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S4 - Bolt through rear underbody

PostPosted: Wed Nov 20, 2019 7:13 pm
by Gorpon73
Hi,

Anyone possibly tell me what the bolt is protruding from the underside of the right rear body? I see most cars with this having a washer and nut affixed to this bolt on the outside of the body. Having trouble finding this in my manual and not keen to pull my fuel tank to discover what it is for?

Cheers

Re: S4 - Bolt through rear underbody

PostPosted: Wed Nov 20, 2019 7:16 pm
by seriouslylotus
Fuel tank fixing....

Re: S4 - Bolt through rear underbody

PostPosted: Wed Nov 20, 2019 7:51 pm
by MarkDa
+1 to fuel tank.
I put a dome nut on it to smarten it up a bit

Re: S4 - Bolt through rear underbody

PostPosted: Wed Nov 20, 2019 9:39 pm
by Gorpon73
Fabulous, thanks!

Possibly know the thread pattern for this bolt? Nothing I have around seems to fit....

Cheers, DJS

Re: S4 - Bolt through rear underbody

PostPosted: Wed Nov 20, 2019 10:02 pm
by MarkDa
1/4" probably unc if I remember correctly.
I fear I may have cut to length and cross threaded a 6mm dome nut onto it as I view it as a "one time" fixing.

Re: S4 - Bolt through rear underbody

PostPosted: Thu Nov 21, 2019 4:49 pm
by Gorpon73
Haha. Sound logic from where I'm standing. Thanks for the info.

Cheers.

Re: S4 - Bolt through rear underbody

PostPosted: Thu Nov 21, 2019 7:48 pm
by Pastapesto
Not sure but I think it's an UNF thread & not UNC......I'll check later & if I'm wrong.

If it has a non original tank then there is the chance it is something else of course.

Hope that helps

Adam

Re: S4 - Bolt through rear underbody

PostPosted: Fri Nov 22, 2019 8:37 pm
by Gorpon73
OK, thanks for the info.

I've tried everything I had in my various piles, but nothing fit yet.

Looks to be a very narrow thread....

Re: S4 - Bolt through rear underbody

PostPosted: Fri Nov 22, 2019 10:34 pm
by MarkDa
Could be 6mm?
Do you have a diameter and thread pitch?

Re: S4 - Bolt through rear underbody

PostPosted: Sat Nov 23, 2019 2:54 pm
by oldelanman
If your fuel tank is original it will definitely be 1/4" UNF as stated above (just checked mine to be sure) but if it's a replacement tank it could be anything and as Mark says you will have to measure it. Could it be that your thread is corroded or gummed up if the nut has been missing for a while and just needs cleaning up ?

Re: S4 - Bolt through rear underbody

PostPosted: Sat Nov 23, 2019 5:33 pm
by MarkDa
Yes - a bit of oil and then hand run a 1/4 unf die down it ought to do the trick to get it operational.

Re: S4 - Bolt through rear underbody

PostPosted: Sat Nov 23, 2019 5:53 pm
by oldelanman
MarkDa wrote:Yes - a bit of oil and then hand run a 1/4 unf die down it ought to do the trick to get it operational.

Or ... if you don't have a die you can just use a nut with a saw cut at right angles to the thread, works just as well.

Re: S4 - Bolt through rear underbody

PostPosted: Sat Nov 23, 2019 9:35 pm
by Gorpon73
Thanks for the advice.

It's a 1/4-28. Got it all stitched up....

Cheers

Re: S4 - Bolt through rear underbody

PostPosted: Sat Nov 23, 2019 10:22 pm
by MarkDa
Well done - yes that's standard unf.