rodsob,

I don't think you problem is caused by a bad speedo cable. If one end of the cable is driven the other end of the cable goes the same speed or the cable breaks. I have never known a cable to slip at higher speeds.

More likely your problem is a bad speedo head. Best way to fix is to replace with a used head.

Which MB is the problem with? You should always specify the body model or engine model number.

P E H