I have a 1982 300 TDT. The speedometer does not hold steady, but
instead jerks. It's worse at low speeds. Yesterday it was jumping
from 5 mph to 60 mph when I was going about 5 mph.
I have recently replaced the speedometer cable with a new aftermarket
cable and also replaced the original speedometer which had 423,000
miles on it with one with 332,000 miles on it. Neither of these
replacements has solved the problem.
Any ideas? It is somewhat inconsistent as sometimes the speedometer
runs smoothly, but not very often anymore. At 60 mph usually the
"bounce" is only a few mph, but it's enough to make the cruise control
oscillate. Could it be a worn gear of some kind in the transmission?
And if so, what would be involved in changing it?