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Hidden rust - rear seat mounts under arch liners

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Cookeh
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Hidden rust - rear seat mounts under arch liners

Post by Cookeh »

There is a hidden rust spot on these P80s that I've only just recently been made aware of, thanks to this post on a UK forum - link. It seems this affects a significant number of P80s, but is largerly un-noticed due to its location. Eventually it will result in an MOT failure in the UK as the rust appears to be localised around the rear seat mount.

Below are pictures showing the rust my car presented with, I got lucky and it only required wire-wheeling and undersealing. Bear in mind my car has never lived near an ocean, and being in the UK we do not get harsh winters, so there has been minimal salt present. Despite this, all 850s I've come across on that forum have had the same rust or worse.

With the arch liner off, here is the rust I am highlighting:

Image

In my case I could get away with wire-wheeling, and using a flap-disc to get to this position:
Image
Image

From this point I was able to apply rust convertor (Bilt Hamber Hydrate80 is the best on the market, and reasonably priced, if you can get your hands onit) and a coat of Dinitrol 4941 underbody.

Image4941 applied

Excluding time taken for paint to dry both sides took me around 2 hours, with a materials cost of £30 (Bilt Hamber Hydrate80 and one 500mL can of Dinitrol 4941 - the latter will be sufficient to do both arches, and everything behind the rear bumper with plenty to spare). The added bonus is there is a small reduction in NVH thanks to the underseal on the arches.

For the time and small cost investment I would certainly recommend you take a look under there - it could potentially save you a big headache down the line.
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Re: Hidden rust - rear seat mounts under arch liners

Post by Cookeh »

As a reference how quickly this can become an issue, this next photo was taken around 11 months ago, and we had an especially mild winter this year with no grit being applied.

Image
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Re: Hidden rust - rear seat mounts under arch liners

Post by amblerman »

Wow.. thanks for the notes on this. I have been so impressed with Volvo's rust protection that I wouldn't even bothered looking there.

Just to be clear, jack up rear, remove wheel, remove plastic liner and inspect. Correct? The reason people don't notice this until it's too late is it's hidden by plastic wheel liner correct?
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Re: Hidden rust - rear seat mounts under arch liners

Post by Cookeh »

Exactly, yes - on both points.
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Re: Hidden rust - rear seat mounts under arch liners

Post by abscate »

I’m inspecting mine really closely, I’ve heard this can spread to the rocker panels
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Re: Hidden rust - rear seat mounts under arch liners

Post by misha »

:mrgreen: :mrgreen: :mrgreen:
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Re: Hidden rust - rear seat mounts under arch liners

Post by misha »

Cookeh wrote: Tue Jul 21, 2020 8:45 am ...Eventually it will result in an MOT failure in the UK as the rust appears to be localised around the rear seat mount.
Why would MOT test require arch liners to be removed?
It's funny...because sills(rocker panels) are covered with plastic side skirts.Do they remove them too to inspect sills condition for MOT testing?
'97 850 2.5 20v / fully equipped / Motronic 4.4 from the factory / upgraded with S,V,C,XC70 instrument cluster / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic
History of Volvos in the family:
'71 144 S
'73 144 De Luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS
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Re: Hidden rust - rear seat mounts under arch liners

Post by abscate »

They probably see bubbling on the inside.
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Re: Hidden rust - rear seat mounts under arch liners

Post by Sveedy »

You just answered a question of mine on another thread.... :)
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Re: Hidden rust - rear seat mounts under arch liners

Post by Cookeh »

misha wrote: Tue Jul 21, 2020 3:54 pm
Cookeh wrote: Tue Jul 21, 2020 8:45 am ...Eventually it will result in an MOT failure in the UK as the rust appears to be localised around the rear seat mount.
Why would MOT test require arch liners to be removed?
It's funny...because sills(rocker panels) are covered with plastic side skirts.Do they remove them too to inspect sills condition for MOT testing?
They inspect seat belt anchorage points and seat mounts as part of the test. In this instance, as abscate rightly pointed out, they'd see bubbling and investigate further. You can also just about notice rust peeking out beneath the arch liners (even on mine, which is relatively clean compared to other cars).

Sill covers are generally not removed, unless as above, they are given reason to investigate - such as rust patches or bubbles close to that area.

The test is a bit weird, nothing can strictly be removed from the car, so you can 'hide' a lot of issues with covers. However, if they notice something relating to structural rust or rust around mounting points then they can investigate further in order to show you what needs to be fixed.
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