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M42 M20 Manual trans question

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    M42 M20 Manual trans question

    Total n00b question here.

    I'm new to BMW, so please go easy on me. I just bought a 1989 325i that's super clean, but has an automatic trans. I plan to swap it down the road, but I want to make sure I get the right parts.

    My local pick and pull had a 1991 318 with a 5-speed. I went ahead and pulled the pedal box, the driveshaft and transmission, because these cars don't turn up too often in our area.

    Logic tells me that the driveshaft is probably going to be too long for my M20, as I'm sure the 6-cyl pushes the transmission back down the tunnel a bit further than the M42 does. Logic also tells me that the relay arm for the shifter linkage may also be too long, for the same reasoning.

    Can anyone confirm these two facts? I'm thinking I'll have to return the driveshaft, and possibly the transmission, and start to look for a donor car.

    TIA

    #2
    Really the only thing you will want to use from an m42 car is the pedal box. The 318 gearbox is a Getrag 240, the 325 is a Getrag 260. The g240 is shorter than the g260, so the m42 shaft may just work, but it's kind of a "backwards swap". High HP m42's go to the g260.

    The shifter carrier arm will also be a mystery. Normally with the g260, the carrier from an m42 car would be too long, but now that you are attempting the g240 behind the m20, it may work.

    Also, the ring gear for the starter on the m42 flywheel will be wrong for the m20 starter. the ring gear is larger on the m20 FW.

    Well, ultimately I read this back and it may be more confusing than when you asked lol.
    john@m20guru.com
    Links:
    Transaction feedback: Here, here and here. Thanks :D

    Comment


      #3
      Thanks!

      From what I'm reading, it seems like the trans will bolt to the M20, but will sit at the wrong angle. Then there's the linkage issue, and the length of the driveshaft.

      Looks like I'll be returning all of these parts this week.

      On the plus side, I didn't spend too much time getting the transmission and driveshaft out: maybe 1-1.5 hours of my total time in the sweltering Alabama sun.

      I spent more time trying to get the pedal box out. Though I probably didn't need to do more than grab the pedals, I figured I should cover all my bases.

      Comment


        #4
        Good on you getting the whole box. Realistically you only need the pedals and hardware, but some auto pedal boxes don't have the threaded holes for the master cylinder. They can be tapped, or nut added, but since you have to pull the box to do that anyways, might as well plug the whole new one in.


        Not sure how much your yard charged, but you might be better off selling your purchase and using the funds to buy m20 stuff. At least you might get a little back for you labor.
        john@m20guru.com
        Links:
        Transaction feedback: Here, here and here. Thanks :D

        Comment


          #5
          Thanks. I’ll look into that.

          The Getrag 240 seems popular-ish for 2002 engine swaps. But I don’t know many locals with BMWs much older than e30s around here.

          Thanks for the tip.

          Comment


            #6
            You could undoubtedly overcome the the issues of getting the linkage to work with a G240 on an M20, but it's just not worth it as you'll be continually over stressing that gearbox (even though it can take stock M20 power).

            Consider shopping for a disused 325/325e MT as a parts car, and keep the G240 as a trade/sale item. In fact, if you posted it on r3v I suspect it'd sell within a month.

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