Axle Tunnel Filling & Prime

I enjoy momentum on projects.  Once I get into a groove and things start clicking off according to plan, I really like the feeling.  Perhaps it’s the confirmation that comes from planning the work and working the plan when the results are exactly as intended.  Either way, I love the feeling of accomplishment, and lately that’s been a frequent thing.

On the heels of completing the rear wheel tubs, I moved directly to smoothing up and finishing the axle tunnel in hopes I could get it in primer.  As luck would have it, things lines up pretty nicely and I was off too it last weekend with a vengeance.

Early this past spring I was able to repair the rust damaged front trunk floor as well as weld in a patch to fill the hole that was once occupied by the rear staggered shock mount.  Once the metal work was complete, I moved on to repair the rear trunk floors and tail light panel with the intent of coming back to the axle tunnel to finish the area and prime everything at one time.  Well, the time was right to do just that.

During my last sand blasting episode, I was able to get the axle tunnel and trunk floor repair areas well prepped for the coming finish work.  The rear subframes cleaned up very nicely following all of the welding for trunk floors and suspension brackets, and the new rear rotisserie mounts allowed excellent access to the areas around the original leaf spring bushing holes as well.  At the same time, I made sure to hit the weld seams on the axle tunnel repairs to make absolutely sure they would be cleaned of any nasties that might have been living there over the spring and summer.

After what seemed like days vacuuming sand from every conceivable nook and cranny of the car just to keep my shop floor from looking like a beach, I went over the entire axle tunnel with a 60-grit disc to clean it up and give the surface good “tooth” for the All-Metal filler and the Rage finish filler I would use to tidy the area up.

I started my filler work with All-Metal applied generously over and into each weld seam area and rather widely applied filler to each side of the repair.  I like All-Metal for its strength and similarity to lead body solder when working it.  It’s a much more “structural” filler than Rage  and I like it as a base along areas where patches have been welded in but the down side is it’s a bit of a b*tch to sand.

Once the All-Metal base fill was cured for a few days, I drew it down with some 80-grit on my D/A sander and finished the surface with the same paper on several hand blocks.  This gets the contour pretty well established and makes for a very good base for the following coats of Rage filler to get the final contour perfected and finished.

I tend to go kind of heavy on my first coat of Rage to make sure I have plenty to grate off with my cheese grater files.  It makes for a bit more dust on the ground, but I can get the low spots filled pretty quickly that way and not have to come back as many times to get the areas filled.

After an overnight cure, I sanded the first coat of Rage by hand (no DA required or desired) using some of my longer sanding blocks and some 180 grit paper to ensure the surface wouldn’t get lumpy and bumpy.  This would have been a very tedious job if not for the excellent sanding characteristics of the Rage filler.  Awesome stuff.

The third (and final) coat of filler was applied in a thinner and less extensive layer and I tried to keep it as smooth as possible to reduce the amount of sanding required and to keep from messing up the contours I had worked to achieve.  After a few minutes, I grated the surface down and left it to cure overnight.  Then, as before, I started at it by hand with long sanding blocks and 180 paper until I had the surface ready for primer.

With the filling complete, I added the grommet hole needed for the fuel sender wire to pass into the trunk and sanded the remaining surfaces on the bottom of the trunk floor to prep them for primer.  Then, after tacking off the surfaces and swabbing everything with wax and grease removed a few times, I masked the areas I wasn’t ready to prime and tacked everything once more time.

I was pretty excited to try a new spray gun upgrade I added to my gravity feed HVLP gun.  I upgraded to the 3M PPS cup system which makes spraying consistency, paint utilization and clean-up a TON easier.  The biggest plus I find with the 3M system is that I can now paint with the gun in any position (even upside down!) and never miss a beat.  When clean-up time comes around, you pop the liner and cap out of the cup and toss it in the trash.  Then a little wash of the gun head with reducer and you are pretty much ready to go again.  The cost savings in reducer alone will pay for this system very quickly even though the liners and caps are kind of pricey for what they are.  At this point, it doesn’t matter to me one bit as I LOVE this system and will be purchasing the small and medium sized cups for the future as well.

With my new painting weapon in hand and a fresh mix of PPG DP40LF primer in the cup, I laid down two medium wet coats of primer on the entire axle tunnel and bottom trunk floor with about a 20-minute flash time between coats.  Then, I cleaned up what little mess there was, removed the masking very carefully and then shut off the lights and left the primer to cure overnight undisturbed.  The next day I was thrilled with how everything looked and it was quite inspiring to see the entire bottom of the car in one color and looking mighty solid. 

Next on the agenda is to make the small repairs at the front of each rear wheel opening, and a tiny repair to the right rear lower window opening flange, which will mark the completion of all of the rust repairs required on the car!  Whooooohoooo!  Any rust left to address is simple surface rust on the interior surfaces of the body bracing where no factory primer was ever applied.  This will be an interesting application for my trusted chelation rust removal techniques and should work very well.  More to come!

Passenger side rear subframe cleaned up nicely after sand blasting.

Driver side subframe was also in good shape after sand blasting.

I am very happy with the decision to make the new rotisserie mounts that use the rear leaf spring shackle bushing locations as mounts.  This allowed me to blast the entire area surrounding these mounts without a problem.  Should make priming and painting far easier as well.

Here you can see the joint line that I blasted nice and clean before going forward with filling.  I am very happy with how this repair turned out, especially given the amount of rework that was required to get the trunk floor patch panel to even come close to fitting!

After a good going-over with my 2" angle grinder and some 60-grit discs, the axle tunnel was ready for the base coat of All Metal filler.

All Metal filler is awesome stuff indeed.  It is very tough (and therefore tough to sand) but is has excellent mechanical properties and behaves much like lead body solder when finishing.  I love this as a base filler where patch panel repairs are made.

I sanded the All Metal filler with my D/A sander with 80 grit paper to give the next layer(s) of filler good "tooth" to adhere to.

Here is a look at the first coat of Rage filler after it has been knocked down while soft with a cheese grater file.

After hand sanding with long sanding blocks, the first coat of filler is ready to be tacked off and a second coat applied.

The second coat of Rage filler is less extensive and far thinner than the first.  Here, it has been grated down and will be left to fully cure.

And there it is.  Though the different colors of filler make this area look rather lumpy, the actual surface is quite smooth.

One detail I had to add before primer is the grommet hole required for the fuel sending unit wire to pass through into the trunk.

With everything cleaned and tacked off, I masked off the trunk area I didn't want primed yet and started mixing up the DP40LF primer.

The first medium-wet coat of primer is on and after a 20 minute flash time, the second can be applied.

The second medium-wet coat of primer is on and looking great!

Here's a look down the driver side rear subframe rail.  Soooo much nicer than where we started!

A look at the passenger side rear subframe and trunk floor.  Nice!

 

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.