SLS Ride Height and Vibes

[TJ 450]

The rear end of my 450 has been subject to some criticism lately, as it seems to be too high. I have noticed on cars without SLS and my 6.9, that the half shafts are more or less level, whereas on my 450, the diff housing and wheel carriers are offset by a good inch or more. No amount of tweaking the linkage will reduce the height, however it will raise easily.

I'd be more than curious to know what the norm is here.

I'm trying to solve a low frequency wobbling vibration at between 50 and 60 km/h, that is either driveline or rear end related.

Also, regarding the flex discs,... I stupidly outsourced the work to have them replaced about a year and a half ago. I had a good look at them, along with the centre support and I think they may be installed incorrectly.

When looking at the diff housing from the front of the car and the tailshaft is rotating clockwise, the thick sections are being compressed, while the thin sections are being stretched. Would I be correct in saying that they should be installed in the exact opposite orientation, so that the thick sections are stretching and the thin sections are being compressed? This is how I installed them on my 6.9 and there is no vibration issues whatsoever on that car.

Tim

[s class]

TJ, I presume you are concerned about this following some of the 6.3 related discussions on this subject over at M100.cc

I recently changed the front flex disc on my 280SE (old one was splitting up) and I found that it is in fact only possible to install it one way - effectively pulling on the thin sections and compressing the thick sections.  It didin't seem logical to me, but I couldn't see how else to do it. 

[koan]

I'm trying to solve a low frequency wobbling vibration at between 50 and 60 km/h, that is either driveline or rear end related.

I had a vibration at 40 - 50 kmh when given a bit of throttle that was solved with a new centre bearing support.

I had a good look at them, along with the centre support and I think they may be installed incorrectly.

the thick sections are being compressed, while the thin sections are being stretched.

Thick sections, thin sections? I'm worried.

When I had that area apart I didn't notice any thick or thin sections in the flex disc, thought it was a uniform piece, possibly with raised lips around the bolt holes alternating side to side around the disc so it could only be installed at 120 degree intervals.

What have I missed?

koan

[TJ 450]

I read those discussions at the time I had the tailshaft removed from the 6.9. I didn't replace the flex discs on the 6.9 though, because it seemed unnecessary. The were they original 107 part number version with the obvious thin sections and they were assembled in the same way I found them; with the thick sections leading and the thin sections trailing behind, in reference to the flange arms on the forward side.

These ones on the 450 are the later 126 part. There is approximately 2mm difference in thickness between the thick and thin sections.

I'm actually beginning to doubt that the flex discs are a possible cause though, because the vibration is such that it suggests something is moving considerably. The vibration also occurs when coasting at 50-60km/h and is far worse when the ambient temperature is cold. The first possible cause I jumped on was that maybe the half shafts are working too hard.

The centre bearing support was replaced at the same time as the flex discs, although I noticed that the bearing is now quite sloppy, however the carrier is fine.

Last but not least, I was also thinking that the sliding spline could have something to do with it. If the nut was tightened (overtightened) at operating temperature on a hot day, presumably this would lock the shaft in that position? So, when the ambient temperature cools down, perhaps this would load up the tailshaft and force it out of alignment in the centre?

Edit: Having thought about this further, that seems pretty far fetched as well. The actual situation might just be the opposite, ie more clearance at the centering sleeves.

When I refitted the tailshaft on the 6.9, I made sure that the sliding spline was in fact able to slide... I thought that was the point of the sliding spline; to allow for expansion and contraction of the parts.

Tim

[Big_Richard]

didn't you say the other day, that if your 450 looses hydraulic pressure to the self leveling rear the rear end ends up very low ?

i suspect it is still an adjustment issue to that rear valve rod, something is causing the lack of adjustability to the length it needs to be. Isn't the ball mount position on the torsion bar adjustable aswel ?

I do second the notion that it rides too high at the rear, when driving behind nothing is left to the imagination, the drivetrain is visible and that's not appropriate behaviour, for a Benz

[GreaseMonkey]

I recently had the SLS reinstalled in my W116 Crayford wagon, (it had been removed by a previous owner) and although it was all working it was riding a bit high and harsh, feeling a bit like a one-ton ute with no weight in the back.
It too had camber going the wrong way, and yes the driveshafts should at least be horizontal.
Some careful adjustment on the link rod that connects the sway bar to the hydraulic actuator has made it ride like new. I think the mechanic who installed it left it riding at it's highest, but this means the struts are pressurised to the max and the springs can't do their job, but backing it off a touch, means the springs can now give a smoother ride and the SLS keeps it on the level.
The connecting rod has a ball joint at each end and an adjustable length rod with lock-nuts (one of course is left-hand threaded) and making the rod longer should let the car sit down a bit more, shortening it stiffens it up.
Fiddly bu**er to reach though unless you have it up on stands.
Good luck,
Chris M.

[oscar]

the drivetrain is visible and that's not appropriate behaviour, for a Benz

Very undignified. The Benz equivalent of "plumber's crack".   
My 350 has it too TJ.  I tried adjusting the rod as long as possible but wouldn't bring mine down.  I bled the levelling valve a few times, then test drove and after each bleed, the rear pumped up way too high again, but it can go higher if I adjust the rod and lever accordingly.  Two days ago I put 100kg of concrete in the boot (forgot my trailer) from a hardware store which sat the rear down a bit.  When I got home the rear was still high, rear wheels are like \   / to some extent. 

When I spoke of this problem before two suggestion seemed plausible.  Something in the return line causes over pressurisation (valve, blockage or otherwise) - or I need a new, used or rebuilt levelling valve.  My car doesn't sink overnight or after a few days at all and the only time it sits level when the engine is running is when the spheres have gone flat.  So I'm thinking it's to do with the levelling valve more than an over pressurisation but I haven't tried another valve yet like I said I would well over a year ago. 

FWIW, when I remove the adjusting rod and operate the lever by hand, one direction it's smooth, the other direction it feels like there's grinding happening.

[TJ 450]

Yes, it looks slightly agricultural from the rear, particularly with all that red dirt under there!

If I open the bleed valve to depressurise, it sinks right down to the ground. With the rod disconnected, I can move the valve manually, but all it does is raise the height too.

It sounds like it may be time to swap in the valve from my 126, and rebuild the existing one when it's off.

Thanks for all the excellent information.

Tim

[koan]

Think there's a kit to fix SLS valves, shame there isn't one for 6.9 valves.

koan

[Big_Richard]

the SLS valves arent even that expensive to buy as a new assembly, very, very common and were around for many years on various models too.

If i were you, id buy a new one, they are on eBay all the time - betcha its what the problem is

[TJ 450]

Alrighty, when the 6.9 is on the go, I'll look into getting a new valve and anything else that needs replacing back there on the 450... this includes the boots on the SLS struts and checking the spheres.

Tim

[Big_Richard]

Alrighty, when the 6.9 is on the go, I'll look into getting a new valve and anything else that needs replacing back there on the 450... this includes the boots on the SLS struts and checking the spheres.

Tim

Its about time the 450 received its share of love - the 6.9 will be making it jealous

[goldacre]

Hi folks, just picked up on TJ450s vibrations issue. My 280SEL has  exactly the same problem and after getting the rear wheel bearing replaced and the front flex disk replaced it still had the problem. This car was high on mileage and i put it down to just been a bit long in the tooth and having an issue hidden somewhere, don't you love how these old cars always hide something.

Well, f*&k me,    my museum piece one owner, always garaged and 103K on the clock 450SEL has exactly the same freaking problem. It is most noticeable coming down Greenmount Hill with no accelerator  (ie coasting) and when its around 50 - 60 kl/h the vibration/mild shudder comes in.

When i told my mechanic about the issue in the 280SEL he said it wasn't the center bearing as (read with heavy German accent with cigarette in mouth)  '...when you accelerate suddenly, best when going up a incline (ie steep driveway) you will hear/feel a knock, you car does not do this.'

Anyway, picked up a center bearing and support from AutohauseAZ '...because it was there.' for a future install on the 450

2 out of 2 owned Mercedes, surly more people out there experience this... (please)

[s class]

I may or may not have a similar problem with my red 6.9 - on power application, I get like a low frequency 'wobble' from the rear end.  I admit I haven't yet applied too much effort to locating the problem. 

[TJ 450]

That definitely sounds like the same problem, goldacre.

PB assisted me on the weekend by installing the leveling valve off my 380SE on the 450. It appears that the old valve was so worn that it was allowing excess pressure through to the struts. Now the rear end is down to a normal level, if slightly too low.

However, the vibration is the same, if not worse! Theres obviously something wobbling around majorly, but everything "looks" OK. I think I'm going to have to remove the tailshaft and inspect, although it's my daily driver, so I will have to be very well prepared. Even though the main vibration is at 50-60km/h there is a constant overall harshness. I will say though, that this car has never been smooth... there has always been a vibration, although it is particularly noticeable now that I've compared it to the 6.9. There is also a different set of wheels on the car, so I've ruled out them as a possibility.

My 6.9 is dead smooth, even without the shim under the trans mount.

Tim

Edited to add some additional information.