Project ROKTOY - 4-Link Rear

http:/www.4x4wire.com/toyota/projects/roktoy13/

Short Cuts

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By: Jay Kopycinski - 11/2006

It's hard to believe that I started this project rig over 5 years ago (Fall 2001) and it has been wheeling for almost 4 years. I had been running the same Mazda hybrid spring packs on the rear of my truck/buggy since 1996. I had broken and replaced a few main leaves, but the rest of the packs remained the same. The rear packs flexed great and had a smooth ride, and climbed reasonably well with the added track bar. However, all the guys I run with in the BTG Rockcrawlers had long ago linked the rear of their buggies, many had swapped to Dana 60s, and some had moved up to a V6 or V8. It was time to upgrade the rear in an attempt to keep up with them a while longer.


Running Pet Cemetery north of Phoenix	The venerable Mazda packs & track bar	Signs of trail use	The old beat and used axle housing


All cut up and ready for a remake	The old tail end and suspension

I whipped out my sawzall and cut away everything from the b-pillar back. The plan was to add link mounts and rebuild the back half of the chassis to accomodate the new suspension and shorten and narrow the tail. I really liked the storage box I had behind the seats, but it was bulky and heavy and would be replaced with something smaller. The frame rails were cut off just beyond the b-pillar and capped with steel plate.

For the suspension, I took advice from fellow club members as to what worked well for the kind of wheeling we do. I decided to build a double triangulated 4-link using Fox air shocks. With the tail of the buggy cut off, I started on the link mounts first. I built a crossmember for the lower links from 2" x .25" wall DOM and a set of upper link towers from 1/4" plate. The crossmember was welded between the frame rails and was reinforced with two smaller tubes running from the middle of the crossmember to each frame rail. The frame rails were plated to widen the top surface and the upper link towers were welded there. I provided 3 holes (spaced 2" apart) to allow for some adjustment of the link geometry. The 3 holes were drilled across an arc to keep the link length constant at each position.

Scratch built frame crossmember Frame link towers for the upper links Offset axle tabs from Blue Torch Fab Flange end of newly built DOM axle

My previous rear axle housing was pretty beat from long-term use. I started with a straight used housing and cut it up. I decided to build a jig and retube the housing with 2.75" x .25" wall DOM tubing so I mated the new outer tubes to the housing and attached cannibalized flange ends to the DOM tubes. The center section was shaved and plated as well and the drain plug eliminated. Once this was done I attached lower link brackets from Blue Torch Fab and built an upper link bridge starting with 1.5" x .25" wall DOM. I also added tabs to accomodate a limit strap.

I used Rubicon Express joints for the lower links combined with 2" x .25" wall DOM tubing. This should be strong enough to resist bending in most cases if I don't slam them too hard on the rocks. Upper links are 1.5" x .25" wall DOM with 3/4" shaft x 5/8" eye rod ends from Rod End Supply. Link lengths are all 40" making it easy to carry a single trail spare. Vertical separation at the axle end is 9 inches and can be varied from 5 to 9 inches on the frame end. New brake lines were run on the axle housing and up across one of the upper links to the middle of the chassis.


Shot of frame end of link setup	Overall view of link assemblies	Rear axle bridge and link mounts

I fabricated a new tail end for the chassis from 1 3/4" HREW tubing and also reworked some of the roof bars and the door areas to make the rig a little safer. The exhaust was shortened and the muffler moved forward.

Starting fabrication of rear chassis Checking shock clearance & planning mounts Side view of the rear chassis/cage tubing Tabs and mounts being added Tail shot

I swapped in a RCI 8 gallon fuel cell in place of the stock 17 gallon truck tank I had been running. I fabricated new Power Tank mounts, and added places to accomodate a tool bag, storage box, ammo can, and a cooler.


8 gallon plastic fuel cell	Fuel cell positioned in chassis	Small dune buggy tail lights	Ready for the rattle cans	All blue again and ready for assembly


Rear view of completed axle & bridge	Tail shot of the completed rig	Interior of rear chassis before completion	Top rear view of cage	Shot of completed links and axle


Still sporting the old truck license plate	Crossmember on frame for lower link mounts	Bump stops mounted on chassis tail	12" limit strap tied to chassis and axle	Upper link mount tower on frame rail


Interior shot showing overall layout	Military surplus fuze box for storage	Power tank mounted behind passenger seat	Snatch strap storage on inner rear panel	Ready to go & built to grind


Advanced Air Systems XP300 regulator	Shock inflator tools makes filling/setting easy

I took the weight off the tail end and pressurized the shocks, finalizing on a pressure of 240 psi to get the buggy ride height level. I used a nitrogen bottle and one of the new Advanced Air Systems XP300 regulators. This setup flows fast and the liquid filled gauges work well. With the shocks pumped over pressure I used one of their shock inflator tools to set the final pressure. This setup has a threaded fitting that screws onto the Schraeder valve on the shock and then allows you to read the pressure on a gauge and bleed off or fill the shock through a valve plumbed to the gauge and fill/check hose. It's easy to use.

With the assembly done and the shocks set to pressure, I ran the rig up and down the street. My old leaf packs hooked up pretty good with the track bar, but the 4-link was obviously much tighter without spring wrap of any sort. I would soon find that dirt road stability was also much better and with the current pressure and ride height, the suspension is nearly as soft as the old setup. This makes for a still decent ride on bumpy roads and trails. Me and a couple of guys from the club hit a few trails up at Table Mesa north of Phoenix to give the buggy a shakedown.


Out playing on the Table Mesa trails	Finishing out the Z-turn on Terminator	First waterfall on Annihilator	Second waterfall on Annihilator	Coming up the chute on Anaconda

The rear hooks up better when climbing ledges and the former side sway from the shackles and leaf packs is gone. The movement of the rear feels a little different when side-hilling which I think is due to a difference in roll axis, but the setup feels just as stable and the articulation seems about right. I like it....and it's time to get some more trail running in.

Thanks for reading!


Scratch built frame crossmember	Frame link towers for the upper links	Offset axle tabs from Blue Torch Fab	Flange end of newly built DOM axle


Starting fabrication of rear chassis	Checking shock clearance & planning mounts	Side view of the rear chassis/cage tubing	Tabs and mounts being added	Tail shot