I have a 1996 Grand Caravan, 3.3 engine. The trans will "pop" while driving. Not consistently, usually while I am accelerating or going up a hill, but sometimes while on flat roads at a constant speed. I may go a day or two with no issues at all. I've replaced a seal to stop a leak, and the output speed sensor but the pop still happens. Some places on line tell me I need to have my computer "flashed" in order to have it accept the new sensor. The local Dodge service shop said no way. Two questions: Do I need to flash the computer? Do I need to also replace the input sensor? Thanks in advance.

 

That's a good one. No, no flash required. Are you getting a check engine light and have you checked for codes? "Pop" isn't a word normally associated with a transmission. Is it jerking or maybe "popping" out of gear? Going into "limp mode" meaning it won't shift past 2nd gear? When was the last time you changed the fluid and filter? Using only ATF+4 fluid?

 

Thanks Cougar41. I do have a check engine light but when I took it in to be read the codes said I need a tune up. Nothing else was indicated. I had asked Midas to flush the transmission and replace the fluid when I had the seal replaced but they said it was a bad idea due to the age of the transmission. That did not sound right, but I am not much of a mechanic. I know just enough to be dangerous. I bought this van for very little, it is a salvage title. The work on it has been a lot less than what the previous owner thought was needed. I could not say when the last time was that the filter and fluid were both replaced. If this is something a shade tree mechanic can do, I am willing to try replacing the fluid and filter. I want to get another year or two out of this van, after that, I will sell it. As for the 'pop'...While driving, the whole van shakes, like it drops into a lower gear for just a split second, and then pops back into drive. It gives the van quite a shake.

 

The opinions vary on flushing the transmission fluid on a high mileage transmission that hasn't had the fluid ever changed. My opinion is if the vehicle has over 75k on the original fluid I wouldn't flush it. As a transmission wears small particulate wear off the clutches are suspended in the fluid and get deposited in the valve body especially as the fluid breaks down and no longer suspends the particles as much. Flushing the transmission or even a drain and fill introduces new fluid that isn't broken down and the detergents in it loosen up the deposits in the valve body in sections and the get stuck else where in the valve body preventing fluid flow, like clogged arteries. This clogging of the valve body causes improper shifting and slipping which wears out the clutches even faster when the slip, ultimately leading to failure. This is my opinion based on my experiences and observations but I have experienced many vehicles with improper shifting transmissions after a fluid change that were high mileage and original fluid. Every vehicle that had this issue that I decided to remove and clean out the valve body and reinstall with new gaskets would once again shift as they should. Problem is most people change the fluid too late then drive around a bunch with it slipping, destroying the transmission.

 

if you have a 3.3 or 3.8 engine, you probably have bad spark plug wires and the "pop" is actually an engine mis-fire, pull the wire from the coil one at a time and see if any of the coil terminals are corroded, if they are, change your plug wires.

 

Thanks! The spark plug wires turned out to be 90% of the problem. What a pain in the butt to tune up! Worst car I've ever worked on, by far! There is still a bit of a problem. The speedometer is not working well so I am wondering if it is sending false signals to the computer about when to shift or when not to. That's my next line of attack. Who would have thought a tune up would cure a "transmission" problem.