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Discussion Starter #1
It's a 96 t-bird V8 with 146,000 miles.

I was driving from Milwaukee to St Paul yesterday. 330 lime trip, all highway, no problems what so ever. 5 miles from my house, I have the cruise set at 60, then all of a sudden the revs start creeping up and the spedo starts to drop. I shift out of OD into third. No problems there. I tried 4th again, same problem. It won't accelerate in 4th, it barely holds on to the speed, almost like being in neutral. Got home the rest of the way in first, second and third with no problems.

I drive the car today. Everything is fine. There is no hand up when shifting from 3 to 4. It is actually a fairly quick shift. Torque converter locks up fine in 4th.

Any ideas?
(I spent most of the morning searching the forums, and most of what I found was the 3-4 shift, not so much the slipping problem described above)


2nd part:

I have a 98 Mark 8 with 46,000 miles that is sitting in the garage for various reasons. Would it be worth swapping that tranny into my t-bird? Just wondering if I am on borrowed time in the t-bird. If I swap the mark 8 tranny into the tbird, then I can get a build tranny for the mark 8. :cool:
 

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#1 - My guess is original TC dying &/or Main VB O/D circuit getting tired - You've gotten your moneys worth out of 96 tranny I'd say as stock it's pretty poor.

#2 - Much better Tranny & TC than the 96 ~! - Certainly should have some great miles left in it - I'd do new tranny Cooler & Flex Plate swap for 11 inch TC too.
 

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1997 Thunderbird 4.6, 1998 Mark VIII LSC
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Might be the OD band slipping when the fluid is hot. The way to check that would be to drive it for 30 minutes or so and see if it starts slipping in OD again, then if so go into 3rd like you did before to see if it stops. If so then go into manual 2nd to see if it slips again. If so, then it's the band. Don't go from OD to manual 2 though; turn off OD first before moving the shifter.
 

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Sounds like a slipping OD band to me. It's more common on the older AODs than the 4R70, but with 146K on it, parts in that trans are getting pretty worn. I would swap it out before you start having more problems and it leaves you stranded. In the meantime, I wouldn't use OD at all, since every time it shifts into OD, that is more of the band wearing away and mixing in with the rest of the trans fluid, which could start causing other issues.
 

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Discussion Starter #5
Drove to work today and it was fine. It's about a 27 mile commute, mostly highway. I called a local transmission shop and they suggested that it might be the neutral safety switch. I'm going to borrow a code reader from a friend at work to see if I can catch it. Anybody else have any issues with the Neutral safety switch?

Since the connector in the 98 is different than the 96. Do you just swap the pins in the connector to get them to match up?
 

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If you swap the trans, you would have to swap your mlps onto the new trans. I highly doubt that is the problem though. If that were bad, or out of adjustment, it could possibly cause the trans to not shift into OD at all, but in your case, it is shifting into OD no problem, but slipping once it is in OD. I think on that long drive, the fluid got hotter than it does on your daily commute, and the OD band that is barely holding on wasn't able to grip anymore at the higher temps. If you don't have an external trans cooler, that may buy you some time, but pretty soon that trans is going to need to be rebuilt or replaced.
 

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Because the resistance readings within the MLPS are different, so even if the current is flowing in the correct path, if it is getting a different resistance reading, it will throw off the computer and not work properly.
 
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