1981 Toyota Trekker - Import Upgrades: Part 2Posted in Project Vehicles on March 10, 2015
In the last installment, we introduced our ’81 Toyota Trekker 4x4 and tore into the axles (“Import Upgrades,” Mar. ’15). Our truck had many of the common popular aftermarket Toyota solid-axle improvements. For the most part, our truck worked great as a trail crawler. But we were getting bored with going slow and wanted to steer the truck into high-speed terrain without decreasing capability in the rocks. To do this, we needed to rethink our suspension. In this installment, we’ll cover the rear suspension. Next installment we’ll move on up to the front suspension and get it out on the trail.
In most cases, a well-thought-out leaf-spring suspension can be built to control the axles in many different off-road situations. Some race-inspired leaf-sprung suspensions offer up to 18 inches of vertical wheel travel. These long and complaint leaf springs don’t come cheap and don’t always fit in the confined parameters of a trail rig. So we decided to take the leap into link-style suspensions front and rear.
Designing a properly functioning four-link requires a lot of knowledge of the forces being applied to the vehicle and axles. So rather than shoot in the dark with an unproven custom suspension design, we decided to use a kit. Mayhem Metal Works specializes in extreme custom fabrication, but the company offers a solid-axle link suspension swap kit for the front and rear of Toyota trucks. The entire system is based around a buggy-style skidplate that correctly locates all of the suspension links to the frame, which is one of the most difficult, yet key parts of designing a solid, properly working link-style suspension. The kit includes quality RuffStuff Specialties rod ends and allows for a lot of flexibility so you can choose your preferred wheelbase length and shock locations, among other things. Since the Mayhem Metal Works kit is designed for doing a solid-axle swap on later-model IFS Toyota trucks, we had to make a few tweaks for it to work with our vintage solid-axle Trekker. A pre-’86 version of the kit should be available by the time you read this.
The heart of the Mayhem Metal Works Toyota link suspension kit is this three-piece buggy skidplate. It correctly locates all of the links for best performance, supports the drivetrain, and protects the underside of your 4x4 with a flat skidplate. The gusseted middle portion of the skidplate is removable to easily service the transmission and transfer case without removal of the suspension links. Mayhem Metal Works is working on universal weld-on skidplates with four-link mounts for other popular 4x4 applications, which may be available by the time you read this.
The rear suspension is comprised of a double-triangulated four-link. This locates the axle under the 4x4 and causes minimal suspension-related rear steer when flexing over boulders. The upper links are made from 13⁄4-inch, 0.120-wall DOM tubing and the lower links are made from massive 2-inch, 0.247-wall DOM tubing for rock-rash resistance.
All rod ends, threaded weld bungs, and misalignment bushings are high-quality parts from RuffStuff Specialties. The lower links ride on 11⁄4-inch rod ends (left), the uppers on 7⁄8-inch rod ends (middle), and the front track bar moves on 3⁄4-inch rod ends (right).
We started by stripping the rear portion of the body and suspension from our truck. The factory fuel tank and exhaust need to be relocated for the suspension kit to fit. Originally, we planned to keep the rear framerails. After taking a few measurements, we found that this wasn’t going to give us enough room for the wheel travel we wanted, so we removed the rear framerails entirely.
Since the Mayhem Metal Works link suspension kit is designed for later-model Toyota trucks, we had to remove one of our factory crossmembers. The skidplate assembly ties into this crossmember on later trucks. We simply incorporated the skidplate into our frame-mounted rollcage to achieve the needed support.
Every frame is just a bit different because of abuse, modifications, accidents, and so on. Mayhem Metal Works designed a transmission mounting assembly that could accommodate some misalignment, simplifying the installation. We upgraded our transmission mount, but the original Toyota transmission mount bolts up to this plate that it fits into and is then welded to the skidplate assembly.
The skidplate/suspension structure is simple to locate because it keys into the Toyota frame and the included transmission plate. Thanks to the clever design, it would be really hard to screw up this important step of the assembly. We needed to grind a couple clearance slots to fit the skidder over our rocker guard mounts. A floor jack is extremely helpful in positioning the assembly.
Once the skidplate assembly is properly located, you can burn it into the Toyota frame and tack weld the transmission locating plate into place. From there, you need to unbolt and remove the center portion of the skidplate to fully weld the transmission plate.
We laid out a 105-inch wheelbase by locating the rear axle in the correct position. The included link tubing is cut to length before welding the RuffStuff bungs into place.
The Mayhem Metal Works suspension brackets fit factory Toyota axles. However, they can be easily modified to work with any number of different axlehousings. The lower link brackets are gusseted top and bottom to spread the load over the largest possible area. Once you have them positioned and tack-welded in place, you should weld the top and bottom first and then the inside portions. The mounts themselves act as gussets to combat warping caused by the welding process.
Like the lower link mounts, the upper rear link mounts are designed for a stock Toyota axlehousing. A little cutting and trimming allowed them to fit over our aftermarket Trail-Gear housing. Axlehousings with cast-iron centersections will need some sort of truss structure added for proper link attachment.
We replaced our original rear frame structure with 11⁄2-inch, 0.120-wall DOM tubing. It looks long to rockcrawlers and short to desert racers. It’s a compromise to work in both environments. The fuel cell in the rear helps with the weight distribution for improved handling at higher speeds in the dirt.
We ordered our 18-inch 2 1⁄2-inch-diameter King coilover shocks and coils from Off Road Evolution. Our new rear frame structure makes room for the shocks and provides a suitable mounting location. Our Mayhem Metal Works rear link suspension will cycle at about 22-23 inches of vertical wheel travel once we get the limiting straps in place.
We also ordered 2 1⁄2-inch diameter King hydraulic bumpstops and mounting cans from Off Road Evolution. When locating and welding the bumpstop mounting cans into place, don’t weld on the lower inch of the tube. The resultant warping makes installation of the bumpstop infinitely more difficult. We learned this the hard way.
With the rear suspension put together, we’ll focus our attention on the front end in the next installment, tie up a few loose ends, and hopefully get our truck out in the dirt.