If your symptom is what I think it is, you're in for a bad day.
This exact thing happened to my '98 Windstar (w/ 140,000 miles). My symptom was that the cruise control would malfunction. Early signs were that the accellerator pedal would shiver and "hunt" for position. Speedometer was not accurate as well, until finally the speedo stopped registering and engine would run awful. (Reason is, the car computer needs to know the vehicle speed in order to accurately calculate the load, fuel, ignition timing, and other etc parameters.)
To make this long story short, the speed sensor gear and the drive gear inside the transaxle are both plastic. In my case, they both wore down until the gears did not mesh any more. Speed Sensor then stopped turning.
Unfortunately, the drive gear for the speed sensor is all the way inside the transaxle housing. The only way to gain access is to remove transaxle from vehicle and tear down entire transaxle unit. . Well, might as well have tranny rebuilt if all the gears and clutches need to be removed in order to gain access to the speed sensor drive gear.
You, or the repair shop, can perform this simple test to verify if your speedo is bad, or if the drive gear is bad:
Unplug the speed sensor (even though it is very difficult to get to), and hook up another known-good speed sensor. Spin it and have an assistant see if speedometer registers or not. Doesn't matter which way sensor is being spun. If your speedo is good, the needle will move. If needle moves by spinning sensor by hand, you know the drive gear is worn out.
Transaxle needs to be rebuilt. Sorry for the bad news.
Realize there are two types of speed sensors: 1 is completely electronic, and the other type is the older version mechanical drive type. Chances are, you have the electronic only, which does not have a flexible drive shaft attached to it. The two sensors are not interchangable. Be sure you or the shop is ordering the correct one.
Friday, February 27th, 2009 AT 9:35 PM