AUDI A3 8V5 2016 - 2019 S LINE SALOON REAR LOWER DIFFUSER WITH TRIM 8V5807521S

Part number 8V5807521S. We take parts off vehicles every week, and this page is updated with a link straight to the part as soon as another one arrives.

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About part number 8V5807521S

A rear lower diffuser with trim is an exterior body part that fits into the lower section of the rear bumper. It forms part of the bodywork and aerodynamically channels airflow beneath the back of the vehicle. When it is correctly fitted and undamaged, it gives the rear end a clean finish and keeps the lower bumper trim secure.

To confirm that this is the correct part for your vehicle, you must check that the part number on your original item matches 8V5807521S exactly. Manufacturers usually stamp or mould this number directly into the plastic on the reverse side of the diffuser or trim panel. Matching the exact part number is the only way to guarantee correct fitment.

This part is most often replaced because of impact damage from low obstacles, reversing incidents, or broken mounting clips. When installing a replacement diffuser, you may also need replacement trim clips, plastic fasteners, or additional bumper fixings if the original mountings were snapped or lost during removal.

About this kind of part: trim mouldings

A trim moulding is a long, narrow strip that finishes an edge or a joint on the outside of a car: a door moulding, a sill cover, a wheel arch trim, a window finisher or a roof strip. Most are plastic, either painted to match the body or supplied in a textured black or a bright finish, and they clip to studs or to double-sided tape. They are cosmetic rather than structural, but they also cover the panel joint underneath, so a missing one leaves a gap where water and grit collect.

Why people replace one

  • A knock or a car wash has pulled the moulding away and broken the clips behind it.
  • The painted finish has chipped along the leading edge, which happens from stone strike on anything low down.
  • A textured black trim has gone grey and chalky in the sun, which cannot be cleaned back.
  • The double-sided tape has let go in the heat, so the strip lifts at one end and flaps.
  • A panel has been replaced and the original trim was broken getting it off.

Fitting it

  • A clipped moulding comes off by releasing each clip in turn from one end rather than pulling in the middle, where it will crack.
  • The clips themselves are usually separate parts and are normally replaced rather than reused, because they stretch once they have been off.
  • A taped moulding needs the old adhesive cleaned off the panel and new tape of the correct width, applied to a warm, dry panel.
  • Check which way up the strip goes before fitting. Many are handed and look symmetrical.

Making sure it is the right one

  • Match the part number. A moulding from the front door and one from the rear door of the same car are different lengths and different numbers, and so are the two sides.
  • If the trim is a wheel arch or a sill, check whether yours has openings for parking sensors. One without the openings cannot be used on a car that has them.
  • Compare the finish: the same moulding is made painted, in textured black and in a bright finish, and each is a separate number.
  • Count the clip positions along the back and compare them with the studs on your own car.

What to look for in the photographs

A Part number — Moulded or printed on the back face, usually towards one end.
B Clip positions — The row of clip seats or studs along the back. Count them and compare the spacing with your own car.
C Sensor openings — Openings for parking sensors, where the trim is an arch or a sill. Their presence or absence decides whether it fits your car.
D End profile — The shape of each end, which is what tells a front strip from a rear one and one side from the other.
E Leading edge — Look along the lower or forward edge, where stone chipping collects. It is the part a flat photograph flatters most.
F Tape or clip channel — Whether the back has a tape bed or a clip channel. These are not interchangeable.

This section describes trim mouldings parts in general. The numbers and the photographs above are this part.

Free next-day delivery in the United Kingdom Sent with DPD on a tracked, next-day service. Most mainland addresses are next day; the Highlands and Islands, Northern Ireland, the Channel Islands and the Isle of Man can take a day longer.

Returns Thirty days to change your mind, and we pay the return postage in the United Kingdom and Germany.

Trade and VAT C.E.J Haime Group Limited is VAT registered in England and Wales, and every order comes with a full VAT invoice.

Not sure it is the right part? Send us your registration or VIN and we will check this part number against your own vehicle before you buy.

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