HYUNDAI H1

Despite its name, a leaf spring serves multiple purposes. Its main function is to link the axle and chassis, making it a crucial component. Consequence: If the leaf spring, particularly the main spring leaf, is broken or missing, the axle is not properly fixed to the chassis. In extreme cases, the axle may even move out of position, causing the vehicle to lose control on the road.

The leaf spring is responsible for keeping the axle in the correct direction. As a result, if the leaf spring does not have the correct dimensions, or especially if there are leaf springs with different dimensions on the left and right sides, the axle will not be parallel and the vehicle's driving conditions will be negatively affected. For example, there may be excessive tire wear or the vehicle may pull to the left or right.

The leaf spring is a crucial component of the suspension system, which typically includes the following main parts:

• leafSpring
• Shock absorber
• Bump stop
• Stabilizer bar (optional based on different models and axle load categories)

The suspension system is composed of these parts, which work together to maximize tire-road contact, provide stability and good handling, evenly support the weight of the vehicle, and ensure passenger (and cargo) comfort by absorbing and dampening shocks.

Although leaf spring suspension is over 150 years old, it is not outdated. Leaf spring technology has developed significantly, especially in the last 40 years with the invention of the so-called parabolic leaf spring. Leaf springs remain the most efficient suspension for commercial vehicles.

Leaf springs are commonly used in the following vehicles nowadays:

• Heavy-duty trucks and trailers: 60% - 70% of these vehicles having leaf springs on their axles (front and/or rear). Nowadays, 70% to 80% of these vehicles use parabolic leaf springs, while 20% to 30% use multi-leaf springs. The remaining vehicles have air springs.
• Light commercial vehicles 3-7 tons: 90% of these vehicles have leaf springs on the rear axles and 10-20% also on the front axles. Most of these vehicles are equipped with parabolic leaf springs, while the rest have either air springs or torsion springs.
• Pickup Trucks: 90% of successful pickup truck brands use leaf springs, mainly traditional multi-leaf springs.

The spring steels commonly used for producing leaf springs in modern European vehicles are:

• 51CrV4: contains 0,51% Carbon, 1,1% Chromium and 0,2% Vanadium (mainly for parabolic leaf springs)
• 55Cr3: contains 0,51% Carbon, 0,7% Chromium and 0,7% Manganese (mainly for conventional leaf springs depending on cross sections)

Leaf spring breakages can have several causes, and it can be difficult to determine the exact root cause. However, the typical causes are listed below. Please note that these explanations are simplified for easy understanding. Leaf spring (suspension) technology and steel technology (metallurgy) are special sciences.

• Micro cracks on the surface can originate from production or mechanical damage during assembly or usage, such as when a stone hits from the road.
• Non-metallic inclusions are compound materials embedded inside steel during the manufacturing process. They have a different chemical origin and give different mechanical properties to steel, such as formability, toughness, machinability, and corrosion resistance.
• Improper heat treatment process: When producing spring leaves, heat treatment is one of the final steps to ensure that the spring steel is in optimal condition.
• Surface decarbonization can occur when repairing leaf springs in a small forging shop. Heating the spring leaf in an open fire can cause significant carbon to burn out from the surface, leading to the formation of microcracks.
• Corrosion that begins on the surface of the steel will spread throughout the material.
• Breakage on the leaf spring center hole: U-bolts were not tightened to the specified torque.
• Breakage on the leaf spring eye may be caused by a production failure, worn leaf spring bushings, or corroded spring shafts.
• Continuous overloading of the vehicle.
• Intensive/extreme suspension usage due to poor road conditions.
• Design mistakes by vehicle manufacturers may occur when the leaf spring or suspension design is inadequate.

Overall, if the leaf spring is broken, you cannot blame yourself for any mistakes. However, you must purchase a new leaf spring as soon as possible.

There are six main criteria to consider when deciding whether you can drive with a broken leaf spring:

1. Where (in which position) did the leaf spring break?
2. Is the leaf spring a single leaf or a spring pack with multiple leaves?
3. If your spring has multiple leaves, which leaf is broken?
4. Is your vehicle loaded or empty?
5. Does your vehicle have a stabilizer bar?
6. Are you willing to take a risk? (Consider the potential consequences of driving without a replacement.)

The most dangerous combination is when the single leaf (mono leaf) spring, or the main leaf of a spring pack, is broken between the axle and front fixing point, and the vehicle does not have a stabilizer bar.

In some cases, if the main spring leaf is not broken or if it is just another spring leaf that is broken, or if the main spring leaf is broken between the axle and the rear fixing point, the vehicle can still be used for a certain amount of time, but without carrying significant loads.

Leaf springs can have problems, other than just breakages.

• The main issue is usually that the leaf spring is too weak, causing the rear of the vehicle to sag or sway. Leaf springs wear out over time, typically after 5 to 10 years. The solution is to replace the leaf springs.
• Weak leaf spring design is a common issue, especially when the vehicle is carrying its maximum payload or is constantly under load, such as vehicles with cranes, lifting panels, or camper vans.
• The leaf spring may weaken after a few months of use, which is often due to a production issue resulting from improper execution of the heat treatment process.
• Furthermore, leaf springs may produce squeaking noises during operation. This typically occurs when plastic or rubber parts between the spring leaves are worn or missing.
• Leaf spring suspensions may be too harsh for some users, especially if the vehicle is not carrying any cargo. While leaf spring suspensions have several advantages, comfort is not their main feature.

Our Online Shop offers four options for selecting and ordering leaf springs:

• If you know the article number (OEM number) of the leaf spring, you can find it directly in the online shop. This ensures that you order the right leaf spring with 100% certainty.
• Submit the data of your vehicle as an online inquiry. Based on the production year and VIN number, we will identify the appropriate leaf spring.
• To order the appropriate leaf spring, provide the production year and number of spring leaves.
• If you measure the main dimensions of your leaf spring, such as length, thickness, width, and bending, we can offer a matching replacement.

Note: If you are unsure whether the suspension (leaf spring) of your second-hand vehicle has been modified, you can send a photo of your current leaf spring.

70% of our customers do not buy leaf springs in pairs and it rarely happens that they have to buy the 2nd leaf spring to the other side. However, it may be necessary to purchase leaf springs in pairs in certain cases:

• The vehicle is old and the non-broken leaf spring is weak. If a new leaf spring is installed, it may be stronger than the old one and cause the vehicle to become unlevel.
• The vehicle was driven with a broken leaf spring for an extended period of time, causing the opposite spring to be under tension and at a risk of breaking soon.
• Companies that aim to reduce risk and minimize service downtime typically prefer to replace both leaf springs once the vehicle is in service.

U-bolts are responsible for securely attaching the leaf springs to the axle, making them a crucial component. The nuts on the u-bolts must be tightened to a specific torque. Always refer to your vehicle's specifications for the correct torque.

• M8: 35 Nm
• M10: 75 Nm
• M12: 130 Nm
• M14: 200 Nm
• M16: 315 Nm
• M18: 440 Nm
• M20: 610 Nm
• M22: 830 Nm

These values apply to U-bolt thread surfaces that are free of oil or grease. If the surface is lubricated, reduce torque by 10% to 15%.