Tranny (Neutral Slams)

My '98 Windstar drives fine, except after harder stops it acts like it slips into neutral. Then about 1000-1500RPM it slam into gear and drive fine again. I am hoping to fix this before it tears the transmission apart, not to mention doing burnouts in a minivan looks a little odd. Fluid is full and I have changed the TRS and VSS but neither has had any effect.

On the rear of the tranny there are two "servos". 1st - 2nd and 3rd -4th, I think they are called. Each is easily (that is... if the tranny is out of the vehicle) rebuildable in that piston seals and gaskets are available. I think the low range servo is your problem. You're lucky that the low range servo is accessable ... tho still a bit of a knucklebuster. Its a no-brainer to rebuild once you have access.

Doesn't that control the shift from 1st to 2nd and back? Mine seems to shift into neutral on coastdown. If I manually shift into 2nd about 30mph and then back to drive once stopped everything is fine. Any suggestions?

I have exactly the same problem. It's getting better if the trany heats up. In case I'd like to check the servo what can i expect under the cover? I 've downloaded the scheme, there is a spring, gaskets and the regulator, not so many parts to get cracked, is the problem usualy in that spring? Does the oil leaks when opening the servo cover? Thank's a lot, there are not so many AutoTrany specialists here, in Czech Rep. like in the USA so that's why I have to do all the stuff myself :-)

Tip: Those springs are strong and long ... and the cover screws somewhat short. This means injury, or lost parts, if one is not very careful as the servo is dismantled! One way to work carefully is to replace the screws, one-at-a-time, with longer screws ... this will keep things from flying apart.

The most common way for the servos to fail is not broken parts ... but worn parts. One of the o-rings acts as a piston seal and, once worn, will lessen the force that the piston can exert. Each of the two servos is very similar in design.

Hopefully your problem is with the servos ... as they are relatively easy to repair. But there are other things that cause similar symptoms.

I'm not a tranny expert by any means either ... just have often been lucky to find some easy problems to fix. If it gets very difficult ... I give the problem, and my money, to someone else.

Well, thanks for your post, I've rebuilt the engine half a year ago so putting trany away of the car is not a good idea for me. I'll check this because it's easy and quick the trany was rebuilt 15000 miles ago. In the worst case I'll rebuilt it :screwy:

I rebuilt the servo. No change. I dropped the pan and there is almost no dibris in it. I flushed the system and changed the filter. No change. It acts like the one way clutch sticks. It does it almost every time the engine would be required to hold back in 3rd or 4th. If I manually shift to 2nd as I stop it does not have a problem. I checked line pressure and it is fine. I checked the electronically regulated pressue and it seams fine. It still will not go after a medium to hard stop and then slams into gear when I step on the gas about 1200 RPM. Bang.

As I wrote here before, exactly the same problem and behaviour on my windstar. I have checked the servo and found it a bit worn at the end of the servo-pin, but this seems not to be a problem at all. Please is there anybody who might have an idea what to check before the trany goes away from my car?

Thanks a lot, MarPac

I had this problem in a 91 taurus that I had about 10 years ago. It is basically the same trans. Had only 71k on it when this happened. It was diagnosed as a cracked forward clutch piston and required a complete rebuild. The earlier years had some kind of fiber type piston that was prone to cracking. Ford update was to use a cast aluminum replacement.

nice :-(

I have learned that if I turn off the OD by pressing the button on the end of the shift lever the problem goes away. When driving around town it is no problem as long as I remember to turn OD off. When crusing on the highway I simply turn the OD back on. I just have to remember to turn it off when I get off the highway.

I have been driving the van for a few months now by turning off the OD and it has been driving pretty good. If I start the van and forget to turn the OD off is will not move when I am cruising in OD and then stop. It will sit until I rev the motor a little and then SLAM. I am not sure why turning the OD off allowes me to drive it, but for now I am living with it.

I was playing with this for a long time, using a digital osciloscope and trany cable reduction where I can measure all the signals. I've found that all the speed valve's signals goes correctly, Owerdrive valve as well. The only strange thing I've discovered is Preasure regulating valve. The PCM gives the PWM signal into it to regulate the preasure inside the trany. You can measure it with a normal multimeter as AC signal. This signal is based on fluid temperature, air flow measurement, TPS and maybe some more stuff. If you increase the RPM, the PWM signal goes longer and preasure goes up. If the car cannot drive, it's enaugh to turn RPM up to 2200rpm, the PWM signal is longer and trany shifts correctly. I found some vacum leaks in my Windstar, after replacing new tubes the situation is better (more air flow through the sensor), but still not good. Sometimes it's enaugh to turn the engine off and on after 5s.

And this is the end of a story, still hate driwing with cold van :-(