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Fix for sticky 5th gear

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  • Fix for sticky 5th gear

    For most of the five years that I've had the MC, I've had the "sticky 5th gear" problem, where, after you take it out of 5th gear, the stick doesn't move back to the normal position under 3rd, making it hard to reliably select 3rd as you've got nothing to guide you. This problem has always been worse when the car is cold, and has slowly got worse to the point where I finally bit the bullet and fixed it.

    The fix involves replacing the bushing for the 5th gear locking pin, which requires dropping the gearbox.

    There's quite a bit of info on the web already about this fix, but I've written up my own notes here:

    http://www.ex-parrot.com/~pdw/mcoupe/5th-gear-fix/

    Hopefully this will be of use to anyone who has to do this in the future.

    This is the source of the problem:



    I also replaced the flex disc between the gearbox and the prop shaft while I was at it. Probably didn't really need doing, but there were a few cracks in the old one.

    Paul

  • #2
    I did mine recently as it was driving me mad. Removed the box as with pdwarren`s and removed all the plungers, one at a time. The inserts were all fine, so I lightly honed out the bores until the pistons didn`t stick any more and moved with hardly any effort. Reverse was fine, so just cleaned and went back in. The plungers were oiled and re-inserted.
    The box is now transformed to how it should be on my low mile MC.
    I did have the new insert ready, but decided it didn`t need it, so we`ll wait and see on that. It wasn`t too bad a job as I had an excellent mechanic give me a hand, or the other way round, as he has a good four post lift and very reasonable labour rates.
    I think the design is a little poor with the plunger to piston clearance being too tight. There is no real oil flow in and out to clean and lubricate the friction surfaces. It is relying on a little splash feed, which ends up with the worn particles gumming up the components.
    Still it`s done now, wish I`d done it sooner.
    Thanks to all that have posted about this problem, as it helped immensely.

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    • #3
      Probably not something you both want to hear but mine suffered from this especially when cold or in winter months but since I changed the gearbox oil to AMSOIL MTF I don't think it's ever done it even in the recent very cold weather.

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      • #4
        Nice work Paul. It's posts like that which keep me on this forum.
        Imola S50 1999

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        • #5
          I don`t think mine would have been affected to a great degree by a different oil. The detent pistons were sticking in the bore due to lack of clearance, ie, slightly interference, so they wouldn`t return under the spring pressure until the box was warmed up. 5th gate was more affected than 1-2 to 3-4 gate, which is also now a lot easier.
          Maybe it`s luck of the draw with this, and it`s probably time related as my car is 10 years old now, although only covered 24,000 miles. Pleased it is relatively easy and inexpensive to fix, compared to some jobs!

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          • #6
            Originally posted by c_w View Post
            Probably not something you both want to hear but mine suffered from this especially when cold or in winter months but since I changed the gearbox oil to AMSOIL MTF I don't think it's ever done it even in the recent very cold weather.




            the last 3 bimmers that I have owned have had this same exact problem of the infamous 5th shift gate sticky.
            1) 99 Z3 2.8 coupe(sold)
            2) 99 M-coupe(current summer driver)
            3) 00 323I Touring(5-sp)(current bad weather cruiser & crap hauler)

            In the northern US, I am in Minnesota we can regularly get down to -30 farenheit in the winter. I have found that nothing solves this issue when its well below zero.

            BUT.....the Amsoil Synchromesh trans fluid has completely solved this issue with all 3 cars.

            Its a must do for the 5-sp owners before dropping the trans. I cant believe anyone thinking that the trans fluid is a lifetime fluid.
            99 M-coupe alpine white(s52) sunroof delete & black nappa/evergreen guts.
            00 323IT(5-sp)
            05 Rubicon Unlimited triangulated long-arm 37" meats
            04 Dodge ram 2500 crew cab long-box
            03 KTM 525 EXC
            06 YZ250F 290 athena
            05 GAS GAS Pro 300 Trials
            06 TTR125L (spec class ice racer)

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