My speedometer on my 87 GN is off and I wanted to know if tightening it and lubing the cable will remedy this or not?
No, you need to change the speedometer gears in the tranny.
Oops, sorry about that, I see that the subject line says your reading 15 MPH when your sitting still. What does it read when you're going 60 MPH? (Have someone ride along with you or follow behind them) If the thing reads 75 Mph when your going 60 then I'd say the needle moved somehow.
I think Kirbans works on speedometers, but I'm not sure.
Greasing it won't help, don't know what you mean by "tightening it"
The needle is attached to a small steel drum. Inside the drum is a small magnet that rotates with the cable. The magnet pulls on the drum and that's what makes the needle move. There is no direct connection between the cable and the needle. The drum is spring loaded and has a shaft the needle is connected to. Somewhere in this area it is sticking. DON'T lube it! Your best bet is to remove the speedo head cluster. Disassemble it down to just the speedo and take it to a Delco speedo shop. Ask your local GM dealer where the closest one is. There are several across the US.
If I don't get this fixed right away will it screw up my mileage too?
No it won't. The VSS looks at the cable part, not the needle part.
Ok thats a relief until I get around to getting it fixed.
My 86 GN read 10 MPH while sitting still when I bought the car. All I did was remove the face, and twist the needle to read zero when sitting still.
Worked like a charm and was accurate throughout the 85 MPH range after that.
Loyd when you say "removed the face" what do you actually mean? Did you have to remove the dash or what?
Lance said "Loyd when you say "removed the face" what do you actually mean? Did you have to remove the dash or what?"
The face is the plastic cover over the speedometer. You do not have to remove the dash, or even the speedometer cluster.
First you need to pull the speedometer cluster trim panel. It is held on with metal clips around the perimeter. It should easily pull off straight toward you sitting in the driver seat. The easiest place to start pulling is just below the steering column on either side. Be sure to pull as even as you can to avoid breaking this difficult to replace part.
You may need to remove the lower panel as many of the clips will probably pop off while pulling the trim panel off. At least mine seem to most of the time.
With the cluster trim removed you should see the screws that hold on the clear plastic face over the speedometer. Removal of these screws should allow pulling off the plastic face then access to the speedometer needle. You may need a small screwdriver to gently hold the magnetic drum from twisting while tweaking on the needle.
Hope this helps