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Rear spring SEC stock vs. HR

5K views 34 replies 10 participants last post by  GreenT 
#1 ·
Coil spring Tire Automotive tire Auto part Suspension


Hope that helps someone.
 
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#3 ·
Im not an newton based engineer! I can say that others have experienced elongation of the stock as they get older. Some have cut them off without incident. So I cannot attest to the safety aspect of it. It appears to my naked eye that the two share the same diameter, but the rate is obvious to me, the stock is a softer spring. It is my contention that cutting off a coil with the softer (greater space betwix coils) stock will give you same effect. I have no idea how the two will support car. I have proper lesjofer springs in the back, but they are not the right ones. they are different rate than stock and were sold as the w126 rear sls spring by online retailer. So, I did not install the rear HR but the harder sporty ride may be more than I want. I may "consider" cutting my fronts and swapping out the HR for the cut stocks.
 
#4 ·
Sorry, I wasn't directing my question just to you but to the forum in general.

The only thing I can see happening when cutting the stock spring is reduced travel and therefore a lower stance. It would not change the rate of stiffness.

OTOH, that same rate seems a lot higher on the HRs perhaps to compensate for the shorter travel so it must be a stiffer ride in comparison.
 
#5 ·
Both H&Rs and stock springs are 17 mm in diameter, within a couple of thousandths of being identical. Probably any difference is the thickness of the paint.

IMHO, the difference is in the tempering. My SEC with the H&Rs rides *noticeably* firmer than stock. My SEL, with exactly the same ride height due to cut stock springs, rides comparatively soft. When I want a pleasant ride, I take the SEL. When I want to carve some corners, it's the SECs turn. But... the SEL is a bit firmer than a stock car. I drove a full stock SEC and a stock SEL within the last few weeks, and I like my SEL better.
 
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#11 ·
Cutting springs WILL make the car firmer and neither of mine has EVER bottomed out. A coil spring is just a long torsion bar. Shorten a torsion bar (cut a coil) and it takes more torque to twist it.

Both my cars have a little more problems with the concrete blocks at the end of parking spaces, but not much else. They are both 1.4" lower than US stock but essentially the same as a Euro ride height. There is still plenty of ground clearance.

The SLS is pretty much either "good" or "bad", mostly "good". Lose too much fluid, bad. It probably won't hold proper height, but the reservoir has a significant excess of fluid. Accumulator blows, quite bad. Ride height is fine but the car rides like a truck. The SLS is a very good system, that, with minor care, is trouble free.
 
#7 ·
good dicussions,perhaps more will participate.
 
#9 ·
I have Eibachs, which if I'm not mistaken, is the manufacturer of the original AMG labelled ones.

These are significantly thicker and shorter than stock. The ride is MUCH harder than stock, especially combined with Bilstein HDs. Hence switching from 18" AMG Monoblock IIs to 16" Pentas was a welcome change.

H&Rs may have different thickness and spring rates, I have no experience with them....
 
#10 ·
I have H&R's and have had a few w126's with stock suspension - I prefer the feel of the H&R's, the w126 is a big car and the springs make it a little bit more nibble. It also depends on what wheels you have - I switched from 16x9's to 16x8/7 and its still a very comfortable ride.

-much less body roll
-stiffer ride (I prefer)
-cornering is much improved - feels much more confident
-more responsive

These are not progressive rate springs, you can cut them but you won't get the same effect as H&R's - you'll improve things aesthetically as the w126 has the worst fender gap ever and end up with a slightly stiffer ride due to less travel. This was common practice for AMG, especially when they couldn't keep up with demand. Springs were cut and decals were applied :). I had an AMG car I parted that had these types of springs.

I haven't tried Eibach but I have also heard that they were the original manufacture of AMG springs. From what I remember, when compared to H&R, they are same.
 
#13 ·
Viagra and Cialis discussions are on another forum.
 
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#14 ·
Going back to the OP picture... I notice that the end loop on both ends of the spring is flat as to make a base for even contact. I'm wondering if cutting below the flat loop should be a safety concern since now all the spring's pressure is on a single point of contact, where the coil was cut.


 
#15 ·
Spring rate is absolutely affected by length.

From your linked source (parenthetical statements mine):
What affects Spring Rate
There are 3 primary variables that affect Spring Rate
1. Wire Diameter: When the diameter of the wire increases so does the Spring Rate. When the wire is thicker it becomes stronger and more difficult to deflect. (we don't change this)
2. Spring Diameter: When the diameter of the spring increases the Spring Rate decreases. (we don't change this either but it appears to be a function of adding more wire for a specific coil height)
3. The number of coils in the Spring: As the number of coils increase the spring rate decreases. (which indicates more wire in the spring)

Number 3 - the inverse works too, as the number of coils decrease, the spring rate increases. Take a spring out of a ballpoint pen and see how effort it takes to compress it 1/8", cut the spring in half and do it again. Or, do the same thing with a paper clip - full length with an "L" bent into each end and twist it, cut it in half, put the "L" back into the cut end and twist it again.

What they do not mention, since it is generally far beyond us backyard mechanics, is the significant effect that the tempering has on spring rates. It's my supposition that the H&Rs,while the same wire diameter and coil diameter of stock springs, must have a different temper to achieve a higher spring rate. But that's just my (educated a long time ago) guess.

It's been FAR too long since college and learning about elastic modulus on spring rates so I'm going to defer to someone with a recent mechanical engineering background. Whatcha think??
 
#19 ·
The lower spring perch has a "groove" or cup stamped into it that takes the end of the spring "over here" and then cradles the next maybe 1/2 coil. Yeah, the top is flat and goes up against the rubber spacer up top. I think I have a lower spring perch loose in the garage if y'all would like me to post a picture.

Just in case this hasn't been accentuated:
These MB springs are EXTREMELY strong. Only an internal spring compressor has the oomph and enough safety to compress these things.

Always, always, always treat the ends of a compressed spring like a loaded gun. I've heard that if the spring compressor fails, it can damage or even break a cinder block wall, if the soft lumpy air breathing mechanic doesn't intercede to protect the wall. This can kill you. But.... like many dangerous tasks, if proper care is taken, nothing goes wrong or only the nearest wall is damaged. Y'all be careful out there!
 
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#20 · (Edited)
Yes everything Mike says. Can't cut the top of the springs as they are flattened to sit flat against the rubber shim up top. At the bottom the groove in the spring cup still works nicely.

If you were to cut the spring too much though, there's always the feint chance it could enable the spring to dislodge over a humped bridge or something. To be honest the springs are so stout it's hard to imagine, but probably possible.
 
#22 ·
281lxm, can you take total length measurements?

I have some brand new in the box Lesjofors #4256802 , which I think are for the 560SEC they measure 14.25" from the flat bottom to the tip of the top coil.

I vaguely remember that SEC and SEL springs are slightly different due to location of the fuel tank. Where is the fuel tank in a SEC?
 
#23 · (Edited)
Fuel tank is behind seat backs, vertical. I will measure Tire Automotive tire Auto part Tape measure
 
#24 ·
Tire Automotive tire Automotive wheel system Tape measure Auto part

Stock rear
 
#26 ·
I think it has to do with the fuel tank being directly over the rear axle versus just after the rear axle in the SEC?

I'm assuming all the springs here are for the 560SEC w/self levelling suspension. Whats interesting to see is that the old spring is 14.5" which looks like it stretched 0.25" if my new in box springs are 14.25". Or is 0.25" just manufacturing variation?

The 12.75" H&R spring is then 1.5" shorter than stock.
 
#27 ·
H&R says they are progressive rate. I would thing there is an advantage with a better ride quality till the spring starts to compress and rate increases...

Quote from the H&R website:
H&R Sport Springs lower the vehicle center of gravity and reduce body roll for better handling. The progressive spring rate design provides superb ride quality and comfort.
 
#28 ·
Despite H&R's claim, I don't think they're actually progressive rate. A true progressive rate spring has much tighter coils for about 1/3 of the spring; as it compresses, the tighter coils bind and the remaining spring is stiffer as a result. A progressive spring would be a nice thing to have for these cars, you could have both a better ride and tighter handling, but I suppose for the people who could do it the R&D required is too much relative to the market volume.
 
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