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Discussion Starter · #1 ·
some one told me that the rear leafs from a furd is the same eye to eye distance as a dodge p/u or r/c. if any one has some ford leafs around would you measure the eye to eye center for me and possibly compare it to yer dodge. id do this all myself, but im in the middle of the freakin desert. :mad: im comin home soon, and i gotta build another truck...ringo
 

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Dodge rear springs measure 51" long, 24" from the front eye to the center pin.

I don't know about all Fords, but some Ford rear springs are real popular for use in flexible shackle flips. They mearsure 57" longs, 24.5" from the front eye to the center pins. I'm not sure which Ford application these are from though.
 

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I measured some off a early 90's ford f350, and they were the same measurements mentioned. I was looking at them cuz the rear hanger buckets are made better than the dodge ones....they actually let the shackle move more without contact.
 

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Discussion Starter · #4 ·
do the furds use a block like ma mopar did? cuz if a guy were to flip his dodge shackles, or like you say, use the ford ones, might be able to get rid of block in back.
 

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Furds used blocks too.

Ed
 

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Yeah, they did.

The advantage of the ford (or even chevy) rear hangars is the dodge one only allow roughly 60 degrees of shackle movement before the shackle or spring will hit the side ribs on the hanger (the side ribs go out away from the frame).

The ford/chevy ones will allow 180 + deg of movement (the side ribs go front to rear along the frame).

You can also use the ford/chevy front hangers, as they mount in such a way as to hang lower below the frame, which can lower the spring enough to get rid of the block and NOT flip the shackle.

I have done some talking about the shackle flip to an engineer, and some common sense thinking, and I personally won't be flipping it. It has benefits, but you actually lose some wheel travel when doing it. I have come up with another way to gain the same benefits, but not lose wheel travel by mounting it still in the upward orientation, but rotating the rear hangar a bit.If you want me to explain, I will, but not here...it would take too long to type it all in. Basically, for the axle to drop, the shackle spring eye has to be able to drop, and it can drop no more than it already is when flipped upside down. The only way to gain more drop, is for the spring to flex, and even then, it won't gie you much.

I know many of you have done it, and that is why I can't figure out (neither can the engineer) how you claim it gives you more axle movement.
 

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Mark, no comment on the engineer ;D, but not everything can be totally anyalyzed mentally. I call that mental mastubation. Then again, I am an ME so I guess I can say that.

The compression shackle (shackle flip) has a lot of advantages and disadvantages compared to a tension shackle (stock shackle).

The stock tension shackle is best suited for high load capacity, and minimal wheel travel. The compression shackle is best suited for smooth ride, and increased wheel travel. Now, that doesn't mean that either style can't excell at either job function, but the basic design lends its self for certain jobs.

But lets try a little "mental masturbation" here if you'd like.

On a stock tension shackle, the nominal shackle position is straight up. As the suspension droops, it swings forward and allows for decent droop. But the eye-eye length of the spring must shorten dramactically for the shackle to swing it's full potential. On compression, the shackle swings rearward. In this rearward swing, the spring eye must also move down, directly opposite of the load and axle movement. This tends to artificially stiffen the spring rate of the system. The shackle length and spring arch will both greatly affect these results.

On a compression shackle, the nominal shackle angle is NOT straight up and down. At regular ride height, the shackle should be angled rearward, probably about 30-40 degrees from vertical. This allows significant shackle movement forward and down for shackle droop. On compression, the shackle swings rearward and up, WITH the load and axle movement. This tends to soften the suspension and greatly increase upward axle travel and soften the ride. This is why shackle flips are often not recommended for heavy towing. Again, shackle length and spring arch will greatly affect these actions.

As a rule, a few things can be done to increase axle flex:
Use
  • a shackle flip
  • longer springs
  • softer springs
  • longer shackles
  • proper shackle angle

I've tried to integrate all of these in the rear suspension on my RC. I used Mrpeals shackle flip (reveresed side to side), 56" GM springs, and custom 8" shackles.

The results:

This is approximatly at regular ride height (only pic I could find):


Compression:


Droop:


Works pretty well:
 

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I agree with the ride qualities, but if you use a stock length shackle & springs on your truck, you will loose a significant amount of your axle drop, or sacrifice compression to gain axle drop.

Yer way (compression shackle), on your truck, for max axle drop, the shackle swings down and towards the bottom of it's arc of travel. You also need to compress the spring once the shackle eye passes the bottom of it's arc. Once the eye is past the bottom of the arc, it begins to move upward, and the only axle drop you have past that point is due to spring flex. So, once the shackle is past the lowest point of it's arc of travel, it begins to negate the drop of the axle by moving upwards (just like you mentioned the tension shackle moving the opposite direction of the load in your post). In other words, if the spring did not compress, once the shackle was past it's lowest point of travel, it would actually start to raise the axle, not drop it (granted, this would not happen as the physics of it would be offset). Look at the pic of your truck on the rti ramp. What's the position of the rear shackle...straight down at max droop. This being said, the max I would expect to see the shackle move forward in a compression shackle set up would be roughly 5 deg past straight down, as past this point, it would be lifting, not dropping the spring eye. The only reason it will move past straight down, is the spring compression.

Where as with a tension shackle, the shackle eye drops as it travels along it's arc (which drops the axle), and the spring is compressed (which also drops the axle), there is never a point at which the shackle eye begins to try and lift the spring eye, and as long as the shackle has a free arc swing, it will continue to swing down until it gets to roughly 45 deg below horizontal, or max droop. So, yes, the spring does compress as the shackle eye moves from straight up to horizontal, but it gives you a lot more drop of the axle for the same swing of the shackle (again, I'm talking stock shackles here), and does the spring really compress any more than the compresion shackle spring does once the shackle eye has passed the bottom of it's arc ??


Let's assume that the spring hanger has no obstructions that will prevent the shackle from going to horizontal, even tho we know it does. Let's assume this because your hanger has no such obstruction.

Ok. With the setup you have on your truck, the MAX drop you can have is the result of the shackle moving 90 deg (from horizontal to straight down), since after that, it begins to lift the spring eye, and that is if you have it straight back at rest (which gives you no upward travel due to the shackle eye binding on the spring itself).

On a tension shackle setup, the max drop you can have is when the shackle moves from straight up to horizontal, and depending on the orientation of the hanger, you maybe able to go past horizontal to gain more than 90 deg of arc travel (up to as much as 135 deg of arc swing), which equates to more down travel of the axle. The only draw back, is you need to make some kind of stop so the shackle does not move to straight down at max droop, but instead rotates back up.

Ok, on the set up you have, the max upward travel of the axle would be if the shackle was straight down at rest, and swung up to horizontal, or 90 deg. If you are set up this way, you have at best 5 deg of arc swing for downward travel, and 90 deg for upward travel.

On a stock tension set up, you have roughly 85 deg of arc swing max that will give upward travel before the spring binds on the shackle, and this also gives roughly 135 deg of downward arc swing capability.

I'm thinking I would prefer the latter.

The reason you have so much wheel travel in the pic on the rti ramp, is 1) longer shackles, 2) longer springs, and 3) you don't have the mechanical limits imposed by the way dodge made the rear spring hangers (I'm talking about the fact that the shackle can not physically move more than roughly 105 deg TOTAL, because the side ribs interfere with the shackle rotation). If I take and put the ford hangers on my truck rear only), which have no limits on shackle arc swing inherent in their design, and still have the tension setup, I will have just as much or more travel than your truck, for the same length shackle & spring.

Looking at your truck in the pic, you have roughly 70 deg of shackle swing arc that will result in upward axle movement, and roughly 25 deg of shackle swing arc that will give axle droop. AND if you look at the pic, when you are at MAX axle drop, the rear shackle is straight down, which further emphasizes my point about limiting axle drop. The majority of your greater axle drop is due to the longer shackle and longer springs. Yes it works, and works well, but it is more from other things than the shackle flip.

If I used the same shackles and springs as you did, on a tension set up that allows 215 deg of shackle swing, I will have much more drop AND upward travel on my rear axle. The best of both worlds so to speak.

This may be mental masturbation, but I have made actual models that agree with what I am saying (does that make it physical masturbation now ??? lol). Yes, it will still have some rough ride issues, but I'll trade them for increased travel both up and down any day.

I plan on using a ford/chevy rear hanger, which will allow almost 220 deg of arc swing on the shackle, and rotating it roughly 15 deg from horizontal, so that the front of it is lower than the rear. I am doing it this way cuz I want to limit upward travel (tire-body issues) and increase the axle droop possible. I will make a mechanical stop to prevent the shackle from moving past 45 deg from horizontal downward, so it won't be able to lock down.

I will also probably lower both the front and rear hangers enough to remove the factory block by also using the front hanger from the same vehicle.

Don't get me wrong, I am not saying your set up doesn't work well, I am just saying, these are my thoughts on why I am not going to do the shackle flip, and why I think the dodge engineers that designed it, used a tension set up. You have the best of both upward & downward rear axle movement, where as the compression set up gives up some downward movement, in exchange for easier upward movement (softer ride).

 

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This is where mental masturbation gets you. I can tell you've put a lot of thought into this, and no amount of proof will change your mind. You have made a lot of assumptions, and ignored certain variables. I never said my setup was ideal, infact the shocks are limiting droop right now, and I have plans to tune and improve the system.

For example, a major variable that you are ignoring is spring arch. The springs I used are very flat. That means they are very flexible, but total spring length changes very little from ride height to full compression or droop. My shackle has far more "swing" room available than it is using. In fact, at full compression, the spring flattens and goes into negative arch and the shackle starts swing forward again. At full droop, the shackle still isn't vertical, which might mean I have the mount too far forward. But, since the springs are so flat, I should actually move the mount forward more and use more of the shackles vertical motion, and less of the horzontal. This will change the ride height of the truck, making it sit lower in the rear, it's already a little low. I already have 2" blocks in the rear, and with such soft springs, I don't want taller blocks, so maybe I need to buy springs with a few more inches of arch. Then maybe my shackle mount location might work better since the deeper arched springs will change length more during flex than the flatter springs. Spring arch alters the setup greatly, and with tension shackles, you normally need much deeper arched springs for the same ride height. So you'll have to have more shackle movement for that reason alone.

Like I said, I can tell that your mind is set, so more disscussion is pointless. Build your system, then show us.
 

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My mind isn't set, but I have had this discussion with several others, and they all seem agree after all the conditions and variables have been presented. BTW, the engineer is also a mech engineer. I didn't tell him my thoughts, but gave him two diagrams, and asked him to figure out which one was best OVERALL for suspension travel. He did say they both had good and bad points, but agreed with me, without me telling him my ideas that the tension set up was the best compromise.

I am trying to see/understand how the shackle flip ALONE gives you improvements in both compression and droop. I see how it helps in the compression arena, but it's the droop arena that is hard to swallow.

Your truck works great, while it may not be ideal for what you want yet (your own admission). I'd venture to say that the biggest factor in your excellent axle droop is the longer, flat springs, but the shackles help too.

I am not knocking what you or the other people have done one bit, I am just trying to understand how it is better in ALL cases as everyone seems to claim it is. It's just that the ones who claim it is better, did more than just flip the shackles.

I was just trying to point out that you have done a lot more to your truck than just flip the shackle.

If someone just flips the shackle and nothing more, then they should/will actually lose travel...that's what I am saying. You made up for the loss by using longer springs and shackles.

True, I did not account for spring arch, but a flatter spring will give you a greater change in spring arch for the same change in eye to eye dimensions (not spring length--that is constant). This means the axle will be pushed down more (forcing more droop) for the same eye to eye dimensional change. And since the eye to eye dimensional change requires the shackle to move forward, a flat spring will actually give you better droop, as the change in arc of a flat spring is much greater (initially, but will become the same as the arcs become closer to the same) for a given change in eye to eye length than a pre-arched spring of the same initial eye to eye length.

This is also why a flatter spring will give you a softer ride. Because it takes less energy to bow a flat spring up or down, than it does a pre-arched spring.

If the spring is flat, and the eye to eye dimension is lets say, 57", then when the spring is forced to flex, that eye to eye dimension will shorten to lets say, 55.5". Ok, now something has to take up that 1.5" change,and the shackle does this. But, for this shackle to take up this change in length, the shackle has to be able to move in enough of an arc so that the horizontal vector of the change is equal to 1.5". On 6" shackle this is gonna be around 25 deg or so. Now, for that 1.5" change in length, the spring arch changed by a given amount. On a heavily arched spring, the same change in eye to eye length will result in the same swing of the shackle to take up for it. BUT, the percentage of the change of the arch of the spring will not be as much.

The first couple of inches of eye to eye length change will have a very pronounced effect on the arch of a flat spring, but not on a heavily arched spring. Just like the first 45 degrees of shackle swing from 90 deg to 180 deg is a much greater change in the horizontal vector of it's motion than the last 45 deg is.

I know you are an engineer, but I deal in simple examples, so please don't be offended, I'm not trying to offend you, just explain an idea as simply as I can. Take a flat piece of any material, and lay it down on the table. Now, shorten it's length from end to end by bending it like a spring. Notice how much the material bows out from this change in length. Write down the change in overall length as a ratio of {original length minus final length} over change in arc. Now, using that same peice of material, start with it bowed out already, but shorten the length by the same amount. Now, write it down the same way (ratio of {original length--with bow--minus final length} over change in arc--not total arc). The second number will be smaller than the first. Just like it is easier to take a peice of metal rod that is already bent and bend it more, than it is to start a straight piece of metal bending, if you are only pushing on the ends as if to shorten it in both cases. Some of this is due to the torque angle you are pushing on and other factors (like it's harder to START a car moving when pushing it than it is to keep it moving) but a good portion of it is due to the fact that for a given length of change in the horizontal vector, the vertical vector does not change as much, until you get to that magical point, when it stops bowing out, and the rod ends start to come together, and the arc or bow actually starts to shorten, or move back in.

Have you ever noticed that when you are driving up a rolling hill, with a constant throttle position, the car seems to slow down as you start going up the hill, but seems to speed up as you get closer to the crest ?? This is because for the first 1/2 of the hills height, the car's vertical motion vector is greater than it's horizontal motion vector, but after that, it's horizontal motion vector is greater than it's vertical motion vector, so for a given throttle postion, the car will speed up as more of it's energy is being used to move horizontally than it is vertically. This change in power vector changes the load on the engine. Hence you slow down initially, then speed up finally. Same for the down hill side...you speed up more the closer you get to the bottom, because the vertical vector increases as the horizontal vector decreases.

This is just like the example with the piece of material above. The shortening of the material length wise results in a greater change in how far it bows out initially, but as the bow increases, the rate of change of the arc lessens for a given change in length, and at a given point (roughly 1/4-1/3 of the total length of the material, not initial length) the bowing stops moving out, and begins to move back in.


So, after this dissertation, yes, I did not account for spring arch, but from where I sit, it appears to me that a flat spring will actually give you more axle drop for the same change in shackle position.

I would like to continue this discussion, and maybe you can show me where my thinking is wrong, but we might should do it somewhere other than here, as this thread has been hijacked in a big way with the discussion. My mind is not made up, and originally, I thought the shackle flip was a great idea, but when I started looking at the physics of it, I began to have doubts. Please, don't give up....show me where I am wrong. Maybe we will both learn something. Maybe just I will, but we won't know if we don't continue.

I do plan on doing the set up I mentioned, and will do a how to on it also, but that is a few months down the road, I think. And to get a fair comparison, I'd have to do the shackle flip, and measure it's results, then do my set up, so a direct comparison would be possible. I don't have that much time, so when I do it, the comparison won't be exact.

PS Man, I just about put my fist thru this puter monitor. After almost 45 minutes of typing and all, just as I hit send, the modem lost it's connection...man was I pissed !!! But, When I logged back on, it had made it here.......time for a new puter me thinks.......lol
 

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Discussion Starter · #11 ·
then again, maybe i'll just go with a coil over. . .might be easier. . .ringo
 
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