My 1994 E320 Wagon has 108k miles. Recently it developed the bouncy ride syndrome typical of nitrogen accumulators giving out. I took it to my mechanic because of the stories I read here about how messy it was to do and how little labor was involved for an expert. My mechanic spent 7.5 hours over two days on it, most of that spent freeing the left accumulator hydraulic line screw, which was frozen solid. He billed me for 3.5 hours of labor ($280) plus $278 for the accumulators. Now I have a knocking sound in the back going over bumps which he says is the right rear shock. It's another $460 for the shock plus labor to do that. Question is - why does the shock go bad (I never heard the knock before), and if you replace one should you replace the other (God, I hope not). This begs a couple of other questions - he only quoted $475 for the accumulator job originally - do most of you think it fair that I pay him a little more than that? And do most people tell the mechanic what they think is wrong when they bring the car in, or just let him figure it out from the symptoms? My wife is convinced I am getting taken on this deal (aside from the car getting very expensive to own with all the repairs that have been done in the last 18 months). TIA

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Chip Johnson

Check the rubber bushings on the shock before replacing it -- they usually only need replacement if they are leaking. Knocks are loose bushings or a loose sway bar mount most often.

The struts are VERY expensive, but only usually fail when driven with bad accumulators long enough to blow the seals out.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

although the amount of time he sent looking for the source of the knocking, I would have thought he would have seen a bad bushing. Could the shock need "bleeding" somehow - I read that in a search I did.

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Chip Johnson

The shocks are secured to the vehicle (or chassis) by using 2 rubber grommets on the top shock mount. The grommets get soft, primarily the one between the shock and body, and when you hit a decent size bump the shock simply hits the body. In my years of service I do not recall running into upper shock mounts that were loose. Perhaps when the vehicle was relatively new (<10K miles) or the shock was serviced within a short amount of time (< 3 months) prior to the complaint. If the grommets are the cause of the knocking noise I might encourage a vehicle owner to replace all 4.

I am at a loss why it would take 6.5 hours to replace two accumulators so for good measure I can only suggest double checking the following items for tightness and or wear.

Sway bar links
Multi-link bushings
Shock mounts (top and bottom)
Outer control arm bushing (hub to control arm joint)
Sub-frame mounts

Good luck

Hi
The foot (= kind of ball joint) of the hydraulic shock is aluminum, and they are known to wear out. Only solution is a new one. One does not need to replace them pairwise. It is possible that they were weak before and that working on the system (ie disturbing them, twisting them out of the way) has killed them. It is worth doing the upper mounts first, they may give such sounds too if they are bad.
I am at the same point, except that I did exchange the upper rubber and it did not help.
Good luck, Bruno

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1992 300TE 160 kmiles

This certainly makes sense although it contradicts some other posts I have read.

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Chip Johnson

Yes, such failure does not involve a leak. It's the low mount that fails. BTW I think your mechanic was fair - the accumulators can and often are difficult to replace because of corrosion, and space is confined too. Replacement of the hydraulic shock however usually does not involve much labor. I do all the work myself (I could not afford the car otherwise). Initially I did not, and I can recommend Benz Den in Belmont. He would probably not be cheaper than your mechanic though.
Good luck, Bruno

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1992 300TE 160 kmiles