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Thread: SLS knock after reservoir hose replacement

  1. #1
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    SLS knock after reservoir hose replacement

    Hello,

    Reviewing the SLS posts on the site but haven't yet found anything directly applicable so thought I would ask....

    While getting the car ready for spring out from winter storage, I noticed that the braided rubber hose between the bottom of the SLS reservoir and the hard line was leaking. I removed the hose and reservoir, cleaned the reservoir, replaced the hose, and refilled the reservoir with the correct (new) fluid. Started the car up and drove it around and everything functioned OK... I noticed that the new fluid in the reservoir went from super clean to a bit darker - indicating to me that the fluid was circulating.

    Everything seemed to be OK for about 60 miles (3 or so commutes to work), when suddenly, on the highway, I started to hear a loud knock from the rear suspension. Sounded like a baseball bouncing around in the trunk.

    Traced the noise to the right rear suspension. I can get the sound to happen by bouncing the rear right rear side of the car. The noise seems to come from the top of the shock vs. the bushing on the bottom. I have had the bushing issue before and replaced the shocks about 20,000 miles ago. This doesn't sound like the bushing failure did before...

    So the question is... did I mess up by not bleeding the SLS system after the hose replacement or am I missing something else? (Or has the bushing failure returned...?).

    Any suggestions/recommendations/comments would be appreciated.

    Thanks!

    Tom

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    Senior Member mercepor's Avatar
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    Re: SLS knock after reservoir hose replacement

    The level of the oil is ok or went down?
    (If went down - accumulator failure)

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    Re: SLS knock after reservoir hose replacement

    Try bleeding the system per the FSM procedure - basically disconnect the valve lever, set to max lift/fill, then after it's fully raised set it to min/empty, cycle a couple times. If the knock persists... could be a failed hydroleg.

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    Re: SLS knock after reservoir hose replacement

    Hello again,

    Finally got the car up on the lift and did the FSM procedure per GSXR. The suspension raised and lowered like it should. Fluid level in the reservoir was at about the same level before and after (thanks for that suggestion mercepor).

    Knock is still there but a bit quieter and I cannot hear the knock when the car is stationary and I bounce the back end.

    GSXR - assume you mean a failed strut...?

    Anything else to consider or try before ordering at least one strut?

    Thanks!

    Tom

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    Re: SLS knock after reservoir hose replacement

    Quote Originally Posted by twb-dbb View Post
    Knock is still there but a bit quieter and I cannot hear the knock when the car is stationary and I bounce the back end.

    GSXR - assume you mean a failed strut...?

    Anything else to consider or try before ordering at least one strut?
    Tom, you could drive the car a bit and see if the noise starts to go away or not. If not, or if it gets worse, it MAY be a failing/failed hydroleg (hydraulic shock). I'm not sure what else to recommend trying.

    If you do replace them... if buying new, replace both sides with new, not just one. If you replace with used, then you could try just one. I'd recommend new unless the ~$900/pair is out of your budget. The new ones should last another 25 years.


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    Re: SLS knock after reservoir hose replacement

    GSXR,

    Thanks. I will likely drive it a bit before buy the struts and probably bleed it one more time. It is frustrating as these are relatively new hydraulic shocks - about 20,000 miles on them. These shouldn't fail this early. I would have expected the accumulators to go as those are much older.

    TB

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    Re: SLS knock after reservoir hose replacement

    Quote Originally Posted by twb-dbb View Post
    I will likely drive it a bit before buy the struts and probably bleed it one more time. It is frustrating as these are relatively new hydraulic shocks - about 20,000 miles on them. These shouldn't fail this early. I would have expected the accumulators to go as those are much older.
    WOW. Well, that changes things a bit. 20kmi on the rear SLS shocks and they are probably fine. I (wrongly) assumed they were original. Failed accumulators typically results in a rock-hard ride, and/or the rear end lifted abnormally high, or both. It may be that you just need to bleed them again?

    Have you ruled out other possible sources of the noise?


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    Re: SLS knock after reservoir hose replacement

    With only 20K miles on the shocks I would be looking at other suspension components. Sometimes the addition of a new part hastens the demise of something else.

    How are the lower A-Frame bushings out by the wheel? If bad they will make noise and are right next to the bottom of the shock mount.
    [Admin edit: These are 'wheel carrier support joints' and tend to creak rather than rattle, click here for more info.]

    If they haven't been changed they probably should be. If the rubber is squishy at all their probably bad.

    Relatively inexpensive and easy to replace.

    Just my $0.02 cents.
    Terry

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    Re: SLS knock after reservoir hose replacement

    Thanks to all for the helpful comments/suggestions.

    The noise continues - I drove the car quite a bit this weekend and the noise seems to be worse. Still sounds like a baseball bouncing around in the trunk.
    Late yesterday, i put the car back up on the lift (a "drive on" storage lift). I cant find anything else under the car that could be making the noise - checked the exhaust, etc. and found nothing.

    When i grab the half shafts from under the car and bounce the car up and down, I hear a noise from the passenger side as the suspension compresses and releases. Hard to tell if the sound is coming from the top or bottom of the hydraulic strut. I did spray some silicone lube on the various bushings that I could get at but that did not make any difference in the sounds.

    Will try bleeding the system again while the car is on the lift but it is looking to me like am running out of options other than replacing the hydraulic strut.

    TB

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    Re: SLS knock after reservoir hose replacement

    Dumb question - were the current SLS shocks brand new when installed 20kmi ago? And did you have them installed, or was it a previous owner?

    If it's a bleeding issue, a new shock may have the same issue, if the bleeding procedure isn't going according to plan...


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    Re: SLS knock after reservoir hose replacement

    to add to this, were the mounting bushings to the top of the strut replaced as well? there is one below and above the frame when you torque the rod down. Originals compress, get hard and are about 5mm smaller than new. That might be an area to look at as well, maybe as simple as one nut came loose. Bad rubber there can be felt with every undulation inside the car. Also have a look (humor me) at the spare tire compartment. See if anything is loose, remove the tire and just check for anything that could be rolling around. Is the battery securely held down, etc.
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    Re: SLS knock after reservoir hose replacement

    Hello,

    The shocks were new when installed. I had it done at a local shop. I will have to pull the file and look to see if they replaced the mounting bushings at the top of the strut.
    The shocks were replaced due to the bad bottom bushing on the right hand strut.

    When I bled the system a few days ago, I just worked the control valve up and down to raise and lower the suspension. Should I try to bleed via cracking the hose connection on the top of the strut?

    nocfn- I will do another check to make sure that there is nothing rolling around... I did check the battery and the trunk area but will again (and pull the spare) to make sure nothing is there - no such thing as a silly idea at this point! Will also try torquing down the top nut for the strut in the trunk also.

    The last thing that I want is to change the strut and still have the problem.

    Again,

    Thanks for the suggestions!

    TB

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    Re: SLS knock after reservoir hose replacement

    Don't crack the hose connections anywhere while the system is pressurized, or you'll get an SLS fluid bath. I'm running low on ideas but I have a hard time imagining a 20kmi shock is rattling.


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    Re: SLS knock after reservoir hose replacement

    I think I've got the same problem ��

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    Re: SLS knock after reservoir hose replacement

    when you said that it is audible when pulling up and down on the half shaft, passenger side... another silly idea is a baseball (or a hunk of contraband of some sort) in the fuel assembly cover. Covering all bases, lower that pan and see if anything is flopping around there (not likely). Also, is the bumper cover there at the fender, preventing debris from getting between bumper and chassis?

    This is getting closer to the failure of the strut, worn upper mount bushings or both.

    Those bushings are not exposed to the elements, but the originals are several MM shorter than the new ones, may be prolapsed when compressed. They could have been put on in the wrong side as well or not replaced when the spring leg was replaced (not a strut). That rubber there is all that absorbs the force/vibration from the compression transferred from the inner action to the frame. The accumulator has a nitrogen bag to absorb most all of the force. Blown seal inside the spring leg may be the noise and one bad actor here contributes to the deficiency of them all. Dirty fluid >> aged and worn strut >>bad accumulator think of the chicken or the egg theory.... I may not be technically, specifically correct in my terms, but the jist I hope you understand.

    When you had the legs replaced, did all the fluid get flushed and new fluid go in? What is the color of your current fluid? is it possible that you have a accumulator on that side that was ruptured, and the shop replaced the spring leg and added more fluid? 9 bills is a lot, but having the knock sux, btdt. When I had that, I replaced the accumulator ($75-100 ea) and the bushings, things improved but not great. The spring leg replacement was required, and I flushed the system out completely before the new legs went on. This was on the C126, but the same concepts in the SLS are on both cars. This system works very well when it is properly taken care of, and mostly from a position of new, fresh fliud when you change out your brake fluid is cheap insurance for expensive and most likely NLA parts at some point. Also, if you had the car on the lift try the empty/fill cycle with the wheels loaded.

    Last edited by nocfn; 05-30-2017 at 08:43 AM. Reason: last sentance add
    1994 E500
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    Re: SLS knock after reservoir hose replacement

    Hello,

    My apologies for being off line for a while. Thanks to nocfn for the ideas. here is the latest:

    I checked and tightened the upper strut mounts from inside the trunk (they seemed tight but I tightened them a bit more) emptied the trunk completely, re-bled the system using the FSM procedure (raised and lowered the rear using the valve) then drove the car around. The noise was still there. It seemed less than before but still the same sound.

    I decided to just drive the car for a while and ignore the noise. I figured that I wouldn't cause any more damage by driving it...

    After about a week of driving it to and from work, the noise has gone away.

    About the only thing I can think of, is that it finally cleared/bled the air out of the strut.

    This problem began when I replaced the short rubber/braided hose between the reservoir and the hard line. At that time I cleaned the reservoir and put in new fluid. The Reservoir had some sediment so I guess that it is possible that some of that got in the line and messed things up. I will check the filter to see if it captured anything since the hose replacement.

    I am also wondering if I wasn't revving the engine fast enough during the bleed process... it was at idle - have seen some posts now that say the it should be above idle during the bleed process.... anyway, this seems a bit of "too good to be true" so will see how it goes and update this post after I put some more miles on the car.

    Thanks again to all for the helpful suggestions.

    Tom

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    Re: SLS knock after reservoir hose replacement

    Tom this is good to hear.
    1994 E500
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