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Mobile drive train whine




 
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n1ps
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Zorch!


« on: September 21, 2017, 07:37:29 PM »

I have a new... old car...1996 Mercedes E320...gas version.  The drive train has a 10-20 over S9 whine that varies with the speed of the car in motion.  At rest, no noise.  It does not vary with the engine RPMs.  Its worse on 75M and barely noticeable on 160 and 40.  The only way I can test is on a lift.  I have some ideas on how to sniff it out.  But would welcome ideas on what the cause is.

I love 75M mobile...but this is a problem.

This car replaced a E300 which got totalled.  I heard that same whine in that one too but at a very low level and was never an issue.  The same antenna is on this car...an ugly one (but beautiful to me   Grin )

TNX

Peter
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KC4VWU
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« Reply #1 on: September 21, 2017, 08:05:41 PM »

Remember the old ground straps that attached to the metal bumpers? That was a loooong time ago. Electrical ground paths on vehicles are a very strange thing indeed. Check your battery ground, especially the connection to the chassis, very good. If somehow it has to make the return through drivetrain components, there you go. Really hard on components like wheel bearings and u-joints as well, causing premature failure.
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KD6VXI
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Making Amplitude Modulation GREAT Again!


« Reply #2 on: September 21, 2017, 09:11:59 PM »

Wheel static springs.

--Shane
KD6VXI
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n1ps
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Zorch!


« Reply #3 on: September 21, 2017, 10:06:45 PM »

that may be it.  Now where to find them? 
TNX
p
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KI4YAN
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« Reply #4 on: September 21, 2017, 10:52:01 PM »

ABS and VSS sensors, usually run in unshielded twisted pair. Only an problem when the car is actually moving-engine RPM would never affect these, alternator whine wouldn't affect these.

Since these are usually a variable reluctance sensor, as the speed of the car climbs, the output frequency increases AND the output voltage increases, sometimes as high as 100V peak to peak as the speed of the reluctor goes up.

Dunno how your car will react, but try unhooking the sensors one at a time and see if the noise goes away. Normally you wouldn't get noise unless the twisted pair somehow became unbalanced, but it could just be that the twisted pair is not really twisted, too.
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