On my '91 last week I was driving on the highway about 60-65 when all of a sudden the speedo dial started climbing to 70-75-80-85 and past. The odometer seems ro be working ok? Still when I drive it still operates in the same manner. It never bounces around or falls back. The needle is sort of stable such if I maintain a speed the speedo will maintain even though it's incorrect. There is a slight wavering of the needle meaning it's not astable as it use to be. With the odometer working I was wondering and don't know. Does the cable drive the needle or is it electrically controlled? I'm thinking of grabbing another instrument cluster it that is the problem, I'd like to know more about it and understand how it works so I don't just throw parts at it until it's fixed.

Thanks,

 

The speedometer is cable driven. In my limited experience the problem is usually a worn/frayed cable. Also not sure how a bad cable can cause the speedo to read a 'constant high' but swapping the cable did solve the problem at least in my case. There's a white tab on the cable where it goes into the instrument cluster that you just push against the cable to pull it out and on the transfer case side just pull/wiggle the cable out (the steel pin stays in).