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 slightly...how 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.

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