SEP/OCT 2010

Stretched FJ40 Revisited

by Ron Baldwin

Those of you with long memories will recall an article in the July/August 2008 issue of Toyota Trails wherein I described a stretching of my FJ40’s wheelbase to 104.5". That modification included the installation of long, limber leaf springs from a full sized Bronco to improve rear wheel travel to a solidly respectable 15".

While the conversion was overall a success with greater stability on and off the highway, I concluded that this type of conversion would be best in a spring over axle (SOA) configuration. To that end, I spent some time doing exactly that: moving the Ford springs over the axle in the rear and putting soft, stock springs over the axle in the front.

Spring over axle conversions have been detailed in Toyota Trails in March 1993, July 1993, September 1993 and more recently in September 2003. Consequently, I will make no attempt to duplicate that work here. Rather, I will give a simple description of what I did and the result of that work in case others are contemplating a similar conversion.

Rear Suspension
When I first installed the Ford springs on my FJ40 in an under the axle configuration, I turned up the spring eyes from a Berlin eye arrangement to standard turned up eyes like those on stock FJ40 leaf springs. I did that to maximize the lift that the Ford springs provided. Even with that change, I had to install spacers between the frame and the spring hangers to get enough lift to run 35" tires. Unfortunately, that approach left the spring eyes low to the ground and they hit things—nasty things like hard, unforgiving rocks. It was those unforgiving contacts that caused me to go to a spring over configuration.
In moving the Ford springs over the axle, the first thing that I did was to cut out the spacers between the fame and spring hangers—they had to go or the lift would have been extreme. I then welded the hangers directly to the frame. In an additional effort to minimize total lift, I reversed the arch of the main leafs to get down turned eyes. Everything else was basic SOA modification, like fabricating new perches and shock mounts and extending the brake lines.
With all the changes, the rear of the vehicle gained about 1.5" of lift over the spring under arrangement. Why so small? As you might expect, a spring over conversion by itself would give about 6" of lift (3.25" from the axle housing, 0.5" from the bottom perch, 0.5" from the upper perch and 1.75" from the spring pack). Removal of the frame to hanger spacers reduced the lift by 2.5" and turning down the spring eyes took off an additional 2" for a total lift of just 1.5".

While total lift was only 1.5", the spring eyes themselves ended up about 4" higher than they were in the spring under configuration. Think about it: the frame spacers only impacted the chassis—like body lift spacers. The 4" came from a 6" lift, minus 2" from turning the spring eyes from up to down.

Front Suspension
In most FJ40 spring over conversions, the front axle presents the greatest challenge due to keeping the steering system whole. In my case, these challenges were minimal, as I had a very long front drive shaft that eliminated the need to cut and turn the knuckles to keep a safe caster angle. My front drive shaft was a healthy 43" long due to the use of a long 700R4 automatic transmission followed by an NP203 doubler, both of which pushed the stock transfer case to the rear. Further, I had stretched the front end by three or four inches by extending the frame rails and reversing the springs so that their long limbs pointed toward the center of the vehicle. The upshot of all this was that I was able to rotate the axle enough to get 4 degrees of caster (stock is 1 degree) without the u-joints binding at full drop. Not bad.

In making the conversion, I elected to move the shackles to the rear of the springs and put the solid mount at the front. To do this, I installed a 1" schedule-40 pipe through the frame rails after many careful measurements. I used 1" pipe for the sleeve, as it was readily available. The experienced among you will recognize that 1" pipe is just a bit too big for stock spring bushings and the use of 1" pipe will allow the bushings to rattle around. I knew that this was so and found an elegant solution that worked amazingly well.

My big tip, for those of you who are considering the use of standard 1" pipe, is...

The FJ40’s 104.5" wheelbase and greatly improved wheel travel make conquering obstacles like this one in The Glade near Farmington, New Mexico, much easier. Along with better off road stability, highway manners were also greatly improved.

The front wheels drop a respectable 16", mostly due to the use of soft, flat stock springs. To further improve wheel travel and allow easy leaf shuffling (ride tuning), I installed bolt-through spring clips that allow the leaf ends to separate under full drop.

Rear wheel drop is a very respectable 17” from full compression, allowing lots of wheel contact with the ground on rough trails. Long, limber Ford springs were used to move the rear axle back about 11”.