Billet Spindles with Bolt On Hub Assemblies
Have you looked at the geometry of the factory suspension? Because it really isn't bad. This article from Mopar Muscle, while being about a brake swap comparison, has the camber curves and bump steer geometry plotted out for the 73+ A-body and FMJ spindles. The FMJ spindles were already slightly improved in some areas with a slightly better SAI. Of course, everything in suspension design is a trade off, so, there are cons to using the FMJ spindles too Swapping Disc-Brake Spindles - Mopar Muscle Magazine Keep in mind too that the article used factory UCA's, aftermarket UCA's typically add caster and improve on the geometry further. The factory bump steer numbers aren't bad at all either, in fact if it's actually to factory spec it's pretty good, a point made when they did all the suspension articles on the Green Brick.
Truly though, the factory spindle design isn't bad. Certainly not bad enough to bother designing a new spindle to work with the original suspension mounting points, which would seriously limit what you could do anyway. There are a ton of brake options for the original spindles as well. DoctorDiff has some very nice 13" rotor set ups that bolt right up with the factory spindles, and of course Wilwood and Baer have set ups as well.
And, about the 1" "off the top" and added to the bottom- that's just a drop spindle. The 2" drop spindles on the market now do exactly that. In fact, they're basically a factory 73+ spindle, just with the axis point moved 2" higher. That's it. What you're suggesting would be the same, just a 1" drop instead. To consider what happens with the roll center, you have to think about how the roll center is calculated. It comes from the angle of the control arms. If you lower the car with the torsion bar adjusters, you change the angle of the control arms, and you end up with a lower roll center than you do with drop spindles. This would be true for a 1" drop spindle or a 2" drop spindle. I had the calculations done for a 2" drop spindle because I ran them briefly on my Challenger. They resulting suspension geometry is worse than just lowering the car with the torsion bar adjusters and increasing the size of the torsion bars to compensate for the lost suspension travel (you need bigger torsion bars for a better handling car anyway).
These are for an E-body, so, not all of this would directly correlate to A-body geometry. But, the FMJ spindles are pretty much the same as the E-body spindles, and I use FMJ spindles on both my A and E body.
Stock E-body, lowered with the torsion bar adjusters
2" drop spindle E-body. These cars sat at the same ride height. Look at the roll center height, significantly higher. Also, look at the angle of the control arms. The camber curves for this set up with the drop spindles would be worse, although I don't have those numbers. Bump steer was slightly worse as well. For an A-body the numbers would be slightly different, I know Peter Bergman had said at one point that his roll center was actually calculating out as negative (below ground!) on his Dart and he installed a set of drop spindles as well as a way to correct that issue. He ended up going back to stock spindles though.
By all means, if you want to get into designing a new spindle and you have the means to produce such an item, don't let me stop you. But consider that the aftermarket drop spindles out there now use exactly the factory design with a relocated axle. Also consider that of all the aftermarket companies out there, pretty much every piece of suspension hardware is reproduced in some kind of tubular or adjustable form -tubular UCA's, fully adjustable UCA's, tubular LCA's, adjustable strut rods, solid tie rod adjusters, full on tubular K frames, giant torsion bars, sway bars, etc. The only piece that everyone uses the factory geometry for is the spindle.
Have you looked at the geometry of the factory suspension? Because it really isn't bad. This article from Mopar Muscle, while being about a brake swap comparison, has the camber curves and bump steer geometry plotted out for the 73+ A-body and FMJ spindles. The FMJ spindles were already slightly improved in some areas with a slightly better SAI. Of course, everything in suspension design is a trade off, so, there are cons to using the FMJ spindles too Swapping Disc-Brake Spindles - Mopar Muscle Magazine Keep in mind too that the article used factory UCA's, aftermarket UCA's typically add caster and improve on the geometry further. The factory bump steer numbers aren't bad at all either, in fact if it's actually to factory spec it's pretty good, a point made when they did all the suspension articles on the Green Brick.
Truly though, the factory spindle design isn't bad. Certainly not bad enough to bother designing a new spindle to work with the original suspension mounting points, which would seriously limit what you could do anyway. There are a ton of brake options for the original spindles as well. DoctorDiff has some very nice 13" rotor set ups that bolt right up with the factory spindles, and of course Wilwood and Baer have set ups as well.
And, about the 1" "off the top" and added to the bottom- that's just a drop spindle. The 2" drop spindles on the market now do exactly that. In fact, they're basically a factory 73+ spindle, just with the axis point moved 2" higher. That's it. What you're suggesting would be the same, just a 1" drop instead. To consider what happens with the roll center, you have to think about how the roll center is calculated. It comes from the angle of the control arms. If you lower the car with the torsion bar adjusters, you change the angle of the control arms, and you end up with a lower roll center than you do with drop spindles. This would be true for a 1" drop spindle or a 2" drop spindle. I had the calculations done for a 2" drop spindle because I ran them briefly on my Challenger. They resulting suspension geometry is worse than just lowering the car with the torsion bar adjusters and increasing the size of the torsion bars to compensate for the lost suspension travel (you need bigger torsion bars for a better handling car anyway).
These are for an E-body, so, not all of this would directly correlate to A-body geometry. But, the FMJ spindles are pretty much the same as the E-body spindles, and I use FMJ spindles on both my A and E body.
Stock E-body, lowered with the torsion bar adjusters
2" drop spindle E-body. These cars sat at the same ride height. Look at the roll center height, significantly higher. Also, look at the angle of the control arms. The camber curves for this set up with the drop spindles would be worse, although I don't have those numbers. Bump steer was slightly worse as well. For an A-body the numbers would be slightly different, I know Peter Bergman had said at one point that his roll center was actually calculating out as negative (below ground!) on his Dart and he installed a set of drop spindles as well as a way to correct that issue. He ended up going back to stock spindles though.
By all means, if you want to get into designing a new spindle and you have the means to produce such an item, don't let me stop you. But consider that the aftermarket drop spindles out there now use exactly the factory design with a relocated axle. Also consider that of all the aftermarket companies out there, pretty much every piece of suspension hardware is reproduced in some kind of tubular or adjustable form -tubular UCA's, fully adjustable UCA's, tubular LCA's, adjustable strut rods, solid tie rod adjusters, full on tubular K frames, giant torsion bars, sway bars, etc. The only piece that everyone uses the factory geometry for is the spindle.