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  #1  
Old 07-18-2011, 12:13 AM
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Join Date: Jul 2011
Location: Portland, OR.
Posts: 7
Another Speedo/odometer problem

Hi folks,

Trying to fix my Speedometer and Odometer on my 1981 380SL.

I've tried to research as much as I can find and have read lots about the broken gears, etc. I've looked at the multiple threads on this forums (whunter's excellent list:Instrument cluster, Odometer, Speedometer, Tachometer links), too.

My case is that the speedo and odo do not work, all other instruments do work. I have the instrument panel out and all the gauges separated. Mine is a VDO type, electric.

I simply don't know if the issue lies with the head unit or the "pulse sending unit" (speed sensor?); or how to figure out.

I wanted to see if I could ascertain if the issue was in the speedo head unit or the transmitter, so I used put the rear of the car on blocks and started it up; first I put the oil gauge wire back onto the oil gauge unit because I didn't want anything spurting out of it, and then started the car and put in drive to idle the rear wheels.

I used my multi-meter to test the wire that has the single-hole plug that goes into the back of the speedo unit; it was reading a voltage on both DC and AC, though I believe this is suppose to be a pulse thing which I know nothing about, but at least there was voltage. Whether it was correct or not I don't know.

Can someone link me information on this "speed sensor" that presumable sends the "pulse" to the back of the speedometer head? All I find when searching for speed sensor are ABS sensors. Perhaps that means there isn't such a thing for this car?

Comments and suggestions appreciated.

Cheers!
Eric

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  #2  
Old 07-18-2011, 03:44 AM
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Join Date: May 2007
Location: Out in the Boonies of Hot, Dry, Dusty, Windy Nevada
Posts: 9,585
I have pulled apart the w123 mechanical speedometers. these electric spedo are something I haven`t jumped into yet.

some info here that may help.
Electric Speedometer Repair

or search electric speedometer or insert SL in the search. look in the blue bar above and click on "search". I did the Google search.
hope this helps.


Welcome to the forum. Iam mostly in the Diesel section and don`t venture over here much.


Charlie
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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works
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Old 07-19-2011, 04:02 PM
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Join Date: Jul 2011
Location: Portland, OR.
Posts: 7
I actually found a good testing page in the online Mercedes manuals. The "sensor" part is called (according to their doc) the "inductance transmitter". A very good testing approach to determining if problems are with the transmitter or with the speedo head unit can be found here:

http://www.startekinfo.com/StarTek/outside/11883/PROGRAM/Chassis/54-252.pdf
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Old 07-30-2011, 06:39 PM
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Join Date: Jan 2006
Location: SF bay area
Posts: 45
Quote:
Originally Posted by riccarr View Post
I actually found a good testing page in the online Mercedes manuals. The "sensor" part is called (according to their doc) the "inductance transmitter". A very good testing approach to determining if problems are with the transmitter or with the speedo head unit can be found here:

http://www.startekinfo.com/StarTek/outside/11883/PROGRAM/Chassis/54-252.pdf
Thank you for posting, I got a 380sl instrument cluster to replace a non working one and was trying to figure out how to make it work.....

Michel

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