Preparing For Bigger Things: More Interior Sheet Metal Prep

As the 2012 thankfully comes to its controversial end, I find it’s been a month since my last update.  And while it seems I have made little progress, I have managed to move forward, albeit with little outward proof of the fact.  The reality is that I am in a phase that is boring, tedious and generally lacking in most of the “fun” associated with the hobby.  Since I last checked it, I have been consumed with preparing the rear interior and trunk area for an upcoming coating of SEM Rust Shield (gunna try something new!) and then the trusty PPG DP40 primer.  Following that, the entire interior will get a finish coat of PPG matte black urethane.  But as simple as that all sounds, I have a lot of work to do before any coatings can be applied and that is the phase I’m in.

The latest concentration has been treating the light surface rust in all the critical areas in any way I could approach.  At first, I ventured to use my trusty chelation process, but quickly found that I had reached a practical limit in its application in consideration of the limits of my space and the difficulties in the recovery of the chelant in such complex structures as those in the rear of a Mustang.  As such, I resorted to the old tried and true wire brush and elbow grease method for the majority of the job.  Of particular interest was cleaning up and prepping the areas surrounding the door openings and the roof drip rails.

As I have mentioned in several posts in the past, I have learned that it is critical to remove every bit of factory seam sealer that can be removed in the process of a proper restoration.  This is especially true of the roof drip rails and window surrounds on any classic Mustang.  In keeping with that, I again turned to acetone to soften the compound and using scrapers and wire brushes of various configurations to remove it from all of the door opening surfaces.  Next, I dove into the task of cleaning up the inner door openings, rocker sills and B-pillar posts.  For the most part, the bulk of this work involved removing the original paint and primer and then treating the slightly rusted spots with phosphoric acid-based “prep & etch” solution to remove it and protect the bare metal until it was time to apply primer.  B-O-R-I-N-G and time-intensive work, but the results were very good and I managed to fit all of it in in spite of the requisite Christmas preparations and associated activities that demand as much time as any resto work ever did!

So, with the door openings in good shape, I decided to tackle a few repairs/modifications on the rear bodywork.  One was by necessity and the other by choice.  Of priority was the need to repair to cracks about 1¼” long that radiated from the top corners of the trunk lid opening out into the quarter panels.  This is a common crack area in Mustangs, especially in car that have been extensively drag raced without added structural reinforcement like a roll cage or subframe connectors.

These repairs are pretty simple in concept, but a bit tricky in that they often traverse many body character lines and welding them up takes a pretty fine tune on the welder to ensure minimal distortion and weld bead size.

The first order of business is to stop the crack’s propagation by drilling a small hole just beyond its end.  In my case, I used a sharp 1/8” bit for the job and this did the job perfectly.

Next, I tack the inboard origin of the crack to lock down that end and to keep the panels as stable as possible.  At this point, the crack is isolated on both ends and can now be repaired.  Using my trust Dremel tool, I used a thin cutoff blade and carefully cut directly along the crack to provide a gap that would allow full weld penetration without buckling.  This gap only needs to be about .030-.050” wide max when using .023” MIG wire and can be as tight as .015-.020” with TIG.

With the prep work complete, the crack was welded up using a step-stitch method with the MIG set at a slightly hotter range than recommended to allow a quick burst of weld that would lay flat and fill well.  After each stitch, I would cool the area with a blast of air and repeat the process until the gap was fully welded.  This technique is a little different than welding in patch panels as it is of much shorter duration and is essentially stacking a series of small spot welds in a row until a complete bead is formed.  The truth is, I often resort to this method when installing patches as it helps keep weld distortion to a minimum, at the expense of considerable increase in repair time.  But HEY, this is a hobby right?  What’s a little extra time?????

With the cracks fully welded up, a few minutes with the sanding disc in the angle grinder was all that was required to get the surface back to smooth with no evidence the cracks were ever there.  Now, not being one to leave well enough alone, I took the opportunity to do one more small tweak to the body that I have been planning since day one.  The fact that it fires yet another shot across the bow of the purist elite makes it all the more enjoyable.

Since I was working in the “neighborhood”, I took the opportunity to fully weld up the seams between the upper trunk panel and the quarters.  As long as I can remember, my eye has been drawn to this area of 69 and 70 Mustangs as one that always seemed unfinished at worst and inconsistent at best.  In fact, I am not sure I have ever seen these seams look the same way twice and it peeves me to no end.  Well not on MY car it won’t!  So, after a quick wave of the magic smoke-wand, they are no more!

And that is pretty much a wrap for now.  I apologize it wasn’t a bit more of an adventure, but those days are coming soon.  But for now, the tedium will continue for a while longer.  Until next time!

I was very luck that the B-posts in my car were in great shape.  After stripping the seam sealer away and scrubbing the old paint and primer off, the bare metal was treated with phosphoric prep & etch.

The driver side rocker sill was pretty nasty, especially along the "wire groove" just underneath where the aluminum sill plates attach.  But once the munge was removed, the metal was found to be extremely solid and in fine shape. 

As fortune would have it, the passenger side rocker sill was also in excellent shape after clean-up and etching.

Although a crap picture, the quarter glass surrounds cleaned up well and are completely solid.

The underside of the roof drip rails required quite a bit of work to remove the seam sealer and surface rust.  However, the end result was good clean metal around both the driver and passenger side openings.  Bonus!

While I failed to document the "before" shots of the trunk-to-quarter cracking, here you can see the 1/8" "stop hole" I drilled at the outboard end of the crack and the inboard anchor tacks welds at the root of the crack.  Also, I have already cut a thing groove along the crack to allow full weld penetration.  You will also note that I have hinted at my next modification as evidenced by the short string of weld along the gap between the upper trunk closeout and the quarter panel.

As a middle-finger salute to obnoxious "purists" everywhere, I welded the trunk/quarter gaps completely just to watch them point out the "flaw" when the car is complete.  Actually that's bullsh*t.  I absolutely HATE how this area looks on "restored" cars and didn't want mine to look that way (but I still like my original story better).

Though a slight bit of finish work is still left, this shot shows the gaps filled and the crack repaired.