Vibrating Mk1 Cortina 1.6 Xflow

Hi all,

I have a Mk1 440 with a crossflow 1600. It is a column shift and everything is standard. One of the things i'm trying to work through and to be honest, is DRIVING ME CRAZY, is the vibrations it throws at me in 4th, and when at most cruising speeds.

I have replaced the engine and gearbox mounts, they were trashed - no difference.
I rebuilt the tail-shaft and had it balanced - no difference.
Thought it was the gearbox, so i rebuilt that... guess what - NO DIFFERENCE!
I've switched wheels, balanced etc.... - no difference

I then got talking to an older friend who asked me if my Cortina was one of 'those ones that shakes its self to death' and i replied YES!

He suggested that back in the day, (when the issue made grown men cry) they worked it out to be the harmonic balancer/bottom pulley on the crank. He said they replaced it with a rubber lined unit, (which Ford didn't want to know about) which solved the issue. The vibrations were thrown out from there, at certain rev ranges.

So... does anyone know, or has heard anything like this? Or have had any similar problems of their own?.. any help would be appreciated... it's making a grown man cry!