04 E55 AMG: Rear end clunk/feels off

[kevm14]

Elevating this to its own thread now.

From the general thread, preparing for road trip:

Here's a list of stuff for my NC trip:
[X]- Investigate rear end, specifically right rear. I think something may be clunking back there and just need to wiggle all the things and see if I can find something obviously worn out.

Suspension stuff
Nothing seemed amiss. The only thing is I wiggled the shock and it may be clunking a little? According to the forum, clunks on an up and down motion can be shock failure. So maybe I am in the early stages of that. I'll let it get worse before I do anything. It's fairly minor though annoying because when the rear hits certain bumps there is a harshness that feels like a bad bushing. It's subtle but will likely get worse. Then I will do something about it. If it doesn't get worse well, then I may ignore it.

I found nothing amiss when I inspected before my diff fluid change. Research suggests that it is the shocks going bad. It's not just an occasional clunk but on certain impacts the rear will actually sort of jump like a solid axle car. I honed in on this more specifically when driving back to back with my STS which does not do this. So I guess eventually I will need to buy a set of rear shocks. I may not bother with this for my trip as it's mostly going to be smooth driving. They are easy to change and I could be convinced to splurge due to my influx of cash but maybe I'll just wait on this one. I should inspect again to see if either rear shock is actually leaking. Leaking is a fairly good indicator of impending shock failure and could put me over the edge to replace. If dry I guess I'll wait. That's a plan.

So that thing I said at the end. Here is the passenger side.

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Normal road grime? Well, no, because nothing else is covered in it. Including the driver's side, which looks much cleaner:

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According to what I said this means I will do the rear shocks before my NC trip. They are like $300/ea so there's that. But I probably should just suck it up and do it.

[kevm14]

https://www.rockauto.com/en/moreinfo.ph ... 97&jsn=436
$311.79/ea.

FWIW, here's this:
https://www.fcpeuro.com/products/merced ... 2113266800

The numbers are the same and the shock picture even looks the same. For $200 more per shock.

Ordered a pair from Rockauto for $645.63 shipped. Pricey but obviously it's been leaking and is slowly failing. I could drive it for probably thousands of miles but with decreased enjoyment/performance. Unlike what I'm used to, the failure mode seems to cause stiffening or uneven damping, rather than just softer and softer performance. I mean my STS front right MR shock seized after looking like this the entire time I owned it. So maybe this is what modern shocks do.

The good news is this job looks incredibly easy.

[kevm14]

Here are the instructions. I also found a video.
https://www.youtube.com/watch?v=SNVMtURD2vA

The only real annoyance is having to remove the wheelwell liners (like the front) to access the plug for the shock. Otherwise it looks pretty easy. Removing the wheelwell liner isn't hard but it can be a little annoying working on the ground. Tackling this now. Hopefully will be done by lunch?

[kevm14]

Tackled this today. I used the FSM but did watch that video when I posted it. Nothing really differed although they didn't torque correctly (or at all).

First I removed the trunk side panels. Not too hard. Just have to pull it out from where each side locks on the panel at the front of the trunk area. You have to remove the rear plastic hinge cover first but I seem to be doing this every other weekend for various reasons so this is becoming second nature. Just 6 push rivets, snap out from the light areas on each side, disconnect lights and remove. Then 2 more push rivets hold each side panel on. Unscrew the trunk tie down hooks. Remove the plastic lock piece that goes around the trunk supports. Then just finagle out out. I have never removed the passenger side so I took a picture. There is a large tank in there that I assume is for the suspension but maybe it's for the seats? The air line looks like suspension even though it can't be.

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Obviously this is how you access the top of the shocks.

Next I jacked up, pulled the wheels and removed the wheel well liners. Just some 10mm nuts, 3 push rivets and one 8mm screw that's kind of hidden. Not too difficult. This exposes the rear electrical junction and the yellow (middle) one is for the shock damping control.

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I then loosened but didn't remove the upper shock mount. WIS says 15 lb-ft on this so it wasn't very tight and being inside the car had zero corrosion. So just hold the shock rod from turning and back the nut off. Easy. But I didn't remove because I began to suspect that the shock was holding the suspension up and with the air bag under pressure it didn't seem like a good idea to just let it all fall. WIS does say to deflate the rear bags and this must be why.

Then I removed the lower mounting nut from the bolt and, yeah, the bolt was tight. I wasn't going to touch the top until I was sure things weren't under pressure. So I got out my small jack (the one I bought when the STS shift rod linkage broke) and used that to jack up and support the knuckle. Sure enough this was a great idea because the shock was actually coming down from the body as I backed the nut off, and the jack kept it in place. Then I removed the upper nut. I think the shock has an internal bump stop because it still sort of broke free and surprised me. It must be a foam/soft bump stop, not a hard limit.

Anyway then just remove the upper rubber mount, washer and nut. Remove lower bolt and leave jack on the knuckle. Wouldn't want it to drop and blow out the air bag or something.

Here's the empty upper mount area.

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No shock

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The old one still had some gas charge, shockingly (get it?), so I had to slowly compress it and then quickly pull it out of the area. Sure was leaking though.

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New shock. Comes with long harness wrapped around the damping control thing, like a vacuum cleaner or something.

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Compress the shock (which is harder) and slip it in the same way. Get the rod poking through the upper mount and the lower eye in the lower control arm. Slip the bolt in the lower mount and start the nut. I had to jack up the knuckle more at this point (the shock will extend more but only with the car's weight squishing the internal bump stop). Once I got enough thread up in the trunk, I was able to reinstall the mount, washer and nut. That's right, these expensive-ass shocks came with NO hardware or mounts. I had to reuse everything. Good news: everything was in good shape which seems kind of miraculous to me.

Tighten the upper nut to 15 lb-ft and that is done. Run the harness through all of the various mounting points and there are a LOT. Mercedes used a ton of care (which I am not used to) in routing this. There must be like 7 places and that doesn't include the run up to the junction block which has like 3 more channels. Plug it in and snap all the things back together that need to be snapped. Install the wire lock on the junction block.

Install wheel well liner. Just sort of fight with it and it goes back where it should. Install fasteners. One side done.

Here's the driver's side.

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Put wheels on, torque lug bolts. Lower car. Then I pulled it out and backed it onto ramps so I could torque the lower shock bolt/nut. Spec is 50 Nm + 90 degrees. Because they like angle torques on a lot of things like this. So first I did 37 lb-ft and then for the angle I just marked a socket with a line and turned it until it was about 90 degrees. Never did that before but it felt pretty ingenious. Do both sides. Pull off ramps. Done!

Road test next.

[kevm14]

Needless to say I was a bit nervous. I just dropped $645 on rear shocks and while I did have symptoms (leaking shock + occasional clunk + some really unsettling ride behavior but only in certain circumstances), a normal person would probably have driven it before and thought it was great. That's how it is. I have reason to believe that these are the original rear shocks but hard to say for sure. 135k so if so that's really quite reasonable.

Anyway I drove around locally first and found plenty of bumps. It was feeling great so far! Then I found the bump that really unsettled it (just at 25 mph through a corner). This is where I noted the STS did NOT have an issue while the E55 did. I went over the bump the first time. Nothing happened. Did I hit it right?? Turned around and tried again. Hit it differently. It didn't even feel like much. That's insane!

Kept driving because I was feeling really excited at this point. Did some harder driving and, again, there are always bumps. Everything was feeling mint! I tried Comfort. Wow, even more supple than before. Before it was softer but would still feel unsettled which is....B-body mode? Anyway, took it on a 25 minute drive and I am thrilled to report that this issue is 100% solved. Expensive but worth it!!