Tuesday, September 8, 2015

Fender apron patches - a typical vintage Mustang trouble spot

Patching fender aprons is like chicken pox in these old Mustangs. Everyone gets it, and it leaves scars where you can see them. Most every Mustang will have this issue at one point in its life and it's easy to spot the ones that still need this repair at any hoods-up car show. No amount of spray paint will make this better. The rotten metal has to be cut out and replaced.

There are two apron overlaps on each side...and both need to be repaired. This all happens in the engine bay. Once the fenders are removed, you can see there are three pieces of sheet metal that make up each side of the engine bay - the front apron, the shock tower, and the rear apron. The shock tower is the middle piece. It's thick metal at 14 gauge. The aprons in front and behind are made of thinner 19 or 20 gauge metal.

Where the apron meets the shock tower, the metal is just overlapped and spot welded. The only thing that was used to protect against corrosion was hope and a short warranty period. The seams between the layers of metal are open on both top and bottom, so any moisture from the engine bay, or - more likely - the wheel well, will get in there and just rot the metal away.

Doing this repair, you get to learn how to drill spot welds, butt-weld different gauges of metal, and then use plug welds to join the two pieces together to simulate the spot welds from the factory. In fact, I'd recommend this as a good first welding project on a car to get a feel for how it's done - the metal is basically flat, and mostly unseen, so you can relax a little bit. Very early on, when I was figuring out what I was getting into, I read about this in detail on this blog by a hoopy frood named Alex, and it sort of gave me confidence that I could successfully do this, and other work, on this car. So I blame him.

I'm only showing one side since the other side is a mirror image. Plus, I'm about to discover I need new aprons, shock tower, and frame rail on that side anyway...

Here are the two rust nuggets in question. This is a shot looking at the top of the engine bay looking towards the back of the car.

I start with the rear apron overlap...

Rust, glorious rust! The junction of these two pieces is in trouble. The rust is clearly evident on top as well as from below, so we'll be cutting and replacing chunks of both the shock tower and the apron.

Strip the paint off the top to locate and then drill out the spot welds. I'm using the Communist Freight spot weld cutter. At $5 each, it's hard to beat. A single bit should get you through this entire post. 

Factory weld/sealant manual says there should be 5 or 6, but here I found 8. Then I made a cut just aft of the shock tower metal and up along the inside edge so my patch piece can be mostly plain flat sheet metal.

I also cut out the rotten piece from the shock tower part of the junction. Use protection, kids - primer applied at the factory would have kept this from getting this bad. It's scary to think most overlapped/spot-welded joints on the car could look like this -- but remember, this particular junction sees extreme duty because it's exposed to water and dirt in the wheel well.

Bad metal gone - square up the edges and strip back the paint in prep for welding.

Patch piece of 14 ga. metal, clamped in and butted in tight. Thick metal like this is easier than the fender patch I just finished.

I did a series of tack welds and then filled in with bead welds in between.

Welds ground down flush and sanded for that lovely clean, new metal look.

Now the apron patch. Made of 20 gauge metal, with a bend on one end to match the existing outer flange and holds drilled for fake spot welds (plug welds). Weld-thru primer on the top of the shock tower and on bottom of the apron piece. The primer is scraped off  (by me) at actual weld points. Cleaner welds are better welds. The primer is to protect the bare metal after the repair is complete.

Tack welds all around. At 20 gauge, more care must be taken. Ideally, this patch should be clamped flush with the piece underneath to you don't get blowouts while welding.

Mostly finished. The pinholes will need some clean up work later, but the metal is smooth and rust free. I'll use seam sealer underneath when the car gets primed so this won't happen again.

On to the front apron overlap....

Same story - both pieces are rotten. Cut out the rust, and replace with new, primed, rust-free metal.

Looks just like the first one - maybe not as bad?

Again - strip paint, locate and cut spot welds, and mark for cutting. 

Another favorite tool when removing spot welds - the 5-in-1 painters tool. This and a mallet makes quick work of separating that last 10% of each spot weld the cutter misses.

Seriously - this is what is inside that junction.

Cleaned up to bare metal. You can see all the pitting and thinning of the metal on the shock tower. It has to go. You won't be able to weld to it very well, and there a rotted out hole in it.

Zing! Out goes the bad metal.

New patch going in.

Bead welded in place.

Welds dressed and metal all smoothed out. And more pinholes to deal with. I'm not gonna show that, but they need to be dealt with.

New apron patch, just like before. There are 4 or 5 plug welds going in here, but the clamps are in the way. Needs to be clamped up nice and tight - vertical gaps between these two pieces makes it more difficult to weld.

Isn't that nice?

Blamo! Rust nuggets are gone, Once it's all sanded and epoxy primed. it should look good as new. Remember, once the fenders are on, the only part of the top of the engine bay that is visible is the inner half - the outer half is under the fenders.

Wednesday, September 2, 2015

Drivers side fender, part 2

1967 Ford Mustang Fastback right side fender patch and prime Now that we can see the extent of the damage on the bottom of the fender, I'm going to attempt to cut out and patch the metal so that it'll just need a skim coating of body filler during the paint stage.

I marked the boundary of the thinned metal - if it's thin, it gets cut out. I then marked the area needed for cutting out and patching - right angle cuts only to make it easier to create the patch piece.

Bad metal cut out. Now we're committed!

I ordered the lower fender patch from Rock Auto - the part is branded 'Goodmark' and was a pretty good match. I only needed to bottom half, so I made a cut and started fitting the piece to the fender. 

Lining up the patch so I can trim to fit.

Good contour on the patch - matches the fender curve well.

The holes for fender mounting bolts are not pre-drilled and it'll need careful trimming all around to fit the hole I've cut in the fender. The patch is close enough to work with, and it's the same metal gauge as the fender.

Here's the patch trimmed to fit and held in place with magnets. Important tip - the patch needs to be trimmed so that there is a very small, uniform gap between it and the fender. Too big a gap, and the weld won't be good. I try to get the gap tight, about the same width as the welding wire I'm using, 0.023 inches.  I tacked it in at just a few points away from the magnets and  then pulled them out to do the rest of the tacks.

First series of tacks. I'm planishing each tack as I go to reduce warping or shrinkage. No one wants to see shrinkage. I used this thread as a tutorial on how to weld in big patches of curved metal.

To weld in a patch like this, I'll weld the entire length of patch using individual tacks all the way around. A continuous bead weld would put too much heat into the metal and warp the metal or blow a hole in it. Add a few tacks, planish each one, and walk away for a while. Again, heat build up will warp this in no time, so it's best to do this in short bursts, just a few tacks in each round. Of course this means it'll take hours to compete, but it makes for a better fix.

Here's the finished patch. Nice, right? I still need to hammer the edges of the patch down to just below the surface of the fender so it'll take a skim coat of body filler. But I was pretty jazzed to get this to work as well as it did.

Priming the fender brace areas before welding it back together. The edges are bare to make welding easier. Primer will contaminate the weld puddle, so keep it clean!

Original brace piece welded back in. 

I need to fabricate a patch piece to join the fender brace to the fender. The replacement Goodmark piece I ordered was made of  14 gauge metal, not 19 gauge like the original stuff is made of. It was laughably too thick to weld in, so I threw it aside and made my own patch out of a few separate pieces. Maybe not pretty, but it works.

Patch panel didn't come with cutouts for fender bolts - so I have to cut them to match the original contours.


Backside view of all the patching. Still some weld cleanup to do, but it's looking better (and rust-free).  While the seam may still be visible on the inside of the fender once finished, it won't be visible on the outside after body work. 

Frontside view of the repairs. Looks pretty good to me.

Final DA sanding and wipe down with W&G remover. Shiny!

Two coats of SPI black epoxy. If you look real close you can see the dimples from the filled badge holes and the patch panel. That's on purpose. A better metalworker probably wouldn't leave it at this stage, but work the metal flatter and flatter until no filler was needed. I'm not there yet.

The fender is now ready for test fitting on the car as needed and ready for the body shop to do its work. I'm glad I did this as I now know the metal is good and there aren't any lingering rust spots that'll show up six months after it's painted. Again, over 50 hours of work in just this fender. At  just over minimum wage, I could have bought a Ford OE fender for my time. But this was way more fun.