Saturday, March 19, 2016

Shock tower bracing - like a Boss!

I'll show a couple items here - I have a single crack in the drivers side shock tower that needs to be repaired, and then I'm going to install some new/non-stock braces in the bottom of the shock towers that are inspired by Ford's factory Boss 302 in the late 60's.

The shock towers in the 67-68 mustangs have a tendency to crack due to fatigue and abuse. The earlier ('65-'66) and later ('69-'70) shock towers are different designs and different shapes, and less susceptible to this issue. While some cars have cracks that look like the San Andreas fault that you can see daylight through, all I found is one little crack in the bottom of my drivers side tower.

Just to reorient ya'll where we're working -

The drivers side shock tower is in the middle there. Way down in that pocket is where the crack is hiding, but the metal had to be stripped bare to find it.

Way down low in the pocket where the shock tower meets the frame rail, there's this little crack. It goes all the way through to the other side. My passenger side shock tower is brand spanking new, so it has no cracks, and in fact has a lot of extra welds and bracing to provide extra strength in this area.

First, I drilled holes at the end of the crack (called a stop-gap), and used a dremel cutting wheel to make a little groove down the crack on both sides. The stop-gap holes keep the crack from spreading, and the grooves let me weld deeper in the metal for proper penetration.

Blamo. One crack sealed up. I cleaned up the welds on the other side since they'd be visible in the engine bay otherwise. On this side, though, I'm about to seal this area up forever with a brace, so I stopped trying to make it pretty. Those compulsive behaviors must be kept in check. If I had more cracks, I'd just follow the same procedure for all of them.

Now I need to install some additional bracing in the pocket to keep this from happening again. Ford developed a solution back in the day during the factory-backed Boss 302 racing program. Really all it needed was some extra metal 'dog-bones' that help brace the shock tower to the frame rail to prevent flexing under load which caused the the stress fractures like the one I just repaired. In the end, the fix is just a properly sized piece of Sturdy Metal triangulated in the right place.

I had to trim both braces a bit to get them to fit per the drawing, but it's easier to trim these than fabricate them directly out of metal if you don't have the tools for it. Primer is applied to the inner facing side of the braces.

Primer is also applied to in the areas that'll never see the light of day again.

Fit testing with the new upper control arms in their newly located mounting holes from the previous post. The UCA should not hit the brace, as the outside edge of the brace goes inside that pocket.

And after than it's just a matter of welding them in. In this video from West Coast Classic Cougar, they suggest at least 80% of the perimeter should be welded for proper strengthening benefits. I got closer to 90% coverage with good penetration, but I decided to leave open gaps at the corners to allow me to blow crud out if I ever felt the need. There are still drain holes in the backside as well, so this area shouldn't accumulate standing water and muck during normal use. 

You can go nuts welding every seam in the front end of the car if you're going autocrossing or drag racing - I'm not, I just felt like this mod helps correct a design weakness inherent in the original car. 

This pretty much concludes all the metal work on the car forward of the firewall. It's now ready for stripping, epoxy primer, and then installation of suspension, steering and brakes. Which is all coming up next...

Thursday, March 10, 2016

Mr. Arning and the Shelby Drop

In keeping with the "my car, my rules" philosophy I've been spouting off lately, I'm ready to make some Not Quite Original modifications to make the car handle better.

First up, is the "Shelby Drop", or more accurately, the "Arning Drop", named for the Ford Suspension Engineer that came up with this mod even though Ford didn't incorporate it into the assembly line (probably because it reduces understeer a little). Shelby liked the idea, though, so he modified all the GT350's and GT500's of the same period with this improvement.

This is a common modification to all the early Mustangs that relocates the mounting position of the Upper Control Arm (UCA) bolts. Basically, you just use a template to mark and drill new holes in the shock tower that are about 1 inch lower than the originals and mount the UCA in there. Thus the term "Drop".

In the pic below, if you peek into the shock tower, you'll see two sets of holes that look like colons

:  :

The original factory holes are the upper set, and the new location is just an inch lower. Easy, right?

The entire purpose of this is to improve (1) the car's center of gravity by lowering the car right at the suspension mount, (2) improve the camber curve of the front wheels, which will in turn, (3) improve body roll control in turns. I'll just have to remember to use the Shelby GT350 alignment spec's when I set up the front end, not the original Mustang specs in the factory service manual.

All this for the price of a $10 steel template and the pain of getting this far into the front end of the car. I found $10 in the couch cushions, and I'm already all torn down to this point, so no problem.  Plus, I already have one side done from the previous owner, so I'll only have to do the new passenger side shock tower and call it done! I'll knock this out in an hour, tops!

Nope...wrong again...

See the holes in the drivers side shock tower? You can't tell from here, but the new holes are you say..."off".

I started with new passenger side first. I just used the new template to bolt into the original holes, and mark the new hole centers.

Pilot drill with 1/8", final drill with 1/2" (supposed to be 17/32", but they're expensive and likely a one-time-use bit, so I just used the 1/2" and a round file to make it work. Snug, not loose, is the goal here. Took no time at all, and was easier than falling in love. The old holes are just left there, no need to fill them - they just get unused. I guess I could cover them with a grommet or seam sealer if I was worried about it, but I'm not.

Off to the other side...

Driver's side is already done, and so I'll thought I'd just "double check" with the new template so I know it's good and move on. I've even already started to fit the new lower shock tower braces (the dog bone-looking thing in the bottom there).

Just mount the template again and check the fit....

...and the view from the backside shows the previous owners' holes are off a bit - shifted aft and down about a quarter inch. No big deal, right? Wrong - the new UCA won't fit in the shock tower, and checking the fit of the old one, it's obvious it was "persuaded" into place and was in fact contacting and wearing through the metal wall of shock tower (!). It's super tight in there when things are in the right spot, but if you shift a little left or right, that new control arm just won't fit right.  Plus this would show up when I align the front end, and I don't want any more asymmetrical silliness in here if I can help it. So, now I have to weld up the old holes (perfectly, no air pockets) and then drill new holes to exactly match the Drop template.

Filled the big holes, smoothed out the welds. I used a copper backing bar to keep the weld in place, and cranked up the welder to 11.

mounted template to new UCA and marked the new holes...

and NOW I could drill the new, properly located holes. The UCA fits now, and moves through it's full articulation with no interference. And I managed, once again, to turn a one-hour job into an all-day thing. Whatever, it's still better than golfing. 

Next up, Welding in Big Metal Braces.