Speedometer needle not working

I would say its probably a short or a ground problem at the turn switch or a wire in that area. you need a test light and probably a multi meater and some nohow a ground or wireing problem can even drive a master teck crasy.

Could be the speed sensor on the transmission or the speedometer on the dash. Does the odometer work ?

If everything else works ok, the vehicle drives normally, and all the other gauges are working then you may have a bad speedometer servo motor. This servo is what actually moves the speedometer needle to match the speed you are driving at. The cluster would need to come out and be repaired to fix this problem if this is the case.

The speedometer sensor - VSS - vehicle speed sensor is a input to the PCM - powertrain control module -engine computer . The signal from the PCM to the instrument cluster for speed info. is sent on a serial data communication network (class 2 ) I would think it would be an instrument cluster problem . Get a used one from a auto salvage yard 15 - 20 bucks an see if it fixes it . If it does ,send your's out an have it repaired .

The speedometer drive and driven gears inside the transmission needs replacing

Easy one. You need a new speedometer cable. The cable inside the outer sheath is sticking and binding. Don't bother lubing it on a '86, that'll only help a month or so. You may also need a new nylon drive gear inside the transmission housing (needle nose pliers will pull it out when you remove the speedometer drive cable from the tranny.) You may be looking at $40. Probably less. You'll get to stand on your head to disconnect and reconnect it to the dash. Buy one of those LED "headlights" for working on the dash. Your knuckles, arms and hand skin will appreachiate it! And you won't have to try to hold a flashlight in your mouth while working!
It's very unlikely that the "clock spring" inside the speedometer is bad these days. It did happen in the 60's, but I haven't seen one since.

Pretty common problem with these. Here's a guide to learn how to fix GM instrument clusters yourself, I used it to fix mine and it worked great.How to guide for Silverado instrument cluster repair

About the only way is to diassemble it, but it sounds like it's not wrth doing. Your speedometer is having some real malfunction issues anyway. Might as well get a new one (or used). If you did get the needle to the right place, it's just going to end up in the wrong one again.

get the original company service and repair manual from the given link it will help you to fix all the facing problem along with diagram

have the dsme problem. need to chech each of the 3 wires for continuity between the v.s.s. and the e.c.m. if good then the speedo is bad.