[MSCW list] Rocker Rust

[Timothy Metzinger]

With the unibody construction of our Miatas, there are two areas that tend
to rust - the front fenders where they join the body underneath the side
mirrors, and the rear rocker panels.   The prime cause of front fender rust
is that water drains from the firewall/wiper area down into the fender area.
but so does all sorts of debris from leaves/seeds/other stuff, and this can
trap moisture for a long time.  The best preventive measure for this is to
loosen your front fenders, including the wheelwell liners, and clean out the
voids between the fender and the body.  You can also prep the body areas
hidden behind the fenders by ensuring they are rust-free, primed and
painted, so that if you DO get fender rust that it won't spread to the
internals.  You can get replacement fenders from both Mazda and the
aftermarket.

 

At the rear of the car, there is a similar outer/inner structure.  It's not
an easy replacement to get the rear outer skin repaired (as Collier
mentions, this is surgery best done by experienced people), but the
important part is to ensure that the inside areas are not damaged.  I had
some rust on the outer skin, and my short term method was to cut it out
(maybe 4 sq. in) and ensure that the metal underneath was in good shape and
clear.  I then ensured that I primed and painted the edges of the good metal
remaining, and so far (six months) there has been no rust forming.

 

The WORST possibility is that you get rusting along the insides of the door
sills.  This is almost always caused by clogged drains.  There are gaps at
the bottom where the three different sheets of steel come together at the
front and rear jacking points.  Too often people jack the car on the steel
edge rather than on the corrugated sills on the inside of the edge, and this
closes the drains.  Use a screwdriver or drill bit to ensure that these
drains are open.

 

The good news is that repair is possible at reasonable costs for these
issues, but it's important to address rust as soon as you find it.  The
corrosion process does not stop, period, and the only true fix is to remove
and replace the damaged metal.  Strongly recommend NA and NB owners attend
the event when it's available and learn how to keep these areas clear and
dry.

 

-Tim