Why Coil-Overs on an Expedition Vehicle?
Abstract Review
I chose the Donahoe coil-over’s for my truck for two reasons:
- Ride Quality: The stock Tacoma strut suspension is punishing! The front is too soft (does not control the truck’s weight through compression travel), resulting in the suspension bottoming out. And the rear is too stiff, and out of tune with the shocks.
- Durability: On my first trip into Mexico with my Tacoma, I drove the road from San Felipe to Gonzaga Bay in Baja California. The section of road from a few miles south of San Felipe to Puertocitos is probably the worst road surface I have encountered in 15 years of OHV travel. The route was originally paved, and has been left to decay, resulting in deep pot holes, cracks, ledges, washouts and severe corrugation. Within 10 miles, the stock shocks had completely faded, causing the front suspension to bottom frequently, and not control the cycling tires. Donahoe coil-overs are designed for exactly that type of punishment, with large shock bodies and aluminum construction for good heat dissipation. I have now used the Donahoe coil-over’s for nearly 10,000 miles on trails throughout the Southwest, Baja and mainland Mexico, and have never experienced fading or harsh bottoming! The ride quality is incredible.
On a typical expedition, the driver will spend hours behind the wheel every day for weeks, and even months on end. Ride quality and the method in which the suspension controls the payload is a measurable factor in reduced driver fatigue.
One of the strongest endorsements for the use of these coil-overs is Donahoe’s racing results. A nearly stock Tacoma Double-cab, running the Donahoe coil-overs won the 2004 SCORE Tecate Baja 1000 Stock-mini class and the 2004 Score Championship.
Understanding the Donahoe Coil-Over Technology
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Billet Aluminum Upper Mount: Billet aluminum components are typically lighter than cast components, as less material is required to maintain the same strength properties. The coil-overs billet aluminum parts are machined from solid bar stock and turned to finish diameter before being placed in a mill for final machining, boring and threading.
200 PSI Nitrogen Charged Internal Reservoir: The Donahoe shock does not use a remote reservoir, but an internal floating piston design. This is far superior to the typical nitrogen shock that is an emulsion design, which houses the oil and nitrogen in the same cylinder. Under high cycle rates and heat, the emulsion shock will fail as the oil and nitrogen mix cause foaming, which degrades valving performance. The nitrogen in the Donahoe coil-overs internal piston forces the oil through the shock valve during compression, resisting cavitation and improving shock responsiveness.
Cadmium Plated, Threaded Body: Cadmium plating is used for corrosion resistance. Cadmium can be applied at minimal thickness to maintain desired stack up tolerance (body to collar), yet still provide a minimum 120 hour corrosion resistance. Corrosion is measured by a 5% salt spray test to the point of development of white rust, which is the degradation of the chromate surface.
The threaded body allows infinite adjustment from 0″-3″ of lift at factory curb weight. The ride height is varied by the amount of preload on the coil.
Flutter Stack Compression Valving: The Donahoe coil-overs use a race piston with small valves (for low speed movement) and apertures (for high speed and impact response). The apertures are controlled by shimming, which is the most common method of making compression and rebound valving adjustments. The shims only deflect under high pressure (like hitting a hole at 30 mph) and allows the shock to react quickly to the impact force. The flutter stack valving used by Donahoe allows the shock shim stack to respond more efficiently to minor road surface imperfections and slow speed impacts.
TORCO Semi Synthetic 7wt Race Shock Oil: Donahoe uses Viscosity Grade (VG) 7, Torco RFF (Racing Fork Fluid) that has a high Viscosity Index (VI) formulation to ensure VG throughout a wide temperature range. Torco also formulates their oil as a synthetic blend with anti-friction and anti-stiction (stiction is a word combining physic elements of static (load) and friction) additives to improve shock efficiency and life. RFF is also blended with seal conditioners, anti-foaming and anti-oxidation additives. Shock oil quality is critical to maintaining consistent performance throughout the shock temperature range and service life.
(Specification: Viscosity at 100°C: 5.05, at 40°C: 16.1)
Chrome Silicon Coil Spring: Coil springs are manufactured from alloy spring steel wire, heat treated after drawing (for tensile strength) and formed into a specific diameter and wind rate. Chrome silicon steel is manufactured to the ASTM A 401 specification, which has the design characteristics of high endurance (cycling) and high heat tolerance. The high quality steel used allows Donahoe to fit a shorter spring (13″), which results in less coil bind at higher lift (preload) settings. The coil is rated as a 650lb. unit and is powder coated for improved corrosion protection.
7/8″ NitroSteel shaft: NitroSteel is manufactured by MacSteel, and uses their Nitrotec surface hardening process, which combines the nitriding (steel conversion at the surface to epsilon iron nitride at a depth of .001″) and iron oxide (also at .001″ thick), produces an extremely hard, corrosion resistant surface with a surface finish of 16 Ra. max. This allows the material to be used with no plating. Though costly, NitroSteel is a major quality advantage, providing longer surface life, better corrosion resistance and durability (pitting).
5/8″ PTFE Lined Spherical Bearing: The base of the coil-over is lined with Polytetrafluoroethylene (PTFE). PTFE is a vinyl polymer and is also known as teflon. The flourine atoms of PTFE are what gives the polymer its non-stick (lubricating) properties. The flourine atoms literally repel the metal surfaces of the machined bearing, reducing wear and allowing for smooth movement.
With the exception of the shock body, all aluminum components are black anodized.
Installation
Note: The reader assumes all responsibility for using these installation instructions. Expeditions West does not warranty these instructions as being accurate or appropriate for your application. Use them at your own risk.
Jack up the front of the vehicle and remove the tire. Secure the truck with jack stands, put the transmission in park (or 1st if manual) and set the parking brake.
For my application, I decided to permanently remove the front swaybar. I am not recommending this; it is just for information. My truck is not a daily driver and is only used on trails, expeditions or en route to those activities.
The first step is to remove the lower strut bolt. It may require light downward pressure on the lower control arm (LCA) to allow removal. With the bolt removed, the strut will be hanging by the upper mount.
There are three studs in the upper mount that secure the strut to the suspension bucket. Loosen the front nut, and then remove the back two. While holding the strut with one hand, remove the front bolt and slide the strut out of the bucket.
The lower mount uses a spherical bearing and two machined inserts to bring the id to diameter (of the lower mounting bolt) and position the coil-over correctly fore and aft. The positioning of the inserts is really the only critical item of the installation. The longer insert half must positioned on the midline side of the vehicle, which will space the coil-over further away from the CV axle.
Lift the coil-over into the bucket and hand thread the three bolts into the upper mount. The positioning will face the DR towards you. The Tacoma mounting holes are indicated by a machined marker (dimple) next to the holes. The newer versions of the coil-over come from the factory with studs already threaded in place, making the installation even easier.
Next, the lower mount needs to be positioned onto the bracket of the lower control arm. For my installation, only minor hand pressure was required to slide the mount into position. Some Tacomas may require the use of a lever bar, positioned above the upper control arm (UCA) body, and below the UCA mount. This will allow downward pressure to be exerted on the LCA (because of its connection to the UCA via the knuckle) and the coil to be moved into the mount. Use the stock lower mounting bolt.
The last step is to tighten the upper mounting bolts (3).
I used a spanner to lower the truck from the factory Donahoe setting (about 2″). My final setting was 1.5″ above stock. The CV axles are only at a slight angle at this height. The height of the truck can be varied by using the supplied spanner wrench and changing the preload on the coil spring.
Impressions
The Donahoe coil-overs have been on my truck for nearly six months now, and I could not be happier. This is a race proven, high quality, precision valved solution, with great attention to detail. They are noticeably stiffer than stock at slower speeds, but much smoother and controlled at medium to high speeds. When driving improved dirt tracks and fast trails these units are incredible. I have to keep slowing down, as I end up driving my 5,000lb. expedition truck like I am in the Baja 1000! Too much fun…
I will be fitting a bull bar and winch to the truck shortly, and will report back on any performance changes.
Picture courtesy of Bajataco.com
Vendor:
Donahoe Racing Enterprises (now ICON Vehicle Dynamics)
7929 Lincoln Avenue
Riverside, CA 92504
Phone: (951) 689-ICON [4266]
Fax: (951) 689-1016
Cost:
$950
*Pricing subject to change, contact vendor
Weight:
18 lbs. each for Donahoe coil-overs
3.5 lbs. each more than the stock strut
% of Available Payload:
Nil
Installation Time:
30-45 minutes with air tools; 90 without
Difficulty (Easy, Moderate, Difficult):
Easy
Specialty Tools Required:
None
Vehicle:
Expeditions West 2004 Toyota Tacoma Double Cab TRD
