whenever i get going up over 100 km/h my spedometer will basically go back and forth from the speed im going, to 100. so say if im going 110, the spedo will keep going back and forth from 110 to 100. same if im going any other speed that is over 100.

is this the speed sensor? if not what else could it be?

 

drive 100 or less, your truck is pissed at you for going so fast.

what year is your truck? I had a truck that did the same. start my changing your speedo cable.

 

your speed censer on the rear may be going bad I had the same problem easy to replace

 

The wire from the speed sensor to where it meets up the the body can get chaffed and worn causing an intermittent short. Usually hitting a bump with start or make wore the wonkee-ness.

If not the wire then likely the speed sender as others have commented.

 

Yea I have this same issue. I have replaced the VSS and it didn't fix the problem. Does anyone have any photos of where this wire is located under the truck?

 

as my uncle once said when in doubt tach it out
after 16 years the plastic spedo gear might be worn out a bit.

 

is yout truck auto matic cause those old truck if a bad sensor it will shift rought and not stay in over drive , the cluster gets bad in them to mine did in my 95 it did the same thing

 

Probably the wire or sensor. Follow wire from sensor to where it makes up to the body. The flex in that area causes the wire to go bad.

 

It is your speed sensor, I just replaced one on my 95 f150 xlt 4x4 auto tranny. Mine would start at around 40mph and by the time it hit 60mph (about 100km) the needle would be bouncing all over the place. You can replace it yourself if you are handy with tools and if you don't have the warning lights going off on you instrument dash. If you do, reprograming and dash stuff with labor is under $200. You can remove the old one and see if it has crude on it or shavings but for a $40 item, I'd replace it, if it's like mine it's located in the rear housing.