2001 T&C Speedometer Calibration

[TCGrove]

I have a 2001 Chrysler Town and Country w/ 3.8L engine and 196,000 miles. Several years ago the transmission was rebuilt. Since then the speedometer was off 1-2 mph at 65 mph. I recently bought new tires and now the speedometer is off 2-3 mph at 65 mph. My question is: How do you calibrate the speedometer? I know all about the reset for a bouncing/stuck needle. That does not calibrate the scale. I've read about gear replacement and found the Hyper-Tech calibration programmer (which is not available for the 2001 T&C). Any ideas? Thanks....

[RIP]

Head to the dealership or well equipped shop and have the pinion factor reset with their DRBIII scanner.

[TCGrove]

I talked to the local Chrysler service department and was told that the only programming they could do was to change the tire size in the program. This in essence is changing the "pinion factor." The tire size has never changed on the vehicle. I guess one could put a different tire size than what's actually on the vehicle to get the speed right, but it would be trial and error. (Unless I had all the actual pinion factors behind the tire sizes to do the math). In a nutshell I was told to live with it by the Chrysler rep.

[RIP]

Welp, that leaves me out of ideas other than to check with another dealer or tranny shop.

Welp, one just popped. This is a bit off the wall but over the years some have written in complaining their speedo needles have popped off, usually after banging on the dash to get them to work (cluster solder joint issue). They usually push them back in place but sometimes have to go back and forth with them to get it to read correctly.You could try holding the speedo needle stem with a pair of pliers and tweaking the needle a bit to where you need it. Like I said, off the wall.

[Mbriggs]

Or, you could use this Tire Size Compatibility Site to find the tire size that would correct your problem

[Bill Grissom]

3 mph off sounds pretty accurate to me. I am guessing that w/ new tires it read even slower than before, at the same true speed. That would be because the circumference of the tire was greater. As the rubber wears, it will read a slightly faster speed. BTW, tire inflation has minimal effect. One story (true?) says that engineers designing an early tire-pressure monitoring ASSumed the wheel would spin faster at lower inflation pressure. Seems logical, because a balloon expands as you blow it up. But, tires have a steel belt around the perimeter, so the circumference barely changes with pressure. However, there is a slight effect, which could explain the nits you are looking at.