new speedo drive and cable installed

I searched for this issue and came up with the speedo drive being bad or the cable being bad when the speedo needle jumps around erratically. I installed a new aftermarket speedo drive and a new cable, but the speedo needle seems to bounce around wit the bumps in the road now? With the olc smiths drive and whatever cable I had before the speedo was very steady. I thought I read something about this recently. May have been on a different forum, but I can't find the thread. Any ideas? I'm trying to get things sorted before the run to barber.

When my speedo was acting erratically I made sure that the cable drove the speedo properly using a drill. It was very steady so I figured it was the drive unit. Replaced the speedo drive and still had some problems. I corrected that by making sure the drive unit was perpendicular to the axle and cable properly inserted at both ends. No issues after that. Seems a little erratic at low speeds but once in the range of 50-80 mph doesn't move more than 2 mph. Above 80 mph I'm usually not focusing on the speedo.

I am kinda thinking it is the new drive, but I'll try and redo everything again

Check the inner cable length. If it is inserted into the head too far it will cause problems and damage to the head. When you slide the cable into the head make sure the cable does not bottom out in the hole before the housing meets the edge of the threaded portion. Jim

I couldn't tell if it was fitting into the head right because of the tight fit, but I'll look at that as well. Hate to ruin a good speedo.

Going by recent posts - the speedo cable end should stick out-enter clock 7/16".
I know that Smith speedo and tacho can both be more accurate and steady than new age digital units, but it just don't last but a few 1000 miles before read out get a bit blurry or erratic. Shoot who'd believe the moderns I ran ahead of telling me they were afraid to go over 140 indicated to catch up. I know naked Peel could not hit 140 unless on 1/2 mile long 45' down slope with strong tail wind and my face plate on clock faces. Do take heed to inspect for dragging drive tearing cable off and wrapping it around axle. If in doubt disconnect before riding till re$olved.
Search up mods to extend life of speedo drive if not giving up like me and just stocking extras on sale for the inevitable renewal after couple rear tire changes.

I fitted a new drive & cable & had an erratic speedo operation, jumpy. it got slower & slower then stopped completely. Turned out the square on the cable was too small for the hole in the drive, I cured it by some slivers of shim on 2 sides of the square.
Terry