Custom Long-Travel Leaf Spring Rear Suspension
Published by Trails Less Traveled on April 9th, 2004
INTRODUCTION
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In comparison to the supple long travel Total Chaos front suspension, the shortcomings of the factory Tacoma rear suspension become painfully evident. Literally. The stiff overload springs are great for hauling loads, but severely limit the compression travel of an unloaded truck and greatly decrease the ride quality and performance off-road. On-road, our stock rear suspension has a tendency to skip and slide through corners instead of finding the traction we are looking for.
To keep up with the front suspension, the rear would need to clear 33” tires with minimal lift and maximum suspension travel (at least 16-18”); and it has to handle like a rally car on-road. If your experiences have led you to believe that these goals are in conflict with each other, please follow along through the first round of rear suspension modifications and check back often as we continue to build-on and improve the performance of the TLT Tacoma.
Deaver Spring is known as THE manufacturer of custom leaf spring packs for off-road vehicles, and has developed a line of race-quality Tacoma leaf springs that cover almost any application. In every case, they can improve the performance of a vehicle on and off-road by increasing the amount and quality of the suspension travel.
With only 3 leafs in each spring pack and less than 10” of total vertical suspension travel, we didn’t think twice about scrapping our 52” long stock leaf springs in favor of an 11 leaf, 62” long (61.5”) set of Deavers that are capable of over 18” of useable travel. They are also tuned for the weight and specific ride height of Tacoma trucks. There are currently three different Tacoma spring packs in production, F55 (+1.5”), F67 (+3”), ___(+5”). We ordered the F67’s thinking they would keep the vehicle/weight as low as possible, but still allow for a decent amount of compression travel.
The new Deaver leaf springs mount under the axle, as opposed to the stock springs which are mounted over the axle. Before anyone objects, there are advantages and drawbacks to each setup and in this application, installing the springs under the axle will provide more room on top of the housing for additional suspension travel on compression, a lower center of gravity and increased lateral stability, as well as reduced axle-wrap/wheel hop on acceleration.
Fiberglass bedsides are mandatory with this much wheel travel. For all those people that would rather stay spring-over, Deaver has an excellent bolt-in spring pack that we plan to install and test on another truck in the near future.
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Because of their additional length, the stock spring hangers will not work with this kit. We chose to use Total Chaos replacement spring hangers. Longer/relocated shackles are required in order to cycle all of the available spring travel. Total Chaos has just released an awesome new tubular shackle; sold in lengths from 8-12” in 1” increments, and includes the bushings as well as the weld-on shackle hangers. Kartek sells all of these parts at a discounted price in a box kit that includes the parts mentioned along with the other important small parts needed, such as an extended stainless braided brake hose and axle spring pads with u-bolts & nuts.
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The primary function of a leaf spring (or a coil, torsion, or any other type of spring) is to support the weight of the vehicle. The dampening at each wheel is provided by a shock absorber. The 2.5×16” Swayaway piggyback reservoir shocks are some of the best dampeners available. The billet aluminum piggyback reservoirs provide double the flow rate to the reservoir as compared to remote reservoirs. Like all Swayaway RaceRunner shocks, they are completely rebuildable and can be easily tuned & re-valved to suit any application. Note the Swayaway 4” hydraulic/nitrogen charged bump-stops and mounting cans in the first picture. Our long-term rear suspension plans have always include these very effective, progressive-rate secondary dampeners. Stay tuned!
BLUEPRINTING
This installation is involved and technical. Any performance gains are dependant on a well designed and professionally executed installation. Modifications this extensive must be considered custom, and are often best left to a qualified fabrication shop. We have included the basic blueprints used for our project vehicle for reference, in hopes that it inspires some creative variations. The Tacoma body/chassis vary a great deal between years and models (standard cab, extra cab and double cab, etc.). Do NOT assume that the measurements discussed or published here will transfer to your vehicle exactly. Some math is required. Not to discourage anyone, but numbers are unavoidable. We used a simple CAD program to plot the fixed points of the chassis and then designed the suspension (leaf spring, shackle and shock mounts/angles) using the dimensions of our new suspension components.
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Because the main spring eye is being relocated forward and the spring is relocated under the axle, we needed to determine the ideal placement for the front spring hanger that would locate the axle and tires in the center of the wheel-well on compression travel. The front spring hanger-to-axle pad is a fixed distance, so the axle travels in an arc around that pivot point. Because the leaf spring flexes along it’s entire length, pinion angle is set at ride height and does not change as predictably as a link-type suspension through the range of travel.
The second fixed chassis point is the shackle hanger. The shackle’s mounting point needs to take the shackle length into consideration. Determining shackle length should take into account the amount of swing, or linear travel, that is required of the shackle, the desired angle of the shackle at ride height, the plane the spring is mounted on, and lastly, the desired ride height. A simple rule to remember is that the distance between the main spring eye and the shackle hanger (measured in a straight line), plus the length of the shackle (measured eye-to-eye), must add up to a number greater than (but close to) the length of the leaf spring (measured eye-to-eye in a straight line, while the spring is flat).
For our application, using a 61.5” long leaf spring, a front spring hanger-to-shackle hanger distance of 55” (measured aligned), and a 10” long (eye-to-eye) shackle, mounted directly on top of the frame rail offers the best suspension travel and associated geometry. A 10” shackle has more than enough swing travel to allow the spring to cycle unrestricted from full extension through full compression, but is no longer than absolutely necessary. When mounted on top of the frame rail as specified, the shackle was designed to clear the bottom of the frame rail on compression by at least 1/2”. Longer shackles will NOT provide any more suspension travel, they will only provide additional lift.
Determining ride height will also be important in planning the amount and percentage of compression (bump) and extension (droop) travel. We tuned for about 10”(60%) bump travel and 7”(40%) droop travel from the desired ride height. The springs and shackles can squeeze out over 18”, but on further extension the leaves would start to fan out (pull apart) and that is not considered useable travel. It is not desirable to force a spring into a negative arch by more than a small amount on compression either.
To take advantage of all the available rear suspension travel, a suitably long pair of shocks must be used. We ordered a set of 2.5×16” stroke Swayaway piggyback reservoir shocks after calculating that we could pull over 17” of travel out of them if they were angled forward slightly (10? on full extension & 25? on full compression). 18” shocks could have been mounted near-vertically, but we had plans for the bed-space that longer shocks and interfered with.
The shock mounts we designed would protrude through a stock bed by 12-14”, but can be made to work reasonably well. We actually cut apart and remounted the stock bed just to see how it fit, but decided that we could create more useable space by removing the bed entirely and designing a purpose-built utility bed that we could reattach the fiberglass bedsides to. This article only addresses the fabrication related to the rear suspension, but we’ll follow up with an article about the custom rollcage/utility bed that we designed and built to accommodate a 22 gallon fuel cell (replacing stock 18 gallon tank), a 35” spare tire, haul two dirt bikes and two mountain bikes, along with our camping/riding gear, tools, etc.
FABRICATION SHOP
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With our plans finalized, we headed over to Rock Star Trux in San Jose, CA, where Mike Jimenez and his crew are turning out some of the cleanest fabrication work in Northern California. We removed the bed before delivering the truck because we didn’t plan on doing the bodywork there, and we wouldn’t be able to fit the stock bed back onto the frame after the shock hoops were installed. As soon as we showed up, the guys got right to work stripping down the chassis to the starting point. They removed the gas tank, brake lines, E-brake, rear axle, and taillight wiring harness.
UPPER SHOCK MOUNTS
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Chris Vierra is Rock Star’s head fabricator, and he began by laying down critical measurements in marker pen on the chassis. The forward crossmember of the shock hoop spans the two frame rails, and anchors the entire assembly. Here the framerail is marked, checked and drilled out to receive the 1.5”x.120”DOM tubing. We used the 1.5” to span straight, low-stress areas, and 1.75”x.120”DOM for the all the load-bearing/structural, suspension and perimeter rollcage tubing.
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The crossmember is shown here installed and then welded. It was also plugged and welded on the outside of the frame rail.
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The upper crossmember is shown on the left, held in position by two temporary uprights. They will be removed as soon as permanent uprights are cut and fitted. The forward uprights are then cut, fit and tack-welded into place. After the positioning of everything is verified, the temporary uprights are removed to fit the rear uprights.
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The rearward uprights are designed to intersect the crossmember through the frame rail. In the picture on the left you can see the angle marked, and on the right you can see the tube being test fitted where the frame must be drilled.
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Note how the hole-saw is used to pierce the frame rail cleanly and then the upright is refitted and tack welded into place.
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After the completed assembly is double-checked against the blueprints, it is finish-welded. Chris laid down some great beads, even upside down.
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The upper shock mounts are shown here painted and with the shocks installed. They wrap around the back of the crossmember because there is not much material below the centerline of the tube and we didn’t want it to shear off under load.
FRAMERAIL EXTENSION & PLATING
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We planned to create a tubular rear crossmember and rear subframe to take the place of the stock rear bumper. That work is beyond the scope of this article, but we had to extend the frame rails by 7.5” so that we could plate the inner frame rail to the added length in one piece. Note the diamond-shaped gusset where material was butt-welded. This is a thoughtful detail from Chris in an area that will most likely see some impact.
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Stock Tacoma frames are only boxed-in from the front of the frame back to the spring hanger, but the previous generation Toyota trucks (89-95) had fully boxed frame rails all the way back to the shackle hanger. We took the opportunity we had while everything was ripped apart to reinforce the frame all the way back to the rear bumper. At the same time, we also removed the stock bump stop extension from the frame rail above the axle because we could not calculate full compression with the interference.
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To box the frame, we marked the material to be cut using the frame as a template, and then hit it with the plasma torch. We used .080” sheet-metal for this.
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The material was cut slightly oversized because we were tracing on the outside of the frame, so we made a pass with the grinder to clean up all of the edges and then tack-welded it into place before coming back to stitch it together.
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At the seam between the two pieces of material on either side of the crossmember, Chris added another diamond-shaped gusset with opposing seams to those in the plate material.
FRONT SPRING HANGER
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Chris transferred the blueprints to measurements on the frame where the front spring hanger needed to be relocated. Careful work with an air chisel and angle grinder reduced this area to a smooth surface and only left behind the reference points needed to position the new spring hanger.
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The new Total Chaos spring hanger is installed what looks like backwards to give the springs additional the clearance that is necessary for to avoid interference on full compression. We welded all available surfaces and then moved on to locating the shackles.
SHACKLES
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The Total Chaos shackles come with new shackle hangers that are designed to be welded into the frame. We located our 10” shackles above the frame in order to sit the vehicle as low as possible without resorting to a shorter shackle that compromises suspension travel and a smooth arc. Chris created these gussets to run down the side of each frame-rail so that the load is distributed across a wider and stronger area of the frame.
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Look at the difference between the stock Toyota shackle and the Total Chaos parts. Compare the arc that each shackle would make through the suspension cycle. Check out those stock leaf springs. One-Two-Three Springs. Three Springs?
AXLE SPRING PAD & U-BOLT PLATES
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The stock spring perch does NOT have to be removed in order to mount the new spring perch, but we cut this one off because our plans include mounting hydraulic bump stops in the frame rails over the axle. We need to fabricate a contact point that would have interfered with the stock perch.
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The Total Chaos replacement leaf spring U-bolt kit is absolutely the lowest profile U-bolt kit on the market. The hardware is all countersunk and the only material under the springs is a single plate of 0.25” chromoly. It’s great for sliding over obstacles, but unfortunately, it’s also prone to flexing under torque/load or tightening. We’re currently working on an improvement and will keep you posted.
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At this stage of the installation, if your axle/tires aren’t centered in the rear wheel wells on compression, note by how much and compensate by drilling additional holes fore/aft of the stock center-pin location to make small adjustments in axle location. Make sure to drill corresponding holes in the U-bolt plate AND the axle pad. Also be sure that the adjustments are symmetrical from side-to-side.
GAS TANK CROSSMEMBER
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We have designed the rear framework to accommodate a fuel cell, but for the time being we have reused the stock fuel tank and had to modify the crossmember to fit the plated frame rails. This is how it bolted together before we tore into the truck.
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We basically just cut off the flanges at the inner plates and welded the crossmember back into the original location. It will be easy enough to cut it out and scrap it when we are ready to mount a fuel cell, and it works just fine in the meantime.
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Everything (gas tank, fuel lines & exhaust) is reinstalled just as when the crossmember was bolted to the frame. Note: this is a good time to paint, before you reassemble.
PAINT
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Prep the bare metal, Apply primer coat, Don’t forget the Small parts.
SUSPENSION INSTALLATION
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With the spring, shackle and upper shock mounts installed, we needed to cycle the suspension to pin down the lower shock mount location. We pulled the leaf spring pack apart and installed the main leafs with the shackles in order to run through the entire range of suspension travel unrestricted. This picture shows the axle at full droop. We recorded those measurements and then calculated where the shock needed to be at full compression before reassembling the leaf springs.
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We used the measurements from cycling the suspension to determine the mounting points for the lower shock mounts. Actually, we didn’t double check the first pair of lower mounts and look how that turned out.
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The first lower shock mounts were a communication error. With projects of this scale, there’s always something that will need to be corrected. A simple mathematical error was limiting out compression travel by over 4”!
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We knew that the shock mounts were going to stand off the housing about 3”, but the first time we didn’t get the rotation of the mounts right. The second time around we got it nailed, and now we’re pulling 17” of vertical travel, using every bit of the shocks at each end of the suspension travel. Check out the gusseted construction and the sleek underside of the shock mount.
PINION ADJUSTMENT
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The pinion angle should be set at ride height with a representation of a typical load for the vehicle. Example: you may need to simulate the weight of a bed, etc. With a spring-under pack of this quality, axle-wrap should be significantly reduced, so the pinion angle should be directly inline with the transmission/transfer case output.
DRIVESHAFT PLUNGE
Measure the driveshaft length through an entire cycle of the suspension from full extension to full compression. This is easiest to do while the spring pack is disassembled and the suspension is being cycled for shock placement. If the driveshaft is too long, it could bottom out and crack your transfer case housing. If the driveshaft is too short, it could twist the splines on the driveshaft, or even fall-apart at the slip yoke. If there is more than 2” of plunge in your driveshaft, there might be something else wrong with your suspension geometry.
BRAKE LINES & E-BRAKE
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The stock load sensing proportioning valve cannot be used with the long travel rear suspension because the valve’s axle-link can’t accommodate the extreme travel. A temporary solution is to cut it off a few inches from the proportioning valve and use a zip-tie to adjust the upwards tension on it to get the correct braking pressure. This is what it looks like after we installed new brake lines, removed the whole LSPV and installed a manual proportioning valve.
The stock E-brake can’t be used with this kit either because the crossover cable could actually bind on the underside of the frame rails and lock-up your brakes on full compression. There is a transfer case pinion mounted alternative that we are looking into.
COMPLETED INSTALLATION
Here’s a quick look at what else is in store for the TLT Tacoma.
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This Article was originally published on Off-Road.com February 2004
Update
Click here to see how Deaver custom-tuned our leafsprings.
Click here to read about how we added 2.0×4” hydraulic bump-stops from Swayaway to the rear suspension.
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