Repair SLS or replace with conventional suspension

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3DB
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Repair SLS or replace with conventional suspension

Post by 3DB » Sat 05 Nov, 2016 1:17 pm

I think it is fairly safe to say that my SLS is Donald Ducked. It is showing all the signs of basically every component needing replacement.

I flushed the system and added fresh oil and it is black again, which I understand could be a result of having some residual old oil in the system, but also engine oil leaking in via the hydraulic pump?

The system also leaks like a sieve. It has gone through about 2L of oil in less than 500 km, despite potential top-ups via the engine oil. Major leak appears to be around the levelling valve.

It bounces badly over bumps....etc...etc.

I know of a wrecked circa 1980 / 81 300D that I have salvaged a few bits and pieces off and it has a fully intact conventional suspension. Will it bolt into my car without any custom fabrication?

Assuming the 'new' suspension will fit and I can get t at the right price (happy to take recommendations on that price might be), what is my simplest (hours labour) and cheapest path to trouble-free rear suspension? Repair SLS or swap it out?

Some points I'm taking into consideration:
1) The 'new' suspension is still on the car in a paddock, having sat for I would say nearly 10 years, so will require a bit of gardening and pest control to access comfortably
2) It would be a pain to get a compressor and rattle gun out to the paddock (mainly as I don't own either) to assist with removal of ceased suspension bolts. I have been tempted to get a good battery-operated impact tool, so this could be the excuse.
3) I do have access to a friend's coil spring compressor.

As always, any thoughts or comments graciously received.
3DB
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Re: Repair SLS or replace with conventional suspension

Post by redlaser » Sat 05 Nov, 2016 1:45 pm

It's not difficult to replace the air suspension and it is so much better than springs..u will regret changing what Mercedes have designed for a smoooth ride!!

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Re: Repair SLS or replace with conventional suspension

Post by julian » Sun 06 Nov, 2016 11:48 am

redlaser wrote:It's not difficult to replace the air suspension and it is so much better than springs
These cars have hydraulic suspension, but I think that is what you might mean.

Your question (do I rebuild existing or replace with conventional?) has been posed so many times, here and elsewhere. The design of the w123 system is pretty simple and components are simple to replace. I have never met a w123 owner who has said they were happy with conventional spring/shock setup. You would regret it and it is false economy. Ride inferior.

Let's go through what problems you have or might have.

1. Contamination
The black oil in the system indicates that the seal in the SLS pump on the front of the engine has failed, and is leaking sooty contaminated oil into the suspension system. It is a delicate but not too hard thing to change. Parts are cheap.

2. Control valve leak
Not the most common place to leak but there is a seal kit. Again it takes patience but not overly complex. Kit from Mercedes is available.

3. Struts
You haven't mentioned these. Many w123s have signs of dirt/oil buildup at the base of the struts where minimal chronic weeping from what is essentially a constantly pressurised hydraulic ram has taken place over what could be up to 40 years now.
They don't need to be replaced routinely and are probably the most robust (and also costly) items in the system. Easy to remove but be careful with the fittings (under rear backrest covered with plastic panels) as they are awkward to get to and rather soft metal. Grab them from the paddock car- 2 big bolts accessed easily from underneath once you scrape the crud away.

4. Strut top rubbers
Absolutely buy new strut top rubbers (2 per side) and new copper washers (2 per side) from our forum sponsor regardless of whether you are replacing the struts. They are super cheap and the difference between old hard rubbers and new soft ones makes a significant difference to ride.

5. Ride quality.
Replace the spheres. They are the part of the system that controls damping. Bouncy or a hard ride indicate failing or failed spheres. Price should be $120-$200 each for aftermarket.

6. Springs
Often overlooked aspect, but the unladen weight of the car should be resting entirely on the springs. The w123 will (or should) ride on its springs but float on the spheres if you take my meaning.
Worn springs require increased pressure from your hydraulic system to maintain a static height and therefore displace a greater amount of space in the sphere nitrogen to compensate. As the rebound from the spheres is dynamic (rather than linear as is the case with a conventional shock and spring setup) you sacrifice the initial soft part of the damping and will prematurely wear out the spheres. This can be likened to carrying a very heavy load- the ride height with SLS remains the same but you lose some of the initial damping that makes these systems peerless. You should be able to depressurise the SLS system and not have the rear sag badly.
If you release the SLS pressure and it does then then consider swapping out springs. I recently put a set of w126 rear springs in a w123 and the height was perfect and ride much improved- I am not advocating you do this but it might be a cheap option if yours are bad.

7. Tools and safety
As always with these systems, ensure the car is supported when you work on the system.
Use flared nut spanners on the lines to avoid rounding off the fittings and resultant heartbreak.
No big or air tools are required to remove anything you might need, other than a spring compressor to make quick work of the springs. Biggest bolts are on the bottom of the struts, and easily done with a 1/2" breaker bar.
Save your money by not buying a cordless impact gun and put the money towards new spheres instead.
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Re: Repair SLS or replace with conventional suspension

Post by 3DB » Mon 07 Nov, 2016 11:41 am

Julian - thanks again for another very comprehensive and logical summary.

I will price up the parts I need and make a decision. It isn't a part of the car I really want to spend the time (and even less so, money) on, but the rate it is going through fluid may force my hand and bring it up the priority list.

Here's a question - I understand SLS was used on other later model cars and the entire W123 wagon range, but why did they discontinue it on the W123 sedans in 1980 or thereabouts?
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Re: Repair SLS or replace with conventional suspension

Post by julian » Mon 07 Nov, 2016 7:33 pm

3DB wrote:why did they discontinue it on the W123 sedans in 1980 or thereabouts?
As far as I was aware it remained a standard item throughout the series. Some cars came without it, and others have had it removed.
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Re: Repair SLS or replace with conventional suspension

Post by pastelgrey300D » Tue 08 Nov, 2016 11:26 am

I'm guessing it was a cost cutting measure? Maybe keeping the SLS for the upmarket models or the wagon variants where heavier loads were expected in the rear?

The vacuum adjustable headlights replaced the SLS function - although on my 1980 300D it had both the SLS and the vacuum headlight aiming feature.
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Re: Repair SLS or replace with conventional suspension

Post by peterac » Tue 08 Nov, 2016 6:48 pm

My mechanic said that very poor roads in South Africa blew the sls systems often and Mercedes responded with changing to conventional suspension in that country. He has removed many sls systems and blanked off the pump when they have come in leaking (not my view). My 300D 1980 has factory non sls ie no provision for sls pump. He is the Newcastle classic mechanic and said he has never seen one factory before. Never looked to see if it was oz delivered or not. Just assumed it was an import.
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Re: Repair SLS or replace with conventional suspension

Post by tsharkey » Thu 10 Nov, 2016 9:29 am

My experience is nearly all AU delivered Series I sedans, coupes and wagons has SLS. => Pre 1980.

Series II and III were only on wagons.

All AU delivered wagons I have come into contact with have had the vacuum adjustable headlights with the standard SLS.

There would be a rationale behind dropping it on the Series II & III sedans and coupes. Probably cost.
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Re: Repair SLS or replace with conventional suspension

Post by mydave1910 » Wed 28 Dec, 2016 11:25 am

It's not difficult to replace the air suspension and it is so much better than springs..u will regret changing what Mercedes have designed for a smoooth ride!

Im also one who regrets going conventional"". Even my mechanic was PO that he encouraged the change as it was a difficult job in the end.

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Re: Repair SLS or replace with conventional suspension

Post by roylefamily » Fri 13 Jan, 2017 7:45 am

I have a set of good bulbs and the ride level valve, You can have them cheap.

viewtopic.php?f=5&t=23505

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Re: Repair SLS or replace with conventional suspension

Post by CraigB » Fri 13 Jan, 2017 10:43 am

good summary, the only addition is to check the hose from the pump. These often leak but can be remade by a hose place - enzed etc but they must reuse the plastic bits inside the hose as i recall. For the cost involved and time, i would do the seals in the pump and see what happens, unless there are leaks you can see elsewhere.
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Re: Repair SLS or replace with conventional suspension

Post by roylefamily » Sat 14 Jan, 2017 4:44 pm

3DB wrote:I think it is fairly safe to say that my SLS is Donald Ducked. It is showing all the signs of basically every component needing replacement.

I flushed the system and added fresh oil and it is black again, which I understand could be a result of having some residual old oil in the system, but also engine oil leaking in via the hydraulic pump?

The system also leaks like a sieve. It has gone through about 2L of oil in less than 500 km, despite potential top-ups via the engine oil. Major leak appears to be around the levelling valve.

It bounces badly over bumps....etc...etc.

I know of a wrecked circa 1980 / 81 300D that I have salvaged a few bits and pieces off and it has a fully intact conventional suspension. Will it bolt into my car without any custom fabrication?

Assuming the 'new' suspension will fit and I can get t at the right price (happy to take recommendations on that price might be), what is my simplest (hours labour) and cheapest path to trouble-free rear suspension? Repair SLS or swap it out?

Some points I'm taking into consideration:
1) The 'new' suspension is still on the car in a paddock, having sat for I would say nearly 10 years, so will require a bit of gardening and pest control to access comfortably
2) It would be a pain to get a compressor and rattle gun out to the paddock (mainly as I don't own either) to assist with removal of ceased suspension bolts. I have been tempted to get a good battery-operated impact tool, so this could be the excuse.
3) I do have access to a friend's coil spring compressor.

As always, any thoughts or comments graciously received.
Just got your PM but can't reply till I have more posts. Will when I can. I had a wagon converted to conventional. A bad result, very disappointing. The wagon used to float over the speed humps and handled very well. After the conversion it was like a Holden.

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Re: Repair SLS or replace with conventional suspension

Post by CraigB » Sat 14 Jan, 2017 10:15 pm

Not sure how many when you posted the last message but you have 9 posts now so should all be working.
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Re: Repair SLS or replace with conventional suspension

Post by 3DB » Sun 19 Mar, 2017 4:24 pm

I've now got a partially refreshed SLS thanks to spheres from tsharkey's 230TE and leveling valve from roylefamily's 280TE. Had to do a bit of shuffling of hose fittings around to make the wagon bits work on the sedan, but seems all good. Haven't had a chance to properly test drive yet, but wanted to check whether any bleeding is required. I saw a couple of bleed points on the valve.

If this goes well I will put a seal kit thru the hydraulic pump too.
Last edited by 3DB on Sun 19 Mar, 2017 8:59 pm, edited 1 time in total.
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Re: Repair SLS or replace with conventional suspension

Post by CraigB » Sun 19 Mar, 2017 4:28 pm

My understanding is it will bleed itself.
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Re: Repair SLS or replace with conventional suspension

Post by tsharkey » Sun 19 Mar, 2017 4:57 pm

CraigB wrote:My understanding is it will bleed itself.
Correct - run for a while and bounce the rear end. The nipples you saw is to depressurise the system for servicing.
W123 1981 300TD - Family Kid mover
W202 1998 C250D Factory OM605A Turbo - Partner's daily driver
W123 1982 300CD Retro fitted OM617A Turbo - Mine
W123 1984 300TD 5 Speed Manual, to teach the kids how to drive
W123 1982 300TD Factory OM617A Turbo (Hans) - Project
W123 1985 230TE - Brother's
W123 1985 300D - Sister in Law's
1962 S-Series Valiant (Tho Daimler & Chrysler divorced, still part of the extended family)

Past benzes
W114 1969 250CE - PO put in an M110 transplant and nearly sent me around the bend
W123 1981 300TD - "Matilda" - RIP hit front side & rear but left my brother + niece A-OK

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Coupe restoration, Turbo Wagon freshen up

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Re: Repair SLS or replace with conventional suspension

Post by 3DB » Sun 19 Mar, 2017 8:58 pm

The nipples you saw is to depressurise the system for servicing.
Those would have been handy prior to cracking the lines at the sphere to avoid the moderately spectacular gush of hydraulic fluid that ensued! Fortunately I had a jar sitting on the control arm underneath and a 7L oil drain tray under that that caught most of it.

Truth be told, I didn't even know the nipples existed on my old valve as it was so caked in crud from the constant ongoing leaks over who knows how long. The level of filth on that levelling valve was something to behold, even after a good blast with Brakleen. I will post a photo.
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Re: Repair SLS or replace with conventional suspension

Post by 3DB » Mon 20 Mar, 2017 10:54 pm

Finally took it for a decent drive tonight and it is like a different car. I hit every pothole and manhole cover I could see it and it just soaks it all up. I only feel those bumps in the front - the rear just soaks it all up. Amazing transformation. Definitely a success.
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Re: Repair SLS or replace with conventional suspension

Post by CraigB » Tue 21 Mar, 2017 9:49 pm

interesting reading for those keen to chuck the sls and put in the not inconsiderable effort of fitting springs. Will try and remember this thread and refer to it next time the question is asked.
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Re: Repair SLS or replace with conventional suspension

Post by 3DB » Wed 22 Mar, 2017 4:46 pm

I've been thinking about that a lot too, Craig.

It was a bugger of a job and took me ages, but if I had to do it again tomorrow I would do it in half the time by not making the same mistakes.

But on balance, I definitely agree that swapping to conventional springs would have been a much bigger job.

I have still yet to rebuild the hydraulic pump though......

Here is that photo of the lovely old levelling valve too by the way...almost unrecognisable as such other than where I cleaned it
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Re: Repair SLS or replace with conventional suspension

Post by 3DB » Fri 17 Nov, 2017 7:30 pm

So I had a rush of blood to the head this afternoon, having replaced the turbo on my Rodeo last week and finally solved my coolant issues on the Merc, I decided to dive into the SLS pump rebuild.

Can I say it has been one of the more satisfying projects I've embarked upon lately.

Anyway, it is all back together but I just wanted to get some thoughts on the new shaft seal where it bolts onto the engine block.

As you can see in the attached photos, the original fitment had two smaller, seemingly identical, seals (left in photos).

But what I got in the rebuild kit from MB Spares just has the one seal (right in photos)

What are your thoughts? Proceed with the new seal? Seems to fit ok.
IMG_6566.JPG
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Re: Repair SLS or replace with conventional suspension

Post by mathuisella » Sat 18 Nov, 2017 1:12 pm

Hmm, well 2 seals is always better, depends on how the condition of the original seal is. If it's nice and rubbery and not age-hardened I'd stick to the original, but that's just me, i like to have all original parts as much as possible.

I have the SLS hydraulic pump as well as 2 new nitrogen bulb things if you need as well :)

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Re: Repair SLS or replace with conventional suspension

Post by brycedunn » Sat 18 Nov, 2017 6:44 pm

3DB wrote:
Mon 07 Nov, 2016 11:41 am
Here's a question - I understand SLS was used on other later model cars and the entire W123 wagon range, but why did they discontinue it on the W123 sedans in 1980 or thereabouts?
From the Factory, rear SLS was standard on the wagons and optional on everything else. What options were standard on the cars here in Australia was down to the importer (Mercedes Australia) and they made some odd decisions over the years. Not sure about the entry level cars like the 230 and 240D, but MB Australia specified rear SLS as standard for other W123's in the first half of production. After that it was not a standard option here but certainly available from the factory. They were still specifying rear SLS as standard on the S Class.
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