Anyone ever had this problem?

[Chevelle454]

My speedometer did not work before. I took the gear out that the cable hooks to, looked fine. I took the rear off the trans to get to the other gear, the gear is fine but spun freely on the shaft and the retainer clip was lying in the bottom of the transmission. I don't have any idea how the clip could have come out. I put it back together and the speedometer worked fine, but the speed was off quite a bit. When I got back from the test drive, I think when I put it in reverse is when it stopped working again. The clip must have somehow fallen out again. Anyone ever experienced this? Do I possible need a new clip? I don't see how it could move back far enough to let the clip out of the hole on the output shaft and clear the keyway on the plastic gear. The smaller gear won't allow it to move back I don't think... Any input would be great...

Thanks

Scott