I love my wife's car (and my wife), but the car has been driving me crazy lately.
We had to put it in the garage to paint it, that project stretched to taking over a year. After a long time sitting the speedometer quit working. Everything was functionally perfect before this (Cars should not sit).

So I made some attempts to figure out the issue, I have the Factory service manual, and I am decently competent as a mechanic.

There was no signal coming to the pin behind the speedometer.

So I removed the speed sensor and cleaned it inside as instructed by a post I found. When I went to put it back in it didn't really seat smoothly. So I ended up sticking my phone down there to take a picture. I figured this wasn't a big deal and cranked on the 10mm bolt till it was seated.

Not quite seated

The speedometer still showed 0mph after the cleaning.
So I acquired a new sensor from ebay.
When I went to remove the old sensor this happened.



Only half came up at first and I had to use pliers to get the bottom half out of the transmission.
At least I already had a replacement sensor.

So before I proceeded I tried a bench test of the new sensor that I witnessed someone do on youtube. 12v+GND and spin the sensor while watching for pulses on the voltmeter. It worked, the new sensor seemed to behave axactly as expected.
Into the car it goes, It also go hung in the hole the same way the old one did, and I did the same thing, cranked it down. at one point it snapped and I thought, good now it's seated, or alternatively, the 10mm bolt gave out. The bolt tightened in there..so lets test it.

Nothing, no reading...
I checked the connector again, 12v Gnd..
Started looking at the speedometer again, tested the pin I previously identified, nothing.

Continued below

 

So today, I got some new toys for electronics diagnostics and went to the junkyard to acquire some 3 pin connectors to mess with more testing. But I was starting to suspect a mechanical issue, maybe the speedometer gear gave out?

So I connected my connector and 12v and gnd and watched the pulse pin on my multimeter, and spun the tires, Nothing!

Ok, out with the new sensor.

Unscrewed the 10mm bolt and, the bottom didn't come.

I started fishing with my pliers AND...

It seems like the bottom of the sensor left, possibly before I even tried to take the top off.

I called it a day and closed the garage and left.

 

Here's a before after picture of the paint job on the car.



I've also restored the headlights and gotten it new engine mounts and sway bar bushings and brake lights and several other annoying things I cant get to when my wife is driving it.
All that remains is the speedometer and an interior detail.

 

Great job!

You got the speedo working?

 

No not yet.
I did get granted a minor miracle today.
I managed to fish the bottom of the sensor out of the transmission
.
I think next steps will be to drain the gear oil and check the guts of the transmission, with my flashlight and boroscope. I need to determine what is breaking these sensors. Before I break another one.

At least I don't have to pull the transmission out and disassemble it.

 

Does anyone have any help for a non-working speedometer?

I think I know why I broke the other two sensors, but I'm not certain yet. I think that is a separate problem from the electrical system. I drained the transmission and put my boroscope down the speed sensor hole. It seems like the gear is still there and isn't warped.

I got a new sensor again and did some testing, the sensor puts out the pulses as expected. When I plug it into the car there's no speed displayed.

I attempted to find where the speedometer plugs into the ecu, but I could not locate it. Google search is such crap now. The FSM that I have doesn't give me a plain pinout diagram for the ECU.

I probed around all 5 connectors in the ecu blindly, didnt find it. I unplugged the battery and all the ECU connections and hooked by (telecom) toner into the wire on the speedometer. It did not work at all I got no tone.

The FSM says the speedo signal goes into the radio as well, but we have an aftermarket (pioneer) radio, installed by yours truly. I did not check for that connection yet.

 

I'm lost as to what I should do next.

 

I think this is the speed sensor-> ECU ..

 

Need ECU plug type layout to find pin number on plug. The service manual has drawings of every plug type but doesn't list where it goes.

 

Tonight I went to the ECU and looked for that color, it was pin 17 of the 2nd connector from the top.

The circuit seems to be undamaged.

I ended up trying to install the sensor again and then I noticed something. One of the o-rings was missing (there should be two and the new one for the new sensor).
I looked down the hole the sensor sits in and thought I could see it, I plunged a hook down there and tried to retrieve it but could not.
After trying to retrieve it, it had fallen and was no longer visible/accessible, so I shrugged it off and tried putting the sensor in. It worked! It went all the way in and clicked into the hole, then I reassembled all the other things (airbox etc) and decided to test it.

The speedometer works!

I installed the gear oil that I had drained, this was probably a mistake.

I am thinking about going back into the transmission to try and retrieve that o-ring, is it worth it?
My friend who is a mechanic is concerned pieces of the o-ring could end up clogging some of the bearings.

I can get a grabber and try to fetch it from the sensor hole, or I can pull one of the axles and attempt to get it through there.