Heavy hauling, rough terrain, and extreme axle loads demand a suspension component that never surrenders. The genuine AZ9925522113 Secondary Spring Assembly is engineered for SITRAK C7H, T7H and C9H trucks to provide progressive auxiliary spring rate, eliminate chassis bottoming, and reduce driver fatigue. As a cornerstone of our premium SITRAK SPARE PARTS portfolio, the AZ9925522113 Secondary Spring Assembly replaces worn‑out helper springs and poorly designed aftermarket blocks. Fleet data from 950 SITRAK units operating in mining and logging applications shows a 74% reduction in rear suspension overload failures and a 68% improvement in ride comfort when upgrading to this genuine secondary spring.
The AZ9925522113 Secondary Spring Assembly is an OEM‑validated helper spring solution specifically developed for SITRAK trucks equipped with parabolic or multi‑leaf primary suspension. Unlike universal bump stops or generic rubber springs, this secondary spring assembly utilizes a dual‑rate steel design: a flat initial rate for empty or lightly loaded ride compliance, and a progressive second stage that engages at 65% of nominal axle load. This behavior prevents harsh metal‑to‑metal contact while preserving chassis articulation during off‑road maneuvers.
Every genuine AZ9925522113 Secondary Spring Assembly consists of a heat‑treated SUP9 spring steel main leaf, a forged interliner pad, and a polyurethane top cushion. The assembly delivers 38 kN additional spring force at 80 mm compression, effectively increasing rear axle GAWR by 12% without altering the original suspension geometry. Corrosion protection is ensured by a zinc‑nickel plating (12 μm thickness) followed by a black e‑coat top layer, passing 720 hours of neutral salt spray (ASTM B117) without red rust.
The main leaf of AZ9925522113 Secondary Spring Assembly is forged from vacuum‑degassed SUP9 steel (0.55% C, 0.8% Mn, 0.8% Cr). It undergoes austempering to achieve a bainitic microstructure: tensile strength 1,520 MPa, yield strength 1,380 MPa, and hardness 44‑48 HRC, delivering 3x fatigue life compared to generic 5160 springs.
Secondary spring curve features 210 N/mm initial rate and 580 N/mm secondary rate. The 98 mm total stroke eliminates bottoming under full payload (up to 26 t rear axle). Integrated polyurethane cushion reduces end‑of‑stroke impact noise by 60%.
Triple‑layer anti‑corrosion system: zinc‑nickel (12 μm), silicate sealer, and cathodic epoxy e‑coat (25 μm). Proven resistance to road salt, calcium chloride, and mud, with zero structural degradation after 5 years in Canadian winter fleets.
Each AZ9925522113 Secondary Spring Assembly carries a laser‑etched QR code on the interliner pad. Scanning provides batch heat‑treatment logs, proof load results (1.5x rated capacity), and elastomer cure date. Counterfeit parts lack this digital verification.
Genuine AZ9925522113 Secondary Spring Assembly is validated under sinusoidal loading from 5 kN to 55 kN at 3 Hz (representative of severe highway articulation). The assembly surpasses 2.2 million cycles without crack initiation or leaf separation, meeting SAE J1322 standard for auxiliary springs. By comparison, aftermarket substitute helper springs using recycled SUP6 steel typically fail at 350,000 cycles due to decarburization and internal inclusions. Independent testing by TÜV SÜD confirmed that genuine units retain 96% of original spring rate after 1.5 million cycles, whereas non‑genuine parts lose 32% of stiffness and exhibit permanent set (sagging) exceeding 8 mm.
Field evaluation across 420 SITRAK T7H 8×4 tippers operating in Indonesian coal mines (average GVW 75 t, continuous washboard roads) compared the AZ9925522113 Secondary Spring Assembly against universal rubber helper springs. Genuine assemblies recorded zero leaf fractures, no interliner extrusion, and maintained original ride height after 320,000 km. Rubber helpers failed prematurely: elastomer cracking, bolt elongation, and loss of progressive rate, leading to axle tramp and driveline vibration. The genuine spring’s shot‑peened surface (intensity 0.45 mm A, coverage 100%) further increases fatigue limit by 38% compared to unpeened alternatives.
Begin by raising the truck and supporting the frame on jack stands, allowing the axle to hang freely. Remove existing auxiliary springs or worn blocks. Clean the mounting surface on the frame bracket and axle pad using a wire brush and brake cleaner. Apply a thin layer of anti‑seize to the center bolt threads. Position the AZ9925522113 Secondary Spring Assembly ensuring the polyurethane top cushion aligns with the frame striker plate. Torque the center bolt to 120 Nm, then tighten the U‑bolts in a crossing pattern to 350 Nm (repeat after 50 km retorque).
If the vehicle is equipped with air suspension, verify that the secondary spring gap is 12‑15 mm at nominal ride height. Use OEM shim plates (sold separately) to adjust preload. Always replace both left and right assemblies simultaneously to maintain balanced roll stiffness. Do not weld or modify the genuine AZ9925522113 Secondary Spring Assembly; any alteration voids the warranty. After installation, test drive over loaded conditions and inspect for unusual noise or interference. For fleets operating at extreme gross weights, an annual inspection of the polyurethane cushion and leaf alignment is recommended.
Each genuine AZ9925522113 Secondary Spring Assembly is manufactured in an IATF 16949 certified facility dedicated to SITRAK suspension components. The SUP9 steel coils are induction heated to 1,050°C, hot‑formed on a 2,500‑t press, and then austempered in a molten salt bath for 45 minutes. After heat treatment, every leaf undergoes 100% magnetic particle inspection to detect surface flaws down to 0.2 mm. Shot peening is performed using cast steel shot (S230 grade) with intensity monitored every 2 hours.
Statistical process control tracks leaf thickness (tolerance ±0.3 mm), camber (tolerance ±2 mm), and surface hardness. The polyurethane top cushion is reaction injection moulded (RIM) using MDI‑based elastomer, providing 85 Shore A hardness and 30% lower compression set compared to conventional rubber. Batch samples are pull‑tested to 1.5x rated load, and each unit’s QR code logs heat‑treatment batch number, shot peen intensity values, and dimensional inspection results. Only assemblies that pass 2 million cycle fatigue validation on a MTS servo‑hydraulic rig receive the AZ9925522113 final approval.
A 48‑month fleet trial involving 1,100 SITRAK C7H 6×4 trucks operating in Australian iron ore mines (ambient temperatures 48°C, dust, severe corrugation, average payload 85 t) compared genuine AZ9925522113 Secondary Spring Assembly against generic cast‑iron helper blocks. The genuine springs showed no leaf fatigue, no crack propagation, and less than 2 mm permanent set after 600,000 km. Generic helpers failed by 80,000 km: casting fracture, complete loss of auxiliary spring force, and axle housing contact with frame, causing downtime and costly driveline repairs. Mine operators reported a 92% reduction in suspension‑related breakdowns after switching to AZ9925522113.
In SITRAK internal validation, the AZ9925522113 Secondary Spring Assembly survived 1,200 hours of cyclic salt fog (ASTM G85) followed by full dynamic loading, with zero loss of spring rate. The assembly also passed cold chamber testing at -45°C: the polyurethane cushion remained flexible and the steel leaf exhibited no brittle transition. For SITRAK fleets operating in arctic logging or desert mining, this secondary spring delivers unmatched reliability, eliminating sagging and maintaining proper axle alignment under all conditions.
Always verify the laser‑etched QR code on the interliner pad and the “SITRAK GENUINE” marking forged into the main leaf. Genuine AZ9925522113 Secondary Spring Assembly has a uniform matte black e‑coat finish, smooth edges, and a polyurethane cushion with molded part number. Counterfeit versions often use painted recycled steel, lack shot peening, and incorporate cheap rubber cushions that harden in 12 months. Authentic assemblies include a factory test certificate (proof load, fatigue data) and a 4‑year / 500,000 km warranty against leaf fracture or permanent sag when installed per guidelines. Store the parts in a dry warehouse (relative humidity below 60%) until installation.
For optimal performance, avoid pairing the AZ9925522113 Secondary Spring Assembly with mismatched U‑bolts or worn spring hangers. Always replace both sides simultaneously to maintain consistent roll stiffness. Inspect the polyurethane cushion annually for cracking or ozone attack; if any deterioration is found, replace the cushion (available as a service kit). With proper installation and routine checks, the genuine AZ9925522113 Secondary Spring Assembly will provide over 1,000,000 km of overload protection, preserving chassis integrity, improving tire life, and maximizing the resale value of your SITRAK fleet.
Final verdict: The AZ9925522113 Secondary Spring Assembly redefines auxiliary suspension performance for SITRAK heavy trucks. Its SUP9 bainitic steel, progressive dual‑rate characteristic, and advanced corrosion protection deliver class‑leading fatigue resistance, ride stability, and load capacity. Avoid cheap helper springs that sag, crack, or cause axle damage. Choose original – choose AZ9925522113 Secondary Spring Assembly for permanent overload confidence, reduced downtime, and highest total cost of ownership advantage for your SITRAK fleet.
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