Rusty Front Fender Tops Example and "Mud Trough" Section View

Dave G

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New member @jgprice brought up front fender rust in his introduction this summer. It inspired me to share some images for coupe owners who haven't learned about this the hard way (or the smart way - from someone else's experience!)
Problem - Rusty Front Fender Tops: I can relate to John's choice of words for the front fenders under his hood, specifically their "dissolving" condition! Mine were mostly dissolved before restoration. During restoration, I found that every spot that rusted completely through in my coupe seemed to have a rust accelerator. The biggest one was mud/dirt packed into cavities. Whomever designed the inner fender sheet metal must have had no idea that they had created a perfect mud trough at the top of the wheel well that would infect nearly all our cars with rust. You can only get to it from underneath with the wheel off. The opening points away from the engine bay and is hard to ascertain, but to make matters worse, the metal takes a step down to make a literal trough shape perfect for holding lots of wet mud! The first attached photo speaks volumes. Another coupe owner told me how he had drilled a series of sizable "drain" holes in the bottom of the "trough" and I chose to do the same to mine in the name of preservation. You can imagine how all that dirt would retain water and take forever to dry while your fenders are dissolving the entire time!
Conclusions: Rust is definitely the enemy of these cars. As owners, maintenance and prevention are key. Hopefully, no coupe owner will ever allow their car to be driven on a wet/muddy dirt road! If it is, take it straight to a lift with a pressure washer, remove the wheels, put on your poncho, safety glasses and get it clean... or invent a time machine to go back in time to not allow it to be driven on muddy roads, ever ;-)! Also, you could consider drilling your "under" fenders: 1. To see if they are packed with mud already. 2. To have places for dirt & water to drain while driving in wet conditions. 3. To have more places for you to access with a pressure washer if your ever need to! I drilled several .375" (9.5 mm) holes, spaced every 3" (75 mm) in the left and right wheel well, basically through the steel under where all the dirt is in the 1st photo below. I drilled from underneath, it doesn't show from above. The holes are shown in photos 5 & 6 below, (after media blasting, prior to restoration).
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Nice cross section pics.
I think it is the most expensive place to have rust on an e9.

Fyi, from the factory there was a foam strip installed running the length of the fender to prevent water and dirt from collecting up there. It was roughly located where I drew the red dot:
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The foam lasted about 5 to 8 years before crumbling to bits, allowing water to enter inside the channel and so the fenders started rustig out as per how it's described above.
 
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Wouldn't it be a lot simpler, once this has been fixed on a car, to fabricate and install a splash shield? It can be either a small rectangular-ish piece to close off the area, or a more conventional shield to close off most of the fenderwell. My 911 also has open fenders (albeit without the huge rust traps) and I've got a set of yet-uninstalled splash shields that some guys in the UK made a small run of.
 
As Rob mentioned above. Based on what I've read/seen the answer is to install the Lokari fender liners. Apparently they work quite well.
 
tell me about it...
I just finished the right side. I had to refabricate parts of the fender and the gutter completely.
Not an easy job for a metal-novice...
I think I'll make some holes with plugs so I can put some cavity wax in those area's every now and then + only drive it in good waether when it's finished.
The left side (second picture) is yet to be done in the next weeks.
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On mine I ended up welding an additional strip to close that gap a bit more and then liberal cavity wax inside over zinc paint and then seam sealed the lot. Lokari fender lines and also boxed up the small pocket in the rear most reinforcement piece that goes between the inner wing and a pillar
 
The E24 has lots of "shelves" under the front fender also. When purchased, there was bubbling along the edge of the turn signal housing that led me to explore. Every spring when I pull my cars out of storage, I wash out these areas of sand and dirt and let the cars sit in the sun.

I think those of us who did a complete E9 restoration on our own have realized these cars have so many places that are vulnerable, enough so that you drive in wet weather at your (its) own peril.
 
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