mounts are easier to unbolt if the shocks aren't at full extension. The shocks are compressed at ride height, so either leave the tires on and begin with the car on the ground or use a floor jack under the wishbone. The plate/"pancake"/tension-style internal spring compressor is highly recommended. Assuming it isn't damaged, this type of compressor leaves less to chance than the external jaw-style tools that are typically available for rent or on loan at local parts stores. Never use air tools on the spring compressor's telescoping rod. Visually inspect to compressor's plates and rod for visible signs of damage before using the tool. Also verify that the snap ring on the telescoping rod is seated tightly. Wear gloves and glasses as a safety precaution. The Mercedes-Benz WIS recommends shielding off the work area to minimize collateral damage if a coil springs free. Be sure to use the proper-diameter clamping plates for the coil. The tool has different plate sizes, and different tools are offered for different cars. Position the clamping plates so that their lips face the car's exterior. Once the spring is compressed to where it isn't solid on its mounts, it'll spin as the compression rod is tightened. At this point, the spring might come out if a pry bar is used to push down slightly on the wishbone. If installing aftermarket springs that change the cars ride height, professional wheel alignment will be required. Shock torque specs: Wishbone nut: 55 Nm / 41 lb-ft Piston nut: 18 Nm / 13 lb-ft; 30 Nm / 22 lb-ft (self-locking)

Leave the car on the ground or use a jack under the wishbone to partially compress the rear shock.
Figure 1

Leave the car on the ground or use a jack under the wishbone to partially compress the rear shock. The upper mounts are accessible through windows in the trunk panels; we removed the panels to facilitate photography. The shock's piston needs to be held with a wrench. A 17mm wrench is then used to remove the self-locking bolt.

With the car raised and secured, the rear reinforcing brace is unfastened using a T50 Torx bit.
Figure 2

With the car raised and secured, the rear reinforcing brace is unfastened using a T50 Torx bit. The WIS recommends removing the brace at both ends; we undid the rear mount and swung the brace inboard, away from the suspension.

Next, a 10mm socket is used to remove the plastic wishbone cover shield, which has a bolt on both of its inboard sides.
Figure 3

Next, a 10mm socket is used to remove the plastic wishbone cover shield, which has a bolt on both of its inboard sides. The plastic can then be slid off the wishbone.

We removed the caliper's two mounting bolts and secured the caliper out of the way to expedite photos and also to create better access to the spring.
Figure 4

We removed the caliper's two mounting bolts and secured the caliper out of the way to expedite photos and also to create better access to the spring. The shock's lower mounting bolt comes out next, using a 17mm wrench on the nut and a 16mm one on the bolt head.

We unclipped the brake wire so it wouldn't over-extended when we lowered the wishbone to remove the shock.
Figure 5

We unclipped the brake wire so it wouldn't over-extended when we lowered the wishbone to remove the shock.

Pelican Parts offers pro-quality tension-plate-style coil compressor tools for safe spring removal.
Figure 6

Pelican Parts offers pro-quality tension-plate-style coil compressor tools for safe spring removal. The tension/clamping plates (fingers and arrow) need to be placed as far apart as possible. The plates' thick lips should face outboard.

A floor jack is used to raise the wishbone/control arm until the axle shaft is about horizontal.
Figure 7

A floor jack is used to raise the wishbone/control arm until the axle shaft is about horizontal. Then the compressor tool's telescoping rod is passed through the tension plates and secured in the upper plate's retaining recesses. The rod is compressed using a 19mm socket. The wishbone might need to be raised or lowered slightly with the jack to keep the telescoping rod centered in the wishbone's hole.

When the spring is tightly compressed, it will spin in the upper tower.
Figure 8

When the spring is tightly compressed, it will spin in the upper tower. Releasing the jack and gently depressing the wishbone with a pry bar can create enough clearance to slide the spring out of the tower. If the telescoping rod is compressed all the way and the spring still won't come out, reverse and remove the rod, place the tension plates farther apart, and perform the compression process again.

Before unscrewing the compression rod, note which coils have the plates.
Figure 9

Before unscrewing the compression rod, note which coils have the plates. Then release the compressor, transfer the tool to the replacement coil, and compress it for installation. The isolator has a groove that seats on the spring's pigtail.

Clean any debris out of the wishbone's coil pocket.
Figure 10

Clean any debris out of the wishbone's coil pocket. Note the recess for the lower pigtail. The wishbone has a 3mm hole at the end of the recess (arrow), permitting proper coil position to be verified from underneath.

When installing the replacement spring, make sure that the isolator stays seated when the coil is inserted in the tower.
Figure 11

When installing the replacement spring, make sure that the isolator stays seated when the coil is inserted in the tower. Then carefully spin the spring if necessary to seat the bottom pigtail in the wishbone's groove. Carefully jack the wishbone up to hold the spring in place while unscrewing the compressor tool's telescoping rod. Reverse the rest of the disassembly steps to complete the job.

The coil compressor is the only specialized tool required.
Figure 12

The coil compressor is the only specialized tool required. The rear brace takes a Torx bit, but basic hand tools and possibly a pry bar are the only other necessary tools.

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Comments and Suggestions:
cafeman Comments: I bought my first slk 230 last week, it is a fixer-upper,,, this is the best site i have found,,, i cant wait to get it on the road. thanks guys
August 28, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
louie Comments: Thanks for the prompt feed back..
November 16, 2014
  Followup from the Pelican Staff: Glad to help. - Nick at Pelican Parts  
louie Comments: I have a 2000 MB slk230 R170. Your tech information has help me greatly in repairing and maintaining my car. Trying to locate a repair manual.
November 13, 2014
  Followup from the Pelican Staff: Give our parts specialists a call at 1-888-280-7799. They can help you find one.
- Nick at Pelican Parts
 

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