My speedometer doesnt work at low speeds then when i get to about 35 it starts jumping like crazy and at higher speeds it starts to work ok but still not steady. What could it be?

 

What year? if older truck it might have a cable, they need to be lubed occasionally.

 

sounds like a bad spedo cable lubeing could help but sometimes it doesnt

 

It has a speed sensor on top of rear differential - check the connection, if possible - trace wires to make sure that there are no loose connections and wires are not damaged.

 

Sounds like a cable driven speedometer with either a worn cable or worn parts inside the speedometer itself. I have seen some that the speedometer insides were bad and causing the same problems.

 

'93 has an electric speedometer, no cable. Do what Hampster says, as well as try cleaning the sensor. It may help. Common cause is bad wires to the sensor though.

 

i had the same problem so i replaced the dss that did not work,then replaced the speedo. that also has a sensor,still did not help, went to ford and again replaced the dss and it worked. i guess make sure what ever you choose, only use factory ford parts. ps theres also a sensor in both front wheels any of the sensors bad can make a change,oh the e.c.m. is in the pass side kick panel and double check the fuse just replace it its cheap money, good luck