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#1
04-20-2004, 07:47 AM
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Chassis Ear System
Hi. When I drive my '88 420 SEL over a bump there is a knocking noise coming from the front right suspension. The bushings/joints were checked and there is no looseness/freeplay. The car just returned from the shop and the right idler arm was one of the repair list items completed. The use of a chassis ear system has been recommended to pinpoint the problem. Does anyone have any experience with this type of diagnostic tool? Does anyone have any idea about what might be causing the problem? Thanks.
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#3
05-17-2004, 08:25 AM
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Never heard of this system. Link?
I am confused when you say "right idler arm." There is only one idler arm. Get the car on a lift and check your track rod carefully for movement. THis piece controls forward/aft movement of the wheel. If you hit the brakes hard, you can feel a clunk if the mounts are shot. If they get bad enough, you will be able to feel the wheel actually move foward.
__________________
'90 300SE 298k -300K and it gets put into retirement. '80 300D 255k Purchased new by family in 1980. Had a: 1973 220 (gas) 1980 300SD 1992 400E
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#4
05-17-2004, 09:32 AM
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Agree, probably guide rod mounts (one of their many names).
__________________
Mike Tangas '73 280SEL 4.5 (9/72)- RIP  Only 8,173 units built from 5/71 thru 11/72 '02 CLK320 Cabriolet - wifey's mid-life crisis 2012 VW Jetta Sportwagon TDI...at least its a diesel Non illegitemae carborundum.
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#5
05-17-2004, 07:36 PM
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I have a chassis ear, they work very well but it can take some time to pinpoint the source of the noise. What would really be slick is a wireless chassis ear setup.
I've used it five or six times and I've always been able to find the source of a noise. I'm surprised they are not more widely used. Tim
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#6
05-17-2004, 09:09 PM
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Check the exhaust, catalytic converter etc. The whole assembly can come loose if the tech are not careful while lifting the car.
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Zafar 94 E320 58000 Miles
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#7
05-19-2004, 12:27 PM
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Thanks for the feedback. I'll check the track rods. Disregard the idler arm comment - my mistake, sorry.
TimFreeh, could you describe how the chassis ear system works/what it looks like? A wireless system makes more sense. Thanks.
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#8
05-19-2004, 04:30 PM
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The strut rod leading to the lower control arm is anchored to the chassis via the Brake Force Support bearing/bushing. Does the suspension knock more when you apply the brakes or just hitting bumps in general? I would scrutinize these supports for excess end play, they could very well be the source of your noise.
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#9
05-19-2004, 04:41 PM
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Its a black box about the size of a cigar box that has a rotary selector switch, a jack for headphones and 8 jacks for microphone inputs.
To use the it you temporarily attach the microphones to wherever you think the noise might be coming from and run the wires back to the central black box. You then operate the car with the headphones on and selectively switch the microphones to the headset via the rotary switch. Using the differently placed microphones makes it pretty easy to zero in on the source of a noise. Depending on how well you guess where the noise was coming from you might have to re-position the microphones a couple of times. The thing is very effective for finding bearing noises on transmissions of differentials since you can place the microphones on different points of the differential or transmission. Its also more effective on noises that constantly occur as opposed to intermittent noise since you have to be able to rapidly switch between the microphones to compare the noise signatures. I'm not sure how much it costs, I received mine as a gift but I would think you could build one for about $50 in parts. There is nothing 'high tech' about it. Tim
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