2000 3.8 Windstar, no OD when hot

[Mac2002]

I have a 2000 Windstar with a 3.8. 247,000 miles, but only 142,000 miles on this transmission. It was replaced at 105,000 miles in 2005 with a Ford replacement unit, at least that's what I paid for. Now, when I begin a trip from a cold start, I can go for about 45 minutes with the transmission working perfectly. I can put a load on the van climbing hills and the transmission stays in OD like its supposed to. After about 45 minutes, the transmission will not take a load in OD. It will not stay on OD on level ground, though if I hit a steep enough downhill or coast, it drops right into OD until the next time any kind of load is put on it. Then it drops into 3rd. Any idea what could be causing this and is there anything I can do short of a total rebuild? Thank you

[12Ounce]

You might try a total pump down and refill of the fluid. I would recommend synthetic .... unless, of course, you've just changed it. It'll take about 15 qts or so.

I have approximately 230k miles on my Ford reman. Lots of trailer pulling, and the tranny is just now beginning to act a little peculiar. And, I need to follow my own advice ... My fluid has over 100k miles on it, maybe more. !!

[tomj76]

How does the torque converter clutch behave when this is happening? You should be able to see it lock up when cruising at >50 mph by watching the tachometer. It will drop about 300 rpm when the TCC lock happens. I think the normal engine speed is ~2000 rpm at 60 mph (maybe 58 mph) with the transmission in OD & TCC locked up.

Are you getting any blinking of the O/D light? If so, have you read the codes to find out the reason?

Also, did you check the level (at operating temperature, on a level surface)?

Transmissions need tight seals in the hydraulic passages. They can behave strangely if they lose pressure due to any leaks. I don't know for sure it was the cause, but before my recent problem with the main seal falling out, I'd lose TCC lock-up on long trips after driving 100-150 miles. Since that seal is near the torque converter I wonder if the two were related. I haven't seen the problem with the TCC since that was repaired.

I should probably add the PCM 'decides' when to shift gears using data from the engine and transmission sensors. It calculates the 'engine load' (in percent) and if that number is too high it shifts to a lower gear or if it is too low it shifts to a higher gear. It is possible that a faulty sensor is leading the PCM to change the gears incorrectly.

[Mac2002]

Thank you both for your ideas. I have not done a complete fluid flush. I have recently dropped the pan and replaced the filter. That only replaces 7 quarts.

Last winter, when driving in the mountains, often near the top of the mountain I would get a 'check transmission' warning message. Most of the trip the OD was not working, as usual. Up until about 4 months ago I was also having shift problems from 1st to 2nd. This had been going on for a couple of years. This set code P0720. I replaced the vss (not that hard but definitely not Fun) and that went away. Since then I haven't driven far enough on the highway with the OD not working to get the message again.

Now, when driving on the interstate after the OD quits, when I push the OD button to disengage the non-functioning OD, it feels like the engine speeds up just a little. Probably no more than 100 rpm.

I like the idea of a bad sensor, assuming I can replace it myself.

Any recommendations on where to get transmission codes read for free? Autozone won't do it.

Thank you again

[12Ounce]

Actually, AutoZone can't do it ... not with the scanners they typically have. It will take a transmission shop or the dealer to read this one. Good luck on getting it free. There are some transmission shop supply centers who might do it for free, or a low fee, on hopes that they might make a parts sale.

[tomj76]

Some of the transmission codes are available on the scan tools used at Autozone. It depends on if they are "generic" codes or "manufacturer" codes. Generic codes are defined in the OBDII specification, but manufacturers have added additional codes for their own use. So, for example my Actron scanner will report codes like P0741. Tools like a SnapOn scan tool will (with additional fees) read the codes listed in the factory service manual that are not part of the OBDII specification.

Regarding your O/D light issue... when everything is working correctly, the rpm at 60 mph in overdirve (4th gear) with the TCC engaged should be about 2100 rpm. With O/D disabled the rpm should be about 3000 rpm.

However, when the TCC engages it should cause the rpm to drop from 2350 rpm to 2100 rpm (with overdrive engaged). I'd expect a similar change for 3rd gear (O/D disabled), but I've never tracked it.

It sounds like you may be confusing shifting to overdrive (4th gear) for torque converter clutch engagement. There is a big difference in the two, because from my experience the torque converter clutch failure is a fairly "normal" problem, while loosing 4th gear is less common.

If your problem is with the TCC, then you might be able to repair without removing the transmission. However, in my case the problem was only cured by removing and rebuilding.
This documents gives the gear ratios of many transmissions. To get the engine RPM, divide the distance traveled in one minute by the circumference of the tire to get the wheel rotations per minute, then multiply that by the gear ratio and the final drive ratio to get the engine rotations in one minute.

RPM = Gear_ratio * Final_ratio * (distance per minute / tire_circumference), so for my '96 Windstar with the 3.8 L, the numbers are (5280 ft per minute / 6.883 ft/rev) * (0.69 * 3.98 ) = 2106 rpm

In 3rd gear: 2106 * 1 / 0.69 = 3053 rpm

http://www.atra.com/Dash/Ratios/GearRatios.pdf

http://www.taurusclub.com/forum/atta...rt_numbers.gif

[Mac2002]

Tom, no confusion here. When I'm driving at 80mph and the OD is working, the engine is spinning at about 2500 rpm. When the OD decides to quit its spinning somewhere well above 3000 rpm. It's unmistakable. I can't really tell what the tach is reading as I lived through the 'gauges gone wild' scenario and bent the tach needle. A quick resoldering on the circuit board for the gauge cluster fixed that issue.

Turning on and off the OD manually works just as you describe when the OD is functioning. When its not, and I'm cruising in 3rd gear, if I manually turn the OD off, I notice a slight increase in rpm, but I don't believe its 250 rpm. This is my wife's car so I don't drive it much.

My scanned must have read the generic code P0720 for the VSS, but not the manufacturer-specific codes, if any. Looks like I'm off to a local professional.

Thank you for your help.

[tomj76]

For what it's worth, I think the RPM change you're specifying is more likely pointing to a problem with the TCC. Any time you shift between 3rd & OD you see the RPM increase by 45%. At 80 mph this is a change of (guessing here) about 1400 rpm (2800 vs 4200 rpm)