Rear Undertray

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Rear Undertray

Postby Jon » Mon Dec 08, 2008 11:39 am

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Re: Rear Undertray

Postby paulr » Sat May 22, 2010 6:14 am

we have got to fit ours - front and rear - what is best way to fix them ?
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Re: Rear Undertray

Postby Jon » Sat May 22, 2010 1:56 pm

Paul,

I didn't ever have a front undertray so can only advise on fixing the back one.

I never used self-tappers which was the Midas factory suggested method. At the rear I used double-lug floating anchor nuts rivetted to the inside of the back bumper, and M6 roofing bolts with nice wide, flat heads to spread the load on the undertray. At the front, using the same type of bolts, I bolted through the floor with the washer and nut inside so the thread stays clean and dry.

I also made up a couple of brackets that sat above the undertray and hooked on to the trailing edge of the rear sub-frame side members. I reckoned this would take some of the aerodynamic load, but it was primarily to make putting the undertray on a much easier single-handed job. I could offer it up from the rear of the car and it would support itself while I put the bolts in.

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Re: Rear Undertray

Postby Hans Efde » Sat May 22, 2010 3:07 pm

Selftapping screws are a big nono. Alistair recommends SS rivnuts, his procedure can be found in one of the last club mags I produced. If you don't have these issues I can look up his mail and repost here. He can sell you complete fitting packs for the undertray.
Alternatively the undertrays can be fastened with rubber nuts easily. I ordered these from Ebay in different lengths. Longer ones when there is room as in the bumper, the shorter ones in the sandwich floor (just in the lower floor and foam, not through the upper floor).
As an example:
http://cgi.ebay.co.uk/M5-Rubber-Well-Nu ... 3cab751754
I use these every where I can in my Midas.
.
Very simple and about an hour work. First I positioned the undertray with duct tape, a few pieces of wood supported by a jack. Then I drilled small holes for temporary fit with selftapping screws and marker for the bigger holes. Removed undertray, carefully drilled bigger holes for the rubber nuts, installed rubber nuts and bolted undertray into position. I used SS allen key bolts with large washers under the head.

The coupe does not have a sandwich floor which can complicate things. I never found a good solution for the coupe. It is a single floor that seems to be too thick for rivnuts or rubber nuts. I once had the idea to use a strip of steel and weld nuts to it. This would be fitted at the inside in the cabin, so the bolts would go through the floor to pick up the nuts. But I never got to the practice.
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Re: Rear Undertray

Postby Rich » Sat May 22, 2010 4:42 pm

Does anyone have dimensions for making up a rear undertray? It looks like an ideal use of some aluminium sheet that I could source locally.
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Re: Rear Undertray

Postby johnnyfixit » Sun May 23, 2010 6:10 pm

bare with me as its up side down
width =1050mm
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height =980mm
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exhaust hole is 350mm off left edge
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and measures 210mm x 450mm and is 70mm off the bottom edge
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wouldn't have a clue about measuring the tail pipe hole without making a template hope this is of some help Rich if I've missed anything let me know
The front one is a bit harder to measure as it's more shapley
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Re: Rear Undertray

Postby Rich » Sun May 23, 2010 10:12 pm

Thank you Johnny, much appreciated.

I think I'd be tempted to buy the front one, the biggest problem I can see is actually getting it delivered Any ideas of the part cost?

The rear looks eminently doable in DIY mode.

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Re: Rear Undertray

Postby johnnyfixit » Tue May 25, 2010 12:21 pm

PM sent
:)
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Re: Rear Undertray

Postby Rich » Tue May 25, 2010 8:06 pm

johnnyfixit wrote:PM sent
:)



Gotcha, thank you!

I don't suppose you have any pics of the side plates as well do you?

Rich
;)
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Re: Rear Undertray

Postby johnnyfixit » Mon May 31, 2010 8:19 pm

Bit of farting about but managed to get the front one on
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had to cut out for the front tow eye (still itching off the glass) and drill out the old imperal fixings on the front ,for the rear fixings Alistair supplied Riv nuts so I replaced these with roofing tex from work.Both the front edge and rear have double sided glazing tape (also from work :D )which I will activate when I've done the much needed Castrol oil change .Gearbox cleaned down with nothing more than Johnsons baby wipes magical stuff.
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