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1995 E320
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119 Posts
Discussion Starter #1
Wondering if anyone else has had this symptom. While driving my 1995 E320, a knocking sound started behind the instrument panel, more towards the left side underneath the front speaker. It almost sounds like a vacuum pot closing quickly but I don't believe there is one over there. The sound occurs every few seconds. Maybe the cross-over valve? Of course the moment I stopped the car (left it running) the sound stopped. Any ideas? Thanks, Bob
 

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1995 E320
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119 Posts
Discussion Starter #2
Follow-up observation

My wife has been complaining that there's not enough heat coming out of the heater when the temperature falls below freezing. I was looking at the heater core hose connections and noted that the input hose comes in just about where the knocking sound is coming from. I'm thinking that possibly the heater core may be plugged somewhat. I'll try reverse flushing it this weekend. Interestingly, I had to replace the radiator a few months ago when the inards collapsed completely. Wondering if the heater core may be doing the same thing or possibly some bits from the radiator have plugged the heater core. Any ideas? Bob
 

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W124
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5,169 Posts
Let's start off with the simple possiblities. How about air in the system? Try bleeding the system before doing anything more drastic (and expensive).
 

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1995 E320
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119 Posts
Discussion Starter #4
Speedometer Knocking???

Thanks for the suggestion on bleeding the system. On the weekend I reversed flushed the heater core. Thankfully, there was no obvious blockage in it as the water flowed through the core with no problem. After that I checked the monovalve while I was at it. Turned out that the valve was completely soaked inside. I'm sure that would have an impact on the heating consistency so I've ordered a replacement. In the meantime, I disconnected it so that it stays in the fully open position. I bled the system afterwards and the heat seems to be flowing through the heater core without a problem.

But....the knock behind the instrument panel continues. Obviously it's not related to the heating system as the intensity or timing of the knock does not change no matter what ventilation settings I use. I noticed that the knock stops when I stop the car. I now believe that it's related to the speedometer. Maybe the cable? The knock is regular and doesn't seem to be speed dependant, so I'm not sure about this. It starts up once I'm driving at about 15 mph and knocks about every 3-4 seconds. The speedometer needle isn't jerking around so maybe it's not the cable but another part of the speedometer. Any suggestions before I take it in to the local dealer? I hate taking the instrument panel out as I always seem to scratch something when doing so.

Bob
 

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1995 E320
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119 Posts
Discussion Starter #5
Figured it out! Found the answer on the UK Mercedes Club site. Turns out to be the odometer, not the speedometer. Somehow the reset for the trip odometer was not completed properly and the gears were making the noise. A couple of deep pushes of the button and now it's quiet again. Glad I didn't attempt to pull the instrument panel:).
 

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2008 E350 4M, 2016 Audi Allroad, 2019 Audi Q5
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5,447 Posts
Figured it out! Found the answer on the UK Mercedes Club site. Turns out to be the odometer, not the speedometer. Somehow the reset for the trip odometer was not completed properly and the gears were making the noise. A couple of deep pushes of the button and now it's quiet again. Glad I didn't attempt to pull the instrument panel:).
Glad you caught it. Was about to solve it for you too. I have the same issue every now and again. It makes you go "what the hell is that" until you figure it out :thumbsup:
 

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'92 300TE 4matic 280,000miles, '92 300TE 4Matic 'Ice Blue Metalic' 101,000miles
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Figured it out! Found the answer on the UK Mercedes Club site. Turns out to be the odometer, not the speedometer. Somehow the reset for the trip odometer was not completed properly and the gears were making the noise. A couple of deep pushes of the button and now it's quiet again. Glad I didn't attempt to pull the instrument panel:).
Sorry I didn't see your post sooner, because that was exactly what I was going to suggest as I read the OP. Also they say never to zero the odometer while you are moving...as in never. And I will say, the only problems I've had with mine, was screwing around with it while driving....you can even break/strip the little gear in there that way.

Kevin
 

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1993 300E, 2003 996 Turbo X50
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624 Posts
Yes, do not EVER reset it while moving. I killed the odo on my BMW that way, luckily it was a simple fix.
 

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W124
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Ya gotta love it. LOL Someone OTHER than those of us who have a set of tools and some experience would have pounded on the dashboard or the instrument panel and the noise would have gone away. Us? We would have had the engine compartment torn apart, dashboard scattered throughout the interior and the noise would have gone away after it all went back together. Glad this had a simple fix and I learned something new already today! Thanks for posting the conclusion.
 

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2013 E350 sedan, 2013 E350 cab, 1993 400E sold,1999 ML320
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My wife pushed the reset while moving now my 0-20 sometimes works sometimes not. Everything after 20 is always fine but it acts like its slipping. Think she moved that gear?
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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After having my transmission rebuilt, my speedo lays dead until about 20 mph then kicks in. Works perfect slowing down to O. 400E's have electronic speedo's so I doubt the trip meter reset has anything to do with it.

Jayare
 
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