Techtalk - Monroe Magnum®

Techtalk - Monroe Magnum®

Shock Absorber Technology

The manufacturing process of Monroe Magnum axle shock absorbers includes a series of improved technical characteristics that make this shock absorber line one of the preferred designs of fleets and professional truck drivers around the world. The main characteristics of this shock are:


Monroe Magnum axle shock absorbers are designed and manufactured with a special blow-off rebound valve technology that helps provide better control and stability through higher forces at low piston speeds, thereby minimizing body roll. At the same time, the blow-off valve maintains these forces at comfortable levels at high piston speeds.

This technology helps provide a safer ride due to the fact that these “extra” efforts minimize cabin roll of the truck and increase handling and road holding of the truck.


The operation of this valve is very simple: Low speed disks are designed to provide higher rebound forces than in a normal valve. This produces increased roll control because the valve stops more quickly and effectively the movement as compared to other shock designs.


The base valve, located at the bottom of the working chamber, controls the flow of oil that passes from the working chamber to the reserve tube. Because this controlling function during compression of the shock absorber, the base valve is also known as the compression valve. In order to ensure optimum performance and extended service life, Monroe Magnum shock absorbers are equipped with a range of specially designed compression valves engineered and adjusted to work in the most demanding truck environments

Monroe Magnum Piston rod diameter chart

F5xxx Piston diameter → Ø1 45 mm / Piston rod diameter → Ø2 18 mm

 F1xxx Piston diameter → Ø1 35 mm /  Piston rod diameter Ø2 15.8 mm

  T5xxx Piston diameter → Ø1 45 mm /  Piston rod diameter Ø2 18 mm

T1xxx Piston diameter → Ø1 35 mm /  Piston rod diameter Ø2 15.8 mm

 Vxxxx Piston diameter → Ø1 35 mm /  Piston rod diameter Ø2 15.8 mm

  Vxxxx Piston diameter → Ø1 25,4 mm /  Piston rod diameter Ø2 11/12.5 mm


On commercial vehicles with air suspensions, the shock absorber limits

suspension travel. Shock absorbers also protect the air spring from over Ø1 travel, which could cause premature air spring failure.

The Hydraulic Lockout feature of Monroe Magnum shock absorbers/consists of a secondary piston positioned above the valving piston. This feature helps to transfer mechanical force through the entire diameter of the piston rod. Its primary function is to reduce the velocity at full extension. The hydraulic pressure created as the lockout piston travels into the extended rod guide collar reduces the velocity and minimizes metal-to-metal contact at full extension. This feature is available on 35 and 45 mm bore Monroe Magnum shock absorbers, reference T1xxx, T5xxx, B1xxx, B5xxx, F1xxx & F5xxx.

This prevents the shock absorber from breaking (due to a metal-to-metal contact) when the wheels come off the ground (getting onto ships, trains, unloading of containers, etc.) due to the amount of pressure transferred by the leaf springs or pneumatic springs (which were under high pressure due to the load they carry). This patented hydraulic lock-out piston protects the shock absorber under such aggressive situations, and helps ensure optimal operation where other shock absorbers might be damaged.


The function of the silent blocs is to ensure a good and elastic linkage between the shock absorbers and chassis while absorbing some of the vibrations produced at the shock absorber. The performance and service life of silent blocs are directly related to the quality of the rubber used in the manufacturing process and whether it has been “vulcanized” over the sleeve. The use of the wrong rubber composition could lead to premature destruction of the silent bloc, increasing vibration and potentially accelerating the wear of other components, including the tyres. The Monroe Magnum range features superior quality silent blocks for extended lifespan and outstanding shock performance.

Bonded bushings rubber that has been vulcanized over the sleeve – as used in most Monroe Magnum shock absorbers – is more resistant to wear and therefore offers better vibration isolation and longer lifetime.


Another element that will help ensure longer shock life is the choice of a high quality oil seal. This elastic element should be designed to withstand strong friction forces and high temperatures. Seal failure will lead to gas and/or oil leakage, which will render the shock non-functional and potentially reduce the safety of the vehicle. In order to ensure longer shock life, Monroe Magnum shock absorbers feature a technologically advanced Viton double-lip high-temperature-resistant oil seal designed to minimize leakage and help extend operating life under even the most demanding working conditions. This Viton oil seal allows Monroe Magnum shock absorbers to maintain excellent performance in temperatures up to 200ºC!


Monroe Magnum shock absorbers feature specially engineered semi-synthetic oils formulated for challenging operating environments. The choice of the right oil composition for each shock absorber application is a key factor that will determine its performance and lifetime. Depending on the configurations of the shock valves, diameter of the internal oil chambers, anticipated vehicle loads, operating ranges, effective stroke of the shock absorbers, etc, our Monroe design engineers select the right oil for each application.


A truck shock absorber on average performs around 132 million cycles every 120.000 km. This movement generates contact-related wear between the piston surface and the working chamber. In particular, this contact can generate areas of permanent damage over the anti-friction piston ring, which can then contaminate the oil and create potential leak paths.

Piston wear produces changes in a shock’s rebound and compression forces and resulting deterioration of a truck’s road holding and stability characteristics. This point is especially important while driving over icy roads, where road holding can become a serious issue for heavy vehicles.

 Other important side effect of a shock absorber malfunction, especially on commercial vehicles, is the potential related damage to tyres, which are comparatively much more expensive to replace than shock absorbers.

Safety has always been one of the key manufacturing standards for Monroe and, for that reason, all Monroe Magnum shock absorbers are equipped with rebound valves featuring a highly effective anti-wear coating.


Another important benefit of the Monroe Magnum range is the high-quality electrostatic paint process used during manufacture. In this process, shock absorbers are placed within a paint chamber while being given a positive electrical charge. Paint molecules that are negatively charged are attracted to all metallic surfaces for optimal paint coverage and consistency. Once the shock housings are correctly coated with paint, they receive a thermal treatment inside a heated chamber to harden the paint. Electrostatic painting process guarantees a more even finish, giving shock absorbers greater strength and durability in challenging environments related to water, salt spray, mud and other potential contaminants.


Each truck model has different design configurations: leaf springs, air springs, height, total weight, engine power, etc. With each configuration comes a unique set of ride and handling requirements. For this important reason, each Monroe Magnum shock absorber is individually engineer to meet the requirements of the corresponding axle and vehicle. This ensures that each shock provides a vehicle-specific ride experience, with superior hydraulic characteristics for a given use.


All Monroe aftermarket suspension parts are either ‘Original Spare Parts’ (OSP) or ‘Spare Parts of Matching Quality’ (SPMQ) as defined in Article I, Sections (u) and (t) of European Commission Regulation (EC)1400/2002 of July 31, 2002, commonly known as the Automotive Block Exemption Regulation. This means that all Monroe suspension parts are qualified replacements parts under vehicle manufacturer warranty.


Commercial vehicle shock absorbers control wheel movement to help keep your tyres in contact with the road. Shock absorbers are critical safety components that can affect tyre wear, stability, braking, vibration, driver comfort, and the life of other steering and suspension parts.


 Deterioration through normal operation

Each kilometre/mile of operation averages 1.087/1.750 stabilizing actions.

- 22 million cycles occur - after 20,000 km / 12,425 miles*

- 88 million cycles occur - after 80,000 km / 49,700 miles*

- 132 million cycles occur - after 120,000 km / 74,550 miles*

Monroe recommends to inspect your shock absorbers every 20.000 km!

Hydraulic fluid deterioration

Since you don’t change the oil in your shock absorbers, over time, the internal hydraulic fluid loses viscosity and elasticity, impairing the unit’s ability to dissipate road impacts.

Deterioration of shock components

The components within a shock absorber are made of metal, rubber and plastic, all of which eventually degrade through extended use, extreme on average heat, and adverse road and weather conditions.

Determination of a qualified repair technician

Not all symptoms of shock deterioration are readily noticeable; after a thorough inspection, a qualified repair technician may determine your truck’s shock absorbers have worn to the extent that hose units legitimately require replacement.

Oscar F. Oskarsson Senior Training Manager at Tenneco