speedo not working

[kentonmiles]

had my trans. rebult twice and the speedo broke the firstime. changed speed sensor and checked every wiere. some say my cpu is bad but chevy wants $400 for a new one. any help would greatly be wanted:dunno:

[performabuilt2]

the speed sensor is an AC volt generator. Jack the back wheels pu get a multimeter and put it on AC range and put the vehicle in drive probe the speed sensor and see if it is generating a voltage if not then the speed sensor is not working if it is get a pinout and see if the signal is making it to the PCM if it is then you may have a problem in the PCM or the dash cluster....what year is the truck

[kentonmiles]

its a 90 but it was a basket case before i got it so the trans could be differnt than 700r4 maybe 4l60

[NEUMANNZZ]

Isnt there a DRAC in between the speed sensor and pcm? sends the signal to the PCM and speedometer.
maybe this will help:http://www.tbichips.com/drac/