Lowering a car with SLS

[Deleted member 11979]

As part of refreshing my C124 300CE, I'd like to lower the ride height by about 30mm.

The car has self levelling suspension fitted, does this need to be "told" that there is a new target ride height, and if so, how is this done.

Thanks a lot

 

[hotrodder]

Yep, the system takes it's instructions from a mechanical linkage between the rear anti-roll bar and the SLS valve. This linkage is adjustable to set the valves 'neutral' position (where pumped fluid is returned to the resevoir without letting any out of the struts). The AMG/sports suspension instructions for SLS are here... http://www.w124performance.com/docs/mb/W124/AMG_W124_conversion_SLS.pdf I've only scanned through it but i think it only deals with setting things up using the 'factory' special tools. I've got a vague recollection (for estates at least) that you want a full tank of fuel and about 120kg in the boot to set the neutral position but... Don't take my word for it regarding the numbers and more importantly don't crawl under the car and play with the valve as you could squash yourself

 

[Deleted member 11979]

Thanks very much for that, useful website

 

[hotrodder]

Yeah, although navigation around it is a bit pantshttp://www.w124performance.com/docs/mb/W124/

 

[balge]

Surely, if you just reset the level control valve neutral position, the springs will still be trying to hold their normal ride height, and the sls will be pulling them back down all the time? Or is 30mm not enough travel to start the pump?
cheers

 

[bolide]

I suspect static height is set by the rear springs. If you move the height corrector to the lowest position and let the car idle for a while with some weight in the boot it should move to the lowest position. If that's not low enough you'll need shorter springs. Sports Chassis springs might be a solution

I can't help thinking it's a bad idea unless you do a complete Sports Chassis makeover

Nick Froome

 

[mazza]

As part of refreshing my C124 300CE, I'd like to lower the ride height by about 30mm.

The car has self levelling suspension fitted, does this need to be "told" that there is a new target ride height, and if so, how is this done.

Thanks a lot

Hi CCAALLVVIINN

are you planning to use aftermarket lowering springs to achieve the 30mm drop?? If so, be careful as most aftermarket lowering springs do not work very well with the SLS System. Most aftermarket rear springs are linear and far too stiff to operate with the SLS System.

I have tested a few sets and have only come across 1 set that was specifically designed to work with the SLS system (w201 190).

mazza

 

[hotrodder]

Surely, if you just reset the level control valve neutral position, the springs will still be trying to hold their normal ride height, and the sls will be pulling them back down all the time? Or is 30mm not enough travel to start the pump?
cheers

When the engine is running the pump is running. As Bolide said the springs (and their rubber seating pads) are used (or should be) to set the basic ride height. The SLS system is designed to raise the back of the car when loaded not lower it. My thinking after reading the OP was along the lines of if i fit lowering springs all round will the back of the car try to raise itself to it's origional ride height or does it aim for 'level'?

If you drain the system the car will drag it's butt some as the system needs some 'nominal' pressure to work properly. This is where it gets harder to picture/explain... while the struts aren't dampers in the conventional sense they need pressure in them to provide damping in concert with the sphere's which contain nitrogen at something like 20+ bar. There are check valves to maintain this so even if the height corrector is in it's empty/discharge position the system will prevent pressure dropping below the min needed. At the same time there's also a pressure relief valve which diverts oil back to the resevoir even when the height corrector is in it's 'fill' position. This stops pressures rising too high in the case of a broken spring (or say someone tweaking the height corrector to compensate for tired springs). In either of those cases the SLS ends up doing more than it's 'fair share', oil pressures will be higher which is gonna mess with things as the oil is 'fighting' high pressure nitrogen

Mazza, when you were playing were you using sportline struts? I forgot about that yesterday but (on estates at least) they're different, presumably physically shorter? I get that it's not gonna fix things if the springrates of what's available are designed around convential suspension. I'm guessing sportline SLS coupe springs are a rare beast?

CCAALLVVIINN, as you want to lower it sod's law says that your current rubber spring cups will be the 1 or 2 'nib' variety but it's worth jacking up a back corner and having a look. If you're the lucky sort you might discover they're the thickest flavour and swapping them might get you part way there

 

[mazza]

Mazza, when you were playing were you using sportline struts? I forgot about that yesterday but (on estates at least) they're different, presumably physically shorter? I get that it's not gonna fix things if the springrates of what's available are designed around convential suspension. I'm guessing sportline SLS coupe springs are a rare beast?

Hi Hotrodder

I was preparing a 190e 2.3-16v for the track and wanted to check if the SLS system could do the job. The SLS is fine for mild track applications but for more serious applications the springs rates have to go up and so does the characteristics of the shock absorbers.

for everyday driving, the SLS cannot be beaten! thats for sure.

this is the progressive spring that works with the 190e SLS

springs data

Steel diameter - 12.2mm
Free length - 290mm
Fitted length - 225mm
Lowers chassis by 30mm

Progressive rates

5 mm to 20 mm displacement rate = 40.7 N/mm
20 mm to 35 mm displacement rate = 42.3 N/mm
35 mm to 50 mm displacement rate = 43.6 N/mm
50 mm to 65 mm displacement rate = 45.2 N/mm
65 mm to 80 mm displacement rate = 46.8 N/mm
80mm to 95 mm displacement rate = 48.5N/mm
95mm to 110 mm displacement rate = 63.1 N/mm
110 mm to125 mm displacement rate = 73.6 N/mm

Area "A" marked on the grey spring is the area that retains the OEM spring rate which allows the SLS to level out properly.

Red spring (40mm lowering linear spring)

Free length- 280mm
steel thickness-13.75
spacing between active coils 20mm
spring rate- 58N/mm 0r 5.91kgf/mm
Active coils- 8.5

mazza

 

[Deleted member 11979]

Hi CCAALLVVIINN

are you planning to use aftermarket lowering springs to achieve the 30mm drop?? If so, be careful as most aftermarket lowering springs do not work very well with the SLS System. Most aftermarket rear springs are linear and far too stiff to operate with the SLS System.

I have tested a few sets and have only come across 1 set that was specifically designed to work with the SLS system (w201 190).

mazza

I was thinking of it, but realised that there was more to this job than meets the eye. Looking in the options catalogue I can see that you could have Sportline with SLS on the estate, but am unsure with the coupe.

As I understood it, the valve is pretty simple, so if ride height too high is set to take fluid pressure out of struts, to low the opposite, correct neither add or remove pressure, pretty simple. I also understood that the position of the valve is to be set by a mechanical link somewhere to the car, so, in effect, the car has no idea if you are level or not, but is just trying to get the valve to the neutral position. Therefore, in my simple world, if I adjusted the neutral position of the valve sufficiently, then it would attain the "correct" lowered ride height at the rear.

So, now it seems that this is possible, it is which springs to choose.

I've never really been a fan of cheap parts, but neither do I subscribe to fitting the most expensive as it must be the best.

I'm a bit at sea now as you guys have bamboozled me (thanks very much - it's great to hear from people who know what they are up to) Am I to assume that W201 Sportline rear springs will do the job? If so, then would W124 coupe Sportlines do the same thing, or does the rates etc not suit the car as well?

Sorry if I am appearing stupid, I'm probably nbeing stupid in what I am trying to do which is to "make" a 300CE early Sportline replica with a manual gearbox, the trouble is, that as we are a family, and I have to enjoy my toys with the tribe, the removable tow bar and SLS are a real boon when fully laden, and I don't want to lose this feature of the car.

As an aside - can the sportline suspension be compatible with the MB towbar - yikes!

Thanks a lot for your continued help.

 

[Deleted member 11979]

CCAALLVVIINN, as you want to lower it sod's law says that your current rubber spring cups will be the 1 or 2 'nib' variety but it's worth jacking up a back corner and having a look. If you're the lucky sort you might discover they're the thickest flavour and swapping them might get you part way there

So, the springs sit on a rubber cup or pad, there are two thicknesses avaiable, if I have the thicker sort fitted then replacement with the thinner sort will reduce the ride height by the requisite amount?

How do I know which one is fitted?

Thanks a lot for your help, you guys are geniuses!

 

[Deleted member 11979]

I can't help thinking it's a bad idea unless you do a complete Sports Chassis makeover

Nick Froome

What is a complete sports chassis makeover?

 

[bolide]

What is a complete sports chassis makeover?

You'd have to check part numbers from an sc car and a non-sc car but I imagine it could be springs, ARBs, ARB bushes, front shocks, rear struts & spheres. That's a system designed to work together

If you change two elements - rear ride height and spring rate - the results may or may not be satisfactory. Quite likely the result will be good enough but you have to appreciate that every change has a knock-on effect

Nick Froome

 

[Deleted member 11979]

You'd have to check part numbers from an sc car and a non-sc car but I imagine it could be springs, ARBs, ARB bushes, front shocks, rear struts & spheres. That's a system designed to work together

If you change two elements - rear ride height and spring rate - the results may or may not be satisfactory. Quite likely the result will be good enough but you have to appreciate that every change has a knock-on effect

Nick Froome

Thanks, yes, I was going to also change the front springs and shocks.

One thing, it's always puzzled me, with access to all those lovely W124s, why do you drive a BMW? Just curious is all.

 

[hotrodder]

So, the springs sit on a rubber cup or pad, there are two thicknesses avaiable, if I have the thicker sort fitted then replacement with the thinner sort will reduce the ride height by the requisite amount?

How do I know which one is fitted?

Thanks a lot for your help, you guys are geniuses!

There's 4 thicknesses available and they can identified by the number of 'nibs' (or bumps/pips/lugs) on them for example 4 nib ...

The difference in thickness between the thinest (1 nib) and thickest (4 nib) is 15mm (they go in 5mm steps) but the suspension geometry means they effect ride height by a bit more that than that... i've a vague recollection that a 5mm difference in the spring pads = around 8mm difference in tyre to arch measurement but don't quote me on that. In theory you could get best part of an inch by changing the pads but as i said when you check you're bound to find that the car is sitting on one of the two thinner options as that's how life works

I've no idea if what (if anything) is still available and the only thing i'm sure of is that it won't be cheap new (the SLS struts will be eyewateringly spendy IIRC) but the pdf link i posted yesterday includes AMG part numbers for converting SLS equiped 4, 5 & 6 pot saloons, coupes & estates- springs, dampers and struts.

 

[Deleted member 11979]

I shall look into this, thanks a lot for all your help

 

[jaymanek]

Just as a note, my AMG W124 TE has a special modified AMG valve on the rear.. im guessing that the shorter AMG springs meant that the neutral position had to be modified past the range of the original valve block.