The tach on my 64 gave up this weekend after couple days of squealing and jumping. The tach end (plastic) broke off in the tach head, I feel maybe the result of wrong lubricant(lithium based) applied too closely to the tach may have worked up into the tach (I haven't removed the cluster yet). Cluster restored about 1100 miles ago, so I think not the result of worn out parts. Can the tach be salvaged with cleaning and re assembly, need new parts, other suggestions?

 

The discription sounds like the cable gave up not the tach.

 

I thought so too, when noise first started, I pulled cable (new repro) and cleaned cable, re coated powered graphite, was quiet for about an hour drive, then started again. Removed cable for inspection again, re lubed, spun in sheath by hand(was smooth) re installed to tach, was very hard to turn by hand. Attached to dist and fired car, tach end immediately sheared off, so I think tach head is seized or has excessive resistance at least. So that's why I am back to the tach,

 

in 94 mine started squealing and jumping. not wanting to take it out, i used a LONG 3/16" drill bit and then shot oil into the tach from below. still good now, 18 yrs later.
But, i think it is too late for that in your case