I have a 1991 740T sedan and the speedo is giving incorrect readings. It started with the speedo not working at all for a few minutes and now it floats between 40 and 60mph. However, sometimes it reads correctly. Is this a cable problem or something else?

 

ABS sensor in the Diff Cover in the Rear end.

 

Check your wireing and connections. The fact that it works right sometimes implies to me that it may be a faulty connection. (broken, corroded, just touching, etc)