speedo only works in reverse?
 

title pretty much says it all.

sorry havent set up my sig yet really so here is the info

89 d350. went from 3 speed auto to getrag. the speedo cable literally bolted up with just a little tug for some extra slack.

after swap i had no speedo. checked speedo cable at gauge cluster - check. inspected speed sensor at tail housing of trans - check. hooked a drill up to the cable and bam. the thing only reads the speed in reverse

i couldnt imagine the cable being broken, so did i mess up a gear inside the cluster or something?

thanks for any help or guidance. just learning these trucks as i go. only owned this baby for just over a month now