1998 Grand Voyager 3.3 with 125K miles. Routine service has been done (fluid/filter changes at roughly 50k and 100k). The wife reports that intermittently the van will, from a stop sign or red light, rev and then eventually drop into gear harshly (like textbook low fluid level). Of course it will never do this for me, but I don't think she's crazy (on this point at least...). I have checked the fluid level multiple times ("don't overfill! between bottom holes warm, between top holes hot. idle in Park. don't overfill!") and it is NOT low on fluid. The fluid is not horribly dark or smelly. Looks like 25K old ATF to me (which it is).

I know enough not to expect a fluid change to help at this point (especially if the friction material suspended in the ATF is the only thing keeping this trans from complete failure).

Emotionally, I want to believe that there's a secret $20 externally-mounted flanged niblick control valve that is to blame.

Intellectually, I know that I have a transmission on the way out, and it should be rebuilt.

Is there something I'm missing here (or a secret flanged niblick valve)?

I thought you were supposed to check it running in neutral?

Any MIL on? A loss of prime code would pop up if you were low on fluid. Any kind of slippage would also log a code. Over fill a qt and see what happens.

Over filling an auto will only make it worse, (causes foaming of the fluid)

without any kind of clutch fill volumns to confirm or deny anything I would say the front pump is loosing prime. drop the pan and make sure the filter is engaged in the valve body

If it is ,,,,,,, have fun - sounds like an overhaul is in your future

I have seen 604 filters fall off also we fill to hot full mark right from get go and you would have to get 1 WAY overfull befor it would cause any problems.

Since you are only relaying the conditions,perhaps there is a engine performance issue. How often does this happen? You may have a TPS with a worn spot, this could cause a stumble while accelerating from a stop. They don't usually leave a code.

The trans a-604 is to be checked in park ....the problem that you are experiencing is that it was put in gear to quick...it needs to be relearned can be done with real scanner...poss a loss of prime is the problem....

check the orange o-ring on the filter,ive seen them cut or missing.

First of all, thanks to everyone who took the time to reply.

As for a "stumble" being mis-described, I had already ruled that out between the corroboration with my son, and the description of the tachometer needle climbing when it was slipping.

So, today I dropped the pan and had a look. The magnet was fuzzier than I would have liked, and the smell of a drain pan full of used ATF is certainly more significant than a dipstick tip's worth.

Even so, I am finding some reason to be encouraged...

The o-ring was present and intact. The filter was not residing detached in the bottom of the pan. However, the fit of the filter neck into the valve body was far from firm. When I compare how the new filter feels (tight and solid) when installed, I can sure see how the old one could have been sucking air once in a while.

This finding has reinstated my wife's willingness to give the van another chance. The plan is to use it more (when gas prices peaked, we took my mother-in-law's econobox out of mothballs for trips that didn't require the van's capacity), and to put me behind the wheel most of the time. Most importantly, we are not bound in a headlong rush for the transmission shop come Monday morning.

We shall see.

Thanks again for all the suggestions

might be the trans solenold fading...