rear suspension ride height
 

I've been working on the problem of the low ride height in the back of the SDL for the past several months.

All dimensions will be made from the road to the inside of the fenderwell in the back.

Prior to any modifications, the vehicle would typically have a ride height of 24.50-24.75 inches. This is a pronounced squat in the back.

I changed subframe bushings and differential mount. This increased ride height to 25.50 inches. A small improvement, but not enough.

Then, last Thursday, I changed rear springs. The ride height increased from 25.5 to 27.50 as soon as the vehicle came off the jacks. The camber on the rear wheels went from 1" negative (measured on the tires) to about 1/4" positive. So far so good. I am assuming that it will settle down a bit.

It sat for three days, without moving the vehicle, and the ride height eased down to 27.25". The vehicle looks about perfect.

I take it for a ride for the first time yesterday. 100 miles.

It looked a bit funny at the midpoint of the ride, but, I had no tape measure.

Measured the ride height this morning:25.5" :eek:
Camber: 1" negative :eek:

So, does anybody have any possible reasons of how the rear suspension can compress by 1.75" by simply taking it for a drive? If I didn't see it myself, I would not have believed it. It seems almost impossible. What can allow the body to drop by his huge amount??? :confused:

The springs are German and manufactured by Meyle.

I'm baffled by this. It almost seems like the springs are defective. But, I can't fathom how a test drive would cause the springs to compress more than they did after three days of sitting in the driveway??

I'm now quite frustrated by this whole deal. Nearly $300. in the back end and hardly any improvement as compared to where I started. :mad:

I think that the wire size used may be the cause of this..
How does the size of the new compare to the old ? Mercedes is very particular about this... making the springs and THEN measureing and classifying them....

Brian, is there any way that the springs could have rotated in their seats during that 100 mile drive. If they could, they would -

On cursory inspection (no hard data) the wire appears to be identical.

How can the spring sit for three days under load and then give up 1.75" after working it, unless it is defective? Two defective springs?

I don't think they can, Pete. They are under some huge friction loads. Once you place them, that's where they are going to live. They contact a rubber pad on the top and the friction is very high.

Did you measure the height immediatlt after lowering the jack...or did you move the car back and forth to let it settle...why? off the ground the track will be narrower than it will loaded..it will bee restricted from settleing by the tires inablilty to slide outwards to meet equi;librium....thats the nature of a independent rear suspension...or the front one too.....straight off the jack is not an accurate measurement.

I agree with Pete also...unless there is a physical stop keeping the end of a spring from moving it is certainly possible for them to rotate.... they are just using the ramp model of trying to escape their load... and they will follow ' down hill' if they can... this is particularly true with the constant aggravation of movement which a suspension experiences.
But you need to measure the spring wire size...

Oh, I know the friction is very high, but so is the vector seeking rotation, and I think that rubber is more resistant to compression than torsion. That's the only thing that comes to (small) mind here :o .

"....straight off the jack is not an accurate measurement."

Thus the reason for having to move the car forward to measure and set the toe in accurately...tires can hold a lot of kenetic potential...from getting to the suspension...

Exactly ...Alignment racks have the pads the wheels set on able to move on bearings to eliminate this.......something your driveway doesn't.

Take a look how high your car sits in front when you take it off the jack, until you move it....the rear end does the same unless you don't have an IRS rear end.

Ok, that explains the increased height when it came off the jack. I did not move it back or forth, whatsoever, in the three days that it was sitting there.

So, the measurement off the jack, 27.25", is not relevant.

Thanks for the clarification.

The lower spring perch has a slight shape to it. The very end of the last coil is designed to rest against a small stop in a bit of a depression. For the spring to rotate, it would have to rotate "uphill". This is not likely. If it did happen, the ride height would increase.

I'll probably put it up on a jack and take a look around, but, I'm not optimistic about it.

Easy mistake to make when you are excited about something after doing the work.

"Excited" was an understatement. ;)

This vehicle looked fantastic after the new springs were installed. I was even thinking about 16" wheels because the wheel wells, in the rear, were so large at 27.25" :o

"unless there is a physical stop" -- Leathermang

"The lower spring perch has a slight shape to it. The very end of the last coil is designed to rest against a small stop in a bit of a depression." --Brian

Ok,,, sorry to ask this next question... the springs have a top and bottom I think... either paint marks or closer coils or ground different...So you are sure they were installed in the correct orientation ? I know this bothers you because there are so few parts which could cause this... old blacksmiths are less bothered by this sort of stuff than Trained Engineers ...
I suggest you get the micrometer out for the spring wire size... remember the pages of specs posted when someone wanted to lower their car ?