Axle Flip vs. De-arch Springs

[matt2491]

Can't decide whether to flip the rear axle or de-arch the leaf springs in my '64 F100. I'd like about a 5" drop, which the axle flip would overshoot by about an inch. Yet de-arching the springs will make them flat across or even slightly negative arched with the truck sitting on it. I guess my question is: Which way would ride better? Does the amount of arch in the leaf spring affect ride quality?

[Alan Mclennan]

I`d go with flipping the spring mounts

[Hunter's 64]

https://www.performanceonline.com/1948- ... pring-set/

Not sure what your budget is but this is a nice option they have a 5" drop 5 leaf .


Danny

[The Big M]

The spring rate of a leaf spring is based on the material properties, width, thickness, length, and number of leaves, but is independent of the amount of arch (I just took a look through my machine design textbook to confirm). So in theory a spring with a stock arch would have the same stiffness as one with a lower arch, provided the change in length isn't significant. In practice one would have to pay extra attention to axle clearance and shackle geometry to prevent bottoming out or binding, of course, which would affect ride quality.

I'm really not sure if a flat or reverse arch would behave any differently than a "positive" arch. I would think it would just want to return to a flat state, but I don't have any personal experience with that kind of setup. I've seen a few show trucks running them, but who knows if they see any street time.

If you went with the axle flip you could always add some arch to lift it back up if need be.

[matt2491]

Thanks all. Big M, your reply is very helpful. I think I will go with flipping the axle over the springs, and potentially adding an inch or so more arch to them so I don't get the full amount of drop typically associated with an axle flip. Of course, more arch will bring the spring eyes closer together, which I'm assuming will firm up the ride? Just how much the ride changes between having flat springs and springs with 6 or 7" of arch is the real question! May be insignificant, or may actually be noticeable. Hard to even guess. I just want this truck to ride nicely.

With the springs under the axle, that will grant me the space to run shocks outboard the frame rails, closer to the wheels. Do you think relocating the shocks will have a positive impact on how the truck rides/handles? Most modern trucks have outboard shocks now.

[LM14]

The spring rate is only correct as long as the spring has arc to it and they have the same shackle angle as designed. If I remember correctly, once the spring flattens out or goes reverse arc, the rate decreases drastically because it changes shackle angles. Arc doesn't effect free spring rate but it does effect loaded spring rate because of the angles of the shackle. Less shackle angle = stiffer spring rate when loaded. If the arc change changes the shackle angle, it will change the effective stiffness of the spring.

With the race cars we had with leaf springs, once the arc dropped 1" from stock the spring was junk and the chassis quit working. New spring and chassis worked again. Most guys running leaf springs in race cars (dirt circle track) are changing springs every 4 to 8 nights depending on the track condition.

My '66 was de-arched and rode fine. I hauled a bit of stuff in it but it started sagging worse the further the spring went over center. The ride totally changed.

SPark

[The Big M]

^Good point regarding the effective rate. The actual rate of the spring won't change but depending on the shackle angle the wheel may deflect more than the spring or vice versa. Those dirt track racers really know their stuff.

Alan, does that flipped hanger trick work for 61-64?

[CTom]

I have in the past, reversed the eye on front and rear springs. I make sure the arc of the main spring is the same as it was when it was disassembled. You can get a few inches and keep the old ride. I like to remove a few leafs to get a softer ride. A longer shackle in the rear will get you lower also.

[Alan Mclennan]

[quote="The Big M Alan, does that flipped hanger trick work for 61-64?[/quote]

BIGGY, I can`t say for sure, but I can`t see why not ( rear only ), I haven`t driven on it yet, Ezer has done it and if he ever comes back here , I`m sure he`ll let us know mate!

[The Big M]

Thanks Alan, I vaguely remembered someone doing it on a uni but wasn't sure. It was Ezer's that I was thinking of.

[Alan Mclennan]

I also raised the rear mounts up using the top holes for the bottom holes on the mount and bolted the top mount to a heavy angle bracket to the top of the chassis, you can just see them in this pic

[Alan Mclennan]

here`s a better shot of it...