Shackle forward or shackle rearward

[Slim-Whitey]

So as much as my SAS has been put on the back burner while I set up a shop and gather stuff for a much more extensive swap than welding in a crossmember and 4 hangers, this question still makes me think.

In the 70s, leafs were the way to go in the truck world, and the makes were split on shackle placement on the front axle.
Dodge, Jeep/AMC, and International ran forward shackle. Ford ran a funky reverse mounted front as I recall,and chev ran rear.

By the early 90s, as leafs were beginning to be phased out, Dodge had gone rearward like chev, and Jeep's YJ still ran forward.

There's a ton of debate over placement, with alot of folks saying rearward is better. I've always liked forward shackles, predominantly because of the way the geometry works during upward oscillation. As the axle moves up it moves forward, allowing the driveshaft slipyoke to compress less. Obviously that isn't helping you during droop, but there aren't many times I'm airing my truck anyway.

So what say you? What's superior, forward or rearward?

 

[AssBurns]

So as much as my SAS has been put on the back burner while I set up a shop and gather stuff for a much more extensive swap than welding in a crossmember and 4 hangers, this question still makes me think.

In the 70s, leafs were the way to go in the truck world, and the makes were split on shackle placement on the front axle.
Dodge, Jeep/AMC, and International ran forward shackle. Ford ran a funky reverse mounted front as I recall,and chev ran rear.

By the early 90s, as leafs were beginning to be phased out, Dodge had gone rearward like chev, and Jeep's YJ still ran forward.

There's a ton of debate over placement, with alot of folks saying rearward is better. I've always liked forward shackles, predominantly because of the way the geometry works during upward oscillation. As the axle moves up it moves forward, allowing the driveshaft slipyoke to compress less. Obviously that isn't helping you during droop, but there aren't many times I'm airing my truck anyway.

So what say you? What's superior, forward or rearward?

I’d think forward shackles would be better. I wouldn’t want to slam on the brakes and have all that dive. (Both from shackle movement and suspension geometry.)
It’s also easier to get a lower ride height by frenching the rear pivot up into the frame and having the front shackle mounted on a higher point on the frame.

 

[Rockdawg84]

Both can be made to work but there are some things to take into account when running a leaf on the front of your rig.

Shackle forward:
Pro's:
1. when climbing an obstacle, the tire is forced into the rock and that can be an advantage.
2. Pinion angle is easier to set.
3.

Con's:
1. the Shackle sticks out both further and lower and can be driven into obstacles making climbing more difficult
2. The ride sucks
3. when there is a lot of flex the front driveshaft needs even longer splines as under articulation the axle moves forward and can create problem.


Shackle Rearward:
Pro's:
1. The ride is much smoother as the tire hits and moves back and away from hits.
2. the front hanger is higher and less likely to hit.
3. allows a shorter spline on the front drive shaft. Still needs to be long if there is a lot of articulation.

Con's:
1. there can be more bouncing while climbing, the tire will compress and push back and away from the obstacle.
2. pinion angle can be difficult to set with larger lifts.
3. Axle wrap can be a problem when spring over axle.

from personal experience I have wheeled with a lot of guys who own Jeep YJ's (shackle forward) and unless they were running massive tires the con's outweighed the pro's. I used to own a 85 4Runner (shackle rearward) and it climbed amazing. My 1996 F350 came from the factory shackle forward and I have installed a shackle reversal kit and the ride it sooooo much better. And when it comes to the rocks I will take an 84/85 4runner over a YJ any day of the week. Granted all the con's can be overcome no matter which you chose.

 

[Slim-Whitey]

Ride quality is helped lots with good shackle angle, I know that.

Too many guys run long ass shackles and end up multiplying the spring rate via shackle angle.

 

[Rockdawg84]

yes shackle angle needs to be at about 45 degrees for not only the best ride but the most usable articulation.

 

[Slim-Whitey]

yes shackle angle needs to be at about 45 degrees for not only the best ride but the most usable articulation.

Makes sense.

The rodeo will likely be shackle forward, just because it's easier to set up, and I don't mind a harsher ride.