# Replacing rear trailing arm mount bolts



## willj002 (Mar 9, 2020)

Hi,
I've taken the rear trailing arms off (225 Quattro), to replace the main bush, and now need to put it back on. I have been told that I need to replace the mount bolts (Number 24 in the diagram), as they are one-time use, but I cannot find any part number nor part for sale on the internet. Wondering if it is possible anyone knows part number they are? Even a size would be helpful.
Thanks,
Will.


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## matjonut (Feb 27, 2020)

To my knowledge they are available from TPS, about £3:50 per bolt


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## LesRSV (Jul 5, 2017)

Have a look at this post from last week -https://www.ttforum.co.uk/forum/viewtopic.php?f=2&t=1953559

or here https://www.ebay.co.uk/itm/Genuine-...255105&hash=item2aa4372951:g:tyAAAOSwgc1atVhF(same bolt)but might be slightly more expensive than TPS.


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## willj002 (Mar 9, 2020)

Thank you both for your quick replies, it is much appreciated 

Before I go, not sure if you've heard of the page, but a website called skoda-parts.com seems to have all the bolts I need for a very respectable price, I assume being Skoda they will also be of the same quality?

Finally, I'm looking for the front hub bolts, Part Number *4A0 407 643 A*, and it is listed in different sizes on different websites. They either say M16x1.5x*72* or M16x1.5x*77*. The one I need is the flat flange bolt, which one is it?

Thanks again,
Will.


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## droopsnoot (Sep 5, 2002)

Could you take out one of the existing ones and measure the length of it? Or if you don't want to remove the old one until you have the replacement, buy the 77mm one and cut 5mm off it if it turns out you needed the 72mm one?

Out of interest, on the upper arm mounting bolt, what makes it different to any other M10x35mm bolt of the correct thread pitch? I intend to replace mine when the weather is better, but why does a bolt need to be so (relatively) expensive?


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## GARAGE HERMIT (Mar 7, 2015)

droopsnoot said:


> Could you take out one of the existing ones and measure the length of it? Or if you don't want to remove the old one until you have the replacement, buy the 77mm one and cut 5mm off it if it turns out you needed the 72mm one?
> 
> Out of interest, on the upper arm mounting bolt, what makes it different to any other M10x35mm bolt of the correct thread pitch? I intend to replace mine when the weather is better, but why does a bolt need to be so (relatively) expensive?


find out what's stamped on the bolt head and just buy the bolt's from a fixing distributer,
https://www.fixingsmegastore.co.uk/help ... e-strength


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## droopsnoot (Sep 5, 2002)

Yes, it's important to get the proper strength of course.

Unfortunately the photo in the eBay link above suggests that the bolt head is not marked, and the on-line parts catalogue doesn't give anything other than the size. I want to swap mine at some point because they're rusty, so there's no chance I'll see anything on the heads of those. I don't imagine they're anything significantly different in strength than any other suspension mounting bolt on another car, so perhaps general advice will be relevant.


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## GARAGE HERMIT (Mar 7, 2015)

i've just had the trailing arm mount's+bolt's (genuine audi) replaced, if it's not raining tomorrow i'll have a look and see if there's any marking's on the head's,


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## davebowk (Aug 16, 2019)

I would expect more than 8.8 grade is not needed there especially as there is 4 of them and are used for adjustment. But if you want to be sure just fit 10.9 grade or seriously sure 12.9 grade.
If you can't find the flanged bolts then buy some 2.5 to 3mm thick washers.


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## droopsnoot (Sep 5, 2002)

GARAGE HERMIT said:


> i've just had the trailing arm mount's+bolt's (genuine audi) replaced, if it's not raining tomorrow i'll have a look and see if there's any marking's on the head's,


That would be great, thanks.

I know it sounds a bit penny-pinching, and I'm all for using genuine parts where it makes a difference, but this is another situation where it's not like Audi actually *make* bolts, they're just done to a spec. The only thing that looks a bit special about those bolts in the eBay link is the smaller end to help locate them. In my specific case my plan was to replace one at a time, so that shouldn't be an issue. But I've got a grinder, can always taper them down a bit, if or when I get around to swapping the creaky rear bushes.


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## willj002 (Mar 9, 2020)

Thanks everyone for the replies, you have been a big help 



droopsnoot said:


> Could you take out one of the existing ones and measure the length of it? Or if you don't want to remove the old one until you have the replacement, buy the 77mm one and cut 5mm off it if it turns out you needed the 72mm one?
> 
> Out of interest, on the upper arm mounting bolt, what makes it different to any other M10x35mm bolt of the correct thread pitch? I intend to replace mine when the weather is better, but why does a bolt need to be so (relatively) expensive?


According the Haynes manual I am following they should be replaced every time they are disturbed. As to the question of whether there is a difference between the oe bolt and a same size generic bolt I don't know, but for the sake of like £3 I'd rather not take the risk.

Will.


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## GARAGE HERMIT (Mar 7, 2015)

this is what the T/A bracket's were like so you can imagine what the bolt's were like,
no wonder the car felt a bit lively at the rear,


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## rlszer (Jun 9, 2014)

GARAGE HERMIT said:


> this is what the T/A bracket's were like so you can imagine what the bolt's were like,
> no wonder the car felt a bit lively at the rear,


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## droopsnoot (Sep 5, 2002)

willj002 said:


> According the Haynes manual I am following they should be replaced every time they are disturbed.


Yes, says the same in the manual I was looking at, although they're not stretch bolts as far as I can see, they just tighten to 75Nm. As for using "genuine" bolts vs. others, I certainly wouldn't try to discourage someone from using Audi parts if they prefer to.

I am hoping my trailing arm mounts are better than that, there's been no mention of trouble on the MOT.


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## GARAGE HERMIT (Mar 7, 2015)

droopsnoot said:


> willj002 said:
> 
> 
> > According the Haynes manual I am following they should be replaced every time they are disturbed.
> ...


the bracket's are tucked up inside a body cavity :roll: , they're not really easy to check,

if the manual state's the bolt's have to be replaced every time you loosen them you'd have to take a spare set with you every time you had a 4-wheel alignment done, i didn't and the T/A's haven't fallen off yet,


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## droopsnoot (Sep 5, 2002)

GARAGE HERMIT said:


> if the manual state's the bolt's have to be replaced every time you loosen them you'd have to take a spare set with you every time you had a 4-wheel alignment done, i didn't and the T/A's haven't fallen off yet,


I expected to see that if they were "tighten to x Nm, then a further y degrees", as in stretch bolts, but they're not. So I don't know why they would need to be replaced each time.

The manual I looked at says "Always renew if removed", and I'm not sure what the difference is between loosening to adjust alignment, or removing. But then, in the piece on centralising rear toe, it says:

Loosen all bolts on mounting bracket 1
Move mounting bracket 1 laterally
Tighten bolts to 75 Nm
Always use new bolts!


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## davebowk (Aug 16, 2019)

At a torque of 75Nm they should be 12.9 grade bolts.
The high torque figure and high grade bolts will be to ensure the brackets don't slip on the adjusting slots and not because they could break with the forces applied to them when driving.
Saying they should be replaced when loosened is just either Audi covering their arse, money making or both.
How many wheel alignment places do you think will replace the bolts?????
Mine haven't fallen off yet.


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## GARAGE HERMIT (Mar 7, 2015)

no rain today so jacked the car up to replace a exhaust bracket had a look at the T/A bolt's, better late than never, the bolt head's are stamped 10.9,


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## droopsnoot (Sep 5, 2002)

Excellent, thanks for the confirmation.

The lovely shiny gold bolts I bought at the NEC are, unfortunately, 8.8 spec.


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## GARAGE HERMIT (Mar 7, 2015)

the Audi bolt's are what look's like either galvanised or nickle plated, but i dont think it matter's too much what kind of plating if any are on the bolt's you buy,


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## droopsnoot (Sep 5, 2002)

No, I just had them on my list as I walked around the show. Surprisingly it was the only stall selling metric fasteners of that size, since Spalding Fasteners don't seem to do the NEC any more. I was hoping the passivated finish might help stave off the next round of corrosion, but a coat of Waxoyl-alike after torqueing them will probably do just as well.


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