inside a TH350 Transmission: Speedometer gears

[75stepside]

Hey guys - i've tried everything to get my speedo to work in my '75. First off, the speedo worked before my 4 year restoration began. since completion, the speedo does not work. i have tried all the tricks, and the gauge does work with a drill on the cable down by the transmission. AND the gears on the cable looks good... AND the unit on the transmission turns freely and turns the cable just fine...

so, with that being said, i think the only sensible option is to remove the tail shaft and see what's going on in there... i've never done this type of thing and do not know what to expect... any tips? what to look for? any way to set the tailshaft on the bench and get it to all work on the bench?

any tips, advice, web sites, how-to's etc would be appreciated. i have been on plenty of sites that tell you all about the different gears and how to calculate the best option... i just need to know what's going in there... any thoughts?