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Thread: U-bolt query: Help please, quick...

  1. 20th September 2014, 12:41 PM #1
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    U-bolt query: Help please, quick...

    Hey up,

    Just replacing a few (brand new) u-bolts, and I need some advice quick-ish.

    When I fitted the u-bolts to the front axle a while ago, I realised that the threaded portion was not long enough (I have a nine-leaf pack, not eleven, in the front springs and the u-bolts were longer jobbies with a necked-down threaded portion) and got around it temporarily during the rebuild by bunging in four washers before putting the nyloc nuts on. I have always been planning to fit some properly-sized u-bolts as I didn't like all those washers.

    I recently bought some u-bolts for a 4-cyl petrol 88, the lengths of which are suited to my front end.....BUT fitting them now I see that there is no necking-up above the thread and the whole u-bolt is a smaller (weaker) diameter. The originals were 11mm diameter. These are 9mm (the same as the threaded portion).

    Photos attached.

    Will it make much difference? What's my best option here???


    Thanks,

    John
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  2. 20th September 2014, 12:53 PM #2
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    Shouldn't make any difference, the weakest point will be the root of the thread so the bigger diameter plain section doesn't make it stronger.
    On the smaller diameter U-bolt the threads have been rolled not cut which makes them stronger.


    Colin
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  3. 20th September 2014, 01:05 PM #3
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    Thanks Colin,

    I was thinking along the same lines, but kept coming back to the fact that, whatever the quality of the steel, surely the rest being 11mm was better than it being 9mm.

    Cheers,

    John
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  4. 20th September 2014, 01:58 PM #4
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    Quote Originally Posted by Johnno1969 View Post
    Thanks Colin,

    I was thinking along the same lines, but kept coming back to the fact that, whatever the quality of the steel, surely the rest being 11mm was better than it being 9mm.

    Cheers,

    John
    Yebbut when there's a stress raiser at the end of the threads, the flexing from suspension movement will break the 11mm ones faster than the 9mm ones. That's because the 9mm can more easily flex a tiny bit to cope with stress changes.
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  5. 20th September 2014, 04:37 PM #5
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    Quote Originally Posted by bee utey View Post
    Yebbut when there's a stress raiser at the end of the threads, the flexing from suspension movement will break the 11mm ones faster than the 9mm ones. That's because the 9mm can more easily flex a tiny bit to cope with stress changes.
    Thanks for that. I'm glad that there are cleverer people than me on this forum. Much appreciated.

    John
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