OME Leaf Spring Suspension System
Http:// Short Cuts

By: Joe Micciche. June, 2001.

After finally growing tired of my flattened and leaning rear springs, I started researching replacement springs and shocks for my '94 Extracab truck. The stock springs were 6 years old and had endured hauling, wheeling, and 98k miles and had progressively flattened out, so much that I had to slightly lower the front end to keep the truck level. Additionally, the Rancho 9000 shocks were ineffective at damping the ride on any setting, and I found that they did not last long at all in our long, salty winters.

I began looking for near-stock height replacement springs. Unfortunately, these are in short supply, as most leaf spring packs are geared toward 3" or more of lift. Since I wasn't looking to install an IFS lift or max out on torsion bar cranking, none of these available packs were considered. Longer shackles and new shocks were not a viable option due to the lost load-carrying capability of the stock springs. My shopping list became very short since there just weren't many options to suit my needs. Fortunately, one of the options available - after plenty of research - turned out to be a superior product engineered specifically for my truck.

OME Spring and Shock Features

OME springs, shocks, u-bolts, and bushings ready to install.
The stock springs (top) appear longer than the new OME's.

Old Man Emu (OME), which is part of the ARB family, has a heritage of producing superbly constructed, tuned suspension systems for a variety of 4WD vehicles used in demanding conditions. Each OME system is rigorously tested on the candidate vehicle in harsh Australian conditions, including miles of corrugated track, mountain trails, and every available adverse off-road condition in Australia. Each spring and shock combination is hand-built and -valved for the vehicle by seasoned suspension engineers; then tested, tweaked, and retested until the system works perfectly.

OME's leaf springs are a model of how springs should be manufactured. Each spring is shot peened on the tension side to reduce stress; scragged and load tested to ensure proper set and height; and the ends are draw-tapered and diamond cut to minimize friction and ensure even load distribution. The leafs I installed also feature a full military wrap on the forward end as a safety measure in case the main leaf should ever break, and they also have a flat spring pad surface to mate perfectly to the axle spring pad. Finally, the springs are fitted with greasable nylon inserts at the rear spring end, three clamps with nylon liners keep the springs aligned and squeak-free, and each leaf is finished with a graphite coating. OME's trademark yellow polyurethane bushings are installed in the spring eyes as well.

The OME low-pressure gas charged shocks next to stock replacement RS9000s.

To complement the springs and achieve the promise of the integrated OME system, OME's Nitrocharger shocks are recommended. The shocks are also overbuilt, featuring massive 18mm rods, a steel dust cover, and a low-pressure nitrogen charge. The twin-tube body houses a teflon-coated rod guide bushing for smooth operation, a triple-lip check valve seal for superior oil and gas retention and preventing debris from entering the body, and a compression valve for superior ride control and to prevent bottoming out. The shocks measure 22.75" extended and 14.5" compressed, which allows for full bumpstop travel with the lift springs but is nearly the same overall stroke as stock-length shocks. The real beauty of these shocks is they are valved to work with the springs, as opposed to selecting a separate set of shocks and hoping for the best. OME offers different proprietary valving options depending on how the truck is to be used, and each shock features three circuits: a bypass (or "bleed") circuit controls the rebound and compression at slow speeds and allows for a softer ride over rough terrain, then at speed this circuit is completely open in favor of the normal rebound and compression valves. OME also includes their yellow poly bushings for the shocks.

Ordering and Installation

Keeping in mind all the features of the OME components, I went ahead and ordered the exact wrong springs and shocks. Having a firm grasp of one's needs and working with a knowledgeable OME distributor are key to maximizing the results, but unfortunately I was given incorrect part numbers from a mail order/internet retailer. I wanted modest lift for a truck used as a daily driver, weekend project hauler, and offroader - in essence, I wanted the "regular" OME180 springs and soft shocks, but wound up with the constant-load springs and firm shocks. I failed to cross-reference part numbers and application with my local ARB/OME distributor prior to ordering, which ultimately added some frustration and additional work to this installation. Fortunately, Matt Peters at Peters Offroad (my local ARB distributor) was very patient and willing to help resolve any issues that arose, and offered sound technical advice throughout this process.

The constant-load springs (OME18) are engineered to provide 50mm lift while carrying a 240-pound load, whereas the OME180 springs are designed to provide 2" of lift with no load. The spring rate is the same for both spring packs, but the OME18 springs are arched higher to maintain the 2" lift under load: both springs are dual-stage and the base rate starts out in the low 100 lb. per inch range and concludes in the upper 400 lb. per inch area. The firm Nitrocharger 85 shocks provide a sharper ride with firmer valve codes, again to better manage ride when the truck is loaded.

I didn't realize any of this until well after the installation. Installing the leaf springs and shocks is the same as with any other new pack: lift the rear end by the differential and secure the frame on jackstands, then remove the rear wheels. We lowered the axle with the floor jack to unseat the spring pins, and supported the axle with jackstands so as not to overextend the brake line or emergency brake cable. We then removed the shackles, which required a crowbar to get out since the shackle pins were seized to the metal tube inside the stock rubber bushing. The u-bolts were removed, then the forward spring hanger bolts were removed. The passenger side was quite a challenge since it too was seized to the sleeve in the bushing, so we cut this bolt out - while being mindful of the gas tank and fuel lines. The springs were removed from the axle and discarded.

PB Blaster and an air wrench are invaluable when removing parts in the Rustbelt!

In this installation, I elected to use custom unbraced shackles, so we didn't have to press the stock shackles out of the spring. We installed the OME SB43 polyurethane shackle hanger bushings in the frame and liberally coated the inner bolt surfaces with anti-seize, and applied a coat of anti-seize to the inner spring eye bushings. OME recommends that the outer bushing surfaces not be coated with grease or anti-seize, since the ribbed surface is intended as a "traction" surface and the only components which should be turning are the bolts inside the bushings.

I also used new, longer OME U53B u-bolts on the springs, torqued to 90 ft. lbs. With the springs loosely bolted in the hanger and shackle, we jiggled the axle into location under the springs, jacked it up slightly, and jiggled it more to seat the spring center pins in the axle spring pads. The axle was jacked up to allow reinstallation of the tires, then the entire truck dropped back down. The shocks were installed, and then we torqued down the shackle bolts to 67 ft. lbs. and the front spring hanger bolts to 110 ft. lbs.

Initial Results, Suspension Tweaking, Complete Satisfaction!

Ready to drop the truck down and torque everything. Uh, not exactly what I had in mind.

The truck had a significant rake. Prior to the installation, I measured wheel lip to fender lip at 15 1/8" on the driver's side, and 14.5" on the passenger side with a 2" body lift. Initial results with the 1.5" longer (0.75" lift shackles) was 19" on each side - for 4" of lift! We loosened the spring hanger and shackles, jumped up and down on the rear bumper to help the truck settle, and wound up with - 19"! This obviously was not the result I had in mind, but I drove it anyway and hoped the springs would settle.

I also called ARB's U.S. headquarters to discuss the springs and lift, and this is when I discovered I had the wrong packs. Chris Wood of ARB recommended I load the bed with 350 - 400 lbs of weight to help the springs settle more quickly, and I redrilled the shackles to stock length to eliminate that lift. With the additional weight in the rear of the truck, the ride was surprisingly compliant on our awful, pot-holed roads. And after 500 miles with the weight, the springs did settle to 18" in conjunction with the redrilled shackles, but they were still a bit more lift than I wanted.

The bottom OME overloads were removed, which provided fantastic results and has not yet caused any problems. The full military wrap on the forward end of the springs.

Unsure of what to do next, I sought advice from several sources, and got as many opinions as people I asked. I finally decided to go ahead and pull the lowest, thickest overload leaf from the 6-leaf pack. The 5th leaf (also an overload) has two clamps riveted in and is the same thickness as the lowest leaf, so I thought lowest-leaf removal would be safe.

This move resulted in exceeded expectations! Removal of the lowest leaf meant another 1/2" of lost lift, and the ride was excellent. The soft springs with the firm shocks did result in some sharp impacts on the potholes, but offroad the combination conformed to terrain irregularities better than I expected. The springs helped isolate the body from axle reaction to obstacles, and only after viewing some pictures did I realize how well the springs were working.

But because my truck is a daily driver and completely unloaded most days, the ride with the N85 shocks was a slight bit harsh on the roads where the surface has been eaten away by salt, and the firm shocks didn't seem to fully complement the softened springs. The truck rode well, but I felt it could be even better, so I went ahead and ordered the N94 (softer, or "comfort") shocks. The primary difference between the N94 and N85 is softer compression and rebound valving, which is geared more toward daily use rather than regular loads or towing. With the new shocks mounted, the ride wound up being perfect for my needs!

The shackle angles are perfect. The full suspension, with several months of salt and mud applied. IFS notwithstanding, the rear works superb!

In all conditions, the OME18's with N94 provide a smooth, compliant ride - and after 5,000 miles (2,000 with the N94 shocks) the springs are fully broken in and have settled to 2" of lift. Both the highway and city street feel are confident and controlled, with no discernible additional body lean and no bouncing or floatiness. When I've had the truck on the trails, the combination is perfectly settled: even wheeling with several hundred pounds of gear and firewood I have experienced a smooth ride with excellent absorption of rough terrain and greatly minimized pitch. The springs flex as well - with or without a load - as the worn out stock springs, and provide the best ride since I have owned the truck. In all, the springs have worked out perfectly for my needs and after some slight tweaking, fulfill the superior ride claims of OME's integrated suspension system philosophy.

After installing the new springs and shocks, I started experiencing driveline vibrations. While this may not have been a direct result of the new springs, I did find that the driveline angles had changed. For information on troubleshooting and resolving this problem, please also see the Driveshaft Swap article.

Contacts Related Links
  • ARB / OME
    Dept. ORN
    20 S. Spokane St.
    Seattle, WA 98134
    Phone: 206.264.1669
    Fax: 206.264.1670
    Manufacturer of premium offroad accessories.

  • Peters Offroad
    Dept. ORN
    192 Roosevelt
    Salem, OH 44460
    Phone: 330.337.8903
    Fax: 330.337.8919
    ARB/OME sales, service, and installation.

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