Speedometer issue...
 

The 87 has a problem with the speedometer. I was lazy and didn't really diagnose what the issue was and just bought a new sensor thinking that would fix the problem. I just bought the car so I don't know anything about the history of it so I don't have any of that to help. What I need to learn now is how to go about really diagnosing the problem. I don't have a wiring schematic of how it works and I don't understand what is supposed to happen on the wires so I don't know what to check and where. After replacing the sensor and there was no change, I plugged the old sensor into the wires and put my drill on it to rule out the possibility of the speed gear inside not turning the sensor. When I did that, still no reading on the speedometer. Does anyone have a shop manual and if so, does it provide a diagnotic routine to follow. Or if anyone has experience working with the speedometer, I would appreciate your help.

Usually the plastic gear in the back of the speedo that breaks apart.

Isn't that the odometer only gear? The best I can tell, the speed sensor has a mechanical side to it and then it converts it to an electrical signal. The sensors that screw into the transmissions only have electrical wires running out of them and I'm guessing those carry a voltage to the speedometer and the more voltage, the higher the needle goes but I am completely guessing here. All that I do know is the sensor converts the rpms to an electrical signal and the wires go toward the front of the car. Other than that, I'm lost. You really seem to know a lot about these cars, so if you have some information that might help, I would greatly appreciate the sharing.

Yes the gear is for the O-Do-meter.

The sensor on the trans puts out pulses. These are converted by the motor on the speedo into rpm. I don't have a cluster here to check if the motor drives both the odometer and the speedo needle. If it does a broken gear could be jamming it. If not...

Okay, it's starting to make sense. Whomever owned the car before had been working on it apparently as it wasn't working when I bought it and I'm starting to learn a little more here. Is the speedometer from the automatic any different than the manual. I think I read somewhere that the automatic was supposed to have a gear selector built into it and mine doesn't have that. I'm guessing that it means someone has switched it and wasn't aware of the differences between an automatic and manual speedo. I'll pull my speedo apart and look at the gear and see what it looks like. If it's broken, I'll replace it. I seen one on the web that gave a lifetime guarantee, any knowledge if that gear is any better than the stock one? SoCal, if you are ever in Houston, I owe you big time for all the help you have given me. Thanks

I just replaced my odometer gear, that job was not that bad. Pulling the instrument cluster out is kind of tricky. Seemed the dash opening wasn't big enough.

Go to www.cannell.co.uk/Manuals.htm for shop manuals. You need high speed not dial up to down load. You will find the electrical diagrams there.

Just paying it forward. You learn, you get to pay it forward.