Spring replacement due to loading squat?

[JHZR2]

My 1991 MB 300D drives and rides great. It goes down the road like a well oiled singer sewing machine.

A few weeks ago I took it on. A 1000+ mile road trip. Halfway I bought two group 27 and one group 49 battery. We already had a trunk full of luggage.

Soon after I noticed a very obvious sag in the rear. Sure there were probably 140 lbs of battery right over the rear axle, but nobody was riding in the back seat.

You can kind of see it, though this lot wasn’t flat.

I did a rudimentary measurement. First with the car loaded but all people out:

Barely one finger between the tire and fender.

But when unloaded:

Slightly different angle photo, but three fingers now fit now when empty. That’s a decent bit.

So, are my springs tired? Rubber bushings all look fine. Shocks may be weak, but nothing more than a very small sign of potentially a bit of oil leakage. Car rides great.

The FSM has a wide range of springs depending upon model. I don’t think mine have ever been replaced, but the car has 236k, not a huge number of miles.

Could this be a shock issue? (Seems dubious). Otis this a sign of worn out rear springs?

Is it time to replace springs? I’ve never had to before, but the sag seems like too much…

 

[fantastic]

If the shocks have some age & mileage on them they're due for replacement. I'd try to find a stiffer type shock to compensate for the springs. New shocks should give it some Botox & cheaper than replacing springs. Unless they're struts in the rear then you might be able to replace the whole thing w/just OEM equivalent. I wish they made adjustable shocks for every vehicle to "Fine Tune" your personal preference.

 

[Pterostylis]

Nice looking car.
Sounds like springs are the issue to me, but at that age I would be replacing both springs and shocks on a vehicle that gets driven regularly. I’m just some random on the internet that’s never even been in a 300D though.

 

[Lubener]

As some have suggested, shocks have nothing to do with ride height. If the vehicle is bouncy, then you have a shock issue as well.You have to do an actual ride height measurement per the manufacturers specs when unloaded and a full tank of gas.. Using your hand just won't cut it. A loaded vehicle will sag some. Yours doesn't look that bad to me.

 

[CharBaby]

I agree! It doesn't look that bad to me.
However, if the tires rub with passengers in the rear seats then you need some rear lift.
There are spring spacers that you can buy and they're not too expensive IMO.
I assume that you have a coil spring setup? There are a couple of different designs that I have used on coil springs as well as leaf springs and they work quite well.
Your tires will also tell you a thing or two if your shocks are worn out.
Look into these spring spacers for your application. These might just be the ticket!
https://www.google.com/search?q=coi...QYxwEYrwGYAxqSBwQxMy43oAfXkgE&sclient=gws-wiz

 

[shortyb]

If the ride height stays at the lower position now, could be a broken coil. But at that mileage and age, the springs and dampers are probably real tired. Replace both, along with new bushings, and be amazed at the transformation. Nice car BTW, like a rolling bank vault.

 

[Trav]

As others have said shocks have nothing to do with ride height unless it is a coil over, the springs are probably tired. Don't use the reinforced if you want to keep the original ride, they are not progressive only heavier wire making them stiffer.

https://web.tecalliance.net/lesjofo...blyGroupId:100011;targetId:460;typeNumber:460

 

[Kira]

I've always heard that if the springs are tired, replace them like any other part.
If 236K and 34 years in service leans toward 'old', then the shocks might have earned their retirement.
Is there an airbag kit for that vehicle?

 

[SC Maintenance]

Is there a spec in the manual for wheel-arch height? If its sitting lower when unloaded it tends to get worse when loaded. Its typically a spec of fender height above ground.

 

[JohnnyG]

You could replace the shocks with some "load levelers" to adjust the rear ride height,
I'd check the specifications first, it could be within limits.

 

[86cutlass307]

Bilstein Available Parts
The springs' sole job is to support the vehicle weight and provide chassis balance. I looked up your model year on Bilstein US site, quite a selection including springs, most available at Rock Auto as well. A little coin but your Benz will love it, as will you while cruising at highway speed.

 

[JHZR2]

Nice looking car.
Sounds like springs are the issue to me, but at that age I would be replacing both springs and shocks on a vehicle that gets driven regularly. I’m just some random on the internet that’s never even been in a 300D though.

Agreed, I would do both if I did them.

As some have suggested, shocks have nothing to do with ride height. If the vehicle is bouncy, then you have a shock issue as well.You have to do an actual ride height measurement per the manufacturers specs when unloaded and a full tank of gas.. Using your hand just won't cut it. A loaded vehicle will sag some. Yours doesn't look that bad to me.

Correct, the FSM gives guidance. I didn’t need to measure to know it was sagging.

What surprised me wasn’t that it was lower than I had expected. It’s that it only took around 150 pounds of stuff. To me that is the crux of the matter. I get it if the car was full with multiple folks in the back seat, but the back seat was empty. It just took those batteries. That’s not a lot of weight in the big scheme of things, and it was right over the axle, not all the way rearward.

As others have said shocks have nothing to do with ride height unless it is a coil over, the springs are probably tired. Don't use the reinforced if you want to keep the original ride, they are not progressive only heavier wire making them stiffer.

https://web.tecalliance.net/lesjofo...blyGroupId:100011;targetId:460;typeNumber:460

I’d agree - my gut was springs, though occasionally folks claim some benefit with shocks.

My fronts have no issues but they do have surface rust, which is why a replacement all around seems like it’s not the worst idea.

I would use the color codes per the FSM for the model and outfitting.

I've always heard that if the springs are tired, replace them like any other part.
If 236K and 34 years in service leans toward 'old', then the shocks might have earned their retirement.
Is there an airbag kit for that vehicle?

The shocks work surprisingly well. I know the fronts were replaced but I don’t have a record about the rears. They would be worth a replacement I’m sure.

Not really interested in airbags. The height should be higher and it shouldn’t sag as much, imo. So getting to ground truth on design attributes is job #1.

 

[Carmudgeon]

Dampers can have an influence on ride height. Bilsteins, for example, either through slight differences in the physical dimensions of the damper body, or their high-pressure gas.

However, springs are the primary determinant of ride height, and when they get old, can sag, or in severe cases, break and cause more noticeable drops in ride height. The beehive rear springs BMW has used in the past are an example of the latter.

It's not implemented in the typical online versions of the parts catalogs (though it was at one point when the factory offered an online ETK), but BMW's parts system uses a spring table to determine which part number, of a range of springs, is suitable for a particular vehicle based on which options are selected during lookup, and recommends a specific spring, based on the corresponding weight estimates.

A fully-optioned car with a sunroof and other gizmos may get a "765" suffix spring, while a lighter stripper will get a "762" spring, which is slightly shorter. There is no single, or "universal" spring; it's application specific.

I don't recall if it was officially outlined, but it could also be used to correct discrepancies in expected ride height measurements (taken from the edge of the wheel arch to the lowest point of the wheel rim), as well as in general for desired tweaking.

I'd be surprised if Mercedes doesn't use a similar system, being a very German-like thing to do, but I guess they might not dial in their suspension specs as closely.

 

[JHZR2]

Dampers can have an influence on ride height. Bilsteins, for example, either through slight differences in the physical dimensions of the damper body, or their high-pressure gas.

However, springs are the primary determinant of ride height, and when they get old, can sag, or in severe cases, break and cause more noticeable drops in ride height. The beehive rear springs BMW has used in the past are an example of the latter.

It's not implemented in the typical online versions of the parts catalogs (though it was at one point when the factory offered an online ETK), but BMW's parts system uses a spring table to determine which part number, of a range of springs, is suitable for a particular vehicle based on which options are selected during lookup, and recommends a specific spring, based on the corresponding weight estimates.

A fully-optioned car with a sunroof and other gizmos may get a "765" suffix spring, while a lighter stripper will get a "762" spring, which is slightly shorter. There is no single, or "universal" spring; it's application specific.

I don't recall if it was officially outlined, but it could also be used to correct discrepancies in expected ride height measurements (taken from the edge of the wheel arch to the lowest point of the wheel rim), as well as in general for desired tweaking.

I'd be surprised if Mercedes doesn't use a similar system, being a very German-like thing to do, but I guess they might not dial in their suspension specs as closely.

Correct. Mercedes uses a system that effectively scores the car’s mass and prescribes one of many part numbers. They are then color coded.

Ride height was also changed as the model progressed.