904 Steel Planetary Upgrade

Transmission and Drivetrain Tech

  1. Nick Mailloux

    Nick Mailloux Active Member

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    Hello, rebuilding another 904, this one is from a 1970 challenger that im gonna put in my dart. Ive done a few stock rebuilds on mopar and ford transmissions so thats no issue. Im planning on doing some upgrades, billet rear servo, hd kickdown band strut, red alto frictions and kolene steels, shift kit and so on. But I've been told that I should possibly upgrade the planets to steel versions if I have the aluminum ones. What parts are required for this? Just the planets? Or do I need anything else like the ring gears? Any thrust washers?
     
  2. RustyRatRod

    RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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    I guess you can, but I have heard very little about problems with the aluminum planets in the 904. Certainly if you can afford it, go for it. Also one thing I saw that you omitted was that "I" would recommend running the flat out widest 2nd gear band that will fit. Also of course make it a ridgid band. JMO.
     
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    • Nick Mailloux

      Nick Mailloux Active Member

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      Yes for sure no flex bands hear. Cast rigid only! I got the trans for $50 so Ive got some cash to throw at it, I abuse my transmissions so I want it built to handle some rough stuff. Planning on building a pretty stout small block in the future too.
       
    • RustyRatRod

      RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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      Also, a lot of people say not to run the 5.0 kickdown lever......BUT if you run the widest band you can for 2nd gear, it's a good upgrade to do both. Doing one without the other is kinda a waste though. Again, JMO.
       
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      • Nick Mailloux

        Nick Mailloux Active Member

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        Im probably gonna go with the regular cast ans a 4.2 lever. I really dont see the need for a 5.0 unless going all out racing.
         
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        • 70aarcuda

          70aarcuda Master Hoader of SBM FABO Gold Member

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          Got 6 904s in use...actually one is a spare...all have the 5.0 lever. Some have aluminum planetary gears some dont...dont seem to have a problem with either.

          A very good upgrade for the 904 is replacing the large wound spring in the front clutch pac with a 24 spring kit......or....ATI make a large wound spring but it is wound the opposite direction then the stock one...The stock one will let the front clutches drag at high rpm.....what rpm I dont know...but i use the 24 spring kit and never had a problem with the front clutch pac...I got one trans with the ATI spring...
           
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          • Nick Mailloux

            Nick Mailloux Active Member

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            Ahhh yes I forgot about that, I'll probably get the one from TCS or copes. So pretty much should be fine with the aluminum planetarys?
             
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            • Nick Mailloux

              Nick Mailloux Active Member

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              So I really guess now the only question I have is, if I go ahead and decide to upgrade to steel planets, is it just a simple swap with the planet and annulus gear? Is there any trust washer changes. I see lots of people have done it, just wondering what's actually required.
               
            • fishy68

              fishy68 Tyr Fryr's Inc. FABO Gold Member

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              I put steel planetaries in my 904 and had to change nothing else, just the planets
               
            • Nick Mailloux

              Nick Mailloux Active Member

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              So I can get a red relined cast from cope or I can go with a raybestos pro semi rigid a500 band that's 1.6, what would you pick?
               
            • RustyRatRod

              RustyRatRod 30 Degrees Outta Whack FABO Gold Member

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              I would go with Cope. He doesn't sell junk and he's a member here. Kinda a win win. He may offer a forum discount, I'm not sure, but it won't hurt to ask. He's a good dude.
               
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              • Nick Mailloux

                Nick Mailloux Active Member

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                Just messaged him, thank you!
                 
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                • 70aarcuda

                  70aarcuda Master Hoader of SBM FABO Gold Member

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                  Band...Band on the Run......

                  Got these from Tranzact...

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                • Nick Mailloux

                  Nick Mailloux Active Member

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                  So I tore down the 70 transmission today, it had .056 end play on the input shaft before I started. It has a 77 valve body in it so I guess my worries are gone there. It was already missing the accumulator spring. Has a 4.2 lever too. The rear clutch seemed pretty good but worn. The front clutch had over a 1/4 inch clearance at the snap ring, the most I've ever seen. Bas 4 pinion aluminum planets that seem to be in pretty good shape too. Overall it looks like a great candidate to build a trans that's plenty capable. Since the accumulator spring is missing,is there any way to tell if it has a shift kit installed? I haven't taken the valve body apart yet.

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                  Last edited: May 31, 2019
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                  • Nick Mailloux

                    Nick Mailloux Active Member

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                    Ok so my pump gears are broken. Also there's a spacer ring under the wave ring in my rear clutch. Both manuals and everything I've read online says that the a904 isn't supposed to have a spacer ring.

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                    Last edited: May 31, 2019
                  • 70aarcuda

                    70aarcuda Master Hoader of SBM FABO Gold Member

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                    I had one rear drum that had the spacer ring out of 5 904s that I have....have no idea why
                     
                  • Nick Mailloux

                    Nick Mailloux Active Member

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                    Did you leave it in or take it out? Does really change anything?
                     
                  • Cope

                    Cope Fusing with fire

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                    CRT for the win.

                    And no, I am not affiliated with them but I do use their parts in my trans.

                    :steering:
                     
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                    • Duane

                      Duane Well-Known Member

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                      I would say it depends on the valve body and the line pressure he is planning to run. My tranzact valve body runs at 170 psi.
                      The recommended lever is 3.8 or 4.2. I know when I did the rebuild on my 47re in my diesel truck that initially I had the line pressure at 140 with a 4.2. The shifts were way to aggressive. Turning the line pressure down 15 pounds made the shifts firm but not aggressive.
                      Also in some applications the 5.0 lever aggravates shift overlap when the trans is in two gears at once just momentarily.
                      My current 904 build with aluminum front drum and the widest band available 1.75 inches I am going with a 3.8 for a clean shift. More is not always better with the levers. Just mho.
                       
                    • Nick Mailloux

                      Nick Mailloux Active Member

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                      I actually finished and installed my build last month. I used the four pinion planets that were in it. I used regular steels and high energy green Alto frictions. 4.2 lever with a&a red lined cast bands front is smooth and rear is grooved. It has a late 76 valve body with a tf2 kit installed with all the mods for the hardest shifts. Put in a heavy duty accumulator spring, and a aluminum kickdown servo. Every bushing was also replaced. With the 2500 stall converter it's really smooth and crisp, not hard at all like I would have thought. It will snap your head and bark the tires at full throttle shifts though. All in all its its absolutely the best of both worlds.
                       
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