W124 Wagon Questions - PeachParts Mercedes-Benz Forum

Ghoti · #1 08-26-2010, 03:45 AM

There is a thumping sound coming from what seems to be under the cargo floor or back seat...but from the passenger side. It doesn't happen all of the time. If you feel the lines from the leveling system's reservoir under the hood, you can feel a thump that seems to correspond to the thumps you can hear.

I had seven adults in the car on a coast trip recently. Seemed to stay level and didn't sag at all.

Any ideas?

ashedd · #2 08-26-2010, 04:23 AM

I will take accumulator for $200 Alex

Ghoti · #3 08-26-2010, 04:25 AM

Quote:

Originally Posted by ashedd

I will take accumulator for $200 Alex

Man...that accumulator will fix just about ALL of my problems, won't it!!!

If only my 4Matic problem could be solved for $200. Maybe?

nestorb98 · #4 08-26-2010, 01:24 PM

How is you hydraulic fluid level and have you had it bled?

nestorb98 · #5 08-26-2010, 01:29 PM

I recently replaced the high pressure hose (which is very expensive) and after replacing the Hydraulic fluid I still have the thumping noise you refer to.

Come to find out that the system needs to be bled.

By the way...I had the high pressure hose re-built. MBZ wanted $250 for a new hose...a local shop rebuilt it for $119...same day!

Ghoti · #6 08-26-2010, 01:41 PM

Quote:

Originally Posted by nestorb98

How is you hydraulic fluid level and have you had it bled?

The fluid is right where it's supposed to be. I was also told this is a self-bleeding system.

If not, from where do you bleed it?

Is yours fixed?

babymog · #7 08-26-2010, 02:05 PM

Self-bleeding, no provisions for any additional bleeding.

If the accumulators are shot (diaphragm ruptured) it will cause the car to ride hard, might ride at the correct height but it will ride very hard as the shocks become essentially solid struts.

You say that you feel thumping on the lines to the hydraulic reservoir, which implies that it is thumping when not moving, is that correct? That sounds like more of a pump problem or possibly an issue at the leveling valve.

Ghoti · #8 08-26-2010, 02:11 PM

Quote:

Originally Posted by babymog

Self-bleeding, no provisions for any additional bleeding.

If the accumulators are shot (diaphragm ruptured) it will cause the car to ride hard, might ride at the correct height but it will ride very hard as the shocks become essentially solid struts.

You say that you feel thumping on the lines to the hydraulic reservoir, which implies that it is thumping when not moving, is that correct? That sounds like more of a pump problem or possibly an issue at the leveling valve.

Thanks, babymog.

I lived in NW Indiana for six years. And I LOVE the signature!

It is thumping while the car is not moving. However, it also thumps on occasion when the car is in motion as well. All thumping is intermittent, though, and I have not noticed a pattern of when it will do it and when it won't.

I have not noticed that the ride is hard...but this has been thumping since I bought it. If it rode better than it does now, that would be great!

babymog · #9 08-26-2010, 02:15 PM

Might be more than one problem, but the thumping when you're stopped does not indicate a suspension issue typically. Try it idling in reverse, in drive, in park, ... bring the RPM up to 1000 and see if it stops or changes, sounds more like exhaust vibrating against something or sagging engine/trans mounts, needs further investigation.

The hard ride is likely accumulators, or your ride-height is too high.

Ghoti · #10 08-26-2010, 02:21 PM

Quote:

Originally Posted by babymog

Might be more than one problem, but the thumping when you're stopped does not indicate a suspension issue typically. Try it idling in reverse, in drive, in park, ... bring the RPM up to 1000 and see if it stops or changes, sounds more like exhaust vibrating against something or sagging engine/trans mounts, needs further investigation.

The hard ride is likely accumulators, or your ride-height is too high.

Thanks.

Definitely not vibration of any sort. The thumping (when it does thump) is definite and has it's own "beat". The thumps are about a second apart.

babymog · #11 08-26-2010, 02:21 PM

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Ghoti · #12 08-26-2010, 02:27 PM

Quote:

Originally Posted by babymog

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LOL...me, too. Are you ruling out the accumulator, then?

Maybe nestorb98 will fill us in on whether or not he was able to repair his thump.

Billybob · #13 08-26-2010, 02:58 PM

Quote:

Originally Posted by Ghoti

There is a thumping sound coming from what seems to be under the cargo floor or back seat...but from the passenger side. It doesn't happen all of the time. If you feel the lines from the leveling system's reservoir under the hood, you can feel a thump that seems to correspond to the thumps you can hear.

I had seven adults in the car on a coast trip recently. Seemed to stay level and didn't sag at all.

Any ideas?

Having read through this thread I assume you are referring to this thumping problem on the 4-matic TE in your signature?

If that is true and after you have eliminated the suspension system as the source of the thumping problem, you may be experiencing an issue related to your malfunctioning 4-matic system!

The 4-matic system is a consumer of the same hydraulic fluid pressure supplied to the SLS system. There is a unit under the vehicle with its' own separate accumulator and a pair of solenoid valves which actuate the 4-matic mechanics by directing fluid pressure to engage and disengage the components. This valve unit is controlled by the 4-matic controller but you might to able to do some diagnosis by piggybacking say a 12V LED indicator to the solenoid valve leads and observing if there could be any electrical signaling that may correspond to the thumping. You may be able to ascertain the same by simply getting under the vehicle and putting you finger on the solenoids and feeling if there is action that corresponds to the thumping.

Alternatively, by inserting a guage into the hydraulic fluid system it would allow you to observe pressure fluctuations if that is the source of the thumping, this would be somewhat more difficult and require fabricating or finding the guage and connecting parts to accomplish.

ashedd · #14 08-26-2010, 03:13 PM

Quote:

Originally Posted by Billybob

Having read through this thread I assume you are referring to this thumping problem on the 4-matic TE in your signature?

If that is true and after you have eliminated the suspension system as the source of the thumping problem, you may be experiencing an issue related to your malfunctioning 4-matic system!

The 4-matic system is a consumer of the same hydraulic fluid pressure supplied to the SLS system. There is a unit under the vehicle with its' own separate accumulator and a pair of solenoid valves which actuate the 4-matic mechanics by directing fluid pressure to engage and disengage the components. This valve unit is controlled by the 4-matic controller but you might to able to do some diagnosis by piggybacking say a 12V LED indicator to the solenoid valve leads and observing if there could be any electrical signaling that may correspond to the thumping. You may be able to ascertain the same by simply getting under the vehicle and putting you finger on the solenoids and feeling if there is action that corresponds to the thumping.

Alternatively, by inserting a guage into the hydraulic fluid system it would allow you to observe pressure fluctuations if that is the source of the thumping, this would be somewhat more difficult and require fabricating or finding the guage and connecting parts to accomplish.

Ghoti · #15 08-26-2010, 03:16 PM

Quote:

Originally Posted by Billybob

Having read through this thread I assume you are referring to this thumping problem on the 4-matic TE in your signature?

If that is true and after you have eliminated the suspension system as the source of the thumping problem, you may be experiencing an issue related to your malfunctioning 4-matic system!

The 4-matic system is a consumer of the same hydraulic fluid pressure supplied to the SLS system. There is a unit under the vehicle with its' own separate accumulator and a pair of solenoid valves which actuate the 4-matic mechanics by directing fluid pressure to engage and disengage the components. This valve unit is controlled by the 4-matic controller but you might to able to do some diagnosis by piggybacking say a 12V LED indicator to the solenoid valve leads and observing if there could be any electrical signaling that may correspond to the thumping. You may be able to ascertain the same by simply getting under the vehicle and putting you finger on the solenoids and feeling if there is action that corresponds to the thumping.

Alternatively, by inserting a guage into the hydraulic fluid system it would allow you to observe pressure fluctuations if that is the source of the thumping, this would be somewhat more difficult and require fabricating or finding the guage and connecting parts to accomplish.

Wow. Thank you. Yes, I am referring to the 4Matic TE in my sig.

Quick question:

It thumps regardless of whether the 4Matic system is in "Test" or "Funktion". Does that matter?