Rear Wheel Tub Prep & Fender Lip Rolling

Rear wheel tubs are kind of a pain in the butt for the home-restoration artisan to tackle.  Generally speaking, they are the dirtiest parts of the car, have lots of difficult-to-repair issues and are generally not very friendly from a work space perspective.  Mustang rear wheel tubs are not different, but the time had come for me to finally tackle the tubs on my Boss 302 once and (hopefully) for all.

The first order of business is getting all the undercoating and various levels of crap dislodged from the tubs to see what the base material looks like.  Some of my regular followers will recall the trick I use to remove 40 year-old undercoating quickly and rather painlessly.  In short, I use my air chisel dialed down to low air pressure (~25psi) to “shatter” the coating and then vacuum up the debris.  This method works so well in fact, it is truly amazing how little thought you give to further undercoating removal once you try it.  In any case, after about ½ hour dedicated to each tub, the undercoating was removed and vacuumed up and I could have a look at what the tubs looked like “nekid”.

As fortune would have it, both rear tubs in my car were in remarkably good shape!  Other than the damaged corners which were a “known” when I started the project, the metal was in excellent shape and the center seam was easily cleaned with a little sand blasting work.  From there, I dove into the job of cleaning the bulk of the tub surfaces with my angle grinder and a box full of 60-grit discs.  For the inner surfaces of the fender lips, I used an abrasive brush and wire wheel to clean everything down to bare metal and followed it up with a coat of phosphoric acid-based metal prep to get the surface cleaned of any residual corrosion and prepared for the next phase of the project:  Fender lip rolling.

Rolling a fender lip is a bit of a misleading description.  Actual “rolling” of a fender lip is usually done on a fully assembled car to make room for oversized tires and involves a tool specially designed with a hard-faced roller to gently fold the inner fender lip toward the inner wheel tub.  The fanciest fender “roller” tools bolt to the wheel hub and are quite nifty, but they are of little use when the body is on a rotisserie during restoration.  As such, folding the fender lips on a raw body shell requires a different technique but the results are much easier to achieve in my opinion.

The key to success when folding fender lips is patience and light, purposeful blows with a hammer to gently “persuade” the metal to its new location.  Also, in 99% of the cases, you do not need to fold the entire lip as the tire doesn’t require the same clearance at the front or rear as it does at the top during full suspension compression.  At the same time, folded fender lips are much harder to keep clean and without proper maintenance, can accumulate debris that will work to promote rapid corrosion propagation if left unattended.

I started folding each fender lip with light blows from my 16oz ball-pein hammer.  A ball-pein gives the metal just enough stretch to fold cleanly and not be lumpy along the flange.  I use a wooden paint stick (free @ Home Depot!) as a gage to determine when I have the right amount of fold by placing it against the wheel tub and folding the lip until it is just snug against the stick.  This leaves just enough gap to allow corrosion protective paint to be applied by brush and will allow debris to be washed away if needs be in the future.  Each lip took about 45 minutes of gentle hammer work to get just right and the results are very nice if I say so myself.  A little filler along the flanges will even hide the spot-weld divots and make for an exceptionally smooth wheel opening.

Once the rear fender lips were completed, I moved on to coating the wheel tubs with Zero Rust for corrosion protection.  I decided to apply the Zero Rust with a brush this time as I needed to make sure I got the lip areas fully coated and the resultant brush strokes would be of no consequence when you consider that the entire wheel tub will eventually be primed with DP40LF, seam sealed, painted flat black and finally coated in textured bed liner material as a final finish.  I would have preferred to spray the coating, but the space constraints in the confines of the wheel tubs prevented using my existing spray equipment effectively, so I stuck to the brush and made do with that even though I am embarrassed that there are brush marks to be seen at all!

So there ya go!  Wheel tubs cleaned and prepped.  Wheel lips rolled for fat meats and everything coated to keep it nice for the rest of my lifetime.  Next on the agenda is to finish the axle tunnel and front trunk floor and get the entire outside trunk floor area in primer.  I’m on it!

After cleaning all of the nasty undercoating off the surfaces of the rear wheel tubs, I was stunned to see the underlying metal in excellent shape.  Nice!

The shinier "reddish" area in the center of the tub shows the area that was originally covered in undercoating.

Both wheel tubs were in equally good shape after all was said and done.  This left a lot to work with and made the sand blasting work very straight forward and relatively easy.

Sand blasting could be concentrated on the seam area and the fender lips.  The rest of the surfaces would be easily prepped with sanding and surface conditioning discs.

After a few hours work with the angle grinder and a box full of 60-grit sanding discs, the wheel tubs were cleaned and ready for metal prep chemical etching.

Rolling fender lips is a common technique to gain more tire clearance.  Here, you can get a general idea of what the fender lip looks like before any rolling/folding is done.

Working the lip with light blows evenly distributed along the lip surface, I eventually had the lip nicely formed with absolutely no damage to the outside skin.

Here is another shot of the finished rolled fender lip.  Not there is a small gap left between the wheel tub and the lip to allow paint to be applied to the area and cleaning of debris in the future.  Ignore the body hammer in the background!  This is NOT the hammer I used to form the fender lips!  It was just looking for some temporary recognition it didn't deserve!

I used Zero Rust coating thinned down a bit to coat the inner wheel tubs.  I applied it with a brush to make sure I got the folded fender lips properly coated and the brush strokes will never be seen as them will eventually be covered in textured bed liner material.  Also, this shot shows the rolled fender lip in pretty good detail.

I left the areas at the front corners of the wheel tubs bare as I will soon be making repairs in this area.  No point making it anymore difficult.

Right side wheel tub coated and dry.  Note the folded fender lips are pretty easy to distinguish here too.

Left side wheel tub coated and dry.