Any way to "test" SLS struts? - PeachParts Mercedes-Benz Forum

ps2cho · #1 03-07-2011, 03:18 PM

My wagon feels like it has no more shock element left in the struts....

Is there a test or anything? Any aftermarket SLS struts available from Bilstein anymore or is it OE option only? ($450/each!! ouch!)

p7fan · #2 03-07-2011, 11:06 PM

My understanding is that if they are not leaking, they are ok. The "cushion" is provided by the accumulators/spheres. The accumulators are easily tested. Hopefully you may just have an issue with the ride height setting on the control valve. There is a very good thread on how the system functions as well as testing and adjustments. I cant remember if its on this site or the "other" site under the w126 forum.

John

compu_85 · #3 03-07-2011, 11:15 PM

One way you could test the strut is to fill it with fluid, cap its fitting, then try to compress it. If it moves it is bad.

-J

James Redman · #4 03-08-2011, 03:44 AM

Quote:

Originally Posted by ps2cho

My wagon feels like it has no more shock element left in the struts....

Shock element is a thing?...or are you saying there is no damping?

If you tell us the symptoms in more detail we could help more.

balge · #5 03-08-2011, 05:58 AM

hi
way I read it those struts are not the dampers, damping is done by the spheres, the struts are rams to maintain ride height.

I remember an uncle had an old Citroen with hydro-pneumatic suspension - but as they don't use rams, it would sink about 6 inches when the engine was turned off....bad news if you did it with a door open next to the kerb!

I believe the way to test your spheres is CAREFULLY probe the fitting hole with something small enough to fit in but blunt, and soft enough not to rupture the diaphragm which separates the gas and oil, see if the probe hit anything before the top of the sphere - if you can't feel it, its burst!

Never tried it though!

If the struts don't leak and do move they should be fine?
cheers!

124126140 · #6 03-08-2011, 09:04 AM

If ride is bouncy, car is or was low on hydraulic fluid. If the struts are not leaking the accumulators are most likely full of oil and need to be replaced

ps2cho · #7 03-08-2011, 10:22 AM

The ride is not bouncy while driving, it just feels like the car "drops" really hard on speed bumps...like it is just bouncing off the springs in the rear.

babymog · #8 03-08-2011, 11:03 AM

The "shocks" do all of the damping, if all else is in proper condition.

If the spheres have ruptured, it is I suppose possible that in the early stages of failure some gas from the sphere(s) can make it to the damper(s), which would make it very bouncy / unable to damp motion.

James Redman · #9 03-08-2011, 11:11 AM

My car is a 500E...

My understanding of how the SLS fails is as follows:-

Bouncy Ride is caused by porus diaphragm in the spheres, creamy hydraulic oil at sphere.

Eventually the sphere fills with hydrulic oil giving a solid bone shaking ride.

The damping comes from the hydraulic oil entering and leaving the pressurised sphere.

My hydraulic struts were not leaking but were knocking. Replacing them reduced some of the knocking. Changing the top strut rubbers helped reduce knocking. Changing some suspension struts reduced knocking.
New spheres restored the damping. I did not touch the levelling valve at all. Now the SLS is restored to good working order.

balge · #10 03-08-2011, 12:12 PM

Quote:

Originally Posted by ps2cho

The ride is not bouncy while driving, it just feels like the car "drops" really hard on speed bumps...like it is just bouncing off the springs in the rear.

Sounds exactly like my 230TE - new spheres sorted it straight away and completely, could not believe how much better the ride was!

Car felt like it was bouncing, but with no damping its more of a 'crunchy' bounce than a 'wobbly' bounce?

Check this link, especially number 6 - http://forums.mercedesclub.org.uk/showthread.php?t=43903 all will become clear....

ps2cho · #11 03-08-2011, 01:20 PM

^ Thanks great link! Post #6 is incredible!

My SLS does not work either FYI (fluid level is fine, haven't filled it up in over 4 years now so safe to assume the struts are not leaking?)...SLS hasn't worked since I bought the car, but I didn't worry about it since the ride was fine, only recently has it declined.
I know the spheres are ~$100 x2, is it an easy swap?

I noticed today it does actually have a knock when I go down onto the street turning, sound even more like spheres now? If I replace the spheres, could my SLS magically start working again?

balge · #12 03-08-2011, 01:55 PM

If the struts were leaking it would be pretty obviously oily I suspect....

Changing the spheres is pretty straight forward, I managed it with just a Haynes manual, half a day or so but anyone competent could probably do it quicker!

Only 'gotcha's' I recall was the studs on the new spheres weren't threaded to the bottom like the old ones so I needed washers for them...
if the short pipes are corroded it might be worth replacing them, pretty cheap..I think the big ones are a bit more though...
access to the spheres is through the passenger compartment floor, took me a while to figure that out..

To check the system moves - which will show if the rams are seized - you need to load up the rear of the car, enough to make it sink...then start up and run it up to 1500-2000 rpm or so, should start lifting back to normal ride height fairly quick - a minute or so rather than seconds

You could try getting underneath and twisting the lever from the swaybar to the valve..but you will want it to be on nice high ramps,cos it comes down real quick if you turn it the wrong way......ask me how I know...

ps2cho · #13 03-08-2011, 09:45 PM

If the spheres are bad, should the SLS still work?

babymog · #14 03-08-2011, 09:48 PM

If the SLS didn't level/lift, you either have a bad pump (no fluid will be returning to the pump when the car is trying to lift due to inadequate pressure from the pump), or a bad leveling valve (leaking around the spool in the valve and allowing pressure to bypass and return to the reservoir), or no fluid.

The shocks/dampers do all of the damping, regardless of what some have posted, provided there is oil and not gas in them, they have all of the jounce/rebound valving. The accumulators are just that, accumulators, which store the fluid as it moves in/out of the dampers with counterpressure to provide a higher boiling point, prevent cavitation, and provide the pressure to return the fluid to the dampers.

Replacing the accumulator/spheres is fairly simple, but tedious. Removing the rear floor is a bit of a pain (finding the screws and getting the panel un-stuck from the floor), and getting the hydraulic lines' threads to line up can be difficult (the short one from the leveling valve to the Rt accumulator is my favorite). Be sure to get 4 new crush washers with the new spheres.

With bad spheres the SLS should still lift/level (see paragraph 1). When they go bad, the nitrogen escapes into the fluid causing a reduction in damping, after the gas is substantially exhausted you will have a very harsh ride due to the hydrolock (nowhere for the fluid to go upon jounce).

124126140 · #15 03-08-2011, 10:27 PM

Is the sway bar rod to the valve lever good? To test sls put 200lbs in the rear and rev at 2000 rpm for 30 secs it should lift.