Speedometer Reading all over the place

Sounds like the Speed sensor is on it's way out.

 

It is the Speed Sensor, One way to check it for sure if you are in a Governed truck it will go faster than it has ever before, BE CAREFUL your company may have some S Rule against overspeed... It is simple to reset temporarily The truck needs to be shut off completely wait 5 minutes and turn the ignition on (DO NOT CRANK THE MOTOR) let all the lights go out repeat this step 3 times take a few minutes then crank the truck it should reset the Speed Sensor if it does not you will have to get it in the shop, it should not prevent you from driving it will screw you up if you do not have GPS map program to show you your actual speed..
Keep in mind Faulty Equipment is not an excuse for speeding, and even if you fight it in court it goes against your CSA.. Just saying from experience with the same problem the Judge was easy on me but is showed up on my CSA score....

 

Did you ever find out whats was wrong i got the problem?

 

Yep, sounbds like just the speed sensor. It's located on the tail of the transmission and gets it's readings from a magnet in the tip of it. The driveshaft has a small looking "gear" and the magnet picks up the "nubs" on the gear as it passes by. SOmetimes it just needs wiped off as small amounts of metal can get on the end of the sensor and block it for reading, but it will most likely need to be changed.

Be careful when changing it as well as they are usually made of plastic or pot-metal and will break in the holder when you try to unscrew them. You will see what I'm talking about when you climb up under the truck.

 

If the newer ones are like the old ones you can adjust them by unplugging the sensor harness and loosening the jam nut then screw the sensor all the way in then back it back out just the slightest (very little) then tighten the jam nut back down, and plug back up.

 

The sensor I back it out 1/4 turn. there are two sets of two wires, one will be at about 900 ohms and the other at 1200 Ohms the lower one goes to the ECM the other to the speedometer.
The sensor could be damaged from the tail-shaft bearing being loose or the 16 tooth gear could be loose from a loose yoke nut. I take the sensor out out and look and clean the sensor, then take a flat screw driver and pry on the gear if it moves, it needs repair.

 

Hey guys need help with my speed sensor it broke apart when trying to get it out! It is stuck in the housing. I am afraid to drill it because all the material from drilling will go into the transmission. Any advice.

 

You need to drop the driveshaft, pull the yoke off to get the housing off. Another option may be if you have a second hole for a sensor that is plugged. If you do, just put the new sensor in that hole.