why on full size do they go up and on smaller vehicles they hang down?

axle wrap? what? answer the question....thanks:D

Search for reverse shackle vs. shackle forward. Its an ongoing argument :flipoff2:

Chris

Probly has to do with compression loads, instead of making the shackle stronger manufactures just flipped the bracketry. Flipping it gives you lift for obvious reasons.

Search for reverse shackle vs. shackle forward. Its an ongoing argument :flipoff2:

Chris

reverse shackles is in front like on a jeep...i'm talking like in the rear of a full sized truck....

I think it has an awful lot to do with desired ride height and with frame/body widths. If you look at the ratio of frame width to body width on a compact versus fullsize you will find it is much different. You can only make a frame so narrow thanks to the tranny, engine, etc. With a fullsize you can run a somewhat narrow frame, outboard the spring mounts, and run a tension style shackle so that your ride height doesn't get out of control. Since the springs mount directly under the frame on most compacts the only option is compression shackles.

As a side note...tension shackles such as on a fullsize minimally do better when loaded because they move back (same as a compression shackle), but also move down. In that way the springs move up relative to the frame while the shackle moves down relative to the frame. The tension shackles are also self centering. Even if they are a little out of plumb the weight will pull them back vertical whereas a compression shackle will be pushed even more out of whack.


Again...those are minor things, but enough minor things might just add up to a good reason for one versus the other. I really don't know why manufacturers do it.

Probly has to do with compression loads, instead of making the shackle stronger manufactures just flipped the bracketry. Flipping it gives you lift for obvious reasons.

This is correct. Okay, how to explain this.....

On a Jeep, the leaf spring eye is lower than the shackle hanger. This is OK because the vehicle isn't designed to haul a load. Under a heavy load the two shackle plates want to bend when compressed. In the case of a full size pick-up where a heavy load is carried, it's a bad idea. So they flip the shackle and then when compressed with heavy loads the two shackle plates want to extend, therefore, not wanting to bend. Yes, welding something between the two shackle plates will help. Jeeps stay with the hanging shackle design because it offers a greater range of motion for the leaf spring and shackle to travel. Plus, with heavy axles and light rigs, the theory of the shackle plates wanting to bend can be put into the reverse order. Usually by that time, most wheelers and their rigs advance to linked suspension to carry the extra loads and strain because of the twisting the suspension has to be put through. (and axle wrap and a whole bunch of reason's not meant for this thread)

I personally believe that they are trying to control axle wrap is an additional reason that on the heavier duty trucks they have the shackles pointing upwards.

From all the stuff that I have looked at on light duty trucks and cars it seems that you get one of two versions of suspension. You either get spring over axle with shackles facing upwards or you get spring under axle with the shackles facing down. The only exception to this is the front end of leaf sprung pickups, but I believe that they are using the negatively arched leaves to help control the axle wrap.

to me you could run a flatter spring and have a better ride if the spring was down...i don't truely see how one way would cause a shackle to want to bend...but i do see with the shackle mounting above you would have a heavier arch with would help axle wrap...

i ask because my brother has a f-250 he tows a 34' toyhauler with and the thing is a bucking bronc without load...my thought was to flip it, run a flat spring (continue to use the airbags) and add ladder bars to control the wrap...seems like that would be the ultimate setup...

Truck's are made to haul more than just groceries.

to me you could run a flatter spring and have a better ride if the spring was down...i don't truely see how one way would cause a shackle to want to bend...but i do see with the shackle mounting above you would have a heavier arch with would help axle wrap...


Grab two soda cans. Put one between your hand(one hand ontop one on bottom) and push your hands together. It will crush easy. Take the second can and put it between your hand but try to pull the can apart.

The way you think is stronger:
Pushing the can together is compression(leaf spring eye below shackle mount)

The stronger way and used on fullsize trucks
Pulling the can apart is tension(leaf spring eye above shackle mount)

Compression is mostly used when the leafs are mounted under the frame. Compression can be used on heavier trucks, it just requires stronger shackles so they don't collapse.:flipoff2:

This is correct. Okay, how to explain this.....

blahblahblah

:flipoff2:

Ok. The <insert fast food joint> answer.

Take your straw.

Pull on each end as hard as you can. Can you tear it apart?

Ok, now take that same straw and try to push in at each end as hard as you can, without collapsing it.

Take that knowledge and stare at the shackles on a vehicle for a little bit and think about it for a while. ;)

:flipoff2:

Ok. The <insert fast food joint> answer.

Take your straw.

Pull on each end as hard as you can. Can you tear it apart?

Ok, now take that same straw and try to push in at each end as hard as you can, without collapsing it.

Take that knowledge and stare at the shackles on a vehicle for a little bit and think about it for a while. ;)

Repost:flipoff2:

Repost:flipoff2:

You too :flipoff2::laughing:

[little kid voice on] I said it first, I said it first, I said it first [little kid voice off]:laughing:

Although the can and straw thing is easy to follow. Thank you gentleman.

Ignoring column theory for a minute, I hope everyone realizes that if the load were plumb on the shackle (similar to the can or straw description) the tension and compression load limits would be the same. The issue is that there are lateral loads. Tension shackles better deal with this because they are naturally going to be driven vertically for the most part. I think that there is probably some other design logic behind the tension shackles besides just weight handling or stability.

I think that there is probably some other design logic behind the tension shackles besides just weight handling or stability.

Doubt it. Go back 2-3 generations and you'de probably find some guys prototyping a truck. Loaded it with 1,000lbs of cargo and had the shackles crumple up like a paperbag.

And like you said, there are side loads placed on those shackles as well. Apply the straw theory again, and you'll see why the shackle goes up and not down.

the real question I have is, at what point does this become a problem. My half ton is shackle up, my jeep shackle down. Grand wagoneer (~1/2 ton) is shackle up in back and down in front.

Truck's are made to haul more than just groceries.

wow you are F-N deep...thanks for the input:shaking:

Doubt it. Go back 2-3 generations and you'de probably find some guys prototyping a truck. Loaded it with 1,000lbs of cargo and had the shackles crumple up like a paperbag.

And like you said, there are side loads placed on those shackles as well. Apply the straw theory again, and you'll see why the shackle goes up and not down.



A side load on a shackle in tension will not do the straw any favors either. On a perfectly level road the tension shackles might be more stable, but on a crowned road both will be side loaded. I don't disagree that the tension shackles are probably a little stronger, but for all the steel they use to make the mounts they could make some beef compression shackles and have less riveting and bracketry to deal with. Like I said...I think there is more to it than just pure brute strength.

I think we need a retired 80 year old automotive engineer.

A side load on a shackle in tension will not do the straw any favors either.

Yes, but when a shackle is under tension, it is going to want to straighten itself out to verticle.

When a shackle is under compression, it's going to be more likely for it to fold over before straightening out.

okay here is my question and i could be completely wrong but a compresion shackle under heavy load is going to kick back deflecting the load and putting tension on the shackle...i only see it bending and/or failing if the shackle is not able to move...

okay here is my question and i could be completely wrong but a compresion shackle under heavy load is going to kick back deflecting the load and putting tension on the shackle...i only see it bending and/or failing if the shackle is not able to move...

With a flat spring the shackle will kick inward towards the center of the leaf spring during compression and droop.

With a positive arch spring the shackle will kick outward during compression and inward during droop.

The shackle on a compression setup should always be setup outward at ride height to work right.

The setup your wanting to do on your buddies truck can work, just don't expect the stock shackle to last very long hauling weight or wheeling. The problem of failure is mostly in the shackles design and material thickness. Run a DIY shackle and move the bracket to give it the right angle and it will work like your thinking.

thank for all the replies...

Just to clear it up further....a compression shackle will be under compression as long as the springs are at their free arch height or compressed further. Even if the shackle inverts (moves forward) with a flat spring the shackle is still loaded in compression. The only time it will see a tension load is under droop beyond the free arch height of the spring.

As for a tension shackle wanting to self center...I agree for the most part, but if the truck is on a sidehill it will be side loaded as the truck will act a big like a pendulum. It really is a miniscule thing. I think the shackle bushings would fail or atleast be damaged severely before the shackle is going to bend. Nevertheless...they are not free of side loads.