Splitting lower coffin arms to add shims - Special tool??

Marky911 · 13 Jul 2019

Hi gents,

I want to get some camber off my 996 GT3. We managed (just) to crack the nuts off on the studs from the inner bush, located up in the recesses on the underside of the coffin arm.
We removed the 12mm shims and put 6mm back in but because the studs were then protruding further the socket bottomed out before the nuts were tight.
That was with a standard quarter drive size socket and wobble bit. A long socket won't fit due to the shape of the recesses. Neither will any spanner.

So anyway we've had to refit the 12mm shims until I figure out what tools to get. Not sure I trust my alignment place to do it.

So any info on what tool works best would be appreciated.

Cheers. :thumb:

PS. That was on top of my new air-con rads not fitting my coolant rads so that stopped play there. :frustrated:

infrasilver · 13 Jul 2019

I was looking at fitting a pair of rear GT3 arms to mine but I assumed adjusting would be fine with a ring/open end spanner when looking but without actually doing this I may be totally wrong and hope to be corrected for when the time comes. Although if you are referring to torquing that may be a different story?

Marky911 · 13 Jul 2019

Hi Chris,

Not too bothered about torquing them. I was just gonna tighten them to FT.

See the pic of offending item below. The access channels look wider in pic than real life. Certainly no ring key or any other spanner I have will fit.
It can't be that hard though as I've never heard of anyone else having bother. :bonk:

If you imagine once you've taken that 12mm shim out, there's then 12mm extra stud sticking through the nuts. That makes things tricky.

infrasilver · 13 Jul 2019

FT is always about right :thumb:

But yes looks like I'd be able to get a spanner on it but again what do I know as I've never done them, I have modified spanners before to make fit things in similar situations, I assume a GT bod will be along with the answer soon.

Slippydiff · 14 Jul 2019

Hi Mark, hope you're well ?
How big are your nuts ? :mrgreen:
I ask as the nuts in your image look like 13mm items on M8 threads, they should be 10mm nuts on M6 threads ... Hopefully they're the correct M6/10mm items though ?
Either way, 4 of these little blighters will be your friends and make things easier :

https://tridentracing.co.uk/product/knuts-aircraft-spec/

As you'll know, an M6 K nut has a 7mm hex, and the M8 a 10mm hex, plenty of room left to swing a spanner or a deep 1/4 drive socket once the shim has been removed and the K nuts fitted in place of the standard nuts.

I seem to recall Matt at Fearnsport fits them 'as standard" whenever he's using the shims to adjust the camber.

Marky911 · 14 Jul 2019

Evenin' Chris, it turns out you're half right then. You could get a spanner on the nuts if they were the right size. As Henry has impressively identified below, mine aren't the proper size. Thanks for your input. :thumb:

Hi Henry. All good here thanks, likewise I hope you're well and enjoying the fruits of your labour with the Zanzibar car. :thumb:

Super info above. Top notch.
So my nuts and studs aren't the proper sizes then. They are indeed 13mm nuts, on most likely M8 studs.
Have you seen these before then? Pattern parts?

Thanks for the link to the K nuts too. I'm going to check I can get a 10mm spanner in there tomorrow and then order some of those nuts.
I'm guessing there's no risk to using them. I don't want a coffin arm separating down a mountain pass.

I'm thinking get the ones with the integrated washer so the surface area of the mating face is nearer that of a 13mm nut?

Anyway I'll look into it tomorrow and hopefully that's the solution. I hope it's that simple. My mate here thinks we'll still have bother due to the stud being 8mm instead of 6, as once we drop from 12mm to 6mm on the shims, the studs stick through a long way.

We'll see though. Like I say, that's great info. Much appreciated, as ever. :thumb:

Slippydiff · 15 Jul 2019

Something didn't seem quite right about this issue ... so some further digging was required !!

Double check my thoughts on the stud and nut sizes Mark, I'm pretty sure I'm right in saying they should be M6/10mm nuts/studs, and this screenshot I've taken of a thread about swapping the shims from 6Speedonline would appear to confirm their size :

With the stud/nut size confirmed, I think I've established the other 'problem" that's causing your issue with access to the nuts.

The studs should have each have two 5-6mm thick spacers (you can see them in place in your image) with an ID of 6mm and an OD of 9-10mm, these are 'stacked" under the securing nuts when the thick shims are NOT being utilised.

Their use ensures the nuts never bottom out on the threads of the studs, but they also ensure the nuts end up in a part of the recess in the arm that allows better access with a ring/combo spanner (or socket) when the thick/thickest shims aren't being used.

I've highlighted the spacers you'll need in this image :

and they can be seen in situ in this image of a 991 control arm :

I think with all but the thicker shims in place, you can run a locknut in addition to the securing nut, but with the camber maxed out with the thickest shims, only one nut can be used. Unfortunately when thick shims ate in place, those spacers get left on the bench or popped into someone's tool chest/the 'washer box".

FWIW, aerospace spec K nuts have far, far superior torque capacity than mild steel fasteners. Rich Beaumont will be better able to advise on their merits.

Marky911 · 15 Jul 2019

:worship:

The info got even better with your second instalment. I owe you one Henry.

So yep I double checked things this afternoon and I have now ordered 4x M8 10mm K nuts and 4x M8 6mm thick stainless spacers.
Hopefully that lot will get me sorted. I'll report back after the weekend when it's also episode 3 of my radiator and condenser fiasco. :grin:

Not a relaxing run up to my holidays. :nooo: :grin:

Splitting lower coffin arms to add shims - Special tool??

Marky911

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