TF 999/998 sporting internal diff from the 904 ?

Transmission and Drivetrain Tech

  1. rustytoolss

    rustytoolss Well-Known Member

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    First question. Does anyone know what the first year was that the 999//998 was used in production vehicles ?
    Since there does not seam to be any tell tale signs of which trans you are looking at 904/998/999 externally.
    How can you tell if you've got a 999/998 and not at 904 internally ?
    I know the 999/998 have lower gearset. But if you do not know how to spot the 999/998, tell me what to look for ?
     
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    • Mopar69gts

      Mopar69gts Member

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      There should be a model / ser. number
      On the drivers side just above the oil pan.
      Call a dodge parts dept. With that number they can tell you what it is.
      That's what I did from a 1987 d100 truck it's a 998.
       
    • VOETOM

      VOETOM Well-Known Member

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      You can make some really slick smaller Torqueflites out of 998 and 999s.
       
      Last edited: Nov 8, 2018
    • 408 swinger

      408 swinger FABO Gold Member FABO Gold Member

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      I think all the 998/999 were lock up transmissions. So a quick tell tale sign would be look at the input shaft. There will be a short, unsplined portion on the very end it.
       
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      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        A-998s Were not ALL loc-ups. On the top of the bellhouse behind the Distributor, you should find cast into the bellhouse , the call-outs A998 or A999
        I have one each A-998 non-loc-up, and A999 loc-up. They are wide ratio transmissions and work well with super-high hiway gears, behind stock hi-torque low-rpm engines, and adapt well to slightly juiced up SBMs . But for big-cams, you still need to keep pace with compression and upgraded rear gears and or a higher Stall TC, same-old/same-old. For streeters I recommend to concentrate on what second gear is doing.
        The ratios are 2.74-1.54-1.00,and splits are .56-.65;(versus 2.45-1.45-1.00 and splits of .59-.69 in the regular A904).
        With 3.55s this makes your roadgears 9.73-5.47-3.55....... so the stock 112LSA cams work well. That 5.47 road-gear will get you about 60@4400, kindof a good place to be with a stock 318.
        EDIT; I think someone once told me that not ALL A998s had the wide ratio gearset, so buyer beware. Mine does
        Also, with a 2800TC, your 318 will haul the mail with this combo; and you can forget about up-camming it.
         
        Last edited: Nov 8, 2018
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        • Duane

          Duane Well-Known Member

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          The lockup 999 can be identified by two things. One is the machine ring on the input shaft that is unique to the lockup.
          The second way that I identify a 999 with the low gear set is by taking off the pan and look at the back of the sunshell. The low gear set sunshell has a raised step in the back of it whereas the 2:45 is rounded smooth.
          If you come across a trans that has both the machined ring on the input and the step on the sunshell you can bet it's a 999.
          I don,t think they made any of those lock ups that were not low gear 999s, but I am not certain of that.
           
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          • Mopar69gts

            Mopar69gts Member

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            Just a question for TF guru's
            Do all lockup 998,999's have the lower ratio gears?
            I have a 998 from a 87 dodge truck in my dart.
            Hughes performance modified the converter and made it non lockup also raised the stall to approx 2000.
            Just curious if it has the low ratio..
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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            As far as I have read, 998s could have either gearset, depending I guess on application. But Also as far as I have been able to figure out the 998s were not lock-ups.
            So if you have a 998 that has a loc-up, it would seem to be an oddity. At least to what I know.
            So with those assumptions, I would think your trans should have the 2.74-1.54-1.00 set

            No experience to back any of this up.

            I got my low-gear set out of a 999 behind a slanty. I just transferred it into a 904 SBM case, and got rid of the lock-up in the process.
            If anyone else does this, be sure to keep the M/S with the planetaries together as a set. If you put those A999 planetaries on the 904 MS, you might get 25 or 30 miles out of them, after which the MS will rip all the splines out of the back aluminum planetary, and you will be walking. Dangit.

            Edit.. M/S is mainshaft or in an automatic I guess output shaft.
             
            Last edited: Nov 16, 2018
          • Mopar69gts

            Mopar69gts Member

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            Thank you,
            Yeah it's a lockup 998 with a one wire solenoid.
            But obviously disconnected
            I bought a older 904 VB from a member here to add a TF 2 kit so it would be more of a plug n play, also could put original one back in if for some reason I didn't like it..
            Thanks for the help.
             
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            • Duane

              Duane Well-Known Member

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              Sorry you lost me on the terminology. What is M/S ?
               
            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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              M/S or MS sometimes ms, is Mainshaft,or mainshaft....
              on which the planetaries are mounted in an automatic,
              and upon which, in a manual trans, all the selectable gears turn freely until locked to it by a synchronizer assembly.
              Post 8 edited for clarity, thx for responding
               
            • Duane

              Duane Well-Known Member

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              Oh ok. I always refer to that as the output shaft.
               
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