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:http://www.peachparts.com/shopforum/showthread.php?t=188540), 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

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.
http://www.peachparts.com/shopforum/showthread.php?t=216780

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

__________________
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

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