I had the speedometer go out on me around 12-14K miles ago, and found that the actual speedometer failed in the cluster. I found one on CL and bought it, put a sticker on the face to correct the mileage, etc.
Last week it started bouncing again, and reading 50 MPH while my GPS was showing 65. I had bought a box of spare parts a while back and it had another speedo head in it. Did a quick swap and still had the same issue.
Dug into it a little deeper and pulled the front wheel off. Removed the drive pinion housing and cleaned out the grease to see what was in there.
Now first of all, you can get replacement parts for the seal, the little sheet metal drive tab, and the drive gear, but NO driven gear that is roll pinned into the housing.
I hate it when something is called "Non-Serviceable". Or I just love to take things apart.
So let's back up a moment. I also had a spare drive in that box of parts, so I could afford to start dissecting one with another on the bench. After cleaning up the grease, I spotted the worn out drive gear, and then saw the chipped gear tooth on the driven gear.
I used a 3/32" drill bit and drilled out the roll pin. But the aluminum threaded connector/upper bushing is pressed into the main housing. I had to get creative and tap the driven gear out driving the housing out.
I re-drilled both pieces out to 1/8" and had a new roll pin.
So after really digging into this, I found that the drive gear is spinning counter clockwise (looking into the housing) and that drives the driven gear DOWNWARD. Steel driven gear against aluminum housing = wear of the housing and binding up of the driven gear.
So now the fix. I had enough in the two housings to make one good one.
I added two brass washers to the lower end on the driven gear shaft (there is one steel originally) and dropped a .177 BB into the lower shaft hole to take up space.
Everything lined up, installed 1/8" roll pin.
I also used Lucas "Red & Tacky" lube in the housing this time.
Or you can buy a new housing complete for around $70 USD if you're in a hurry and don't like to take things apart.
See you out there.