I tend to agree. A spring can go bad, but not really often. Willrev has this same issue, and I think we are going to find most of the bushings in the rear of his SD are shot.

My w123 still sits with it's butt up in the air just slightly as it should, even with 280K on it.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

I've rebuilt a fwe W123 and W126's. When all the rubber parts were replaced-they returned to normal ride height. They also rode like new cars.. amazing difference.

Springs are designed for an infinite fatigue life. When full compressed the oter fibers of the spring are below the yield strength of the material.

Rust, marks in manufacturing can start a crack and then a broken coil will make the car much shorter. Seen that several times.

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

I'm in a bit of a quandry regarding this.

The SDL, and many of the M/B "stretched" W126 vehicles suffer from sagging rear ends. I can document that this one sits two inches low in the rear with minimal load and about 1/2 tank of fuel.

I am quite confident that the spring has not yielded over time, however, I am certainly unsure if the spring has "softened" with age. This means that the spring rate has changed and there is more deflection of the spring with a given load.

I tend to think that the spring is the culprit on the SDL for the following reasons:

1) 2" would be almost impossible to make up by replacing rear subframe bushings.

2) The rear tires have a negative camber, meaning that the springs have allowed the rear subframe to travel further upward than would normally be the case. If the rubber bushings were replaced, this situation would not be resolved.

Please chime in here and provide your collective thoughts on this. I would rather not buy springs for the SDL if they are not required, however, I tend to believe that the springs are the solution.

Brian,

" am quite confident that the spring has not yielded over time, however, I am certainly unsure if the spring has "softened" with age. This means that the spring rate has changed and there is more deflection of the spring with a given load"

Do you understand how a spring works- physics? A coil spring let's reduce it down to a straight rod (torsion spring). Rotation (twist) is resisted by the material-function of diameter, length, and material. Since we are talking car springs- they will be somesort of steel. Steel has an elastic modulus(youngs modulus) of 29X10^6 psi. That doesn't soften with age. Yes, the final spring is probably tempered and if they were not manufactured correctly-then they could need replacing.

Replacing springs on Mercedes , on a need basis, is very rare.

While it is impossible for you to understand how the subframe mounts can play such an important role- please consider replaceing them. They are rubber and rubber parts age *POORLY*. Just did my 86'. The rubber parts were all intack, but very hard and the car was a garage kept low mileage creampuff.

What thickness spring pads does the car have now? There are 3 thicknesses available. You could always go thicker if the suspension rebuild doesn't get you enough improvement.

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

Yes, I fully understand your capability of quoting Young's modulus and, as a mechanical engineer, I might be inclined to agree with you. However, I am not fully convinced that an 18 year old spring does not have some surface deterioration that affects the spring rate.

I am fully cabable of understanding how subframe mounts play an important role in the ride height of the vehicle, however, you have not provided any explanation. You have only stated to simply "replace them." You have no way of knowing if they are in acceptable conditon and may have already been replaced in the past. Furthermore, you have provided no explanation on how this vehicle could gain two inches in ride height by replacing these bushings. AFAIK, they cannot compress any more than about 3/4".

BTW, the three thicknesses available for the spring are not designed for you to "adjust" the ride height. The thicknesses are specified depending on the specific vehicle and the options that the vehicle has on it. If the suspension rebuild does not raise the vehicle to the proper height, then the springs would prove to be the culprit. So, you clearly have some doubts, yourself, regarding replacement of these bushings, don't you?

Replacing rear springs on Mercedes Benz W126 and W123 is common.
The springs collapse with age and you must replace them with new.

Thanks Roy.

I appreciate the knowledge of a man with experience.

Brian,

I could look at the mounts and get a 3' prybar -determine pretty quick if they are good or bad. There are some threads here ... or you could post a pic.

Are the 2 surfaces parallel all the way around??????? Done many W123 subframe mounts, and a few W126. Never needed springs in any of them.


For pads- yes they are orginally matched to the springs... but someone could have replaced them for lower ride height.

Pretty hard to armchair guess at this stuff..... really have to put it on the lift=)

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

I can't give you a detailed explanation but changing the subframe bushings and the rear differential mount did raise the rear of my W126 at least 2". The strange thing is it improved a little bit with time. (I have measured it.)
My suspicion is that, with the worn bushings, there must be an "off-angle" stress also placed on the springs. Since changing the bushings and mount are much less expensive and easier to replace, call me tight , I opted for the more frugal option.

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Sam

84 300SD 350K+ miles ( Blue Belle )

Now, that is very interesting. In discussions with everybody, it appears that the change of springs can definitely raise the ride height of the SDL (or SEL) by the requisite 2 inches.

It also appears that these bushings can also have a pronounced effect.

Now to decide if the condition of the bushings warrants their R&R prior to the more costly springs....................

Brian,
I'd say if they've never been replaced, on a 20something year old car, you should install new subframe bushings 'on principle.' It was the single most signifcant change/improvement in handling I've made to any of my cars. I cannot speak to the ride height but I do know that before the change the right side bushing on the 300D was allowing approximately 1/2" of movement in all axis. Considering the complexity of the rear 'sledge' and the leverage that the differential has on the subframe, I can visualize a relatively minor movement of the bushings permitting a lot of squat under acceleration.


just my .02

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Never a dull moment at Berry Hill Farm.

Sub Frame - Trailing Arm Bushings
http://www.peachparts.com/shopforum/diesel-discussion/74439-sub-frame-trailing-arm-bushings.html#post467465

Well, I followed your advice and I have the data to show that you are dead wrong on all counts with regard to the SDL.

The subframe mounts and differential mount increased the ride height from 24.75 inches to 25.25 inches (measured several times after the vehicle had settled for a few days). Hardly a big change. I might be off .25" or so because the data is taken with varying fuel loads.

The spring pad spacers were replaced. They were not hard from age. They were not brittle from age and could have been reused. The identical thickness spacer, 19 mm, was returned to the vehicle. The spring pad spacers were replaced at the same time that the subframe bushings and differential mount was replaced.

After getting this small improvement in ride height, I decided, to replace the only remaining component that can affect the ride height: the springs. I just installed a new set of springs, p/n 116 324 08 04, and the ride height has now increased from 25.25" to 27.25" when measured right off the jack. I expect that this will come down to about 26.5" or so in a few days.

So, in conclusion, and in direct contrast to your opinion on the matter, replacing the rear springs on an SDL makes a far more significant improvement in ride height than the subframe bushings or differential mount.

The relatively short springs, with fewer coils, are quite highly loaded and clearly are shot after 18 years. The vast majority of the SDL and SEL bodies on the road suffer from this same malady.

Great to hear that the new springs helped. So you think they will eventually settle out to a 1.5" increase in ride height on the rear?

Another thing I noticed was that the front seemed a little high on mine. When checking other W126's there was more wheel well clearance on mine. Recently, changing the front sway bar bushings seemed to help "lower" the front end. I am no suspension guru but it seems that every little thing affects the ride height on this car. I may eventually need to go the route, as you did, of changing the rear springs. Currently, I will just have to add that to the "list".

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Sam

84 300SD 350K+ miles ( Blue Belle )

I'm going to make a guess and figure that they settle out to 26.75" or so. This means an increase of 1.5" solely due to the springs.

The front wheel arch measurement has always been too high on this one as well. It is typically 28" to 28.5" depending on fuel load. Right off the jack, the front measured 27.25". There was an immediate drop in the front end once the rear height increased. The vehicle looks quite normal now, and I may delay my planned reduction in the front spring height.

BTW, springs are not a big deal. I went out to change them at 6:00 p.m. tonight and walked back in the house at 8:30 p.m. Job fully complete.

I'm likely going to rent out the spring compressor at a very good price so that other folks can do the rear springs. It's the Klann clone and it works very well with virtually no risk.