I fitted a new cable to my 58 Mk8 and the rev counter isnt very stable after it reaches the right revs. It seems to waver up and down a couple of times before settling to the correct level. Not sure it did this previously.
What is best way to fix this please?

 

DB48, to me it sounds like your new cable has some dried lubricant in it and that is causing it to stick a little. My advice would be to get your hands on a 30ml bottle with a needle attachment. Get yourself some 0W20 full synthetic oil and put that in the bottle. Then, with the cable removed from the car, pull the end of the cable a little bit to expose the inner cable and using the bottle with needle attachment, add some oil to the cable. You will probably need to add say about 5 ml of oil to get it to go the full length of the cable. This will help the cable glide inside the sheath and should even out the RPM issues you are seeing.

 

Many thanks Thermo. I will try that. Sounds like it could be the problem. It’s like it needs a damper?

 

If the cable re-lubrication doesn't fix the problem then it may be an instrument problem.
The Mk1 tacho is a very simple device spinning a magnet against an alloy cup which is the same principle as older house electric tariff meters.
It is very simple to remove the tacho, clean the internal parts with a petroleum-based product and re-oil the pivots in the instrument with SAE 10 or sewing machine oil.
Been there, done that, many times.

 

Many thanks Bill. I will try the cable lube and failing that pull out the tachometer and clean it up. I need to tap the petrol gauge to get it to be active. Maybe that needs pulling apart and cleaning as well?

 

That petrol gauge stickiness is due to the "jewels" ie pivots running dry.
They were originally lubricated when new but 66 years later it will have dried out.
A dab of wd40 or similar will free up the pivots and then a dab of very light oil eg sewing machine oil will lubricate it.