1999 Ford Windstar mileage: 92,000. Recently we had another new transmission replaced (the second one in less than a year and the warranty had just went out on the first one) in our van. They also replaced the speedometer cable, after reaching 40 mph it was swinging back and forth between 40-65 mph making it difficult to get an accurate speed (that didn't work). My question is do we need to have the speedometer head replaced/rebuilt and will that damage the transmission if we don't get it done right away?
The speedometer problem may be caused by the speedometer cable binding or the speedometer head itself. If it is the cable, other than the uneven speed reading, it should cause no problems. If it is the head, it may break the new cable.