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1995 Dodge Caravan Transmission problem

I have a 1995 Dodge Caravan with only 66,000 miles on. The transmission has been acting up for about 3 months now. When I am driving around 35 or 40 miles an hour it down shifts. The spedometer jumps up to 50 then flies down to 20 and back up to 40. I have had the sensors replaced and they have put an additive into the fluid but neither one has fixed the problem. Does anyone know what this problem could be??

Was the Vehicle Speed Sensor (VSS) one of the sensors that was replaced?
If not, it sounds like the VSS is at fault here, since this device sends signals to both the speedometer and the transmission.

As to other transmission issues, has the fluid been changed within the last 3 yrs?
If not, be sure that this is done if you want to eke out as much life from this transmission as possible. Make sure that only the correct Chrysler-specific AT fluid is used, rather than the make-do practice of using Dexron fluid and adding an additive to–supposedly–make the transmission work properly with the Dexron fluid in it. This is a short-cut method that bad mechanics use, and it WILL shorten the life of the transmission.

If the sensors you had replaced were the input and output sensors of the transmission and the wiring has checked out OK, then that points toward a problem with the Body Control Module. The BCM runs the dash instruments and other body functions. It also talks to the Transmission Control Module so if the BCM is acting up the TCM will default to ‘limp home’ mode which is second gear and reverse only. A scan of the TCM when this has happened (engine not turned off since) might reveal exactly where the problem lies.

Maybe, transman618 will pipe in and get us all straightened out.

It was the input and output sensors that were replaced. The transmisson was flushed and the fluid replaced a year ago. Not sure what kind of fluid they used. I will have to call and ask the mechanic.

Do you know if there is a service bulletin for this problem??

I spoke to another mechanic about the problem I mentioned above. He said that perhaps because the new tires that I had put on were larger than what is supposed to go on the van that it could be causing the speed sensor act funny. The tires that should be on the car are 202-70-R15 but what was taken off the car and put on are 205-75-R15. I don’t know for sure if all the old tires were the 205-75-R15 but they were very worn. My usual mechanic thinks that it’s a valve problem and doesn’t think that the tire size differnece would cause the above problem

Highly unlikely that it is related to the tires. So go with the 1st mech. Most the problems related to this car are related to the electricals. Have someone check the shift solenoid.

Thanks. I was curious about that. I will mention that to my mechanic back home.