RD400 Speedo not working

[Spaceman7Spiff]

77 RD400.  Speedo needle suddenly started bouncing, then reading slow, then stopped working altogether and never came back.
 
-Cable seems fine.
-I can make the needle move with a drill attached to the cable.
-I have thoroughly inspected the drive, as well as the tangs on the wheel and I am very confident that it is all good. 
-Visually confirmed that the wheel turns the cable
-I even went so far as to take the speedo completely apart and lube everything and I never saw anything out of place. 
-Finally, at a loss, I went ahead and replaced the cable anyway and still nothing.

I'm out of ideas... What in the living f*** is going on with this thing?! It's beautiful outside, I wanna go ride!

Edit: Just pulled the speedo end of the cable off again to re-verify.  This time it moved a bit as I pushed the bike and then stopped.  Is there some kind of clutch or something in the drive assembly that could have failed?

[Spaceman7Spiff]

Okay I finally figured it out.  The speedo drive washer inside the wheel had been squeezed into a somewhat concave shape causing the tangs to not properly interface with the speedo drive.

So if you're reading this in 2048 and you have this problem, pull your speedo drive washer out and inspect it thoroughly even if it seems fine from the outside.  (Also, are motorcycles still legal in the future?)

[RDryan]

OK, good to know and glad you figured that one out on your own. I read your query and while I am no master I do have a 75' RD250 and was definitely curious to see how this would work out.

I mean there's only so many things that can not fit right and it seemed you covered all the bases. I thought to myself...this sounds like something that sight unseen by the rest of us, with a bit of luck you would just have to retrace your steps and you did and you found it.

I just had the front wheel off my bike all day yesterday into this morning to try and polish the fork lowers as the original finish was yellowing and corroded. Thought about your dilemma and kept looking at the speedo cable on mine (original one) that seen better days but it still works. After I finished my polishing detail I reinstalled the wheel and while thinking of your dilemma I couldn't resist spinning the wheel enough just to make sure my speedo was still working. Got to see the tenth of a mile indicator move a bit and it tempered my OCD's.

The irony is I like the fact that it functions but I definitely don't think it's very accurate. 

[2 Smoker]

I am in Lewiston, Id and almost ready to start up some 2 stroke rides in the region. I will post about it when ready.

 Jim