Shelby drop: how critical are dimensions?

[miketyler]

I just finished drilling in the new lowered location on the the drivers side of my 70 car. I printed out the template and then made a flat plate starter template out of aluminum sheet. However, it became obvious quickly that I needed reference lines on the structure to help keep the hole I was drilling centered in the cross hairs.

I laid those out and began step drilling and about 45 mins later am done. The whole ordeal reminded me of my days doing aircraft structural repairs. Fortunately I have drill busings and guides to maintain straight holes and maybe better equipnent than some have to work with for such machine work. How close a tolerance is there on this mod? If for instance the aft hole was .125 higher or lower than the 1" spec, how does that affect alignment and/or handling?

I see a lot of guys doing this mod when they have their springs out, and I am probably more critical of hole size and location than many. So how far off would you have to be for it to become an issue?

 

[tarafied1]

I'm no suspension expert but I think .125" is a bit more than I would be comfortable with. The overall amount isn't so much the issue as is the difference front to back. I would guess that could effect "bumpsteer" as the UCA would no longer be on the same plane as the LCA and cause the caster to change thru the movement up and down.

 

[johnpro]

Personally, I don't think .125" is enough to cause any concern. The lower LCA is kind of "floating" on the cam bolt, so isn't really on any particular plane, as the plane that it IS on, would be more controlled by the strut rod.

I have heard of some people doing a 2" UCA drop, but then you usually need a wedge if going that deep. Most agree that anything over 1.5" requires a wedge kit to prevent binding.

John (OpenTracker) sells the templates. I have a couple of them hanging on my peg board. I'd be happy to throw one in the mail for you, and you just return it when you're done. His templates take all the guess work out and make it a piece of cake. You bolt the template to the old holes. You, then, simply drill out the pilot holes for the relocation, using the small holes in the template. Quick, easy, and extremely accurate. They're made out of thin steel.

 

[miketyler]

Thanks for the offer, really appreciate that but I think I can manage with the tooling I have. I think mine are within .050" but was just curious what affect it might have if one wasnt paying attention and just started drilling holes.

:craz

So how does the mod affect alignment specs? When I take it to the shop, do I have new custom specs I need to supply them or is it still basically the same as OEM specs? Also, what do you guys do with those 4 open holes left post mod?

 

[Grabber70Mach]

ORP front end alignment Specs
STREET SPECS *
Caster:
+1.5° to +2.5° Camber:
0 to -.5° Toe:
1/8" in


STREET/PERFORMANCE *
Caster:
+2.0° to +3.0° Camber:
-.5° to -1.5° Toe:
1/8" in
* Caster and camber setting must be the same on both sides for proper handling

 

[buening]

Also, what do you guys do with those 4 open holes left post mod?

Most that I've seen just leave the holes open. When I get around to doing this mod, I plan on plug filling the holes to minimize cracking and be a bit more aesthetically pleasing. I haven't really seen any crack though, at least no one has admitted to it happening that I've seen.

 

[gotstang]

This is THE best explanation of Mustang alignment specs (what to use and why) that I've seen. The others have some useful info as well:

http://www.stangfix.com/testforum/index.php/topic,6901.0.html
http://www.stangfix.com/testforum/index.php/topic,102.0.html
http://www.stangfix.com/testforum/index.php/topic,6267.0.html

As far as the holes, I haven't seen anybody have any problems that resulted from just leaving them there. I've been thinking about welding them shut, just to keep it looking nice though.

 

[Midlife]

I would suspect dimensional tolerance of the hole locations relative to one another would be accommodated by your ability to adjust the camber, caster, and toe to compensate. Usually, no more than 1/4" of shims (or equivalent) of difference between one hole or another is recommended. That may give you some idea of how close things need to be.

 

[miketyler]

Looks like one of those things that you would have to be REALLY off for it to have any negative impact. I think any minor deviation from the design adds a different "angle of attack" so to speak on the A frame and but the ball joint should thusly compensate. As for shimming I would guess that the difference in the location one inch below the existing holes relative to centerline of the vehicle would be marginal? I have no shims on drivers side and probably 1/4" or more on the right.

Is that normal for these cars?

 

[Opentracker]

Looks like one of those things that you would have to be REALLY off for it to have any negative impact. I think any minor deviation from the design adds a different "angle of attack" so to speak on the A frame and but the ball joint should thusly compensate. As for shimming I would guess that the difference in the location one inch below the existing holes relative to centerline of the vehicle would be marginal? I have no shims on drivers side and probably 1/4" or more on the right.

Is that normal for these cars?

Sure is. Most of them have more shims on one side than the other. As Mid said, Ford gave the workers 1/4" to play with. From the amount of BEER cans and other items that have been found in the cars from the factory, I bet it was more than that on some of them.

 

[Sluggo]

Drilling the rearmost hole higher or lower will impact the ball joint angle since you are basically pivoting the arm on the front bolt.
Drilling the rear hole higher will draw the ball joint rearward adding positive camber. Drilling it lower will decrease caster.

.125 is negligible. I would not recommend it as a way to gain or lose caster though.

 

[Opentracker]

Drilling the rearmost hole higher or lower will impact the ball joint angle since you are basically pivoting the arm on the front bolt.
Drilling the rear hole higher will draw the ball joint rearward adding positive camber. Drilling it lower will decrease caster.

.125 is negligible. I would not recommend it as a way to gain or lose caster though.

I wouldn't either. That would cause the top of the shock to move forward and backward as the arm moved up and down, not good, causes bind. The way they get a way with it on cars that have it done on purpose is to use a shock with rod ends on the top and bottom. I do agree that .125 isn't much to worry about.