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250 Gte front suspension pin nut preload

Discussion in 'Vintage (thru 365 GTC4)' started by christc, Mar 15, 2019.

  1. christc

    christc Karting

    Mar 3, 2013
    64
    Germany
    Dear All,

    I hope you can help me. I am in the process of finishing my front suspension rebuild. Everything fine so far.
    Now I have the following question: What is the right way to tighten the front suspension pin nut. I mean the big nut you see in the attached photo at the topof the king pin?
    a.) tighten so far that the front axle/hub can still turn freely and secure nut with the according washer by bending over the lashes

    Or

    b.) shim or adjust the shims so the nut can be fully tightend and the front axle/ hub still turns freely?


    Thanks for your advice. I could not find anything on it.

    BR
    Chris
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  2. turbo-joe

    turbo-joe F1 Veteran
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    Apr 6, 2008
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    romano schwabel
    I would do it the way: b.)
    but then I ask myself for what you need the washer with the lashes? only as saftey?
    those lashes are not strong enough to keep this nut when this nut is not really tighten. so the adjustment has to be done with shims.
     
  3. christc

    christc Karting

    Mar 3, 2013
    64
    Germany
    Thanks. Thought so but was not sure. Speak to you when you are back in Germany ;-)
     
  4. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
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    Brian Brown
    The nut needs to be tightened down fully so that the tapered upper portion of the kingpin is tight in the upper pivot. This means that it takes a fair amount of torque to do so, and then the pin needs to be smacked hard with a hammer in order to separate the connection. The brass shim washers for the spindle need to be custom machined so that there is slight drag on them when the upper nut is tight. You may have to assemble and disassemble each spindle multiple times in order to get the correct preload. I start out with the washers too thick and then machine them down in small increments until you can just feel the spindle get hard to move as you tighten up the nut.
     
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  5. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
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    Berkeley, CA
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    Brian Brown
    You want some preload on the spindles, as it helps act a a steering damper, and allows for wear at the shim washers. Each side should have close to the same preload, which you can measure with a spring scale at the end of the spindle shaft.
     
  6. turbo-joe

    turbo-joe F1 Veteran
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    why not use first a thinner washer and test then with a feeler gauge to see how much you would need? so I do it when I adjust the preload for diffs at the flat 12 family. so less work to dismantel always
     
  7. christc

    christc Karting

    Mar 3, 2013
    64
    Germany
    Thanks to you all for the information. Thats how I finally did it, Thanks.
    Chris
     
  8. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    1,946
    Berkeley, CA
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    Brian Brown
    You can do that when you are way out on the dimensions of the shim washer in order to get close. There is only supposed to be one thick brass washer in the the assembly, not a bunch of thin steel shims. In order to get the correct dimension of the thick washer correct it is much easier to machine down a thick washer than it is to machine multiple thicker washers until you get to the correct size.
    When I am getting close to the correct thickness, I am removing just a couple of ten thousands of an inch on a flat plate with some very fine emery cloth. It takes time to get it right. But once you have the method down for popping the top loose in order to get the shim out, disassembling it multiple times is no big deal
     
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  9. turbo-joe

    turbo-joe F1 Veteran
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    romano schwabel
    you are right brian with machining down. but always the work to put together and disassembling again? why not use an old shim or a shim with a little less thickness than the new shim in the set and test then with a feeler gauge?
    how often you had to disassembling and put together each side until ok? yes, not such a big job as for example adjusting the preload for the diff bearings. ;)
     
  10. Motob

    Motob Formula 3
    Professional Ferrari Technician

    Nov 11, 2003
    1,946
    Berkeley, CA
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    Brian Brown
    I usually have to pop the upper A-arm off of the king-pin four or five times to get it right. It is not very hard to pop it off. I use a flat place with some fine emery cloth to sand the shims down .0005" or so at a time to get it where I like it.
     
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