E30 speedometer fix needed

[kf martin <alteredbeast63@xxxxxxxxx>]

Could anyone help me with a problem im having with my
newly-aquired '86 325es?  The speedometer didnt work
when I bought it a few weeks ago, and this weekend 
the tach died too.  

I researched the web and found a great deal of very
detailed information on instrument panel repair...
replacing the service indicator batteries.  I removed
and disassembled the panel...the batteries looked
original, but not corroded or leaking...theyre 3 volt
sanyo lithiums.  i put a voltmeter across each one
and got 3.1 volts, so i assume theyre good (?).

The terminals on the little board with the LEDs were
corroded.  i had read somewhere that simply removing
this board might solve the problem.  so i did.  and
when i reinstalled the panel, i got my tach back...

..so thats half the battle.  but id like to have the
speedo too.  can anyone tell me any further diagnosis
i can perform on the speedometer?  does the LED board
have to be functional for the speedometer to work?

While researching my problem on the web, i didnt read
anything about speed sensor replacement.  do they go
bad?  (i guess everything goes bad...but typically)  
i did check to make sure my connection was tight at 
the differential; a bentley manual recommendation.
does anyone know how to check the sensor (resistance,
etc)?  when i remove it, will i be spilling gear oil? 

any advice would be greatly appreciated.  thank you
for reading.

kurt martin
86 325es
87 535is.
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