Speedo DRIVE gear replacement

My speedo was bouncing around, and now it won't do anything. I've pulled it out and I if I hook it up to a drill, the needle is steady. I've pulled the inner speedo cable core and its in GREAT condition. The needle was bouncing before I replaced the speedo gear to match my new rear gears. I've checked it since and both the old and new gears look to be in great condition. This leads me to believe the speedo drive gear is messed up. Whats the best way to check this and to replace it. I just got a quote of $300 to do the work. I'd almost rather do it myself. Any hints?

Thanks!

When I connected both the old and new speedo to a drill, they showed at full throttle 60 MPH and neither of them wavered. While in the car, they usually show 0, but when they do move, thats when they jump all over the place.

The cable looks good and came out with out ANY effort, but I'm a bit confused. I could see if the cable was binding up (tight corner or lack of lube) and that would cause the erratic behavior, but can anyone explain staying at 0? I think where I'm most confused is when I pulled the cluster I put a pair of needle-nosed pliers into the cable and tried to turn the core. I got no further than 1/4 turn before it'd slip out and spin back to where I started. With that piece of info, I'm less likely to blame the cable/gear/drive-gear, but the drill/speedo test works every time!

I think I'm running the white gear for my 3.55s. I was told it was the highest you could go before you needed to swap the drive gear. My speedo was jumping around before the gear swap though ...

I heard if the cable core was removed, it needed to be lubed with graphite. Is that right?

The inability to turn the speedo cable any further was probably due to the fact that the cable can only turn so far while connected to the gear and the drive gear while the car is at a stop. This tells me the speedo gear teeth are correctly meshing with the teeth on the drive gear which is correctly connected to the tranny. If I can't turn any of it, then my gears MUST be good ... right?

As for the comment about white gears ... if they are problematic (I could see that since they're the "largest" you can put in the '92 with the stock drive gear) it still doesn't explain why the old speedo bounced around but when I hook it up to a drill, its steady.

I'll try re-inserting the cable (ensuring its in the speedo gear correctly. I'll then try turning it. If I'm unable to turn it then I'll pull the speedo gear out of the tranny and turn the cable again. If it spins freely, then its not the cable getting hung up somewhere. It'd also be a great excuse to re-inspect the speedo gear and drive gear teeth.