|Author: Joe Micciche November, 2000||
|Top to bottom: 26mm aftermarket torsion bar, Sway-A-Way 25mm PowerBar, stock Toyota torsion bar.|
Toyota introduced the independent front suspension (IFS) on it's 4WD's with the model year 1986 trucks and 4Runners, and used the exact same setup through the 1995 model 4WD's. The springs used in this iteration of the suspension are torsion bars, which have been in use for decades in a multitude of applications. While the Toyota engineers wisely located the front torsion bar mounts on the upper control arm and the rear mounts inboard of the frame - which keeps these springs well-protected and out of harm's way - the bars can sag over time. An aftermarket front bumper and winch combination, continued off-road abuse, and "cranking" of the torsions for nominal lift are the most common reasons for spring fatigue. The torsion bars can be adjusted to level out the ride, but this action just postpones the inevitable: the stock bars should be replaced with something that can support the use.
|Why aftermarket torsion bars?|
Toyota offered different diameters and spring rates of torsion bars for the trucks and 4Runners, with at least 4 different part numbers available depending on year, model, and engine: some applications cross-reference against significantly different sprung rates. Compounding the effects of fatigue are the additional sprung weight of certain models, vehicle configuration, and the usual random installation of aftermarket shocks not designed for the specific application.
I had the opportunity to discuss the Toyota IFS and torsion bars with Drew Burroughs, an engineer at Sway-A-Way (SAW), which produces torsion bars for many IFS trucks. According to Burroughs, not only will an aftermarket torsion bar provide a higher spring rate to help offset higher sprung weights, but aftermarket bars can provide an enormous increase in strength as well. The Sway-A-Way torsion bars are manufactured from aircraft-quality 4340 nickel chro-moly, and with the heat-treat process SAW utilizes, the torsion bars resist fatigue by more than 50% over stock bars.
Burroughs also explained that the different materials used in producing torsion bars all produce the same spring rate. The differentiators when selecting aftermarket bars include the heat treating process and how this affects strength, and the diameter of the bar which determines spring rate. The manufacturer of the torsion bar should be able to provide an indication of strength versus the stock bars without disclosing any proprietary information, as in the previous paragraph. While the spring rate is determined by size, there is not a one-to-one relationship in diameter vs. rate. Rather, the engineers rely on "Diameter to the 4th", which is a calculation that includes length, diameter, and material. In the case of the SAW 25mm bars, this is expressed as: (new bar diameter: 25 to the fourth = 390625) divided by (old bar diameter: 22 to the fourth = 234256), which equates to a 66% increase in spring rate.
The real-world effects of this increased spring rate can be benign or very obvious, depending on vehicle configuration and use. On a vehicle with a higher-than-stock sprung weight - those with winches and aftermarket bumpers or an engine swap, for example - the upgraded torsion bars can provide increased control on-road and off-road due to the higher spring rate. Fatigued bars on near-stock vehicles with improperly matched shocks can benefit from less porpoising under braking or when taking on bumps. In my case, the SAW bars matched with application-specific KYB gas shocks provide a controlled and comfortable on-road ride even without any swaybars, and excel at absorbing impacts off-road. And, the new torsion bars also allow the suspension to utilize its full range of movement - they do not limit travel.
|Author's Note (August, 2001): After extensive use offroad, I have found that these torsion bars do in fact limit compression offroad in certain situations. With the V6 engine and no aftermarket bumper or winch, the weight of the truck is not able to overcome the increased spring rate. Thus, in cases where the front end is unloaded (ascents), neither side will completely compress to the bumpstops. When the front end is loaded - as it is in descents - the bars do allow full compression. Subsequent testing with stock torsion bars showed that on my truck, the front would fully compress even when unloaded.|
Finally, the SAW torsion bars are epoxy powder-coated, which helps prevent nicks in the bars from debris encountered on- or off-road. Scratches, scoring, rust, or other hits to the bars could cause them to fail. According to Burroughs, the "torsion bars are under high torsional stresses and these stresses are at a maximum at the surface of the minor diameter. When the surface is damaged," he continued, "it creates what is called a stress riser at the damaged location". These risers can increase stress by as much as 50%, and "also greatly reduce the fatigue life".
|Replacing the Torsion Bars|
|Measure the distance from the top of the rim to the bottom of the fender lip before doing anything.|
Note: For this article, I replaced aftermarket 26mm torsion bars with the SAW 25mm bars. The 26mm bars were too "bouncy" for my conditions.
Prior to starting this job, there are two very important preliminary actions to take. First, several days before doing this, be sure to soak the adjusting nut (and lock nut, if equipped) and bolt at each rear mount with a good penetrant: this will make the job easier. Second, be sure to measure and write down the distance between the top of the front rim and the bottom of the fender lip on each side while the vehicle is on a flat, level surface. This measurement is required to return your vehicle to stock height, or to dial in ride height after replacing the bars: and the heights should be identical on each side. It may also be worthwhile to purchase new adjusting bolts and nuts (but not the half-moon spacers) from Toyota, in case the old ones are age- or grime-welded into place and destroyed when removed.
|Jack up the front end and secure with jackstands, then remove the tire.|
After getting the measurements from both sides, begin by jacking up the front end and securing it with jackstands. Place the jackstands on the front lower control arm crossmember and frame, not under the lower control arms. The tires can then be removed to allow each control arm/spindle assembly to hang down as far as possible, which completely unloads the torsion bars. Removal of the swaybar will help with this.
|The driver's side rear torsion bar mount.||The passenger side rear torsion bar mount. Arrows indicate the adjusting bolt and nut.|
To remove the torsion bars, you will need a 22mm 6-point socket and breaker or cheater bar for the adusting bolt, and a 22mm wrench to hold the nut in place. If you don't have air tools, a helper would be good to have as well: if the bars have never been replaced and even after soaking in penetrant, chances are some effort will be required to remove the adjusting bolt. Slide the rubber dust boot at the rear end of the torsion bar up the bar a few inches, then loosen and remove the adjusting bolt while holding the nut in place.
|Tip: If you do not have air tools and find the bolt difficult to remove, try using a large pipe wrench or cheater on the nut and a long breaker or cheater on the bolt. The pipe wrench will almost certainly ruin the nut, so be prepared with a new one. Only use heat as a last resort and with extreme caution, since the fuel lines run by the passenger mount and the O2 sensor wires run near the driver's mount. Using heat will require use of new nuts and bolts.|
Once the adjusting bolt is removed from the mount, lift up the rear dog-leg mount and slide it off the rear of the torsion bar. You can then pull the torsion bar toward the rear of the truck to remove it from the front anchor arm.
|The front anchor arms for the torsion bars are mounted to the upper control arm.|
The first time I removed my torsion bars, they would not come free from the front anchor arm. To solve this, I removed the anchor arms from the control arms, sprayed penetrant on the bar at the anchor arm, and lightly tapped around the arm with a rubber mallet. When remounting the anchor arms to the control arms, be aware that the tab on the anchor should point up, and the torque on the 17mm hex nuts should be reset to 67 ft. lbs.
Prior to installing the new torsion bars, make sure you know which bar is to be installed on the driver side, and which one fits the passenger side: this will be indicated on one end of each bar. Also, take note of where the large spline is on the front anchor arm and on the bar itself. The bars can only fit one way, since one end is larger than the other and the large spline indexes the bar for installation. Apply grease to the inner splines of the anchor arm and slide the new bar in. Reinstall the dust boot to the rear of the bar, and slide it up the bar several inches. Then, grease the splines on the rear end and place the rear mount back on the bar, and seat the mount in the cradle.
|Anti-seize makes quick work of tightening the nut, and adjusting ride height.|
Put the lower spacer on the adusting nut. Liberally apply anti-seize to the adjusting bolt before installing it: this will make adjusting it now and in the future much easier. Then install the bolt up through the mount and upper spacer. When everything's in place, reinstall the top nut and torque it down, then install the lock nut (if equipped). There is no set torque value or number of threads to guide reinstallation, so tighten until approximately 1/2" of the bolt's thread is visible above the nut. Once both torsion bars are reinstalled, reseat the dust boots, put the tires back on, and set the truck down. At this point, the springs are preloaded by the weight of the truck, and adjustments to the torsion bars affect ride height, not spring rate or preload.
|Close on the first try, but no cigar. Adjustments are easy now though.|
In all likelihood, the front end will not be even side-to-side nor will it be right on the measurements taken prior to replacing the bars. Bounce the front end several times to get it to settle, then remeasure the distances from the top of the rim to the bottom of the fender. With the anti-seize on the adjusting bolt, adjustments with the wheels on the ground can be done by one person: so adjust the bars until the desired ride height is achieved. Once set, take a drive to let the front settle again, then remeasure and adjust as necessary. If the bars are cranked to get lift from the front end, have an alignment done as soon as possible.