I have a TH400 and and found that the gear that connects to the the speedo gear is cracked/broken what is the name of that gear so I can explain it to my trans guy with out sounding like a idiot?

Is it the drive gear that's on the output shaft?

I believe is it a white plastic gear that hooks right up to the speedo gear?

On www.richmondgear.com (http://www.richmondgear.com) they call it a Speed O Gear, the one with a snap ring on both sides of it that is on the output shaft....it drives the speedo gear(in this instance, let's call it the speedometer 'driven' gear') we all know that can be replaced for change in rear gear ratios. I'd call it the speedometer driving gear, thus 'driving' the speedometer 'driven' gear....makes sense to me.

Thanks!

The DRIVE gear is the gear on the tail shaft.
The DRIVEN gear is the gear which comes through the hole in the side of the tail housing.

My 1970 TH400 has a steel drive gear that is pressed on the output shaft, a real pain to change.......

If it's white ,then it's the 36T driven gear - GM PN 1359270.
Your "trans guy" should understand that.

Good I hope so i seen a expanded view of the trans and it looked like a pain in the butt to do. I just dont like sounding like a idiot on the phone when I'm trying to get a price or a job.