I got my long speedo cable from RPR and I'm pretty sure I just
said "122 with M41" and I think that the speedo cable connectors
are the same between 122 and the early 140s. I think they are
also close to the same length.

DISCONNECT THE SPEEDO CABLE! Something is binding and it will
break then you're in for one of a couple of messy fixes. Reach
behind the gauge cluster and unscrew it from the back of the
gauge cluster.

Lastly, it's been my experience (mostly with early 140s not 122s)
that the worm gear thingy that turns the odometer freezes up from
poor lubercation. They aren't easy to access so tend to have 20-50
year old grease in them. As soon as my speedo starts making any
noise or twitches at all or if I have the gauge cluster out for
some other reason, I always take the speedo apart and clean and
regrease the worm gear. Of course, I did that incorrectly once
and the gauge cluster went from silent to loud to frozen in 5 miles
on the highway, in a rather exponential progression...
(loud to very loud in 30 seconds and frozen in 10 more)
chris