1998 Gt Tranny Swap From A 2003 Gt

Discussion in 'SN95 4.6L Mustang Tech' started by dylan sharkey, Apr 3, 2014.


  1. dylan sharkey

    dylan sharkey New Member

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    So my 4r70w auto tranny blew up in my 1998 mustang gt and i found a tranny from a 2003 gt. i need to know if that tranny will work in the 1998 gt please help!
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  2. wmburns

    wmburns SN Certified Technician

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    Are you expecting a "plug and play" swap? If so, this isn't it.

    The 99+ model year uses the OSS speed sensor.

    The 98 and older uses a VSS speed sensor.

    The output of the VSS and OSS sensor are NOT compatible to each other. The wiring is different as well as the signal type.

    Not to mention the 4R70W is an electronically controlled transmission and there are differences in the controls.

    Expect problems if this swap is done.
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  3. classypeopleracing

    classypeopleracing New Member

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    what all would be needed to do this swap correctly?
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  4. wmburns

    wmburns SN Certified Technician

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    Swap tail shafts. But the OSS sensor is pressed onto the output shaft. Will need to press off the OSS sensor and press on a VSS worm gear. Of course this will require that the output shaft be removed so that it will fit in the press.

    Swap external transmission wiring harness.

    Swap circuit boards.

    Throw some salt over your shoulder. In the end you may wish you just had the unit that came with the car re-built.

    Consider getting yourself a Ford service manual. This will give some guidance how to disassemble and re-assemble. If interested in getting a copy for yourself I may be able to help. PM if interested.

    Good luck.
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  5. classypeopleracing

    classypeopleracing New Member

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    never got it to work.. its been installed for a while now and could never get it going. i should have just had my 98gt trans rebuild, thanks though
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  6. wmburns

    wmburns SN Certified Technician

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    It might be helpful to anyone else that might be considering this swap to give more details on the problems that were encountered. Obviously there may be others out there with a similar mindset. IE the transmission "looks" the same they should interchange. Or the thought, "How hard could it be?".
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  7. ksustang

    ksustang New Member

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  8. classypeopleracing

    classypeopleracing New Member

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    I couldn't get the car to shift into gear even with the speed cal.

    It does look the same and almost everything plugs in. I should have done more research before doing this swap
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  9. wmburns

    wmburns SN Certified Technician

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    As in the transmission won't shift from neutral into 1st gear drive? No movement at all?

    That sounds like a misaligned DTR range selector. I would have thought that even if ALL electrical connections were disconnected, a WORKING transmission would operate in autonomous "limp in" mode. This would at the very least allow the car to be driven in 1st gear.

    So if the transmission won't even shift into 1st gear or reverse, what was done to rule out a bad replacement transmission?

    The effect of a non-functional speedometer sensor should be incorrect up shifts.

    Back to my original response to your original questions. I'm not surprise that some problems were encountered. I am however surprised to hear about a total failure.

    Have you looked at Thunderbird and Cougar Club of America (www tccoa com)? These guys have managed to swap out way far out transmission combinations. One their web site are some very detailed tech guides on how to swap older/newer transmissions. Some of the swap combo's involve a fair amount of effort.

    http://www.tccoa.com/articles/tranny/index.html

    See chapter 16 which deals with re-wiring.
    http://www.tccoa.com/articles/tranny/transmission/page16.shtml

    Here's a reference to a change in the MLPS (DTR range shifter). The article states there is a design change after 1997 and the two units are not compatible. However, it does state that you will need to keep the MLPS that came with the car.

    http://www.tccoa.com/articles/tranny/transmission/page2.shtml
    Last edited: Aug 1, 2014
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  10. classypeopleracing

    classypeopleracing New Member

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    Yeah it does not shift. the transmission is good i knew the girl who drove it and crashed it. I drove the car after it was wrecked and the trans was fine. I've tried aligning the range sensor multiple times and still nothing. It starts only in park and drive. I've looked at the tccoa and I can't figure it out still.
    Looks like I will have to upgrade to a 1998 4r70w from a race shop.
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  11. classypeopleracing

    classypeopleracing New Member

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    My 98 had a hard line inside the trans so I don't see why I would have to rewire it.
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  12. wmburns

    wmburns SN Certified Technician

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    Doesn't this tell you that the DTR and shift lever aren't really aligned? Or perhaps the length of the DTR throw lever is different between the 1998 and the 2003?

    This opens the possibility that the transmission isn't shifting because the PCM thinks the shift level is in the L2 position? Which if true would stop the transmission from shifting.

    There are mechanical linkages inside the transmission that control operation in addition to electronic signals that go from the DTR sensor to the PCM. Hence the reason why it's so important they be in sync. The fact it starts when the shift lever is in drive likely proves not in alignment (or throw is different).

    Do you still have the 1998 transmission to compare?

    It might be interesting to align the DTR and shift lever in neutral. Should be able to start in neutral. Drive would be one click away from neutral.

    The Ford service manual calls for a "special" tool to be use to hold the DTR in aligned position while the shift linkage is connected and tightened.
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  13. classypeopleracing

    classypeopleracing New Member

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    It will not start in drive only in park and neutral. I do have the 1998 trans to compare it too. Other than the alignment tool how would I get it out of the l2 position? Sorry if you told me how to fix it in the post I can't read it.. I don't have much internet where I am right now.
    #13
  14. silversmith82

    silversmith82 Member

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    That was me. For the auto, the 98 auto uses two sensors, an OSS and VSS. Other than that, the 97.5-03 transmissions are identical.

    But I can tell you why your swap failed... The ECU uses MPH and Throttle position, along with RPM to calculate shift points. With a stock tune, MPH comes first and if you don't have the OSS signal converted to VSS, your car will never work properly in a 96-98 with a 99-up trans. If you haven't already, bug a Dallas Speedcal into the OSS sensor wires and get your correct dipswitch setting. You can find a quick how-t0 on that via the link in the quote above. It will be your current revolutions per mile times your rear gear ratio times 6 since the 96-03 4R70ws use a 6 pulse OSS wheel. Plug that number you get into the Accutach calculator and it'll spit out the correct setting.
    Last edited: Aug 13, 2014
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  15. classypeopleracing

    classypeopleracing New Member

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    I am running a speed cal.. The only thing I can think of is that my cigarette lighter does not work and I will have to run it through a fuse then to the power source.
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  16. classypeopleracing

    classypeopleracing New Member

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    So should I re-pin the OSS not the VSS? I did the VSS because thats what the instructions said to do.
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  17. silversmith82

    silversmith82 Member

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    Even if the 03 transmission you are using came with a blocked hole for the VSS sensor, there may very well not be any teeth on the shaft itself. You can try shining a flashlight in there to see but that could be very well while you are not picking up anything at the VSS. Also, you need to be damn sure the thing is getting power, mine is bugged into the convertible power wire under the console that is always hot and has a pretty big fuse built into it. Big enough to power the foglights anyway. Not that the speedcal needs very much juice...

    To answer your question, verify your wiring is correct, take a probe light and verify you are getting power to the box and then I would indeed bug into the OSS sensor and use the formula I posted in the linked thread and the accutach calculator to figure out your dipswitch settings to convert OSS to VSS for your computer. Like I said, I am running an OSS only transmission in a VSS car and my speedo is dead nuts accurate and scales correctly.
    #17
  18. classypeopleracing

    classypeopleracing New Member

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    I traded out the tail shaft from my 1998 trans to my 2001 trans so it is running both a VSS and OSS sensor. and is getting power, I got a little buz from it the other day.
    #18
  19. wmburns

    wmburns SN Certified Technician

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    As stated early on the VSS and OSS sensors are different. They work differently (VSS generates power the OSS needs power). They are wired differently. The generated signal is different. How the signal is used is different.

    For your set up with an extended range Speedcal, this offers up even more possible combinations of sensor type, wiring/pining, wiring harness (98 or 02). Most of the combinations are likely wrong.

    IF your transmission has a working VSS sensor from the tail shaft swap, then I don't understand why the SpeedCal is even needed (unless there has also been a rear end change).

    Which transmission wiring harness has been used can also make a difference as the harness itself is wired differently (for example the VSS has one pin grounded whereas the OSS has both pins isolated).

    It seems to me the two ways to do this are:

    Use the OSS sensor that the transmission came with. The output of the OSS must go to the extended range SpeedCal unit. The output of the SpeedCal needs to go into the VSS pins of the 1998 transmission wiring harness.

    Or use the output of the VSS sensor wired into the the 1998 transmission harness as the original VSS sensor went.
    #19
  20. classypeopleracing

    classypeopleracing New Member

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    I was under the same impression that a VSS tail shaft swap to the OSS trans would work but it didn't. I am going to try and put the OSS sensor from the 2000 trans back in and try to wire the extended speed cal to it.
    #20

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