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rear suspension holes diameter, why 1/2inch?

Posted: 16 Nov 2018, 03:03
by DavidIt
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!

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

Posted: 16 Nov 2018, 03:26
by freakynami
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?

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

Posted: 16 Nov 2018, 03:41
by DavidIt
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.

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

Posted: 16 Nov 2018, 05:18
by ChrisS
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

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

Posted: 16 Nov 2018, 07:28
by DavidIt
thank you Chris, now is perfectly clear, thanks to you picture also.

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

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

Posted: 16 Nov 2018, 10:13
by ChrisS
You’re most welcome. :)