When a motorist is informed by an auto-repair shop that their vehicle requires a water pump, the customer seldom requests a specific brand. Normally the shop makes the selection.

When it comes to selecting shocks and struts, Tenneco®, manufacturer of Monroe® Ride Control products, wants that service provider to know why Monroe should be the top recommendation whether the customer asks for one or not, said Joe Bacarella, manager of technical assistance for Tenneco. Monroe has had a major presence from the beginning. Today, and for decades, Tenneco, with the Monroe brand, has been an industry leading manufacturer of shocks and struts in the aftermarket and for OEMs, he said. Bacarella isn’t just “shooting from the hip.” He’s been a major team player at Tenneco for more than 37 years.

Constantly evolving

The Monroe brand itself has more than a 100-year history in damping technology dating back to its roots when the company developed one of the first automotive tire pumps using a unique valving technology that later played a role in the brand becoming a global provider of ride control.

For the repair facility, the Monroe name provides confidence on the product’s performance, durability, fit and availability, Bacarella said.

Mark Christiaanse, Tenneco’s director of engineering, ride performance, North America aftermarket, noted that the engineering, research and durability testing of products enables Monroe to produce cutting-edge products that include Quick-Strut® Complete Strut Assemblies and OESpectrum® shocks and struts, as well as additional lines of ride-control products for a variety of vehicles. The vast majority of its ride-control products are manufactured or assembled at its facility in Paragould, Ark.

“The Monroe brand doesn’t have to fall back on gimmickry,” Christiaanse said. “In the simplest terms, Tenneco uses more application-specific designs in ride control technology than any other company to help ensure, for example, that a Cadillac CTS handles like a Cadillac CTS and a Jeep Wrangler handles like a Jeep Wrangler,” he said. “Metallurgy, welding expertise, sealing, the importance of valving response and a multitude of other factors play a significant part in the development of every shock we produce,” Christiaanse said.

Bacarella adds that Monroe offers thousands of application-specific ride formulas to match each vehicle’s OE ride and handling profile, where some companies’ ride offerings are limited to soft, medium and stiff ride-control offerings.

Testing to the limits

The second phase of Monroe quality control involves testing every product it designs to the Nth degree before it ever becomes available to the aftermarket or the OEMs, Bacarella said. Part of the company’s expertise involves engineers designing products and then forcing them to fail under extraordinary testing circumstances. This not only provides longevity estimates, but also provides data to make them even more durable.

To illustrate Bacarella showed examples of two shock piston rods. The Monroe piston, under the most extreme tests will bend, which at worst would cause a vehicle to pull in one direction, he said. A competitor piston rod from an off-brand snapped in half, under the same abusive testing – which could make the vehicle very difficult to control, to say the least.

Monroe premium shock absorbers and struts and Quick-Strut assemblies come with the “Feel the Difference™ Guarantee” money-back offer when the consumer buys ride control products, front and rear. If the purchaser isn’t satisfied with the ride, they can get their money back or receive alternant design Monroe ride control products. The guarantee includes labor and a free wheel alignment.


In addition, the coverage is exceptional, Bacarella said, meaning the shop can easily meet a customer’s needs. Tenneco most recently announced the availability of 14 new Monroe Quick-Strut part numbers, extending coverage of the company’s popular premium replacement strut assemblies to more than 3 million additional late-model imports. With the latest expansion, Tenneco this year has introduced more than 150 Quick-Strut part numbers covering a combined total of about 16 million vehicles.

Technology advancements

The company’s innovative research brought about the introduction of the Monroe Quick-Strut strut assembly; the world’s first single, fully assembled mount, coil spring and strut in one unit, Christiaanse said. The introduction eased shop owner and technician’s replacement concerns; minimized installation time and the need of a strut compressor to complete the job. OESpectrum shocks, struts, truck shocks, and monotube shocks provide the right technology specific to each application, he added.

Ride-performance headquarters

So what happens before any Monroe shock or strut is released for sale? A tour of Tenneco’s North America Ride Performance Headquarters in Monroe, Mich., tells much of the story.

A scanning electron microscope (SEM) is a precision piece of equipment that analyzes testing failures for new designs and allows for the identification of the weakest link. It allows the engineering team to improve process and design prior to starting production on the manufacturing line. It’s capable of magnifying an object well beyond 100,000 times its actual size.

Tenneco’s environmental chambers are used to determine the stability of shocks and related parts by putting them through extreme environmental tests that under normal driving conditions could take years or even decades to replicate, Bacarella said. As a manufacturer for OEMs, Tenneco has continued to increase demands for longevity since vehicles are lasting longer. Monroe has testing chambers that are capable of salt, humidity and temperature change testing to meet the OE specifications and improve aftermarket applications.

“The corrosion resistance is not just for appearance – but the more-important structural integrity,” Bacarella said.

Tenneco’s metrology lab has two major functions, the first being to measure the surface finish of the strut rods. The outside diameter smoothness mates to the oil seal and provides a critical sealing function. A white light interferometer allows Tenneco to precisely measure inner land height of its powder metal shock pistons.


“Shocks must work over a variety of road inputs, from the simple ripple to a full pothole,” Bacarella said. “Bleed paths control the shock performance at slow speeds. Other discs come into play when a vehicle hits a pothole.”

Bacarella often gives the example of a doorway when he explains valve operation. If you are driving down the road and the vehicle crosses over an expansion joint, all the valving is closed, but we have what is called a “bleed” that can be compared to the spacing between the bottom of the door and the flooring. So, the oil can flow through that bleed. If the bleed is really large, the motion will be softer; if the bleed is really tight, the shock will provide the driver with better control.”

Valving discs take over during harsher rides. Depending on the vehicle design, the discs can have a range of bleeds from ½ to 8 bleeds to alter valving.

“If there is a mid-range transition, such as a crossing a bridge, that would require too much oil to flow through the “bleed” so the “door,” which is actually our deflective discs start to bend and open up and let more oil through. How thick those discs are, and how many discs we have stacked will determine what happens when the vehicle hits that transition.”

Another example is traveling over railroad tracks. That’s too much for the discs to open up all the way, and the orifices in the shock pistons take control. If orifices are too big, topping out or bottoming out can occur. If they are too small the ride is too stiff. Our dynamometer can give us numbers at different speeds in order for Tenneco to design a proper ride feel,” Bacarella said.

Component Development

The component-development section of the test center includes a single axle floor actuator that allows engineers to test the performance of a damper (shock) on a corner of a vehicle without taking it out on the road. The tool measures tire force variation of a specific damping combination.

Tenneco also duplicates the OEM tests for aftermarkets parts to make sure the parts comply with OEM specs. If Tenneco is not OE on a part, the team performs testing to determine what the OEM requirements are – to help ensure that Tenneco meets those specs for aftermarket parts.

The second portion of this testing section is exclusive to Tenneco. Fixtures confirm structural integrity of the shocks and struts for OEM and aftermarket. Several OEMs use some of the tests Tenneco has developed for their own standards. For the aftermarket, Tenneco can use this test equipment to fatigue an OE base assembly if Tenneco is not the provider to the OEM.

The lab also has the capability to test units on similar road inputs previously measured at test tracks.

Tenneco’s flow bench helps develop and test the compression and piston valving separate from the assembled shock. This tool fine-tunes new designs such as the company’s patented LST (Low Speed Tunability) and ASD (Acceleration-Sensitive Damping) technology.

The Module Lab simulates the full corner loading for a suspension. It is designed to allow axial and side loading of the complete strut assembly to provide an accelerated durability test.

Tenneco uses temperature chambers to provide -40C to +80C temperature environments to measure the effects on oil it uses in its ride control products, allowing all four corners of the vehicle to be tested at once.

A Tri-Axis test provides cyclic loading into the rod-guide area of the strut or shock assembly. Also included is a dirt ingestion test to replicate the fine sand and dirt that the shock is exposed to during operation. The oil-seal design includes a wiper to keep these type of contaminates from being ingested into the shock.

“All of this comes down to producing the very best ride control product,” Christiaanse said.

Noise, vibration and harshness (NVH) concerns for ride control have increased dramatically over the years. The same type of anechoic chamber used for exhaust testing on Tenneco’s Walker brand is used to measure airborne and structurally transmitted noise from its shocks.

“Reducing NVH factors is more important than ever before since many vehicle components are thinner and more sensitive,” Christiaanse said.

“NVH becomes more noticeable as vehicles become more quiet, as they do with hybrids, electrics and stop/start technology,” Bacarella said. “The equipment identifies the shock’s natural frequency and adjusts the valving or mounts to cut out a frequency that is problematic. 

Engineering Garage

Tenneco’s five-bay garage allows technicians to inspect new vehicles to gather inspection data that is later used throughout the design process and by those who provide technical assistance to shops. Access to local dealer networks is critical to ensure the design and performance is tailored specifically to each vehicle. The data collected includes damping and spring curves as well as chassis suspension information.