A-Body Dart Spring Relocate Question

[1973_Swinger]

1973 dodge dart spring relocate questions:

Can someone tell me the reason why the majority of the spring relocation kits tell you to mount the front spring mount off center to the frame rail? it does not make sense to me. if the rear spring mount is exactly centric on the frame rail using the shackles then why is the front not centered on the rail.

I understand that the frame rail slowly tapers wider as you get closer to the front of the car.. but it appears to taper the same left and right so i would only assume that the front spring mount should be centered as well.

US car tool photo showing not centered on frame rail:

reilly motor sports showing to install their kit centered on the rail:

I CNC cut and bent my own spring mounts so i just want to make sure i install them properly but im getting mixed reviews on my research. I downloaded the 1973 body service manual to try and see what frame measurements tell me but it all seems to lend to welding it centered on the frame rail.... any input?

Frame measurement excerpt:

 

[Kendog 170]

I did mine differently. Used some of the rail to make it stronger. Not saying it right. No issues.

 

[1973_Swinger]

Will this cause the leaf spring to be non-parallel with the frame rail or perpendicular to the axle? or does it really matter?

 

[Inertia]

Some vehicles, leaf springs are not parallel.

The 67 Camaro chassis I used to build, the front spring hanger is something like 5/8 of an inch inboard of rear shackles..
To meet tech.

 

[Kendog 170]

Will this cause the leaf spring to be non-parallel with the frame rail or perpendicular to the axle? or does it really matter?

My rear hangers are installed in the frame rails. I forget where I got the Bushing shackle kit. You weld the sleeve in the rail. There are two different sizes for which eyebolt you have. I had the larger for the SS springs. Sorry no pic. Stole this pic off the site.

 

[1973_Swinger]

My rear hangers are installed in the frame rails. I forget where I got the Bushing shackle kit. You weld the sleeve in the rail. There are two different sizes for which eyebolt you have. I had the larger for the SS springs. Sorry no pic. Stole this pic off the site.
View attachment 1716469835

Yes, That is my understanding that the rear shackle straddles the rear frame rails with a chunk of tubing welded through. similar to below photo from USCT:

 

[crackedback]

Can't really do this with the USCT boxes. Like the USCT concept. I'd be looking at fill the existing holes where they mount to OEM perch and move them over to align boxes with rail edge. Never understand why they center the boxes on frame rails. Takes away a small amount of space for tire.

I use a rod to help align both sides. Capture all for verticals of the boxes Use a factory hanger cut in half to help out. Example from a friends car on how to get it done.

 

[1973_Swinger]

Can't really do this with the USCT boxes. Like the USCT concept. I'd be looking at fill the existing holes where they mount to OEM perch and move them over to align boxes with rail edge. Never understand why they center the boxes on frame rails. Takes away a small amount of space for tire.

I use a rod to help align both sides. Capture all for verticals of the boxes Use a factory hanger cut in half to help out. Example from a friends car on how to get it done.

A bit confused, did you intend this to say (Never understand why they DON'T center the boxes on frame rails. Takes away a small amount of space for tire.)

• USCT kit is basically installed flush with the inside face of the frame rail leaving the worst clearance for tire space.
• Welding brackets centered on the rail it is slightly better for tire space.
• Your photos looks like the bracket is flush with the outer face of the frame rail giving the most clearance.

 

[crackedback]

The box intruding into the wheelhouse is dumb IMO. Any approach that does that is not used around here!

Couldn't see the back side of the USCT box, it look centered. That is the WORST approach, picked the wrong side for rail alignment. Move that ish inboard!

 

[Kendog 170]

• USCT kit is basically installed flush with the inside face of the frame rail leaving the worst clearance for tire space.

I hammered and dollied my frame rail lip straight up. Sorry, what can I say.

 

[72bluNblu]

A bit confused, did you intend this to say (Never understand why they DON'T center the boxes on frame rails. Takes away a small amount of space for tire.)

• USCT kit is basically installed flush with the inside face of the frame rail leaving the worst clearance for tire space.
• Welding brackets centered on the rail it is slightly better for tire space.
• Your photos looks like the bracket is flush with the outer face of the frame rail giving the most clearance.

Having the bracket flush with the inside rail isn't going to reduce your tire clearance overall.

Yes, it will reduce clearance to the springs. But that's not going to be the most limiting part of your tire clearance. The most limiting spot for tire clearance is going to be the inner wheel tub, because the tires deflect and the axle takes on cross angles. So even if the springs were perfectly flush with the inner wheel tub (and frame rail) you'd still end up with more clearance at the spring than you need to get the clearance right toward the top of the tire at the inner wheel tub.

I have a 1/2" spring offset on my Duster, and substantially more distance between my tire and inner wheel tub than I do to the springs. I've never hit the springs, but I can still get the occasional rub on the inner wheel tub because of suspension movement and tire deflection. And I run 295/40/18's, so, I get less tire deflection than someone would with smaller diameter rims.

The spring being flush with the inside of the frame rail probably won't reduce the size of the tire you can run at all, because the wheel tub will be the more limiting factor.

 

[68dodge]

I have mine setting in more for max tire clearance with the inner wheel well. Just like your first picture with the yellow mounts. I can use a 28x13.50x15 and a 325/50/15. Both tires are M/T ET street DOT's with S/S Springs

 

[HPP]

Some vehicles, leaf springs are not parallel.

The 67 Camaro chassis I used to build, the front spring hanger is something like 5/8 of an inch inboard of rear shackles..
To meet tech.

All Mopar E bodies, 73-79 B bodies, and F/J/M bodies all have springs with splayed mounting layout. E bodies are narrower in front mounting, the other are all narrower in the rear.

This type of layout provides increased roll resistance and reduced roll steer compared to a parallel layout.

So no, there is nothing wrong with this configuration. However, the minor amount there may be in a 3" spring relocation in an A body (no matter where you center the new bracket in the frame rails) is probably not enough to even notice.

 

[72bluNblu]

All Mopar E bodies, 73-79 B bodies, and F/J/M bodies all have springs with splayed mounting layout. E bodies are narrower in front mounting, the other are all narrower in the rear.

This type of layout provides increased roll resistance and reduced roll steer compared to a parallel layout.

So no, there is nothing wrong with this configuration. However, the minor amount there may be in a 3" spring relocation in an A body (no matter where you center the new bracket in the frame rails) is probably not enough to even notice.

And like all things suspension, there are both advantages and disadvantages to having the leaf springs splayed out.

This is the AFCO information with their leaf spring sliders, although it also cover quite a bit of leaf spring geometry and addresses the splayed spring geometry

"Mounting the leafs so that the front eyes are slightly inboard of the rear eyes will cause the leafs to have more lateral stiffness. This can make the chassis feel tighter and may help prevent the rear suspension from binding due to excessive lateral deflection of the leaf. However, if the leafs are offset too much, the suspension becomes too stiff laterally and rear side bite is lost. Whenever the body slides over the rear end during cornering, the splayed leafs can cause rear steer that will help the car to turn. Also, if the right front spring eye is mounted more inboard than the left eye (measured from the corresponding tires), the right rear tire will tend to be loaded less than the left rear tire during acceleration. As a result, the chassis will tend to be tighter off the corner. Corner exit handling tends to be loose under opposite. Generally, moving the front spring eye 1-1/2" laterally will produce a noticeable effect in corner exit handling"

This is from the Direct Connection suspension book, it shows the E-body spring angle at only 1.67°, but that actually staggers the front eye by about 1.66".

Moving the front hanger box by a 1/4" or whatever that distance is to make it flush with the frame rail won't likely make any kind of noticeable handling difference. And really, it's probably not going to increase the width of the tire you can run either because the limiting factor will still be the inner wheel tub.

 

[HPP]

True, the simple act of driving up a curb at an angle will put enough angularity in the axle travel that the top of the tire may contact the wheel tub.

I've never seen a tire deflect enough at the leaf spring height to ever make contact with the spring and be a problem. There simply isn't enough lateral load at that spot in the tire to cause that.

 

[72bluNblu]

True, the simple act of driving up a curb at an angle will put enough angularity in the axle travel that the top of the tire may contact the wheel tub.

I've never seen a tire deflect enough at the leaf spring height to ever make contact with the spring and be a problem. There simply isn't enough lateral load at that spot in the tire to cause that.

That's certainly been my experience. When I first installed 295/35/18's on the back of my car I was running drum brakes and had very little clearance to the leafs, probably 3/8" at most. I didn't rub the springs, but before I put my sway bar on I did have issues with a minor rub at the inner wheel well when I would cross axle over speed bumps and driveway transitions. Then I mounted the rear sway bar and solved that issue, and further improved clearance by adding disks in the rear which moved the wheels out another 5/16" or so.

But then I went to 295/40/18's, which initially was fine, but my latest set of Falken's is maybe a little bit larger than the last set, or maybe stickier, whatever, I'm once again seeing a minor rub on the inner wheel tub under hard cornering while on less than perfectly smooth mountain roads. I tightened up the sway bar a notch and still get it, so I may actually go to a slightly stiffer rear leaf spring since I'm only at 121 lb/in.

Regardless, the limiting factor on the rear wheels isn't the springs, it's the inner wheel tub. And that's true with a 1/2" spring offset or the full 3" relocation since both basically co-locate the inner wheel tub with the outer edge of the spring. You can run much tighter to the springs than you can to the inner tub, and the larger the rear tire you run the more that ends up being true.

 

[mopowers]

The box intruding into the wheelhouse is dumb IMO. Any approach that does that is not used around here!

Couldn't see the back side of the USCT box, it look centered. That is the WORST approach, picked the wrong side for rail alignment. Move that ish inboard!

Totally agree. When I relocated the springs on my '66 Dart, I didn't flush out the outer surface of the front mount. Instead, I made it protrude into the wheel house side about about a 1/2 - 3/4" inch. I was dumb though. I only did that to make welding it easier - it made for a nice little "ledge" to weld on the outer side, and made it easier to see the weld joint past the inner "ledge." The stupid thing is now the rearward corner of that mount box limits the tire width. Maybe for shorter tires it's not as big of an issue, but for me I had to step down from 315/60s to 295/65s. All good though - the 295/65s still look pretty cool.

From now on, I'll be flushing out the outer surface.

 

[crackedback]

Totally agree. When I relocated the springs on my '66 Dart, I didn't flush out the outer surface of the front mount. Instead, I made it protrude into the wheel house side about about a 1/2 - 3/4" inch. I was dumb though. I only did that to make welding it easier - it made for a nice little "ledge" to weld on the outer side, and made it easier to see the weld joint past the inner "ledge." The stupid thing is now the rearward corner of that mount box limits the tire width. Maybe for shorter tires it's not as big of an issue, but for me I had to step down from 315/60s to 295/65s. All good though - the 295/65s still look pretty cool.

From now on, I'll be flushing out the outer surface.

Depends on how you mini tub as well. Leave the lip on the floor pan/rail, not really an issue. Take the lip off flush, , mount tub on top edge, then it takes away space. Not a lot of space, just some.

You can sometimes trim that corner off the box, weld horizontal flat edge to rail and blend back out to full width beyond tire bulge.

 

[mopowers]

Depends on how you mini tub as well. Leave the lip on the floor pan/rail, not really an issue. Take the lip off flush, , mount tub on top edge, then it takes away space. Not a lot of space, just some.

You can sometimes trim that corner off the box, weld horizontal flat edge to rail and blend back out to full width beyond tire bulge.

I did trim the flange off the frame rail and re-welded the floor to the frame rail before attaching the inner tub flat against it.

If I end up wanting to run wider slicks, I'll probably nip that corner off the front box like you mentioned. I had thought about it too. Not a huge deal for now though. In all honesty, I probably would've been fine with the 315/60s, but it was a little too close for comfort and I needed new tires anyway.

 

[Woody500]

Some vehicles, leaf springs are not parallel.

The 67 Camaro chassis I used to build, the front spring hanger is something like 5/8 of an inch inboard of rear shackles..
To meet tech.

He's right about springs mouted skewed on some cars, but I can't remember the reasoning, other than it's for proper handling, or tuning the handling.
You'll have to research further to find why.

 

[Woody500]

All Mopar E bodies, 73-79 B bodies, and F/J/M bodies all have springs with splayed mounting layout. E bodies are narrower in front mounting, the other are all narrower in the rear.

This type of layout provides increased roll resistance and reduced roll steer compared to a parallel layout.

So no, there is nothing wrong with this configuration. However, the minor amount there may be in a 3" spring relocation in an A body (no matter where you center the new bracket in the frame rails) is probably not enough to even notice.

Might be more important to you if you want car to road race, or too handle better, compared to a Drag Race setup.
Does it affect the toe-out-in turns that is built in?

 

[HPP]

Toe out in turns is ackerman that is designed into the front suspension. To eliminate this, you would need to have the outer tie rod end exactly behind the lower ball joint and a line between them would need to parallel to the centerline of the car. This is impossible to achieve using stock A body lower ball joints. You would need a set-up like a 74-79 B body with an upper ball joint in the lower control arm and a fabricated steering arm attached to the spindle that is line with the ball joint.

 

[Woody500]

Splayed rear springs apparently help handling by lessening rear axle side to side movement, stabilizing the car in turns, also reducing body roll, and increasing roll steer(when spring compresses or arches more, the wheelbase is changed a small amount), enabling rear tires to help initiating turn in, basically changing the arc they ascribe.
Just a basic description that is probably more involved.
No details on if front or rear splay is better.
Ackerman is unchanged but a more stable rear end makes handling more predictable.
Some day I'll dig out Carroll Smiths' books(race engineer) & see if he discusses it.