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Front Coil Spring Shock Replacement
 
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Pelican Technical Article:

Front Coil Spring Shock Replacement

Tom Morr

Time:

5 hours5 hrs

Tab:

$75 to $222

Talent:

**

Tools:

Heavy-Duty Spring Compressor (BM-924-0231), floor jack, jack stands, adjustable wrench, 1/2-inch drive ratchet and extension, 19mm socket, 17mm wrench, 16mm wrench, extensions and socket

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. Don't be afraid to un-tension the rod and reposition the compression plates one or more times.

Performance Gain:

Better ride and handling
Suspension components can store lethal amounts of energy. However, the hands-on SLK owner can replace their own springs and shocks if they use the proper tools and exercise caution.

Shocks are generally more susceptible to failure than springs. They degrade over time, diminishing their damping effectiveness. 

Oil on the shock body indicates a bad seal. An aural cue to a bad seal/loss of shock oil is clunking sounds when driving over uneven roads. But even if the shock lacks visible signs of failure, its pressurized gas becomes less effective over time. This gas inhibits air pockets from forming in the shock's oil as the piston cycles. The shock's effectiveness fades as air and heat thin the oil. Fortunately, the R170 SLK's shocks are separate from the springs, making replacement straightforward compared to swapping springs onto struts. 

Spring replacement is more involved than swapping out shocks. Springs typically live longer than shocks, but they can break. As the suspension cycles, the spring coils actually twist as they extend and compress. The spring steel eventually fatigues and ultimately cracks. But before they break, springs will often sag as a sign of old age. Since front springs support more weight than the rears, sag can create an always-driving-downhill sensation. 

In some cases, an incessant clunk can actually come from a cracked coil. Also, the rubber insulators/isolators that form a cushion between the coils and their towers wear over time. Annoying squeaks are an indicator. 

The key to safe, successful spring removal is using the proper tool. Tips: Shocks and struts should be replaced in pairs: both sides of the axle. Typical shock life is five to seven years or 50,000 miles. The Mercedes-Benz recommends replacing the shock piston's self-locking (nylock) nuts as opposed to reusing them. Inspect the rubber shock mounts in the engine compartment's "housing eyes". Replacement them if cracked or rotted. For reinstallation, a floor jack can be used to raise the wishbone until the shock's lower mounting bracket aligns with its eyes. The plate/"pancake" style spring compressor is reliable, assuming the tool isn't damaged. It's a professional alternative to the jaw-style tools that are typically available for rent or on loan. Some enthusiasts on the forums buy the premium spring compressor, then re-sell it on eBay after they replace their springs. This is apparently more cost-effective than paying a shop to do the job. 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 shop manual recommends shielding off the work area just in case a spring breaks containment. Be sure to use the proper-diameter clamping plates for the coil. The tool has different plate sizes. 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. Wedging a prybar, tire iron or breaker bar between the coil and its tower will hold it in place wheel the rod it tightened enough to remove the spring. If installing aftermarket springs that change the car's ride height, professional wheel alignment will be required.
The car needs to be at ride height before unbolting the upper shocks mount.
Figure 1

The car needs to be at ride height before unbolting the upper shocks mount. If the wheels are off and the car is on jack stands, the suspension will need to be jacked up a few strokes at the wishbone/knuckle.

In the engine compartment, begin by pulling off the piston rod's protective nipple.
Figure 2

In the engine compartment, begin by pulling off the piston rod's protective nipple.

The piston rod needs to be held stationary while a 17mm wrench is used to undo the nut.
Figure 3

The piston rod needs to be held stationary while a 17mm wrench is used to undo the nut. We used a crescent wrench on this 2000 SLK 230 piston's flat sides. Some models require an Allen wrench ("alien" wrench, according to the WIS) to hold the rod steady.

The shock's lower mounting bolt comes out next, using 16mm tools.
Figure 4

The shock's lower mounting bolt comes out next, using 16mm tools.

Lower the floor jack if necessary, then swing the shock out of its lower mount.
Figure 5

Lower the floor jack if necessary, then swing the shock out of its lower mount. The piston rod slides out of the hole to the engine compartment.

Having the right tools is essential for safe coil removal.
Figure 6

Having the right tools is essential for safe coil removal. Pelican Parts offers this pro-quality tension-plate-style coil compressor. It isn't cheap, but coil-compression failure can have catastrophic results. This "pancake" method is more foolproof than jaw-type coil compressors

The tension/clamping plates (arrows) need to be placed as far apart as possible
Figure 7

The tension/clamping plates (arrows) need to be placed as far apart as possible--a minimum of 7.5 inches or 7-8 coils. We cork-screwed the upper plate upward another twist following this photos. The plates' thick lips should face outboard.

The tool's tension/compression/spindle rod is threaded through the hole in the lower control arm and the holes in the compression plates.
Figure 8

The tool's tension/compression/spindle rod is threaded through the hole in the lower control arm and the holes in the compression plates.

The rod's retaining lugs (arrow points to one) seat in recesses in the upper plate.
Figure 9

The rod's retaining lugs (arrow points to one) seat in recesses in the upper plate.

Using a 19mm socket and extensions (preferably 1/2-inch-drive), begin tightening the compression rod.
Figure 10

Using a 19mm socket and extensions (preferably 1/2-inch-drive), begin tightening the compression rod.

The spring must be compressed until the coils are nearly touching.
Figure 11

The spring must be compressed until the coils are nearly touching. The compression rod retracts up and through the hole in the wishbone. Then the spring can be safely lifted out.

Before unscrewing the compression rod, note which coils have the pancake plates.
Figure 12

Before unscrewing the compression rod, note which coils have the pancake plates. Then release the compressor and transfer the plates and rod to the replacement coil and compress it for installation. The isolator (arrow) is grooved to sit securely on the top of the spring.

When installing the spring, ensure that the coil's lower pigtail seats in the recess on the wishbone (arrow).
Figure 13

When installing the spring, ensure that the coil's lower pigtail seats in the recess on the wishbone (arrow).

The lugs/nubs on the compress rod seat in the plates' indentations.
Figure 14

The lugs/nubs on the compress rod seat in the plates' indentations. A 19mm socket is used to telescope and retract the rod inside the spring.

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Comments and Suggestions:
Torino Comments: Similar problem as morhan, 2001 SLK230, front end too low. I put bilstein springs, replaced the bushings in the lower control arms. Took the car to dealer for an alignment and they are telling me that the front is still to low. Replaced the bilsteins with the OEM part changed the #4 pad with #5 and the front is still to low. Could the control arms be bent and how can I tell? Thank you.
May 14, 2016
  Followup from the Pelican Staff: I wouldn't not assume anything is bent, unless there was an impact. Then it would also be unlikely both would be bent. You likely have the wrong parts installed.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
morhan Comments: Hi, I have a 2001 SLK200K. My front springs sagged in years so I ordered original springs according to MB EPC. But there are 2 things I could not solve. 1 EPC shows No2 pads accoridng to its calculation table. But the car is fitted with No4 pads. 2 EPC also shows lower metal pads A2023210036 for my VIN. But they are not there and currently the springs are directly fitted on the lower wishbone. I ordered the No2 pads and lower pads as well, as they were cheap. What do you suggest, shall I install as per EPC no:2+lower pads or stick with the current setup no4 only? no4 adds 8mm to ride height vs no2. Not sure about the lower pad. My concern is to maintain factory ride height. Attached is my front vs rear fender gap. Thank you.
May 2, 2016
  Followup from the Pelican Staff: I’m not the best with part numbers.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Izhar Comments: You guys are amazing.
I have a 2002 slk 200.
I'm from israel, and there IS NO better site than yours for my baby.
Thank you so much.
July 25, 2015
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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Page last updated: Wed 3/29/2017 02:26:52 AM