Technical Articles Relating To Off-Road Vehicle Development

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Donahoe Racing Tacoma Suspension System

Published by Trails Less Traveled on July 7th, 2004

 

INTRODUCTION

Donahoe kit installed on '99 TRD extra cab TacomaOur black TRD Toyota Tacoma came from the factory with a burly 4X4 drive-train featuring an electric locking rear differential, high ground clearance, 4.10:1 gears and lots of other off-road oriented features. However the stock suspension components are geared more towards hauling lumber than hauling butt through the desert or down access roads. The stock rear leaf springs are as stiff as a board and don’’’t really match the lively and active feel of the independent front suspension, which has a tendency to dive into corners and blow through travel. Not to mention that the relatively small-diameter shocks fade rapidly when subjected to repeated and prolonged high-speed off-road use.

We contacted Donahoe Racing Products, to see what they could tell us about their Tacoma suspension components. After talking with Dylan, we decided that the Donahoe Racing package was exactly what we needed. We had the parts shipped out right away.

Donahoe Kit not installed
This is our complete Donahoe Racing Toyota Tacoma suspension package. It doesn’’’t look like much at first glance, especially when compared to some of the comparably priced “drop-bracket lift kits” on the market (in fact, there’’’s not a single bolt-on bracket provided). But the apparent lack of parts is not an oversight.

Donahoe Race Tacoma in actionDonahoe maintains that they are not in the business of making “lift kits”(although this suspension system can provide a few inches of additional ride height and increased ground clearance). Donahoe chose to utilize all of the stock suspension mounting points to develop a race-quality suspension package that is designed to improve all aspects of the trucks handling and off-road performance. Their extensive product development and testing program includes the Donahoe Tacoma Double Cab race truck, which uses many of the company’’’s production-based suspension products.

FRONT SUSPENSION

Donahoe Coil oversThe shocks come pre-set to provide approximately 2.0” of lift. They can be adjusted to provide up to 3” of lift over stock ride height, but Donahoe does not recommend going any higher than 2.5” because of the additional stress placed on the CV joints (4WD models only).

Note: Installation of Donahoe’’’s coil-over shocks at 2” of lift will clear 33×10.5” tires on 15×7-8” rims or 285/75/16 tires on 16×7-8” rims without any additional modifications.

We contacted Dylan Evans (Donahoe’s suspension engineer) to talk about some of the distinguishing features in their new line of 2.5” coil-over shocks. We wanted to know what set them apart from them from competitive products.

Dylan began by explaining how improvements to the piston design allow for additional valving flexibility (and the valving inside of the Donahoe shocks is the key to their performance). Although the Donahoe shocks are completely rebuild-able, we doubt that most people could improve on their performance right out of the box. It is true that most of the replacement coil-over shocks on the market are rebuild-able, but NONE of them that we have tested ride as well or handle comparably on/off-road.

Donahoe uses a 2.5” diameter shock that carries a larger volume of shock fluid than stock or even 2.0” shocks, and features a nitrogen-charged reservoir with a dividing piston located within the shock body. The internal reservoir serves the same purpose as the remote reservoirs seen on desert racing trucks. By comparison, most of the bolt-in replacement coil-over shocks available are emulsion shocks. ‘’”Emulsion shocks’’” allow the oil and nitrogen to mix, which quickly leads to fading performance.

An internal top-out damper acts as a progressive stop as the suspension reaches full extension. It becomes active on the last 1/8” of shock stoke and helps to reduce the forces transferred to other suspension and chassis components.

Donahoe uses a ‘’Nitro-Steel’’® shock shaft that is superior to chrome-plated shafts because of its ability to resist corrosion (rust) and scratching (causes seals to leak).

It is almost impossible to find a production spring that is ideal for any specific application. So Donahoe chose to absorb the cost of developing a hi-tensile, silicon-steel coil spring rather than compromise on the quality. The 650lb springs have fewer winds (active coils) than most production springs. Fewer winds allow for a greater range of pre-load (ride-height adjustment) and usable spring travel before encountering coil-bind. ‘’”Coil-bind” is when the individual winds of the spring come in contact with each other under compression before the shock has reached full compression. Coil-bind limits the suspension travel and causes harsh metal-on-metal contact that can damage suspension components and cause the springs to sag. The custom-wound springs are also shot-peened and then cycled to eliminate any possibility of them sagging on a vehicle. Donahoe coil springs should last the life of a truck.

REAR SUSPENSION

Donahoe Deaver Leaf springDonahoe add-a-leafDonahoe also offers several options to enhance the rear suspension and level out the ride height. We purchased the complete replacement leaf spring pack made for Donahoe by Deaver Spring. These leaf springs are a bolt-in replacement for the stock springs and raise the rear ride height by approximately 2’’”. Donahoe does offer an add-a-leaf kit as a lower priced rear suspension upgrade, but the Deaver springs improve the ride quality so dramatically over stock that we feel the extra money was well spent.

Donahoe Bilstein 5100 rear shocksBilstein 5100 series mono-tube high pressure gas shocks are spec’’’ed with improved valving to better dampen the rear suspension travel. Tacoma trucks equipped with the TRD package already come with Bilstien shocks, but the Donahoe Bilstein shocks are a slightly larger in diameter shock and also allow for an additional inch of wheel travel. We test-drove the truck with the new leaf springs and old shocks before we installed the new Bilstein shocks, and can verify that they made a noticeable difference in ride quality.

FRONT SUSPENSION INSTALLATION

Installing the coil-over shocks is relatively straightforward and can be done at home in the driveway using basic hand tools in less than an hour even if a person has never done this before. It is beneficial to have a general understanding of the vehicle’’’s suspension components, but Donahoe does provide clear and detailed instructions.

IMPORTANT: Any modifications to a vehicle that involve the suspension or steering should only be undertaken if the person has adequate knowledge of the components and process, that will assure the vehicle can be returned to safe working order before it is driven.

Tacoma front end with wheels reomvedBegin by breaking the lug nuts loose, then raise the wheels the rest of the way off the ground using a floor-jack. Now remove the lug nuts and wheels and then slowly lower the truck down onto jack-stands placed under the frame-rails just in front of the transmission cross-member (as pictured). This is essential because most jack-stands are not tall enough to reach the frame rails with the tires on the truck. If you have extra-tall jack-stands, you can simply raise the truck until the wheels lift off the ground, and then lower it down onto the jack-stands before removing the wheels. We recommend also supporting the truck with a floor-jack as an extra measure of safety.

Removing top coil over boltsRemoving lower coil over boltRemoving factory coil overWith the truck safely supported on jack-stands, remove the three nuts that hold the top of the factory coil-over assembly in place. Then remove the single large bolt at the bottom of the factory coil-over. The lower bolt may need top be driven out with a center-punch and hammer. With all of the hardware removed you can now remove shock.

Inserting Donahoe coil overSlide the new Donahoe Racing coil-over into place and line up the top three mounting holes. Use the supplied hardware to fasten the shock to the upper mount. Donahoe coil-overs have 2 sets of 3 holes drilled into the upper mount. One set of holes is for Tacoma & 4Runner models and the other set are for Tundra & Sequoia models. The Donahoe installation instructions clearly indicate which set of holes to use for each application.

Donahoe coil over bolted in placeSince the Donahoe Racing coil-over provides a small amount of additional wheel travel, it is slightly longer than the factory unit. It’’’s not necessary to take any pre-load off of the coil-spring, but you may need to press down on the lower control arm in order to create enough space for the new shock. It can be helpful to temporarily disconnect one side of the front anti-sway bar to allow the suspension components to move more freely.

Donahoe uses one short and one longer misalignment bushing on the lower mount for their coil-overs to position the coil-over slightly farther away from the CV axle. Mount the coil-over with the longer bushing facing toward the CV axle (rear of the vehicle). Then reinstall the large bolt through the lower heim-joint and tighten it up.

Close up of Donahoe upper mountNote: Donahoe uses a special valve to pressurize their coil-overs with nitrogen. Most shocks use a standard Schrader valve that can easily be tampered with. If for any reason you need to service your Donahoe shocks, it is recommended that you take them to an authorized Donahoe distributor. Do not attempt to tamper with the valve.

Adjustments to the final ride height can easily be made with a spanner wrench. It’’’s best to wait to make any adjustments until after you have completely finished the entire installation (front and rear). That way you will know how high the front needs to sit in relation to the rear. This will also allow you to drive the truck around the block to settle the suspension before determining what (if any) changes need to be made.

After tightening everything up and taking a quick drive to settle the springs, the front end of the Tacoma was sitting about 1/2” lower than the rear of the truck so we adjusted the pre-load on the coil-springs until both the front and rear sat at exactly the same ride-height (ended up being 2.25” of lift). Once you have the ride height set, take the truck in for an alignment.

IMPORTANT: Anytime the suspension geometry or ride height is altered, the camber, caster and toe-in needs to be corrected. After installing the Donahoe suspension, our tires had a few degrees of negative camber with excessive toe-in. This would cause tires to wear prematurely and also adversely affect the handling of the truck if left uncorrected. Our local alignment shop was able to easily bring the front end right back into factory specs. If you only plan to install the front coil-overs, now is the time to have an alignment performed. If you are going to install the complete front and rear kit, wait until the entire installation is completed before taking the truck to get an alignment.

REAR SUSPENSION INSTALLATION

Installing the rear suspension is a little bit more involved than the front suspension, but the average home mechanic should be able to tackle this part of the project in a few hours. The process is not difficult, but does require some physical exertion to wrestle the axle-housing and leaf springs around.

U-bolts painted blackWe purchased new U-bolts from Deaver because ours were rusted, and it’’’s always a good idea to replace U-bolts when changing leaf springs because the threads stretch and they could fail if they are reused. Deaver can custom-make U-bolts in almost any size or shape at very reasonable prices. It’’’s cheap insurance.

Before digging into the rear suspension, we sprayed a few coats of primer and semi-gloss black paint on the leaf-spring u-bolts and hardware. They come unfinished and if not painted, they will begin to rust almost immediately. We did this first so that the paint would be dry by the time we needed the new u-bolts.

Rear wheels removedTacoma resting on removed rear wheels placed under spare tireNow we begin disassembling the stock rear suspension. If you do not have access to jack-stands that are tall enough to support the rear frame-rails with the wheels off of the ground, try using the rear wheels (once removed) to safely support the truck. With the front wheels on level ground, place a floor-jack under the rear differential and lift the truck up until the wheels are off the ground. Then remove the rear wheels and place them directly underneath the spare tire that is mounted under the bed. Slowly lower the truck down until it is resting entirely on the stack of wheels. This really isn’’’t as un-safe as it may sound (or look).

Place two jack-stands under the axle housing to support the axle when the leaf springs are removed. Position the floor jack under the pinion where the drive shaft U-joint attaches to the pinion yoke. That will help to adjust the pinion angle and keep the axle from rotating.

Removing factory rear TRD BilsteinSpray a generous amount of penetrating lubricant on the u-bolts/nuts and give it a few minutes to work down into the threads. Road grime can corrode these bolts in a very short time, making them hard to remove. A grinder with a cut-off wheel can make quick work of stubborn U-bolts.

Take advantage of the few minutes needed for the penetrating lubricant to loosen up the U-bolts to remove the rear shocks. Just remove the two bolts that hold the stock shocks in place and then slide them off the mounting posts.

Removing factory leaf-springsNow go back and remove all of the u-bolts and related hardware. Make sure that the axle-housing is supported so that it doesn’’’t fall and allow the pinion to rotate down (binding driveshaft u-joint or causing the slip-yoke to separate). Lower the axle housing a few inches to take the load completely off of the leaf springs. Keep an eye on the rear brake line, making sure not to damage it by stretching it too far.

Removing rear shackleRemove the upper and lower shackle nuts and then slide the inner shackle plate off. The shackle bolts are pressed-in to the outer shackle plate, so the bolts will come out at the same time the outer shackle plate is removed.

Removing front leaf-spring boltNext remove the single bolt that mounts the front end of the leaf spring to the spring perch. Then remove the leaf spring and set it aside.

Installing new leaf-spring bushingInstall the supplied polyurethane bushing and sleeves into the Deaver leaf spring packs. Make sure to grease the inside of the bushings before installing the bushing spacer. It is not necessary to grease the outside of the bushings before installing them in the leaf spring because they do not rotate within the springs. We like to use general-purpose marine grease because it seems to hold up well against wet and gritty conditions.

Fasteni9ng front leaf-spring to perchThen we installed the new leaf spring onto the truck. It’’’s easiest to install the main (front) spring mount first. Note that the double-wrapped end of the spring goes towards the front of the truck. The front leaf spring mount takes most of the drive-train stress, and the double-wrap also helps to fight axle-wrap (wheel hop).

Installing shackle with new leaf-springMount the rear of the leaf spring back onto the shackle. We decided to grease the upper bushings since we already had everything apart. Then install the inner shackle plate and hardware. We didn’’’t tighten down any of the hardware until all of the parts were installed because it’’’s helpful to be able to shift the various components around to get everything lined up perfectly.

New Deaver 7-leaf packFacatory 3+overload leaf-packLine up the centering hole on the axle pad with the leaf spring centering pin and then use the floor jack to raise the axle into location. Slide the new u-bolts over the leaf springs (reusing the factory bump stops and u-bolt plates). Then tighten down all of the leaf-spring mounting hardware. Notice how the new Deaver leaf springs have seven individual leafs, compared to the stock leaf spring which has only three leafs and one thick over-load spring. The new Deaver spring-pack has a much deeper and more progressive feel than the harsh stock over-load spring.

Comparison of Bilstein 5100 shocks to factory TRD BilsteinsThe new Bilstein shocks (bottom) are noticeably larger in diameter than the old TRD Bilstein shocks that they are replacing. The new shocks also allow for an additional inch of wheel travel on extension. Also notice that in both pairs of shocks, one is slightly longer than the other. This is because the shocks are mounted on opposite sides of the axle-housing to help fight spring-wrap (wheel hop). Make sure to install the longer shock on the passenger-side.

New Bilstein shock bushingInstalling new BilsteinThe Bilstein shocks come with universal bushings installed in the mounting eyelets. You will need to press these out and replace them with the supplied Tacoma specific bushings. We applied marine grease to the new bushings before installing them into the shocks. After the Tacoma bushings are installed you can slide the new shocks on to the stock mounting posts and tighten them re-using the factory flat-washers and 17mm bolts.

COMPLETED INSTALLATION

Tacoma after completed installationWe immediately experienced a dramatic improvement in the handling of the Tacoma on-road. The ride quality is amazing compared to stock. Once we got a chance to take it off-road the performance was even more obvious. The suspension is compliant and progressive. Body roll is less perceptible, and front and rear suspension feel more balanced. In fact, the performance of the Donahoe equipped truck comes embarrassingly close to that of our long-travel Tacoma. For the money, this is hands-down the best investment that any Tacoma owner could make in the performance of their truck.

Front 33x10.50 stuffedThis image shows the driver’s side front suspension at close to full compression with a 33×10.5” BFG Mud-Terrain tire. We experienced minor rubbing on full compression while turning, but that was easily eliminated by trimming a small section of the plastic inner fender-well at the fire-wall.

Rear tire stuffedthree-quarter angle of rear tire stuffedThese images show the passenger’’?s side rear suspension on articulated full compression. It seems like there are some inconsistencies in chassis/body/suspension tolerances from year-to-year or model-to-model. Our 33” tires rub on the forward edge of the wheelwell opening, while other owners have experienced rubbing at the rear of the wheelwell opening. Unfortunately there, doesn’’’t seem to be one fix that will work for everyone, because the problem is Toyota’’’s manufacturing tolerances. We are working on a solution and will update this article with any progress or solutions.
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