[V8] speed sender removal

[dsaad at icehouse.net]

Here is the test setup (that I should have done first but oh well):
There are four wires to the speedo:
+12v
-12v (gnd)
speed (pulse) in
speed (voltage) out (to cruise, trip computer, servotronic, CC, ECU, TCU)

I figured either the "speed in" is failing or power to the meter is failing.
I connected a spare dash light bulb to the 12v pins of the meter and put the 
bulb in an unused socket by the CAT light. If voltage to the speedo ever drops 
out, the light will to. It never has.

I also put a volt meter on the "speed in" pin so that I can drive with it on 
and visable. (dash pad is off)
When the speedo craps out, the voltage goes to 8 volts. (no magnet sensed by 
the sender) When it is working it reads 4.3 volts - no matter the speed, unless 
I am going really really slow in which case I can see the voltage switch from 
near 0 to near 8 volts.
I would expect the voltage to vary more with speed if I used an analog meter 
but on my digital, (a Fluke 77) the readings apparently get averaged or 
something.
The thing that catches my eye here is the 8 volts. This should be much closer 
to 12 volts and may indicate a bad sender, or a low voltage supply to the 
sender. I have not been able to figure out which yet. (It got late and I got 
tired)

I would be tempted to just replace the sender but it costs about $125 so I will 
try a few things first. 

The V8 manual says very little about the sender that I can find, but my old 
paper Bently for the 100/200 says there is some sort of spring clip you undo, 
then twist and lift out the sender. I can not tell for sure if they require the 
drive flange to be removed first. I assume the 016 transmissions are very 
similar between the two models, and there might be some sort of spring clip 
visible on mine.

And - my local Audi wrench says that he replaces lots of speed senders on 
various models of VW/Audis so they do fail I guess. Bummer.

Dave

Quoting "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>:

> No BTDT, nor have I heard of any other V8s having this problem ... but
> how
> many V8 5-speeds are there?  I have heard of failures on 200Qs though
> ...
> some people thought it may have been related to having Pentosin dripping
> on
> it for a long period.  It is too bad I didn't poke around back there
> when I
> had the engine out of #2!  I am pretty sure that you don't need to pull
> the
> drive flange to get at the sender ... and I'm pretty sure the thing is a
> Hall Effect device.  Have you tested it to see if it is good or bad?  If
> it
> is indeed a Hall Effect device, did you check to see that it is getting
> power?
> 
> Steve B.
> San Jose, Kaleefohnia (USA) 
> 
> > 
> > Has anybody replaced a speed sender on a 5 speed?
> > Has anybody NEEDED to replace a speed sender - auto or 5 spd?
> > This thing is really buried in there. I had to remove the 
> > belly pan and exhaust 
> > crossover just to get to the connector. I can not see how to 
> > get the sender out.
> > I am REALLY hoping you do not have to remove the axle drive flange.
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