rear suspension holes diameter, why 1/2inch?

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DavidIt
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rear suspension holes diameter, why 1/2inch?

Postby DavidIt » 16 Nov 2018, 03:03

hi,
i have a doubt.. why in the plans the rear upper suspension-to-upright holes are 1/2 inch if the bolt is 10mm ?
i'm missing something?
thanks!

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freakynami
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Re: rear suspension holes diameter, why 1/2inch?

Postby freakynami » 16 Nov 2018, 03:26

If you mean Fig 24.32 / 24.33 / 24.34, the bolt through the upright is 1/2" and the bolt tying the rear link into the main tube at the "clevis" is 3/8" (10mm ish).

If not - which bolt specifically?

DavidIt
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Re: rear suspension holes diameter, why 1/2inch?

Postby DavidIt » 16 Nov 2018, 03:41

hi freakynami,
i mean picture 24.33.
i just double checked the inner diameter of the rear-upper bushing and it's 10mm. i'm using an 2th serie MX5.

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Re: rear suspension holes diameter, why 1/2inch?

Postby ChrisS » 16 Nov 2018, 05:18

Because the design replaces the stock Mazda bush with a spherical bearing. I tried using some aftermarket poly bushes at first, with the hole reamed out to 1/2”, but they constrained the free movement of the assembly too much, so I went back to book design and used the spherical bearing.

IIRC, Kurt did originally use stock bushes but had issues with the upright moving too much and rubbing against the upper wishbone, hence the book design with the spherical bearing.

Because the lower “wishbone” assembly is effectively totally free to move, unlike in the MX5, this places more loads on the upper attachment so having the spherical bearing there to help locate it better is a very good idea I think.

I initially tried to use poly bushes as I had no way to machine down the bearing cup to fit into the loop on top of the upright. When the result wasn’t something I was happy with, I went back to book and found someone to turn the cups down for me.

HTH

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Re: rear suspension holes diameter, why 1/2inch?

Postby DavidIt » 16 Nov 2018, 07:28

thank you Chris, now is perfectly clear, thanks to you picture also.

download/file.php?id=1803&mode=view

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Re: rear suspension holes diameter, why 1/2inch?

Postby ChrisS » 16 Nov 2018, 10:13

You’re most welcome. :)


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