Just had a re manufactured transmission and torque converter professionally installed ($$$) in my 1998 Windstar, w/126k.

The new unit shifts smooth under hard acceleration and doesn't 'hang' between 2nd and 3rd shifts, like the old one did. HOWEVER,

It still shakes or shudders, between 1st and 2nd shifts, under normal or slow acceleration. I can live with that. HOWEVER,

Upon deceleration, when approaching a traffic light, that turns green before coming to a full stop, the transmission
struggles into 2nd gear and the front wheels lock up and chirp tires, under normal or moderate re acceleration.

Mechanic back flushed old cooler/lines and used fresh Valvoline synthetic Mercon V.

I am at odds. The old transmission and torque converter behaved in the exact same way! Is it possible that the new unit was
rebuilt in a way to simulate my old problem identically? Or is there some other problem? Maybe I didn't need a new trans after all. Who knows?

Did they put a new "TRS" transmission range sensor, aka neutral safety switch on?
That would be a relatively cheap item.
Another would be to clear the PCM....by removing the negative battery cable....and turning the headlights on (to drain any charge from the system) and wait about 15 minutes.
Then reconnect the negative battery cable.......
Now....you may see some strange drivability issues while the PCM "learns" the drivability information.

I would NOT do this if you are comming up on a state vehicle emissions test, as it takes some time to clear the P1000 code that indicates that they OBDII system has not completed its test cycle.

Thanks Wisiwnd. No. They didn't replace the range sensor; they reused the old one which I bought from pep Boys a few months ago. Clearing the PCM sounds like sensible advice. I will try it during my lunch break.

I bought the re-manufactured trans online for $700 and I had a reputable shop, that I use often, install it for another $700. So the parts problems are for me not the shop.

When I conveyed the ordeal to the transmission rebuild company, they said they would mail out a bottle of Lube-Guard. The tech said dump it in the transmission and drive for 15 minutes and 'hopefully' it should solve the problem.

The idea of doling out another $700 install charge, even if they send out a replacement unit free of charge, is daunting! Any thoughts?

I think the only way to rule out sensors is replace them all TRS VSS and for about 78.00 bucks at least here in my area is to have the pcm flash updated for the trans.78.00 meaning dealer cost on the Pcm update on the trans. Now there is a round looking item near the TRS sensor thats plugs into the trans.Not sure if the thats the high low iterm servo. But if the old one was use I would replace it new as well. Just my thinking

Ok, reset PCM and drove for about 20 miles... no change.

Added Lube-gard and reset PCM (again) and drove for about 80 miles. Seems like the first 20 miles were ok. 1st to 2nd shift under slow acceleration shook or shuddered minimally. And down shift to 2nd, under hard or slow acceleration, was positive and smooth. But after about 30 highway miles, the problems returned.

Since then, it seems like the trans behaves better after cold starts and during short city runs. It is only after a few highway miles or after warm starts, when it seems the problems emerge again. Problems occur with or without A/C. And the fans and fan sensors are working properly.

I like garync1's ideas because they seem easy and cheap. But how to explain the apparent improvement after adding the Lube-Gard? Also, the red bottle contains 10 oz. and the instructions indicate 1 oz. additive per quart of trans fluid. I believe AX4S holds 12.5 quarts. Would 2 oz. Lube-Gard make a difference? If it made any difference at all?

PCM reprogram at dealership sounds interesting. Any one have experience on that note?

Hi,
The fact that the problem occurred after several miles of driving points to a sensor issue and not so much a mechanical one. I'll bet on the TRS.

I had trouble with my 98 Winstar decelerating as well - it would grab on downshifts. I brought it back to to AAMCO under warranty. They ended up pulling the tranny and rebuilding it but they could not tell me what was wrong. It started acting up a few months later and then the speed sensor failed (irrattic speed indication and improper shifting). After replacing the speed sensor, I never had any more trouble.

Hi,
The fact that the problem occurred after several miles of driving points to a sensor issue and not so much a mechanical one. I'll bet on the TRS.

WHY? Is the TRS based on temperature?
I can drive for 100 miles or more and after a while between 45 - 70mph the van will lose the ability to decide if it wants to be in 3rd or 4th gear. I completely let off the gas pedal and then I gun it and there is a pause.... and then it GOES as it should. As long as I maintain a certain speed above 70..... it stays in OD fine.... but if I'm maintaining a certain speed between 45-70mph it does the JIGGLE between 3rd/4th. I have had my tranny rebuilt as well 20k miles ago and was FUMED to still be having problems with it. If it can be fixed with a sensor I'd be willing to pay for it.

I had trouble with my 98 Winstar decelerating as well - it would grab on downshifts. I brought it back to to AAMCO under warranty. They ended up pulling the tranny and rebuilding it but they could not tell me what was wrong. It started acting up a few months later and then the speed sensor failed (irrattic speed indication and improper shifting). After replacing the speed sensor, I never had any more trouble.

SPEED SENSOR? Where? Vehicle Speed Sensor? Wheel Speed Sensor? HUH?