Is this caused by too much axle wind up?

[KillerBee]

So I put my Challenger up on the lift to do some maintenance and noticed both my Leaf springs had attacked the rear valance, (see pic below)
I was able to easily get the springs back in their proper location by jacking the car up by the frame and letting the rear axle droop down.
Thankfully very little damage,  just some scratches to the paint.
I've been driving the car with its current suspension for a few years now and this is the first time it has done this.

The car has a very strong running 440 engine with four-speed transmission that really gives the suspension a workout at times.
Admittedly I have been driving the car rather hard lately,  I gave a buddy with a big block Chevelle the opportunity last weekend to check my tail
lights.

I have a unusual rear suspension set up that was suggested to me by Dr. Diff.
The leaf Springs are 2 driver side Super Stock springs for an A body.
The A body SS springs are softer giving the car a little better ride and a little bit lower stance which is what I wanted.
Rear shackles are stock and are oriented vertical. They don't appear too close to the rear valance.
No pinion snubber currently installed.

I checked all the hanger and spring hardware and nothing was loose.

I'm thinking the softer SS leaf springs are causing the axle to wind up too far during hard acceleration making the leaf spring segments separate too far and making contact with the valance.

I tweaked the rear valance a little to get some more room behind the springs and I have a pinion snubber which I'm going to install.

Anyone else have this issue or have any suggestions?

Thanks.

[brads70]

Maybe a spring clamp would help?

[KillerBee]

Maybe a spring clamp would help?

Was thinking about that too.

I didn't remove any clamps and adding ones in the rear might change how the springs work.

Back in the day with SS springs we removed the rear clamps and added an extra one in front of the axle.

[brads70]

Was thinking about that too.

I didn't remove any clamps and adding ones in the rear might change how the springs work.

Back in the day with SS springs we removed the rear clamps and added an extra one in front of the axle.

That is true, its usually added to the front segment ? Maybe a pinion snubber would limit travel enough to prevent this?

[1 Wild R/T]

You don't want a true clamp, you want a guide clamp which is loose allowing the spring to work but locating the leafs.... Obviously there was never one there cause to keep this type clamp in place  there would be a hole in the end of the leaf for a locating pin to poke through.... 

[mopar jack]

The next segment of springs should have a clamp. It's about 10 inches in front of the section in your pic. It shouldn't allow the springs to separate very far.

[KillerBee]

Yes the next segment up has a clamp.

Since I already have one sitting around, I'm going to install a snubber.

[burdar]

I think it's a combination of the SS springs having a lot of arch to them AND the fact that their design is meant to let the rear segments separate during launch.  The SS springs are heavily clamped on the front to act as a solid piece of metal.  This makes the rear section separate more.

What would happen if you trimmed the end of that spring segment?  You could trim it maybe within 1/8" of the plastic insulator tab.  Would that be short enough to not grab the valance?  I doubt that small of a trim would affect anything. 

[KillerBee]

I think it's a combination of the SS springs having a lot of arch to them AND the fact that their design is meant to let the rear segments separate during launch.  The SS springs are heavily clamped on the front to act as a solid piece of metal.  This makes the rear section separate more.

What would happen if you trimmed the end of that spring segment?  You could trim it maybe within 1/8" of the plastic insulator tab.  Would that be short enough to not grab the valance?  I doubt that small of a trim would affect anything.

That's a good option to consider.

I was able to gently pull the area of the rear valance out and away from the back of the leaf spring so there is a fair amount of clearance there now.

I'll try the snubber and see what happens.

I really have to power shift the car super hard to get the springs to separate to the point of this happening so I don't anticipate this happening too often

[Aracer]

Here's what I know that can help anyone.

In 1983, I used a hose clamp on the rear segment to keep separation from happening again. I had removed one of the rear clamps. The guys at the track helped lift the 1974 cuda's back so it would un-clamp from the valance. I have since perfected the valance and reinstalled it.
    The pinion snubber will cause the rear to separate more at the back. It's a lever and it pry's the housing away from the floor pad.
    On my A body, I use the passenger side SS leafs instead, to give me strength in the front of the leaf pack. I've had to remove the middle clamp to clear the tires on an A body cuda. I also tried turning the half leaf around to the back, but it seemed to flatten up front.
   You might try turning the lowest leaf toward the front to help braking with those SS Drivers sides set. CalTrack also makes a cheap set of stock looking leaf clamps.
     I did not like the SS difference in tire placement. The pass. tire was to the front and the drivers side burned the rear of the well edge with big slicks. A difference of  almost 2". That puts the axles askew and pointed to the left, so it goes straight with a real SS engine.
     I use those new front hangars with the 2 holes to help lower the back of the A body and use 4* Caltrc pinion angle plates, the cheapest and the best angle HD part. I use 28" tall 235/70-15 and this gives 3" to the top of the inside well, and no chance of the sidewall getting clipped. 8" wide Welds with 4.5" BS. My #2 front clamps may now be replaced, if I don't put those 29"x10" slicks back on with a 7/16" spacer for the leaf clearance.
     On my 74 I have +2" identical leaf sets, Dr D, 1"offset / B body housing. I tried those Mopar 440 cuda replacement leafs but after 3 months they inverted so much the rear shackles touched the inside of the valance. They are garbage and wont work even if you want the car low riding, the rear of the spring taps the valance.
   

[Chryco Psycho]

Well the springs are working well , the snubber will not make you happy or really help as you are still effectively stiffening the front & causing the rear to separate , I would trim off the second leaf & let the springs work

[brads70]

Is that rear shackle the stock length?  Just thinking if it was shorter would that help? 

[KillerBee]

Thanks for the advice guys.

The rear shackles are the original stock ones and don't appear very long.

I'm going to drive it and if it happens again I'll trim the rear of the leaf springs.

[Chryco Psycho]

It will happen again , the tires are getting traction & the springs are working well , they will dan out at the back as it wraps up

[KillerBee]

I pulled the valance away from the back of the springs a fair amount and I set the rev limiter to 3500 rpm