Undertray

[darich]

Yesterday driving through some slush and snow my car start making a rubbing sound from what sounded like the front nearside wheel.
I thought it was some ice or slush jammed between the wheel and muflap or even the mudflap rubbing thinking it may have been damaged by the snow.

It turns out it's my undertray.
It was hanging off in the centre of the car but still attached at the sill. I removed it and have found that it's cracked and broken in a few places. I can sort that without too much trouble I think - some fibreglass paste should do the trick.

I noticed there are brake pipes which were previously protected are now exposed to the elements. The undertray obviously isn't waterproof but it does protect the underside of the car from debris and flying stones.

I can remember in days gone by that brakes pipes were exposed but everything seems to be hidden away now.

The question I have is can I run the car safely without the undertray?

EDIT : I'm referring to the tray under the passenger seat, not under the engine.

[djgilson]

Interesting question. I suspect the main function of these underbody linings is aerodynamic - to help boost the official mpg figures.

Yes, they will shield the underbody from debris when driving, but they will also tend to prevent the underbody from drying out afterwards, so whether their overall effect on corrosion is good or bad is not clear to me.

If anyone knows better, I’m happy to be corrected, but I’d have thought the only negative effect of running without them might be a (very slight) penalty on mpg?

[darich]

djgilson

Thanks for that.....I'm inclined to agree.
As I posted, years ago I can remember cars having brake pipes run down the underside of the car next to the sill, with no protection, other than the platic coating on the pipe.

I intend to repair and replace the undertray but the main thing is I can continue to use the car

So the next question is - is it audi only for the clips that hold the tray in place?
If so I suppose it'll give me a good excuse for a decent run on the motorbike, even if it's once the weather improves!

[djgilson]

You may find that the plastic nut fixings are rather stronger than the lining itself and are still in place on the underside of the car. The lining may have torn away from the fixings and be in a sorry state, so repairing it could be difficult. Or if you’re in luck, some extra large metal washers (places like B&Q sell them as "repair washers") may help.

Anyway, I would wait and have a look at the fixings before rushing off to the dealer!

[djgilson]

Ah, no. Are these the clips you were asking about?


Don’t know if you can get them from a Motor Factor. Part no from Audi is V8E0 825 267, 10p each + VAT. They are a 2-part plastic rivet, fixed blind (from one side).

When I bought my A4, the lining here was damaged and a chunk was missing, so this was the repair I did. The black plastic part is a joining piece between the front edge of "your" liner and the wheel-arch liner, about £6 from Audi. The join with your liner uses 3 of the rivets as shown. The whitish panel to the right is a repair piece I cut from al sheet, joined with a further 3 rivets. Depending on what happened to yours, you may need a similar repair?

But after all this, I haven’t actually answered your question!

[darich]

DJ......I think I'd need a few of what looks like plastic bolts - they screw onto threaded bars protruding from the underside of the car. I know the clips in your pic above - I had 2 to remove to get the undertray off. They weren't damaged but were a bugger to remove....I ended up breaking them and part of the tray.
The part of the tray I broke is attached above the mud flap and there 2 of the "blind" clips on it....nightmare to remove.

I think I might need to invest in a set of ramps so I can get the car up and have a good look at what's needed/broken/missing. That will at least give me a starter on getting replacement parts or carrying out a repair of some kind.

[djgilson]

When you get round to having a good look, the first thing will be to remove the mudflap, I would think. Really mucky, so give the area a really good wash beforehand. (My car doesn’t have mudflaps fortunately).

I don’t know whether you can get the plastic fixing nuts other than from Audi. You can just see one, attaching the joining piece at the far left of my photo. As I say, I found that where the liner had broken away, the plastic nut was still in place on its stud, holding a little disc of broken liner, and I was able to re-attach using the same nut and a large washer (1.5inch OD/0.5inch ID).