rear coil springs puzzle - PeachParts Mercedes-Benz Forum

Beirut Brit · #1 01-20-2025, 09:27 AM

HI
Some of you will remember my 560 SEL which, when it arrived shortly after from the US, its moroccan owner pulled out the v8 engine and replaced it with a 603 non turbo unit. He also changed the suspension which i just discovered today which is what i need to ask members about.

Originally it has the SLS system, or I assume so as i can see pressurized little bottles on each side of the rear coils. At some point, this was abandoned for a regular, simple coil and shock system.

WHat's the problem? Well, when i put my tool box in the back the car goes down about 3 to 4 cm which i think is not right at all. Aha ! Classic sign of worn shocks you might say, which is what i assumed. But in fact i had them checked on a machine and they re fine. With the shocks out, the space between the tyre and the rear wheel arches are exactly the width of my five fingers, which looks about 2cm higher than normal.

Here's what i;m thinking. I think the PO didn't pay too much attention to the springs he put in. Would this explain why without the shocks it sits a tad too high? Or with the shocks, i should add, its about 2cm too low, visibly. A few weeks ago i put a 70kh solar battery in the back and it must have gone down 5cm.

What is the precise length of those springs? Does anyone know? Can i compensate by searching for a new shock which is 3cm longer? Also, can those springs be easily removed with a spring compressor by simply lowering the axle ?

Any ideas or advice welcome. thanks

MJ

engatwork · #2 01-20-2025, 07:44 PM

Research and see if 560SELs were available with rear springs. That is p/n of springs you need.

Diseasel300 · #3 01-21-2025, 10:08 AM

Shocks have no bearing on how much the rear end sags. Shocks are there to dampen spring oscillations and stiffen up the ride. More than likely the PO just yanked the SLS rams out and threw shocks in. The 560SEL springs are softer than the non-SLS 420SEL or 300SEL/SDL cars and will make the car sag and wallow.

Look up springs for a 420SEL without SLS and install the 3-nub rubber spring buffer. Yes, you can delete SLS from a 560SEL. I've done it twice on cars with bad parts and they drive and handle just like any other LWB car without SLS.

Additionally, if installing the shocks makes the rear end sag, you have the wrong shocks. Period. They shouldn't be limiting suspension travel. The shocks are common to ALL W126 cars. Make sure you have the right ones installed. They should have no effect on ride height. If you're still saggy after replacing the springs and shocks with the right parts, replace the subframe and differential mounts. They break down and sag and if bad enough, count for about 1 inch (2cm or so) of ride height in the rear.

Beirut Brit · #4 01-21-2025, 02:23 PM

thanks. Can i have a couple of follow up questions, as there's a lot to unpack there>

1. How can i know for sure if the shocks i have are the correct ones?
2. How can i know the correct length?
3. So, under normal circumstances, the car is about 2cm lower at the rear with the shocks in. Are you saying that the original springs for the 560 will be too soft when fitted with regular shocks, and therefore i need to order the 420s WITH new upper rubber mounts?
4. If i went to the scrapyard here, i could probably find the springs from a 300 SDL but how would i be sure they are correct? i mean, are they a different length to the ones from the 560? How do you distinguish 'em?

thanks mate!

MJ

Quote:

Originally Posted by Diseasel300

Shocks have no bearing on how much the rear end sags. Shocks are there to dampen spring oscillations and stiffen up the ride. More than likely the PO just yanked the SLS rams out and threw shocks in. The 560SEL springs are softer than the non-SLS 420SEL or 300SEL/SDL cars and will make the car sag and wallow.

Look up springs for a 420SEL without SLS and install the 3-nub rubber spring buffer. Yes, you can delete SLS from a 560SEL. I've done it twice on cars with bad parts and they drive and handle just like any other LWB car without SLS.

Additionally, if installing the shocks makes the rear end sag, you have the wrong shocks. Period. They shouldn't be limiting suspension travel. The shocks are common to ALL W126 cars. Make sure you have the right ones installed. They should have no effect on ride height. If you're still saggy after replacing the springs and shocks with the right parts, replace the subframe and differential mounts. They break down and sag and if bad enough, count for about 1 inch (2cm or so) of ride height in the rear.

Diseasel300 · #5 01-21-2025, 08:35 PM

1: See if the shocks you have installed have a part number and look them up to see what they go in. The W126 rear shocks will NOT affect ride height and should allow the rear control arm to go nearly to it's full travel limit when the rear of the car is raised.

2: Correct length isn't important. Just make sure you have the correct shock. If they're compressing your rear springs, they're clearly not correct.

3: Rear springs on a car with SLS are softer than a car without SLS since the SLS rams are designed to help support the load of the car and correct ride height. Deleting the SLS system will cause the rear of the car to sag. The 3-nub pads with the correct non-SLS springs should correct the ride height, but you can still expect the rear to sag with a heavy load in the trunk, just like any other car.

4: Good luck finding springs for a 300SDL anywhere but the USA. Look for a first generation 300SD, 380 or 500SE, or a second generation 300SE, 300SEL, or 420SEL. The springs should all be the same. Alternatively, just order new springs. They're something like $50 for the pair brand new.

Beirut Brit · #6 01-22-2025, 01:20 AM

thanks so much for this. Your info is very useful. But what i conclude is that i have to change BOTH the shocks and the springs, as the present springs are too soft with regular shock absorbers - so there's not much point in just changing one. Yes, the springs are 50 bucks in USA but im in third world country here and they will end up being 200 once shipping and taxes are added, so its the junk yard. I still don't know what i'm looking for though if the 300 SDL or 420 are the best ones as i don't know their specifications compared to mine. If i understand correctly, they may be the same length but they are a different strength/build.

Don't get mad. Hear me out. WHAT if there was a easy solution here? COuld i put in tougher, stronger shocks so as to strengthen the springs, so to speak. Just an idea.
Also what's the thickness of the pads which go at the top of the coil. A bit of googling reveals there are different sizes. I would guess that mine are original and worn out a bit. Which one would you order?

thank you again

MJ

Quote:

Originally Posted by Diseasel300

1: See if the shocks you have installed have a part number and look them up to see what they go in. The W126 rear shocks will NOT affect ride height and should allow the rear control arm to go nearly to it's full travel limit when the rear of the car is raised.

2: Correct length isn't important. Just make sure you have the correct shock. If they're compressing your rear springs, they're clearly not correct.

3: Rear springs on a car with SLS are softer than a car without SLS since the SLS rams are designed to help support the load of the car and correct ride height. Deleting the SLS system will cause the rear of the car to sag. The 3-nub pads with the correct non-SLS springs should correct the ride height, but you can still expect the rear to sag with a heavy load in the trunk, just like any other car.

4: Good luck finding springs for a 300SDL anywhere but the USA. Look for a first generation 300SD, 380 or 500SE, or a second generation 300SE, 300SEL, or 420SEL. The springs should all be the same. Alternatively, just order new springs. They're something like $50 for the pair brand new.

Diseasel300 · #7 01-22-2025, 03:32 PM

Shocks only need to be changed if they're wrong for the car. I've said it twice now and I won't say it again after this: CHECK THE PART NUMBER ON THEM AND SEE WHAT THEY FIT! If they're not for a W126, hit the trash with them and install the correct ones. Firmer shocks won't help ride height. All non-SLS W126 cars take the same rear shock, so it should be very easy to determine if you have the right one or not.

Springs are commodity items. They're produced both by Bilstein and Lesjofors and are globally sold. I find it next to impossible that you couldn't find them through some reseller in your country.

You also don't seem to understand that the 300SDL was a US-market car ONLY. It was never sold in any other country, so finding one in a junkyard in Morocco isn't gonna happen unless someone imported one of the 13K or so made and scrapped it recently enough for you to find it. You're better off setting your sights on a 300SEL or 420SEL which both share the same rear spring and were sold globally.

The spring pads come in 1, 2, or 3 nub versions. The number of nubs denotes thickness of the rubber pad. 3 nub versions are the thickest and are pretty much required on the long wheelbase W126es to get the ride height correct.

Don't overlook rear subframe and differential mounts. If they're tired and sagged, that's nearly an inch of ride height you've lost from the collapsed rubber.

Beirut Brit · #8 01-23-2025, 01:29 AM

You've misunderstood my point. Calm down. I DID check the number on the shocks and they are for the 300D. And i did understand your point about ride height. But you ALSO said that the original springs on the 560 would be too soft with conventional shocks with the SLS removed so i was wondering if shocks built for a heavier load, for example, would firm up the springs, so to speak.

You also don't seem to understand that all of the mercedes in Morocco are imported from the US, more or less, as was mine. There are plenty of 300Ds here. My concern is that when i go to the scrapyard i get cheated. This is a country where people don't say "i don't know" and it is common for scrap yard folks to palm you off with the wrong part just to get some cash in their hand. That's why i asked you so many questions about how to identify if the springs were really from a 300D or 300SDL.

I actually have a friend in Ireland who is scrapping a 420. I wonder how heavy those springs are and whether they could be posted. I have noted what you have said about the 3 nubs.

I appreciate your point about the diff mount but i can't determine just by looking at it if it's sagging or not.

Weird thing is that now i 've put everything back the rear end is not so soft as it was before.

Don't get so worked up mate. We're on the same side. Well, we weren't in 1776 but that's a long time ago

thanks again

MJ

Quote:

Originally Posted by Diseasel300

Shocks only need to be changed if they're wrong for the car. I've said it twice now and I won't say it again after this: CHECK THE PART NUMBER ON THEM AND SEE WHAT THEY FIT! If they're not for a W126, hit the trash with them and install the correct ones. Firmer shocks won't help ride height. All non-SLS W126 cars take the same rear shock, so it should be very easy to determine if you have the right one or not.

Springs are commodity items. They're produced both by Bilstein and Lesjofors and are globally sold. I find it next to impossible that you couldn't find them through some reseller in your country.

You also don't seem to understand that the 300SDL was a US-market car ONLY. It was never sold in any other country, so finding one in a junkyard in Morocco isn't gonna happen unless someone imported one of the 13K or so made and scrapped it recently enough for you to find it. You're better off setting your sights on a 300SEL or 420SEL which both share the same rear spring and were sold globally.

The spring pads come in 1, 2, or 3 nub versions. The number of nubs denotes thickness of the rubber pad. 3 nub versions are the thickest and are pretty much required on the long wheelbase W126es to get the ride height correct.

Don't overlook rear subframe and differential mounts. If they're tired and sagged, that's nearly an inch of ride height you've lost from the collapsed rubber.

vstech · #9 01-23-2025, 08:23 AM

Shocks will not affect ride height.
Unless they are air/sls shocks
...

Diseasel300 · #10 01-23-2025, 01:38 PM

Quote:

Originally Posted by Beirut Brit

You've misunderstood my point. Calm down. I DID check the number on the shocks and they are for the 300D. And i did understand your point about ride height. But you ALSO said that the original springs on the 560 would be too soft with conventional shocks with the SLS removed so i was wondering if shocks built for a heavier load, for example, would firm up the springs, so to speak.

You also don't seem to understand that all of the mercedes in Morocco are imported from the US, more or less, as was mine. There are plenty of 300Ds here. My concern is that when i go to the scrapyard i get cheated. This is a country where people don't say "i don't know" and it is common for scrap yard folks to palm you off with the wrong part just to get some cash in their hand. That's why i asked you so many questions about how to identify if the springs were really from a 300D or 300SDL.

I actually have a friend in Ireland who is scrapping a 420. I wonder how heavy those springs are and whether they could be posted. I have noted what you have said about the 3 nubs.

I appreciate your point about the diff mount but i can't determine just by looking at it if it's sagging or not.

Weird thing is that now i 've put everything back the rear end is not so soft as it was before.

Don't get so worked up mate. We're on the same side. Well, we weren't in 1776 but that's a long time ago

thanks again

MJ

So you have W123 and not W126 shocks. Hit the trash and get the correct shocks. Heavier duty shocks will not affect your ride height. The reason the SLS springs are weaker is because the hydraulic rams and nitrogen spheres in the SLS system make up part of the support framework of the car. That's kind of the point of the SLS system is to keep the rear end of the car level and it is capable of raising or lowering the car with hydraulic pressure. This is not the case with a traditional spring/shock arrangement, the spring takes the total load and is heavier/stiffer. The shock absorber is only there to dampen spring oscillations over a bump, it has zero effect on your ride height unless it's the wrong shock and it's keeping the spring compressed (very likely since you have W123 shocks fitted).

You ask the same questions with different details again and again. A 300D has never entered this conversation until now and you're looking for springs for a 300D or 300SDL? Why? 300D springs won't be correct for any W126 model and a 300SDL is more of a unicorn than finding a 420SEL or 300SEL, both of which have the correct rear spring you're looking for. Unless you pulled the spring from the car yourself, there's no way to know for sure if they're the right one.

Diff mount is pretty easy to tell if it's sagging. Get under the car and look at it. The bottom of the "U" shaped shackle has a pointed tip pointing upwards towards the rubber bits that make up the mount. If it's touching the rubber, it's done. There should be a fair gap between that pointed section and the rubber.

Subframe mounts are similar. There's a metal retainer over them where the bolt goes through. If the mounts are good, that metal retainer will have a good 1/2" or more gap between it's edge and the rubber of the mount. If it's sagged and worn out, it'll basically be sitting on the rubber of the mount. They can get to the point where they literally fall apart and start knocking the subframe against the bottom of the car and making a rattling noise over bumps.

Sugar Bear · #11 01-23-2025, 02:28 PM

Try to get springs and shocks for/from any W126, preferably a long body. Check the differential and subframe mounts. Get the the car four wheel aligned and enjoy the car.

Mxfrank · #12 01-23-2025, 04:55 PM

The strength of a spring is determined primarily by the diameter of the spring wire. Ride height by a combination of wire diameter, overall diameter of each coil, length, and number of coils. If you’re ambitious, you can calculate your spring rate using an online calculator like this:

https://www.thespringstore.com/helical-compression-spring-design-calculator.html

It’s clear that not many here have visited Morocco. What I would suggest is to take a spring out, and bring it to the yards. Try to find a spring of the same diameter and height, but thicker wire. The strength of the spring increases in proportion to the fourth power of wire diameter, which means not much more thickness gives a lot of extra height. Then sit down for a too-sweet mint tea and strike a bargain.

Beirut Brit · #13 01-24-2025, 12:54 AM

Great advice. I think i will do just that. But im still struggling with the notion that shocks from a 300D/300SDL/DL can't be "W126". Isn't a 300D a W126?
Morocco has hundreds of what people call here a 300D, which is usually the W126 with either 5 or 6 cylinder diesel engine. They were originally hotel taxis used exclusively for the airport run. If you say to a guy in a scrapyard here "W126" he'll just look at you like you're talking Chinese.
thanks!

Quote:

Originally Posted by Mxfrank

The strength of a spring is determined primarily by the diameter of the spring wire. Ride height by a combination of wire diameter, overall diameter of each coil, length, and number of coils. If you’re ambitious, you can calculate your spring rate using an online calculator like this:

https://www.thespringstore.com/helical-compression-spring-design-calculator.html

It’s clear that not many here have visited Morocco. What I would suggest is to take a spring out, and bring it to the yards. Try to find a spring of the same diameter and height, but thicker wire. The strength of the spring increases in proportion to the fourth power of wire diameter, which means not much more thickness gives a lot of extra height. Then sit down for a too-sweet mint tea and strike a bargain.