Well time to put in our 2 cents on this debate. I’ve read many different opinions on this subject both pro and con. The people on the “pro” side tend to have lifted/modified vehicles, are seriously into off-roading, and see a lot of large rocks when they off road. The people on the “con” side of this issue tend to believe something designed by Toyota could not possibly be improved on, and don’t see a lot of rocks/boulders when off roading, and have never driven a vehicle with a shackle reversal either on or off-road.
The modification we are talking about is commonly known as a “Shackle Reversal”. Simply put, we are changing the front suspension geometry of a leaf sprung Land Cruiser, by swapping the locations of the spring fixed pin, and shackle so that the fixed pin now resides at the front of the spring, and the shackle is at the rear.
First let’s start by saying that like many of you I am a fan of all things Land Cruiser. I believe them to be the best all around off road/utility vehicles ever made. I also however know that compromises are made almost anytime a vehicle is manufactured in order to control production costs, while appealing to the broadest spectrum of potential customers and uses. I recently read a rather lengthy technical argument that basically stated; a shackle reversal is not very effective when used with the flat front OEM springs. I actually agree with this proposition. Let me go one further, unless you are looking to lift your FJ40, you will not realize all of the potential benefits a shackle reversal has to offer. Fortunately for me, the FJ40’s I currently own, do not have the stock springs, and suspension on them. Why “fortunately”? Because in stock form the FJ40 suspension has minimal wheel travel, articulation, load carrying capability, and rides like a buckboard from the 1880’s. I don’t even mind the center arm, as it indeed helps dampen “bump steer”, but let’s face it, the stock FJ40 suspension was O.K. in 1950, quite sub par by 2004 standards.
One of the first things most Land Cruiser owners do to their FJ40’s when they get them, is a suspension lift . Whether to get clearance for larger tires, gain some wheel travel, improve articulation , and improve the ride quality, lifting an FJ40 changes the overall geometry, and that OEM stock shackle set up, with flat stock springs combination goes out the window, and so do the arguments against the shackle reversal. Lifted springs for FJ40’s obviously have an arch to them, even when the weight of the vehicle is on them. Consequently the spring is no longer at its’ longest length when sitting static. Instead as the spring is compressed, and looses its’ arch, it indeed gets longer from eye to eye, which means the axle is moving forward, not to the rear, as would happen with the stock flat spring set up. This increases the load transmitted through the suspension as the wheel moves into the very obstacle it is trying to get away from through suspension compression. Basically instead of the suspension soaking up that bump in the road before it is transmitted through the frame, it ends up transferring the shock into the frame(through that fixed pin at the rear) delivering a jolt instead of a cushion. With a shackle reversal in place this situation is reversed. As the spring compresses/lengthens in reaction to an obstacle, with the fixed pin at the front, the axle and wheel will move to the rear and up, allowing the shock absorber and spring to do what they are designed to, dampen and absorb the impact/movement. As the shackle at the rear is moving freely, it will not transfer rearward motion as a jolt into the frame, as a fixed pin would. This is one of the reasons lifted springs with Shackle Reversals ride better than lifted springs without the S/R. But again in order to make the best use of a S/R, you have to be running lifted springs, and since the better designed S/R units will lift an additional 1-1/2″, you’ll end up in the 3-1/2″ or more range of lift.
Another little bit of physics is easy to test, that being “it is easier to pull a wheel over an obstacle than it is to push it over”. Get a wheelbarrel, or one of those kids toys with wheels, that pop the marbels in the plastic dome, basically anything with a wheel(s) attached to a stick or handle that you can either push or pull. Find an obstacle about 1/2 the diameter of the wheel. The handle at the end, is the fixed pin, and you are the frame. First push the device into the obstacle and over. With the wheelbarrel you’ll find this easiest if you hit the obstacle hard enough to bounce the wheel over. Now turn around and pull the device over the obstacle. There’s the rub, by putting the fulcrum at the front instead of behind it is easier for the wheel to react to the surface changes. No magic, simple physics. This is another reason S/R’s improve the ride quality of the vehicles they are used on.
Next is a rather simple testament in favor of using a S/R out here in the West where we have large rocks(I guess trees would work just as well). Take a look at a vehicle with the standard front shackle set up from the side at bumper level(we’ve provided a picture for you). Kinda looks like a grappling hook doesn’t it? And guess what, it works just like one too. Run into something with this, and if you’re unlucky you’ll bend the top leaf in your spring pack like a pretsel. Yes we’ve seen it. Now look at the same vehicle with a 4+Plus S/R kit on it, and you’ll see a sloped ramp. And that’s what we use them for out here, to help us get up onto boulders and other obstacles, without pretseling our leaf springs. But what about the extra stress on the front non boxed frame channels ?? You mean those frame rails we put big bumpers with winches on to pull us out of those “whoops” situations? Well we’ve never seen a frame damaged because it had a S/R on it, but we’ve seen plenty of springs pretseled because they didn’t.
One last testament to the S/R. When Tracey Jordan and Don Robbins were running Land Cruisers in the ARCA (American Rock Crawler Association) championship series, they both ran modified 4+Plus Shackle Reversal kits, and took 2nd and 8th place in the USA(Traceys’ rig took first in the womens division with his fiancee driving), with no failures from the S/R or frame rails.
In closing, if you’re looking to keep the stock springs on your rig, a S/R will only serve to improve your approach angle, allow you to pull your wheel from the front instead of pushing it from the rear and will provide you little other benefit. If on the other hand you are looking to lift your leaf sprung Land Cruiser, the S/R is a proven performer both on and off road, and offers some impressive improvements in ride quality, handling, and off road ability. Sorry I know that was more than 2 cents.