Most leaf-spring Jeeps rolled out of the factory with the front spring shackles hanging on the front of the frame. No one is really sure why they did that, but we say it was just so you can more easily bend your main leaf, and keep the leaf spring companies in business. It's a conspiracy.We are going to concentrate on the movement of the Jeep's suspension when moving forward. This is the motion that your Jeep sees 99.5 percent of the time. Unless, of course, you are Ferris Bueller.
Seriously though, there are some real advantages and disadvantages to a shackle-forward and shackle-reversed setup. We've run our Jeeps both ways, and we'll try to help you through the pros and cons of each. You will still have to decide which way is right for you, and that will depend on how your Jeep is used.
When you hit a bump or rock,...
When you hit a bump or rock, the impact tries to force the front axle rearward. With a shackle reversal, this movement is allowed, resulting in a much smoother ride.
Let's start backwards, so to speak. Most of us are more familiar with the shackles at the front of the spring, so we are going to go through shackle reversal first.
PositivesAs can be seen with our pretty arrows drawn on the blue YJ, as the Jeep is moving forward and encounters an obstacle, the axle is allowed to move in the direction it wants to move. This means you end up with a smoother ride all around.
Off-road, this same movement allows the tires to follow the terrain better. This results in less "float" over washboard roads at speed. Also, either on-road or off, there is more control of the Jeep over numerous smaller bumps. Another nice thing with the shackle reversed is that large bumps won't make you lose quite as many fillings.
NegativesOn-road, the biggest complaint with a shackle reversal is nose diving. Much like a TJ with bad shocks, whenever the brakes are applied, the nose will drop. People who run their shackles reversed just get used to it and frequently don't notice it.
Another negative to the shackle reversal is possible collateral damage. Because the axle is now moving rearward as the suspension compresses, the tires might contact the fender flares or inner fender.
There are a lot of horror stories about putting a shackle reversal on a Jeep only to have the driveshaft push through and explode the transfer case the first time out or separate when the suspension drops out all the way. There is some truth to this. Check your driveshaft travel.
Many Jeeps will require a new, long-travel front driveshaft.On extreme climbs, where the rear axle loses traction, the front axle will start to walk away from the Jeep. This can lead to bent springs and a separated front driveshaft.On extreme descents, the nose diving tendency we talked about earlier could lead to the tail end of the Jeep getting really light.
With the shackle on the front...
With the shackle on the front of the leaf spring, when the Jeep hits an obstacle, the axle is still trying to move rearward but, instead, is forced to move forward and up. This results in a harsher ride when bumps are involved.
Odds are really good that you've got your shackles under your Jeep at the front of the spring. This is, after all, the stock Jeep way of doing things (most of the time).
PositivesThe biggest thing that you get on the road is something you've probably never noticed. That is, your front end doesn't dive whenever you hit the brakes. Sure, the nose dips down a little bit, but it just isn't that noticeable.
Some people cite the axle attempting to move forward under compression as a benefit. Off-road, when beginning a climb, and the front axle is compressing, it is also pushing forward, which can increase contact pressure and help to climb up and over.
You don't have to worry about your driveshaft separating or your front axle walking away from you on extreme hill climbs.
NegativesWith the axle trying to move forward as the Jeep is moving forward, it creates a harsh ride, which can be wearing over washboard or poorly paved roads. It also reacts slower to washboard than a shackle reversal, which results in floating over the bumps at a lower speed.
When encountering a large obstacle at speed, all the force is transmitted directly to the rear of the spring, and your main leaf is more likely to bend than if it were shackle reversed.
Basically, if we were planning on getting wacky off-road with the Jeep, and its primary use was extreme-style rockcrawling, we'd leave it as is. If it's not going to be put into all kinds of goofy angles or it'll be driven on-road (or off-road at speed), we'd put a shackle reversal on it. There is just no comparing the ride quality above 15 mph.