hi, thanks to the people that helped me with my u joint problem.
next problem is once in a while when i start my truck the abs and brake light come on. it will stay on until i shut it off and start it again. brakes are fine. doesnt always happen. maybe 30 percent of the time

any help is appreciated.

 

Speed sensor switch going bad. Its located on top of the rear differential. Pull it out and pop in a new one.

 

Try disconnecting and reconnected the electrical plug on the speed sensor on top of the rear end a few times. It may be corroded.

 

zman already said it, but just in case..

correction here - not neutral safety sw, thats in tranny.
also not the official speed sensor, thats in tranny.
its in the pumpkin but its usually called the anti-lock brake sensor. its rectangular shaped.

 

Yea, duh, my brain said one thing and my hands did something else. Don't you just hate it when that happens?!

 

Yeah, once the ABS sensor goes officially bad then your speedometer won't register until your going 25+. It will sit on 0 until you get to 25 and jump right up and work fine. Then when you drop below 25 again it will fall to 0!

 

Eureka!!!! This just happened to mine! Thanks for the input, I'll have to get one for my pickup... Now, to figure out which one.

 

Like mentioned above it is the abs brake sensor in the rear diff. Be careful removing it as mine broke on the way out and I had to get in there with pliers and wiggle it all the way out. I also changed out the diff. fluid just to make sure no junk got in there when it broke!