i was accelerating my '89 190e2.6 harder than usual on a very cold morning (after proper warmup of course), and suddenly i get this loud high-pitched sound from the instrument panel that sounded like a dentist's drill, so it freaks me out and i start to pull over, but the sound suddenly stops after about 5 seconds.

all instruments - tachometer, speedo, etc seemed fine and no warning lights had come up.

My ventilation fan makes a high-pitched sound also (needs lubrication) but it is quite different. So i guessed that the ventilation system went awry which somehow turned on the "fast defrost" for the windshield, so i turned off the fans altogether, but it was not the cause.

are there any electric motors behind the instrument cluster that can cause this?

can it be related to the speedometer/speedometer cable, and the subzero temperature? Could this have been caused by my sudden acceleration which could have caused moving components of the speedo cable to rub against other components?

it better not be the airbag ...

I had the same thing happen in my 1975 300D, a few years ago. It is, in fact, the speedo cable. The lubrication inside of the cable dries up after many years and starts to make the screeching noise until it warms up, thereby letting the grease left do its job. I have been told the way to fix this is to replace the cable, for most cannot be lubricated. Hope this helps.


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Chris
'87 300E

Disconnect the speedo cable at the tranny, pull the cluster (carefully) disconnect the top end of the speedo cable. Get your hands on a can of Slick 50 lube, (has a little nozzle on it). Squirt some down the inside of the cable housing. This stuff works great, my 87 300e had the same exact problem two years ago and it hasn't made a sound since. The cluster can be a bit tuff to get out, especially in cold weather. You'll need a couple of hooks to pull it with. I made some with a pair of aluminum knitting needles, just hammered them flat at the ends and bent a little hook into the tip. Work like a charm. Good luck

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Jeff L
1987 300e
1989 300e

Most of the time, I find that it is the speedo and not the cable, but if you go and lube the cable, it disturbs the speedo enough to stop the squeal.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

???? Your car has a speedometer cable? Or am I just confused by the S cars that I have. I think that you have an electronic speedometer, with, yes, technically a small stepper motor that drives the odometer. Are you sure that the noicew was from in the instrument cluster, if it was very cold suspect the belt or alternator bearings.

Mark
27 years Master Mechanic
Professional Engineer
Major M-B Fan

i'm positive the noise was from the instrument cluster, definitely from inside the passenger cabin.

when i first heard the noise, i immediately scanned the instrument panel, specifically the speedo and tach, and i did not notice any fluctuation in either reading. (the same thing happened to me in an old japanese car, and the speedo needle went wild, hence my reflex action to check these gauges). If the stepper motors went wild, then won't they register as fluctations on the needle readings?

if it is the speedo cable, then that is a comforting thought, as opposed to having yet another electronic gremlin.

i will have it looked into - thanks guys