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2006 Ultimate Adventure - 2007 Toyota FJ Cruiser Build Part 3 - Bumper, Axle & Suspension

Posted in Ultimate Adventure: 2006 on September 1, 2006
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The Ultimate Adventure is getting closer and our project truck is quickly changing from a stock Toyota FJ Cruiser into the Ultimate FJ. Last month we had the interior redone for safety and some provisions by Poison Spyder Customs and Slee Off-Road ("Ultimate FJ," Aug. '06). After that we headed for Durango, Colorado, where Fab Fours measured for bumpers and then we traveled back to California for initial measurements for axles and suspension at All-Pro Off-Road.

No matter what your project vehicle, it pays to spend some quality time with a tape measure. This is especially true when you are making custom parts like axles, bumpers, and driveshafts. The time and energy involved in painstakingly recording measurements will ensure that once you are cutting metal and welding up new parts, they will be much closer to perfect the first try.

In fact, building an ultimate 4x4 involves a bit of measuring, building, remeasuring, building some more, and lots of constant adjusting since there are times when you need to mock up certain parts and cut off existing parts to make everything fit. This month is measuring. Next month we start cutting it apart and putting it back together.

1. The plan at Fab Fours was to digitize the FJ Cruiser so that a computer-designed bumper could be built. With the Ultimate FJ in the shop, it was put up on jackstands so it would not move or roll around. Engineers RJ Lynn and Dustin Wilkinson set up their Stinger measuring arm. The Stinger arm allows Fab Fours to plot thousands of points across the body and frame of the FJ by slowly moving it along the body lines and corners of each front panel, framerail, and underlying component. As each point is plotted and recorded within the computer, a digitally generated picture of the truck begins to form.

2. This rendition of the front of the FJ and a Fab Fours' bumper was designed on the computer before any metal gets cut. There is always the possibility that actual measurements may vary slightly between different stock vehicles, but when this type of measuring is cross-referenced with OEM-supplied digital files, the results are a bumper that can bolt on with very few issues.

3. Removing the stock rear bumper exposed the corner's plastic cladding, which is integrated into the rear bumper design. Since we know the rear fenderwells will need to be enlarged to fit our BFGoodrich tires and a stronger tire carrier is needed, the rear bumper design is going to be a bit tricky. Holding up a Fab Fours' Jeep Wrangler bumper revealed some similarities in size. Watch for the final design in upcoming issues.

4. In Hemet, California, we met up with Jim McGean from Dynatrac and Jon Bundurant of All-Pro Off-Road. All-Pro is the main shop where the FJ will be assembled, and Dynatrac is again the Official Axle Sponsor of Ultimate Adventure. Since the FJ is going to be running big tires, we decided to remove all the factory suspensions and axles and swap in a set of Dynatrac ProRock Dana 60 axles. Though there are many great suspension kits available for the stock IFS and solid rear axle, our experience tells us that these components need some upgrades to handle 39-inch tires, and we would rather be wheeling than wrenching on UA. Our initial goal was to determine the size of the stock axles and then how to make the larger ProRocks fit under the truck.

5. Our new wheels will be 9 inches wide and have 4.5 inches of backspacing. The tires are 13 inches wide, so measuring from the wheel mounting surface to the inside of the tire should be 612 inches. Thus, if we want the tires to clear the inner fenderwells at ride height, the wheel mounting surface needs to be at least 7 inches away from the inner fenderwells. When we figured in articulation (which brings the tire even closer into the wheelwell), we realized the wheel mounting to wheel mounting surface (WMS) of the rear axle would be best suited at around 70 inches--up nearly 5 inches from the stock 6412-inch WMS to WMS. This is very similar to a fullsize truck axle width.

6. We also noticed that the stock rear axle pinion was offset roughly an inch towards the passenger side in order to keep the driveshaft away from the stock fuel tank during articulation. We will no doubt need even more offset since the rear should be a bit more flexible than stock, but the actual amount of pinion offset will need to be determined after we mock up the suspension. Note how we used a straightedge to measure wheel mounting surfaces since it is not always easy to measure directly from those points.

7. Up front things are even trickier because we need to estimate where the pumpkin will sit, while at the same time measuring around the existing IFS. If you have time to spare, cut all that IFS garbage out and then start measuring. McGean measured the framerails and determined that the engine oil pan sits slightly offset to the passenger side so a driver-side front differential would work best. Exactly how far offset it will be is determined by the space available, where the driveshaft will be coming from, and the type of suspension being used.

8. It is difficult to determine the width needed up front since the tires not only must clear the frame and fenders during articulation, but also during steering. Again McGean and Bundurant measured the stock WMS to WMS using straight-edge rulers. As a starting point we went with an inch wider than in the rear to assist with steering, but both our front and rear axles will be mocked up without fully welding the knuckles on so we can test-fit everything and determine if they need to be changed slightly.

9. Our FJ Cruiser came with a full-time transfer case and doesn't offer the low gearing we want to help supplement the 4.0L V-6. Most Toyota owners run dual transfer cases, but the narrow spacing between the transmission and gas tank will make that a little more challenging than we have time for. Our plan evolved to the new Atlas four-speed transfer case from Advance Adapters, which will offer us a 1:1 high range and 2.72:1, 3.8:1, and 10.34:1 low ranges while still being roughly the same length as the stock case (left).

10. We stuffed the four-speed behind the Toyota six-speed manual transmission and found that other than needing a new adapter, the fit was nearly perfect. Because the shift linkage would be a headache in the spacing available, we opted for the new cable shifters, and will show their placement in a future issue.

11. Here is the biggest hurdle with swapping the Atlas behind the six-speed. The Atlas uses an internal female style input, where the stock Toyota transfer case uses an external male style input, thus a spud shaft will need to be made to go between the six-speed and the Atlas. The splines that run into the six-speed are a unique 22-spline, 112-inch version that will require a one-of-a-kind spud shaft to be designed. Luckily for all you FJ Cruiser owners and hopefully you late-model Tacoma owners this will add the option of swapping a four-speed or two-speed Atlas behind your current six-speed manual, resulting in up to 24 gearing options.


Clackamas, OR 97015
Huntington Beach, CA 92647
Cleveland, OH 44114
Advance Adapters
Paso Robles, CA 93446
Fab Fours
Pineville, NC 28134
Tuff Country
West Jordan, UT 84088
Hobart Welders
All-Pro Off-Road
Hemet, CA 92543
Yukon Gear & Axle
Everett, WA 98204

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