Rear suspension springs question

[GGR]

Yesterday I took my rear axle out and I compared the springs with some I have out of a W108.

The two side springs are quite shorter though they have the same number of coils and the wire diameter is the same, so they may have the same stiffness.

The Pagoda center spring though is much longer with more coils and the wire diameter is quite less. So it must be quite softer than the W108 one.

My question is what would happen if I were to replace the center spring with a W108 one? Would that contribute in any way to reduce the diving issue?

Does anyone have some experience with that?

Thanks!

Edit: I looked in the workshop manual and there are two references for the center spring. Judjung by the tech data one is the longer one I took out from the Pagoda. The other one is most seemingly very similar to the shorter one with thicker wire diameter I compared the longer one with. So both seem to be correct for the Pagoda. What would be the difference then? Stiffer rear suspension with the shorter spring?

[Benz Dr.]

Good question because I don`t have an answer. I have changed rear axles with all of the hardware intact, save the E brake cables and the rear springs, and found it worked OK.

  I think the main thing to consider is that most of the real weight is at the front of the car and changing the front springs even a little bit can have some drastic results. The rear springs are much more easy to change and you can fine tune them with the spring plates on the trailing arms.

[GGR]

Thanks. I will consider changing the front springs when I reach there.

In the meantime, I made some calculations using the data in the BBB.

The shorter compensating spring p/n is 113 329 01 01. Its unloaded length is 276.5 mm and its length once installed is 220 mm. Its travel per 100 kp load is 13.42 mm. So, once installed, it is compressed by 56.5 mm corresponding to a load of 420 kp.

The longer compensating spring p/n is 113 329 03 01. Its unloaded length is 343.5 mm and its length once installed is 220 mm. Its travel per 100 kp load is 29.4 mm. So, once installed, it is compressed by 123.5 mm also corresponding to a load of 420 kp which makes sense.

The "diving" problem of the Pagoda is not that much the front diving, but rather that in the process the back goes up while the car pivots around its center of gravity. By doing so, the rear camber becomes positive and the track also reduces which helps throwing the car sideways or into a spin. Fitting stiffer springs in the front will reduce this phenomenon as the car will pivot less around its center of gravity. But replacing the longer compensating spring by the shorter one may also help.

Lets imagine that during the braking process the rear goes up in a way that the compensating spring is lengthened by 20mm. The shorter one will be left with 36.5mm travel so it will still be pushing the equivalent of 271 kp, while the longer one will be left with 103.5 mm of travel and will still be pushing the equivalent of 352 kp further aggravating the change of camber compared to the shorter one.

So, the shorter spring would stiffen the rear suspension, but would also contribute to reducing the change of camber under braking as its "pushing" rate decreses much quicker while unloading. I think this is worth considering in combination with stiffer springs in the front so as to keep the balance between front and rear suspension (similar stiffness difference ratio between front and back).

I'm no engineer so calculations may seem a bit amateurish, but I guess it gives some sense to the issue. I will be fitting the shorter spring and see how it goes.