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Old 07-08-2018, 03:56 PM   #1 (permalink)
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Shackle angles Leaf Springs Question

Hi Folks
I have been trying to sort out leaf springs and shackle angles from various threads on this fine site.

Would it be accuarate to say that if the movement of the axle and spring causes the shackle to move forwards then you get more traction on the obstacle but a harsher ride on roads?
If the shackle moves rearwards, then you get a smoother ride over bumps?

Context is the very harsh ride of my 1989 Ford E 350 Born Free "President" converted to 4WD. The front suspension is flat leaf with shackles on the rear leaf eyes at 90 degrees.
Since any movement of the axle in response to a bump or a drop will bring the eyes closer together, the rear location of the shackle causes the shackle to move forwards and push the wheel against the obstacle.

At the base of my post is the thought of swapping the fixed and shackle positions on my front leaves to get a cushier ride on most roads, assuming I am understanding leaf spring and shackle physics correctly.

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Old 07-08-2018, 05:30 PM   #2 (permalink)
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The shackle should be at and angle at ride height. Maybe 15 or 20 *. The 90* shackle will cause harsh, pogo stick like ride quality.
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Old 07-08-2018, 07:18 PM   #3 (permalink)
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The shackle should be at and angle at ride height. Maybe 15 or 20 *. The 90* shackle will cause harsh, pogo stick like ride quality.
There is no magic shackle angle, it has everything to do with how much arch the spring has.

With flat springs, all your up travel is negative arch and a 90* shackle in theory work work best. On the other hand, that goes against all rules of proper leaf spring set up.
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Old 07-09-2018, 10:07 AM   #4 (permalink)
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The Born Free I looked at also had a panhard bar that while helping the steering, is putting the leafs in a bind.
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Old 07-09-2018, 10:47 AM   #5 (permalink)
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Quote:
Originally Posted by DuRolf View Post
Hi Folks
I have been trying to sort out leaf springs and shackle angles from various threads on this fine site.

Would it be accuarate to say that if the movement of the axle and spring causes the shackle to move forwards then you get more traction on the obstacle but a harsher ride on roads?
If the shackle moves rearwards, then you get a smoother ride over bumps?

Context is the very harsh ride of my 1989 Ford E 350 Born Free "President" converted to 4WD. The front suspension is flat leaf with shackles on the rear leaf eyes at 90 degrees.
Since any movement of the axle in response to a bump or a drop will bring the eyes closer together, the rear location of the shackle causes the shackle to move forwards and push the wheel against the obstacle.

At the base of my post is the thought of swapping the fixed and shackle positions on my front leaves to get a cushier ride on most roads, assuming I am understanding leaf spring and shackle physics correctly.

regards

Rolf


7.3 IDIT - C6 - NP205 - GV - 3.54 - 285/75 R16 Dia 32.60 in
Hypermax turbo. Cold air intake kit just installed. Fuel screw turned up 1 1/2 flats. Much nicer in the Colorado mountains!
From the way you describe your setup your leaves are flat and your shackle angle is roughly 90 degrees. Your setup will allow the wheel to travel up and down without it moving forward or rearward movement for a good range of motion. Swapping from a rear to a front mounted shackle will not change your ride quality enough to notice. Try taking some air out of your tires.
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Old 07-09-2018, 01:49 PM   #6 (permalink)
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Thanks for the quick replies.
Too Tall, if a flat spring is pushed up or pulled down, won't that bring the eyes closer together? Doesn't the shackle have to move with any vertical displacement of the axle?
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Old 07-09-2018, 02:21 PM   #7 (permalink)
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Slightly but practicaly irrelivant amount.

At 90* on a flat spring youre not cycling enough on the road to warrent any amount of change. Almost all stock vehicles have a 90* shackle angle.

You will greatly improve your droop or compression by moving the top shackle hanger forwards about 1". Youll notcie a bit softer ride but load handling and drivability suffers as you move the shackle further over the spring.
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Old 07-09-2018, 06:21 PM   #8 (permalink)
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Never said there was a magic shackle angle.

Carry on.
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Old 07-10-2018, 12:39 PM   #9 (permalink)
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The front suspension is flat leaf with shackles on the rear leaf eyes at 90 degrees.
Lets see these 'flat' leafs.... are we talking about 6-7 leaf packs as found under a 1stgen CTD, or super stiff 2-leaf TTB packs? A basic F350 leaf rides better than either.

IMHO, some of these conversion companies make crappy design compromises.
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Old 07-10-2018, 01:11 PM   #10 (permalink)
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If that rig rides stiff it's because your stock springs are shit, pretty much all stock springs are .

Front shackles are better for crawling/climbing off road stuff like you said, shackle at rear drives straighter down the highway with less wander, that being said, if you rig is heavy, it's unlikely you will notice much difference in highway driveability either way .

I run my shackles with a little bit of angle to them, just enough to where they are not straight up and down, and not so much to where they run out of travel, it's pretty simple, don't over think it .
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Old 07-10-2018, 01:47 PM   #11 (permalink)
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If you really want to overthink shackle angle, then use them to 'fine tune' your leaf spring rate. 90* is basically as stiff as you can get, less gives lower effective spring rate. Get your actual spring pack rate to a point where you are happy with it and if you need a little softer, lay the shackle back a bit.
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Old 07-11-2018, 08:38 PM   #12 (permalink)
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Here are some views of my front suspension. I was wrong, the shackle is very slightly rearward of 90 degrees.
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Old 07-11-2018, 08:44 PM   #13 (permalink)
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looks like a flat spring and a very short shackle. a longer shackle is better if you can fit it.
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Old 07-11-2018, 08:50 PM   #14 (permalink)
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Here is a side view of the shackle
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Old 07-11-2018, 08:50 PM   #15 (permalink)
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And a view with the shock
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Old 07-11-2018, 08:56 PM   #16 (permalink)
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What do you think of taking out the one inch lift, and the smallest leaf, and putting on a two inch longer shackle.
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Old 07-11-2018, 08:59 PM   #17 (permalink)
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This is my rig
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Old 07-11-2018, 09:01 PM   #18 (permalink)
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Quote:
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If you really want to overthink shackle angle, then use them to 'fine tune' your leaf spring rate. 90* is basically as stiff as you can get, less gives lower effective spring rate. Get your actual spring pack rate to a point where you are happy with it and if you need a little softer, lay the shackle back a bit.
None of this really applies when all your travel is negative arch since the shackle isn't moving rearward on compression.


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What do you think of taking out the one inch lift, and the smallest leaf, and putting on a two inch longer shackle.
You *might* gain a slightly softer ride, but you're really just polishing a turd. They are already clapped out and negative at ride height.
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Old 07-11-2018, 09:09 PM   #19 (permalink)
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What would be the best way to get a softer ride? Coils and A arms, if I had the money or the expertise. But how about given the leaf spring mounts as they are? Is there anything I can do that won't break the bank?
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Old 07-11-2018, 09:39 PM   #20 (permalink)
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What do you think of taking out the one inch lift, and the smallest leaf, and putting on a two inch longer shackle.
Those look like my old sacked-out W250(cummins) springs.

I would find some fresh, factory-style, F350 leafs and go from there.
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Old 07-11-2018, 10:14 PM   #21 (permalink)
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None of this really applies when all your travel is negative arch since the shackle isn't moving rearward on compression.
well that was more to go along with the whole line of overthinking and going to a purpose built spring pack and relocating the hangers

even if the shackle is moving forward on compression it would still be getting softer away from 90*, like was stated several posts up it isn't a ton of movement. I was just piling on to the splitting hairs concept
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Old 07-12-2018, 04:32 PM   #22 (permalink)
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Those springs are inverted not flat.
That shackle angle is good.
Lose the lift block and get some alcans made.
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Old 07-12-2018, 05:16 PM   #23 (permalink)
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If you screw with shackle length you might be throwing you caster and driveline angles out of whack. Best solution is new springs . Someone who makes nice riding springs like Alcan, Deaver or National spring. Then you may be able to get an longer shackle on there to utilize the additional wheel travel if they have more arch. Like mentioned before shackle length and angle will be determined by the spring profile. Most trucks with flat or reverse arch spring ride rough as shit.
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Old 07-12-2018, 09:04 PM   #24 (permalink)
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I have been looking at the suspension of lots of F 250s and F 350s with leaf springs, and they all seem to have bowed / concave-up springs with shackles that move rearwards upon upwards movement of the axle.

Would Alcan Deaver or National be able to take all the dimensions I have;
- horizontal distance of forward eye to frame mount of shackle
- weight on front axle
- vertical distance from axle to eyes
and come up with a spring - shackle combo to give a soft ride? Do they crunch numbers like this?
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Old 07-12-2018, 09:12 PM   #25 (permalink)
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