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2015 SL550
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58 Posts
Discussion Starter #1
Car has about 61K miles. I have recently noticed a hum and the light pedal vibration occurring after a good run. It doesn't seem to occur when the car is cold or on short runs. A site search suggests that this might be the tandem pump pulsation damper starting to give out. Tempting fate, there are no other signs such as caution lights or erratic ABC operation. I haven't done anything that might cause the hydraulic lines to move up against the body (one of the other suggested causes). Any thoughts on other causes?

I have been thinking about changing the ABC hydraulic accumulators as a preventative measure anyway. Aside from buying them at the MB dealership, where do you recommend getting good quality units from?

Thanks
 

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SL55, 300SE, GL450, Daytona 955i
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The brake and SBC has nothing to do with ABC.

Humming at idle is ABC issue, that require damper to be replaced.

Pulsation in SBC pedal is probably an indication that you need to replace the SBC unit soon.
 

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2015 SL550
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Discussion Starter #3
Thanks for the quick response Bayhas. I don't have any pulsations in the brake system. I just feel the hum/light vibration being transmitted through the brake pedal and also a little through the floor if I think about it more.

Any recommendations on a quality source for the dampers?

Also, I have the WIS, but I haven't had a chance to read up on changing the dampers yet. Any tips on replacing these whereby experience may suggest doing it differently to what the WIS states (with all of the usual "at your own risk" disclaimers of course)?
 

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SL55, 300SE, GL450, Daytona 955i
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Any recommendations on a quality source for the dampers?
Your local parts desk at the dealership.

Also, I have the WIS, but I haven't had a chance to read up on changing the dampers yet. Any tips on replacing these whereby experience may suggest doing it differently to what the WIS states (with all of the usual "at your own risk" disclaimers of course)?
WIS is directed toward shops, not end users, and has detailed procedure to replace it, but naturally, because its target audience is professionals, it will not cover common sense mechanic basics (although it comes close).

WIS is always the best and most accurate source for info, however, there are a few DIY articles about the subject on BenzWorld.
 

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2003 SL500
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199 Posts
Have you considered the motor mounts? Generally doesn't create a hum but certainly chassis vibration, and they are known to wear quickly.

I purchased my front accumulator and dampener recently from Pelican Parts and did the job a few weekends ago.

The dampener is very simple to replace. I just removed the fasteners to the rear half of the wheel well lining, peeled the lining back enough to expose the pressure sensor + pressure limiting valve + pulsation dampener assembly, and used a slim wrench (21 or 24mm, I forget) on the dampener and an adjustable wrench on the assembly housing to provide counter torque, and cracked it loose. Then turned the dampener by hand like a light bulb to remove and put the new one on, and tightened. Then made sure the assembly had adequate clearance all around, and then put the lining back and was done. Simple as that. About 30 minutes work. There is no need to unbolt the assembly, but that is an option if you need more working room.

You aren't out much time or money if you are wrong.
 

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2007 SL550 designo
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43 Posts
RocketBoots has a 2008. The pulsation damper is mounted on the tandem pump body. Models prior to 2007 have the damper mounted remotely.

WIS for the later cars creates a lot of unnecessary work by instructing to remove the pump. I unbolted my pump from its mounts and that gave enough clearance (just) to change the damper without unbolting any fluid lines. Just make sure the area is spotlessly clean before starting the work.
 

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2003 SL500
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199 Posts
out of curiosity, is there a seal or gasket that you have to worry about the integrity? Is there much risk that there will be leak afterwards? I agree your approach is much better than the WIS. Why spend all that time tearing down and reassembling for nothing.

I had to replace the right headlight bulb and WIS said the bumper needed to be removed. WIS definitely likes to take the scenic and expensive route at times! RocketBoots was smart to ask.
 

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2007 SL550 designo
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43 Posts
The pulsation damper is supplied with the necessary o-ring already in place. It is simply a matter of unscrewing the old damper and installing the new one.
 

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2015 SL550
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Discussion Starter #10
The pulsation damper is supplied with the necessary o-ring already in place. It is simply a matter of unscrewing the old damper and installing the new one.
Thanks to all. A few questions as I haven't had a chance to get to my WIS yet.
- Is there any retained pressure to be concerned about?
- Does the car need to be supported to prevent the suspension from sagging due to an open line?
- Is there much oil spillage?
- Do you need to pre-charge the new damper with oil?
- Does the system need to be bled afterwards?
 

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2003 SL500
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The ABC system depressurizes when the engine shuts down, except for the lines between the valve block and the strut where the pressure is a result of the weight of the vehicle. Wait about 10-15 mins to make sure all the pressure has dissipated.

Unless working on struts or valve blocks, the car does not need to be supported. But if you plan to be under the vehicle for any reason, it should always be on stands. Don't trust your life to a 10 cent o-ring in the valve block.

If the pulsation dampener has blown, it can potentially be full of fluid. Be sure to pack a lot of shop rags around the area before taking it off.

No need to pre-charge the dampener with oil. when not under pressure, the diaphragm is at the entrance to the sphere, so it can't take in any fluid anyway.

The minor amount of air that gets into the line shouldn't cause any problems. No need to bleed anything. The system self-bleeds. cycling the ride height 15 times can speed the process. In some cases air can get trapped in the line between the struts and the valve block, hence the bleed nipples. But shouldn't be necessary for an accumulator replacement.

Although unlikely, it is possible air could get into the pump. If the system doesn't pressurize when you start the car, you might need to prime it.
 

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2007 SL550 designo
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The pulsation damper is on the top of the pump and on the discharge side.
This means that there is virtually no air to be trapped in the system. Also, by the time you find and remove the pump mounting bolts the pressure will have long gone.
You only need to prime the pump if air enters the suction side which will not happen if you replace the damper with the pump still in the car. If you follow the MB instructions you may have to prime the pump.
I had no issues changing my damper recently and all noises have gone away.
 

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2015 SL550
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Discussion Starter #13
Great responses, thank you.

The damper is being delivered tomorrow and hopefully I will have time this weekend to replace it. I will report how I get on.
 

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2015 SL550
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Discussion Starter #14
I replaced the damper today. Not too bad once I updated my Torx tools.

After removing the Serpentine belt, I removed the top front bolt. From underneath the car, I partially undid the bolt holding the pump rear stay to the engine; below the manifold (not shown in the picture). I then gently levered between the pump and the top front bolt mounting lug. I hardly needed to move it before I was able to remove the Damper. It was toast as I was able to push in the diaphragm quite easily.



Fitted the new one, did a long test drive and all seems to be good. Thanks for the advice on this one.
 

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2007 E350 Sport, 2007 SL550
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378 Posts
Congratulations on your successful dampener replacement, and many many thanks for the explanation and the pic. Well done, Mate.
 

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2007 SL550
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4 Posts
Pulsation Damper

Competed the pulsation damper replacement today. I took me a few hours, but would be much quicker if I did it again. I followed the Rocketboots process and it worked fine. I got no fluid out of the old damper when I removed it (I didn't crank the car the morning I did the replacement).
Thanks to all those who posted about replacement without power steering pump removal. Mercedes wanted $975 to replace it, including the part.
 

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2009 SL550 Black AMG Sport Pkg
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118 Posts
Hi, I'm not the handiest guy ever, but I just got an estimate of $1770. for the damper replacement! So, I ordered one from FCPEuro for $127. + small shipping charge.

btw, 2009 SL550.
I have a few questions: 1) What type of wrench does it take to get under the bulb of the damper to loosen its fitting? I'm mainly asking because someone mentioned torque spec for installing new one. 2) Does anything other than maybe a gravel plate need to be removed for under car access to loosen the bottom pump bolt? I'm assuming the front needs to be elevated on jack/ramps? 3) Is it most likely that the ABC system will "never know I've been in there" when I start the car back up and I should merely need to cycle the level switch several times? 4) For an operation like this, does anyone recommend disconnecting the battery cable?

Thanks much!
 
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