SLS Rear Strut - Replacing a failed lower spherical joint with urethane bushing

[tuttebenne]

Moderator edit: Updated thread title to more accurately reflect content below.

Original thread title:
SLS Rear Strut - Can the system pressure be reduced/removed before removal?

I'm going to repair my passenger side strut to get rid of the clunk these devices develop over time. I repaired the driver's side strut five years or so ago and its working fine but recall a nice fluid bath when I loosened the banjo nut. I can wrap it with a rag this time but was wondering if there is a better/cleaner way to reduce/release the system pressure before loosening the banjo nut.

 

[luckymike]

I'm going to repair my passenger side strut to get rid of the clunk these devices develop over time. I repaired the driver's side strut five years or so ago and its working fine but recall a nice fluid bath when I loosened the banjo nut. I can wrap it with a rag this time but was wondering if there is a better/cleaner way to reduce/release the system pressure before loosening the banjo nut.

I'm interested in this answer as well. I'm also curious how you repaired the other strut?

 

[kubasz]

You can simply set the leveling valve to empting position and allow the car to sit down on the springs. Then you set the leveling valve to the middle position and you can now lift the car and undo the banjo connection. The strut will not be completly empty but the majority of the pressurized oil will be out of the strut at that point.

 

[gsxr]

There is a bleed screw on top of the SLS valve, similar to a brake caliper bleed screw. Connect a hose to this and unscrew it, this will fully release all system pressure.

See FSM job 32-0630, the bleed screw is item 3p in the diagram.

 

[tuttebenne]

You can simply set the leveling valve to empting position and allow the car to sit down on the springs. Then you set the leveling valve to the middle position and you can now lift the car and undo the banjo connection. The strut will not be completly empty but the majority of the pressurized oil will be out of the strut at that point.

Thank you for this, and also Dave (GSXR) thanks for your input. I am leaning toward the bleed screw method and will see how this works.

 

[luckymike]

Thank you for this, and also Dave (GSXR) thanks for your input. I am leaning toward the bleed screw method and will see how this works.

Tuttebenne, would you share how you repaired the clunk on your other strut?

 

[nocfn]

If the bleed screw is too difficult to break free (and you do not have GVZ popeye forearms) then you could just bleed the line associated with the strut at the sphere as it is much easier to access.

 

[tuttebenne]

I'm interested in this answer as well. I'm also curious how you repaired the other strut?

Mike I will try to document what I do. I included a photo to give you some information now.

The repair to the other strut is working well but not elegant. No noise, no change in suspension dynamics. However, I would like to improve on the previous process to remove any potential issues.

It is my opinion the lower strut mount is engineered for something other than a 500e rear suspension. Contained within the lower mount is a pair of Delrin-like inserts that closely fit the shape of the steel bushing that the bolt runs through. This steel bushing is conical spherical which allows the busing to swivel like a heim joint. Clearly, with a bolt running through it and through the LCA there isn't any swiveling going on but that is the design they used. Edit: They may have used the conical/spherical surface of the bushing to distribute the load across more of the Delrin - this is totally possible too, but probably unnecessary as proven by the billions of shock absorbers in use that never wear the bottom bushing enough to be a problem.

On the outside of each Delrin insert but just inside the casting is a rubberlike ring/seal. On the outside of each side of the lower mount is a boot. What happens is the boot cracks at some point, moisture penetrates this assembly, and the steel bushing rusts to the point where the bushing surface becomes rough and it grinds away at the Delrin until there is so much play between the metal bushing and the Delrin that you get the familiar bang/clunk in the rear suspension.

In the photo is an original SLS strut and you can clearly see the rusty dust that is being pumped out of the joint with each jounce of the rear suspension. Since this portion of the SLS strut is hidden deeply within the LCA, we usually never see this until its too late.

I remove the boot, the seal, the Delrin and the bushing (this takes a bit of drilling and picking at the Delrin so you can remove it in bits). At the factory they insert all of these pieces and contain them by swaging the casting, crimping this all in place and making it unserviceable. What I do is open up the swage on one side using a stepped drill but those of you with a Bridgeport will do better. Once this is opened up just enough, I press two eurethane bushings in place. This is a breeze with a standard vice. Although they are not metric, the new eurethane bushings fit perfectly and the I/D of the bushing allows the securing bolt to pass through them with a slight amount of pressure. For those of us who DIY its almost too good to be true. These bushings are available anywhere at less than $7.00 for four. While I am far from cheap when it comes to maintaining my 500e I'm not of the mind to spend upwards of between $650 - $1000 for a pair of struts if all they need is $7.00 worth of parts and a little effort.

If we change fluid regularly and pay attention to the accumulators (and I do), the struts and their inner seals can last virtually forever. The only inevitable failure will be the familiar clunking that SLS equipped cars suffer from. The area of my repair to the original driver's side strut that I want to reengineer is the gap between the new bushings and the LCA and to address the possibility of the new bushing moving out of the lower mount over time. I shimmed the gap on either side of the securing bolt and have a large washer keeping the new bushing in place. Although I have had zero issues with the repaired one and the bushing stays put, I think we can do better. More to come and thanks again guys for saving me a hydraulic fluid bath when I remove the SLS strut.

Right now I am having trouble uploading my photo. I am getting a "file too big" error although its a JPG less than a megabyte. What gives?

 

[tuttebenne]

I figured out the image dimensions were the issue (24 inches wide was a bit of a problem)

A shadow in the photo makes it appear there is a small gap between the casting and the urethane bushing. In reality there is not; the fit is tight. When I did the first repair, I totally removed the swage to expose the entire bore of the casting. The bushings fit tightly into the bore. This time I left 2mm or so of the swage so once the bushing was pressed past the swage the dimension of the opening was less than the dimension of the bore and bushing - it should be even more effective at holding the new bushings inside the casting. I'm sure some of you guys can make some suggestions on how to do this better. I am interested in opinions on the whole concept and how to improve it.

 

[gsxr]

If we change fluid regularly and pay attention to the accumulators (and I do), the struts and their inner seals can last virtually forever. The only inevitable failure will be the familiar clunking that SLS equipped cars suffer from

There are at least 3 different failure modes I know of, possibly 4? The lower spherical joint is one of them. Note that this joint design is very similar to the rear wheel carrier lower support joint, which also fails on a regular basis, but is easy & cheap to replace. Anyway:

1. Lower bushing fails and develops excess play, causing a clunk or knocking noise
2. Internal failure that causes a clunk or knocking noise, unknown root cause
3. Foam stop buffer disintegrates, allowing excess rear suspension travel, and the buffer is not replaceable. This is the most-overlooked failure. I would check the foam stop buffer (click here) before spending any time replacing the lower bushing.
4. Fluid leaks... not very common AFAIK, but they could leak from the shaft seal.

Right now I am having trouble uploading my photo. I am getting a "file too big" error although its a JPG less than a megabyte. What gives? ... I figured out the image dimensions were the issue (24 inches wide was a bit of a problem)

If the pixel dimensions are too large, the forum says "Nein!". Today's so-called smart phones generate stupidly large photos, but if the settings are changed to medium or even low/small size/resolution, they'll still be plenty big enough to see what you're taking a picture of.

 

[tuttebenne]

Dave. That's good info. In my case the originals developed the clunk at about 140k miles. I bought a pair used from Dave Hendy and they solved the problem. I also replaced the accumulators at that time. Six or seven years later, one of those struts developed the clunk and I solved that by doing this lower bushing repair. Now the other one is clunking and that is the catalyst for this thread. I had saved the original struts and those are the ones in the photo. I'm pretty sure from the condition of the boot and from the rust coming out of the spherical joint that the lower joint has failed and that there isn't an internal issue with these struts. Once I install the repaired strut in a week or so, I'll know for sure. But I will check the foam bumper first - Thanks.

With your number 4 failure mode, is it possible that a failed accumulator, (one nearly full of fluid) would put additional stress on the strut seal? I've heard of a few TE's that had the seal failure but yes, not on a 500e.

 

[luckymike]

tuttebenne, thank you for the thorough writeup. Since my E420 doesn't have SLS, I usually think people who use the term SLS are talking about a W126. So I was hoping for a new solution to our (126) clunking issues. Your pics reminded me we're talking 500E here. Still enjoyed reading of your clever fix. Thanks again.

 

[gsxr]

With your number 4 failure mode, is it possible that a failed accumulator, (one nearly full of fluid) would put additional stress on the strut seal? I've heard of a few TE's that had the seal failure but yes, not on a 500e.

I think so, yes. I suspect more 500E owners notice the problem and get it fixed, before it causes the strut to fail... also there are a lot more wagons out there than 500E's! Which is probably why it's been reported on TE's, but not much on 036's.

 

[744Brillantsilber]

Take care when bleeding the SLS: There is only a small spot between a closed bleeding screw and SLS fluid spraying around with high pressure and making a mess

 

[gsxr]

@tuttebenne - I just found this thread again. Back in 2021, I hadn't paid much attention to your urethane bushing replacement, since there was no warning signs that the SLS hydrolegs would go NLA. Fast forward a few years, and here we are.

How are your urethane-bushed repairs holding up? Any issues with wear, noise, longevity?

Also, you used Energy Suspension 9.8101G Shock Tower Grommets, correct?

https://teamenergysuspension.com/product/energy-suspension-9-8101g-shock-tower-grommets/

https://www.amazon.com/Energy-Suspension-9-8101G-Shock-Grommet/dp/B000CN7CEC

 

[je11]

hi, are there any new information about a solution which replacement part fits well and works for the lower bushing ?

 

[gsxr]

hi, are there any new information about a solution which replacement part fits well and works for the lower bushing ?

Not yet, at least no information about a replacement spherical joint.

As described earlier in this thread, some people have replaced the joint with either a rubber or polyurethane bushing.

 

[je11]

it would be interesting if someone could share experience with PU-bushing or rubber. whereby I think rubber is too weak/soft for a long time.
But I think there are only two options for me now: replace the joint bushing or close the SLS system and change to stock shock absorbers(koni/KW/etc.)...
1-2 years ago I could have buy two new Sachs for about 300$ a piece....

 

[gsxr]

I wouldn't replace SLS with standard shocks/springs unless there was a more significant reason, e.g. if the SLS shock was damaged beyond repair and no replacements were available at all.

For the lower bushing, I'd personally try the urethane solution described in this thread. I've never done it, but it's a low-priced adventure, and worth a try. I also agree that rubber may not hold up as well for this particular application, where the bushing is under constant tension of hundreds of pounds / kg's.