1-51385091-0 OEM Fit Lower Spring Seat Trunnion Seat High-Strength Cast Iron for ISUZU CYZ51 6WF1

The Lower Spring Seat with OEM numbers 1-51385091-0 and 1513850910 is a verified direct-fit replacement for ISUZU CYZ51 / CXZ51K / EXZ51K / CYZ51L / CXZ81K heavy-duty trucks equipped with 6WF1 / 10PE1 diesel engines. This lower spring seat is the core load-bearing component of the rear suspension trunnion system, mounted between the trunnion shaft housing and the leaf spring. It is responsible for carrying the vertical load of the leaf spring and transmitting it to the trunnion shaft and chassis frame, ensuring stable suspension performance under heavy loads and challenging road conditions.

The rear suspension lower spring seat is a critical load-bearing component in the rear suspension system of heavy-duty trucks, connecting the leaf spring to the trunnion shaft. It is mounted on the trunnion shaft housing and provides a stable support surface for the leaf spring. When the vehicle travels over uneven road surfaces, the leaf spring transmits vertical loads through the lower spring seat to the trunnion shaft, which then transfers the load to the chassis frame through the bracket. The lower spring seat must withstand high-frequency cyclic loads and impact forces, which is why it is manufactured from high-strength cast iron with excellent compressive strength and wear resistance. Its cylindrical design with flange ensures precise fit and secure mounting to the trunnion shaft housing. The 6WF1 is a 14.256L inline-six diesel engine producing 330–370 PS, used from 1999 to 2007. The 10PE1 is a 15.7L inline-six diesel engine.

Replace the lower spring seat when any of these symptoms appear:

• Abnormal noise or metallic clunking from the rear suspension — worn or cracked spring seat creates clearance between the leaf spring and trunnion shaft housing, causing metal-to-metal contact.
• Leaf spring misalignment or shifting — worn or deformed spring seat prevents the leaf spring from maintaining its correct position, affecting suspension geometry.
• Vehicle pulling to one side or abnormal rear axle alignment — spring seat failure causes uneven suspension height, leading to steering pull.
• Visible cracks or breakage on the spring seat — long-term high-load operation causes fatigue cracks in the cast iron, potentially leading to complete fracture.
• Oil leakage at the trunnion shaft area — deformed spring seat or damaged sealing surface causes trunnion shaft oil seal failure and lubricant leakage.
• Abnormal tire wear — suspension geometry deviation changes rear wheel alignment parameters, causing irregular tire wear.

1. Preparation: Raise the vehicle on a hoist. Support the rear axle and suspension system. Relieve leaf spring tension.
2. Removal: Remove the U-bolts. Remove the leaf spring. Remove the lower spring seat mounting bolts and withdraw the old spring seat.
3. Inspection: Inspect the spring seat for cracks, deformation, or contact surface wear. Inspect the trunnion shaft housing mating surface for wear or deformation. Inspect the leaf spring for cracks or deformation.
4. Installation: Clean the trunnion shaft housing mating surface. Install the new lower spring seat onto the trunnion shaft housing. Torque the mounting bolts to specification.
5. Leaf Spring Installation: Position the leaf spring onto the lower spring seat. Install the U-bolts and torque the nuts to specification.
6. Final Check: Verify the leaf spring is properly seated and centered. Confirm all fasteners are torqued to specification.
7. Road Test: Lower the vehicle and perform a road test to verify proper rear suspension operation and absence of abnormal noise.

• Every 10,000 km: Inspect lower spring seat for cracks or deformation. Check U-bolt torque.
• Every 40,000–50,000 km: Inspect spring seat contact surface for wear. Check leaf spring and trunnion shaft bushings.
• Every 100,000 km: Perform magnetic particle inspection (MT) on the lower spring seat. Replace worn bushings and bracket.
• When abnormal rear suspension noise or pulling is detected: Inspect the lower spring seat and trunnion shaft system immediately.
• At any rear suspension service: Always inspect the lower spring seat and replace if any abnormality is found.

• Standard Packaging: Anti-rust oil + VCI film + neutral carton.
• Custom Packaging: Neutral box, color box, or customer-branded packaging.
• Suitable For: Heavy-truck suspension repair shops, ISUZU parts distributors, fleet maintenance centers, concrete pump truck service stations.
• Supply Capacity: Stable batch supply with batch-level quality reports available.
• MOQ: Small quantities accepted (quantity discounts available).