GTS Rear Fender Liners:
The GTS model came equipped with foam backed rear fender liners. Over time the plastic material for the skin deteriorates and cracks - feeling almost like thick felt paper. The mounting holes typically break away first and its impossible to repair since all the material is similarly weak and just fragments - leaving just the foam behind. The foam itself has very limited strength and deteriorates and crumbles - especially as the foam tends to drop into contact with the tires once the mounts break free.
These appear to have been designed for better noise reduction primarily and the quality of the materials for long term use is very questionable. The GTS liners are now NLA and even when they were available they were approx $600/side for a long term poor quality part.
I decided to come up with a serviceable solution that would match this functionality at lower cost and with better long term reliability.
I sourced 928 S4 rear wheel well front & rear section splash guards for the drivers side - these are stock Porsche parts.
I also sourced a 928 S4 rear wheel well front splash shield for the passenger side, but note that the S4 and earlier years did not have a passenger side rear wheel well rear splash shield. However the rear drivers side S4 splash shield is a flat sheet and is usable if reversed and slightly modified on the passenger side - so I sourced another of these.
These are flexible plastic shields that cover primarily the vertical opening in the wheel wells in front & behind the wheel, they provide no cover to the area above the wheel and this area represented an addition I wished to make - primarily for noise reduction.
To make the splash shields fit I only needed to add 2 glued in angle brackets with speed nuts in the upper inside rear wheel well - all other mounting points were the same as on an S4 & usable as is.
I mounted all these with a modified fastener: a self tapping bolt headed screw with 1 1/4" rubber & then steel fender washers to spread & even the compression load on the plastic. This was a method I developed to prevent the front splash shield mounting holes from cracking.
I shortened the top & top sides of both front & rear splash shields by approx 1/2" in order that I could install a layer of the 3/4" nitrile foam glued directly to the underside of the top of the wheel arch witch contact cement - this is permanently installed and cut tight around the top mounting points. When the splash shields are installed their top edges compress tightly into this top layer sandwiching it to create a good front & rear seal.
To make the splash shields themselves better noise insulators - I also glued 3/4" closed cell nitrile foam on their rear sections flush to the top & bottom but including a slight overlap at the sides for a snugger fit to the inside & outside fender walls. For the open front section just behind the B-Pillar I sprayed in expanding closed cell foam to create a better noise shield and body boom deadener.
I then created top fender liner section from a large heavy duty black plastic trash can. Since it is already curved & has a formed bottom - cutting out the bottom part provides a great starting point allowing it to be cut into an open shape but maintain an inner fender formed section like on the GTS liners. Its also flexible enough to adapt to the non circular fender shape yet is still robust thick material designed for outdoor exposure.
This was treated to more of the 3/4" nitrile foam glued to the top to just short of its ends. This sheet mounts to the existing top mounting points and curves down to the front & rear splash shields where it is mounted via speed nuts mounted in some newly cut slot/holes. This combination replicates the all round coverage of the original GTS wheel liners while using predominantly factory parts on the visible areas. It substitutes long life nitrile foam for the open cell original and utilizes a dual layer sandwiched above the wheel and additional foam in the B-Pillar area for further reduced noise. Fasteners on this section are the same as for the splash shields.
The new 3 part construction is easier to handle in mounting and makes access for PSD servicing a little easier.
Copyright (c): Alan Moore 2006, 2007, 2008, 2009 Page Updated: 04/03/2009