A slight difference in ride height on the drivers side front was noticed from when I purchased the SL over Christmas, so it was no real surprise the spring refresh needed doing.
I put the spring job off (waiting for slightly warmer weather) and it jumped the queue slightly when a torsion bar hanger snapped, obviously because of the constant tension the weak spring was placing on the hanger arrangement.
I ordered up a new pair of the front torsion bar hanger brackets and clamps from the local Mercedes dealer at £13.00 each. (Part numbers: A129 323 0026, A129 323 0126 and two clamps A124 323 1140) and a pair of 15mm diameter OEM replacement road springs.
The job itself is pretty straightforward and requires a Mercedes specific ‘special tool’ to compress the coil spring on the car to enable you to lift out the old spring and simply slot in the new one. With the specially designed tool, the job is very quick, though if you want to separate the ball joints and remove the torsion/roll bar then I have read some reports of being able to do a spring change without the spring compressor, undoubtably by levering the lower wishbone down – Personally for the cost of the tool, (£50) its not worth making the job ‘ten times bigger’ with the increased risk of doing an injury to yourself or someone else – Get the tool!
Jack the car at the front from the jacking point and remove the road wheel. Slide into the spring the top plate of the compressor tool, locate the bottom plate and thread through the hole in the wishbone the telescopic compressor bar. Locate the upper bar tangs through the top plate by turning the bar until the top plate locks into its slots. Pay attention to align the bottom plate correctly as you begin to ratchet up the compressor bar. (19mm socket) Make sure all is located correctly with the compressor and the tool top plates, recheck as soon as you begin to feel tension being taken from the spring. Double check before proceeding to tighten and compress the spring further. It will be under a great deal of tension and you need to be super sure everything is latched and locked before you proceed.
After compressing the spring with the tool almost to the point of the spring being ‘coil bound’, tilt while pushing upward to remove the spring toward the front of the car. Lay the removed spring down and use the 19mm ratchet to unto and relax the tension on the coil spring so the tool can be removed and placed in exactly the same position on the new spring and wound up for refitting.
Swap over the rubber top seat that cushions the spring against the spring perch. Make sure this is in the correct position rotationally, so the springs ‘end of coil’ seats in the moulded slot made prominent by the previous spring. If these rubber spring mounts have split or deteriorated – now is the time to replace them.
Once the new spring is compressed it can be orientated back into position on the car, making sure you clean the spring seat on the lower wishbone of all debris and corrosion.
If you are lucky, you will still have the soft metal seat crescents that afford a little abrasion resistance for the springs final turn onto the wishbone. In most cases these parts will be corroded, worn away or missing, it is optional that you may wish replace these parts before spring reinstallation.
Once the spring is positioned in the upper perch cup correctly and the bottom turn of the spring is located in the ‘pressing formation’ on the lower wishbone, begin to relax the spring compressor. Check the position of the spring and ensure it is seating correctly as you fully undo the spring compressor tool. Once fully undone, the tool bar can be twisted and removed then the plates taken out from the newly fitted spring. Isn’t that quite easy..!
At this point in my case I replaced the torsion bar hangers and brackets (one 17mm bolt and locator bracket into the chassis), not fully tightening the two clamp bush bolts until the spring job was completed on both sides and the vehicle lowered to level ground. A quick nip up with a 13mm spanner and matching socket swiftly completed the torsion bar fixing.
Both road wheels were refitted and the vehicle road tested. Great job done!
Interestingly once the spring is removed it gives a great opportunity to test out the bushings in the lower arm/wishbone and more importantly the lower ball joint. This item is very hard to detect wear in when under road spring tension. In the case of R129 and W124 series lower ball joints are virtually impossible to decern very small amounts of play in, as unusually the ball is being ‘pulled’ by the spring arrangement of the suspension. So check everything out in detail while you have the spring out. In my case all was tight as a drum, although a little play in the near side wheel bearing was noticed. (I will deal with this later!)
I found the above wonderful animated diagram of how the front suspension is set up and how to apply force to test the ball joints. This great animation is credited to Chistian K and has been published on several Mercedes forums. It is by far the best explanation of the front suspension that I have seen to date. Many thanks for sharing this work Christian!.