[TR] Erratic Speedometer

[Randall]

> Is the speedometer the more likely culprit? Has anyone serviced one?  
> Could lack of damping with age be a problem?

I went through this relatively recently with the original speedo from
TS13571L.  In my case, the problem turned out to be mostly the odometer and
trip meter mechanisms.  

There two gear drives from the input to eccentrics that each operate ratchet
mechanisms; which turn the shafts that all of the dials ride on.  Each
individual dial has a slip clutch arrangement to its shaft, which normally
slips all the time.  I believe what was happening was that the entire shaft
& clutch arrangement was so stiff that when each ratchet started to move
it's dial shaft, the speedometer cable would wind up before it could supply
enough force to move the shaft, which let the speedometer needle drop down.
Then when the ratchet stopped moving, the cable would unwind and kick the
speedometer needle higher.

Some of the experiments I tried:
1) Hook the tachometer to the speedometer cable.  No waver seems to indicate
the cable is OK.
2) Hook the speedometer to the tach cable.  It still wavered, but not as
much (due to the shorter cable).
3) Disassemble the speedometer enough to remove the links that operate the
ratchets, then try again.  No waver, indicating the odometer &/or the trip
meter was the problem.

It took me several tries; just cleaning and lubricating all the surfaces was
not enough.  I had to mechanically polish all of the slip clutch surfaces,
which had apparently become corroded and rough from years of disuse.  I
didn't take as many pictures as I should have, but here is a shot showing
the tripmeter components after cleaning but before polishing:
http://goo.gl/fxmS8
The shaft has a groove (which unfortunately doesn't show in the photo) which
engages with the tab inside each brass disc.  So the brass discs turn with
the shaft, and slip against the raised center of the dials (which are held
from turning by the rectangular springs visible inside the frame).  Those
are the odometer dials piled in the background (which work the same way).

I gave all the slip surfaces a light coat of auto body polishing compound
and assembled the dials & clutches onto the shaft outside of the normal
frame.  Then I mounted the shaft in my cordless drill and held the dials
from turning with my fingers, while the drill spun the shaft.  After a
minute or so of that, I took it all back apart, cleaned away all of the (now
dirty) polishing compound, lubricated with a very light coat of synthetic
brake caliper grease and reassembled back into the original frames.

I was also careful to assemble the two gear drives 180 degrees out of phase,
so that only one dial shaft was moving at a time.

-- Randall