1989 300te ...My mechainc feels that a high whine sound (similar to the whine from a radio) is coming from a faulty high pressure line from the pump to the chasis that feels the rear suspension. Says that there are small baffles in that line that dampen the flow...seems to believe that the previous owner may have tampered with that line (different manufacturer- very aftermarket)....Any thoughts????

Have you tried a little cheese with that?

But seriously though...

Under what circumstances does the sound come on?

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Current Benzes

1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"

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Not in this weather!

It is ever-present, inncreasing with engine rev. It does sound like it may eminate from that hose area. He states that the fluid pulsates through that line, and if those dampers aren't 100%, noise can happen...BUT, he also admits to never having had the problem or attempted solution. A new hose is expensive.

You need to use a stethoscope on some of the accessories, like the idler pulley, water pump, power steering pump and the like and see what they sound like. Definately check the fan clutch bearing bracket. My guess without any other imformation is it's the fan clutch bearing bracket, keep in mind this is just a guess.

I had a similar problem. It would feel like an airplane taking off and the whine would increase with the engine rpms.

It turned out to be the belt tensioner. When replacing the belt I found that the tensioner had gone bad. Replaced it and the whine went away. Before I replaced the tensioner, I was told by an indpendant that it was the primary pump in the transmission that was whining.

In the image below you can see the new and old tensioners and see how the position of the piece with the two flats has taken a permanant set in the old unit on the left - basically the rubber bushing that helps maintain the tension has gone bad.

Attached Thumbnails

 

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1986 300E (3/2002) Rear ended and totaled (10/2009)
2000 Xterra (5/2000)
1992 400E (11/2009) -Sold
1986 300E (12/2009) - Sold
2004 E500 Wagon (6/2013) - Sold

And...that tensioner is difficult to get to? I am not that familiar with my Merc, but in all my Volvos, it is a major job. Is it diagnosable (spelling) without opening the cover? WOW...if this were the problem...

Your mechanic is right on the dot!!!

My cousin's 300TE has exactly the same problem, it is a whining noise which fullfils the interior of the car as, you said it, a whine from the radio. It increases as engines revs increase. It is a very different whine from faulty belt tensioner or transmission whine.

It is a faulty hydraulic oil pressure for the rear self-levelling suspension. Pump appears to be involved too. The diagnostic was done by the local M.B. dealer and fixing it requires about two thirds of the Blue Cross annual budget.

The dealer said that if you can live with the noise, do it until the system fails completely. The cost to repair it would be the same at any scenario.

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]

I had the exact same problem with my '90 300te. The problem began when I replaced the high pressure hydraulic hose with one made at a hose specialist. This is one of those places that custom make any type of hose for race cars and such. They removed and reused my fittings onto a new length of hose. The new hose had a slightly smaller diameter. The first time after I installed I got a very fast vibration sound that changed a bit with increased RPM's, but really changed whenever back pressure was introduced into the system by hitting a bump or dip in the road. The high pitched vibration sound seemed to be stronger on the passenger side. The best way I can describe the sound was that it was like the noise you got as a kid when you clipped a playing card to your bike and it made noise when hitting against the spokes, only faster.

I confirmed my suspicions by grabbing the line at at various points with the engine running. I could feel the vibration and it was the strongest at the end towards the rear of the car. I took the hose back to the shop and they re-welded a larger diameter fitting since they suspected that the fluid was being restricted in some way when it was being needed to support the rear suspension. That hose ended up having the same problem.

I read a recommendation from the forum to only use an original MB part for the high pressure hose. I changed out the hose with one from the dealer. Problem solved.

In retrospect, I have concluded that there is a reason MB calls this an Expansion Hose. Just a guess, but I think that when the system gets back-pressure, the hose actually expands. If you replace with a less flexible one, vibration results.

Right, the sound do sounds louder at the passenger side, and as said before, it varies in pitch according to engine speed.

One question: did you only change the hose or did other parts were required (like the hydraulic fluid pump) to cure the noise?

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A. Rosich
CL 500, 1998
S 500 L, 1998
E 320 T, 1995 [Sadly sold ]