is it easy to fit speedometer cable on a car .?

Before taking drastic action like taking the binnacle apart I would check the speedo sensor first. They are normally located on the transmission casing. Make sure there are no loose connections to it and trace the cable back and make sure the cable isn't chafed anywhere. If it is only doing it over 60 It might be the speedo that's faulty but it would be expensive to replace even if bought second hand these sort of faults are a pain to find even if you are an expert and there is a good possibility that fiddling with it could change the problem from a speedo that jumps over sixty to one that doesn't work at all.

Good luck

How easy it is depends on your level of vehicle mechanical ability.

I'm tempted to suggest you'll find it next to impossible since you're having to ask the question.

The instrument binnacle needs to come out, then you need to find where the cable (or lead if it's an electric speedo) fits into, which is probably under the car and I can guarantee even for an experienced tech it's quite a fiddly job sometimes.

the cable should not be the issue. here. the gage in the dash has a problem. from the trans all the way to the point that the cable connects into the dash is a solid link. in the gage itself, is a magnetic assembly that is influenced by the spinning member.there is not contact between the two normally. you could have some thing in that area.

Electric speedo on that, take the car to a garage who specialise on that car, if its under 3yrs old it should be covered by warranty