A trailer suspension equalizer, or rocker beam, is the pivoting link at the centre of a tandem-axle leaf-spring suspension that transfers load between the front and rear springs so both axles share the payload and follow uneven ground. We fit it to dry-van, flatbed, tanker and low-loader trailers as well as to heavy haulage dollies. We cast the equalizer in ductile iron or low-alloy cast steel because it is a compact, heavily loaded beam with two spring-end sockets, a centre pivot boss and deep web sections that see reversing loads over millions of kilometres. Casting allows the web to be tapered and cored so material follows the bending moment, and CNC machining of the pivot bore and spring seats keeps axle spacing, ride height and equalizer travel within specification.
Specifications
| Parameter | Specification |
|---|---|
| Material options | Ductile iron QT500-7, QT600-3; low-alloy cast steel; 42CrMo4 for extreme duty |
| Casting process | Resin sand casting with cored centre boss; shell or investment casting for smaller beams |
| Machining | CNC boring of centre pivot bore, milling of spring-end seats and lock faces |
| Casting tolerance | ISO 8062-3 DCTG CT6 on machined zones, CT7 as-cast general |
| Machining tolerance | Centre bore H8 with 0.05 mm cylindricity, spring seat spacing within 0.5 mm |
| Surface finish | Ra 3.2 um on pivot bore and spring seats, Ra 12.5 um as-cast external |
| NDT | Magnetic particle inspection on the centre boss and web radii, ultrasonic testing on steel castings, hardness check per batch |
| Heat treatment | Normalising and tempering for iron grades; quench and temper for alloy steel to specified tensile range |
| Dimensional validation | 100 percent gauge check of centre bore and seat spacing, CMM layout per batch |
| Documentation | PPAP Level 3, FAI report, EN 10204 3.1, CMM report, heat treatment chart |
Key features
- Tapered web sections place material where the bending moment peaks, cutting mass without losing stiffness
- Cored centre pivot boss machined for pressed-in bronze bushing or maintenance-free polymer bush
- Spring-end seats machined flat and parallel to control axle spacing and ride height
- Controlled nodularity and pearlite content for fatigue resistance under reversing load
- Interchangeable with common tandem suspension geometries; custom centre-to-centre lengths available
- Optional cast-in grease passage and lubrication fitting boss
Applications
- Tandem and tri-axle dry-van and reefer trailer suspensions
- Flatbed and curtain-sider trailer running gear
- Tanker and bulk haulage trailer suspensions
- Low-loader and heavy haulage trailer bogies
- Dolly and converter dolly suspension assemblies
Quality and compliance
Moreover, equalizer rocker castings are manufactured under an IATF 16949 certified system with PPAP Level 3 documentation. First article inspection and full dimensional layout verify centre-to-centre spring seat spacing, pivot bore geometry and seat parallelism, and every batch ships with an EN 10204 3.1 material certificate and heat treatment chart. Magnetic particle inspection covers the centre boss and web radii, the areas where fatigue cracks initiate, at a frequency agreed in the control plan, and ultrasonic testing is applied to alloy steel variants. CMM reports and SPC data on pivot bore diameter are available for each production run, and traceability marks link every finished part to its melt, heat treatment batch and inspection record.
FAQ
Which material gives the longest service life?
Generally, ductile iron QT500-7 covers most on-highway tandem applications. We choose QT600-3 or low-alloy cast steel for heavy haulage, mining and severe off-road duty where impact and overload capacity drive the design.
Can you supply the equalizer as a kit with bushings and pins?
Yes. We deliver bare machined castings or complete kits including bushings, centre bolts, lock nuts and lubrication fittings, packaged to customer part numbers.
How is the pivot bore machined?
The centre boss is cored in the casting, then rough and finish bored on a CNC machine in one clamping so bore axis and spring seat faces stay perpendicular within tolerance.
Do you offer aftermarket replacements for common suspension brands?
We manufacture to drawing for both OEM and aftermarket programmes. Send a sample or print and we will confirm interchangeability before tooling.
What is the fatigue test approach?
Parts from production-intent tooling are rig tested at constant amplitude and block-spectrum loading to the customer duty cycle, with a typical target of one to two million cycles at the rated axle load.
CTA
Need a quote for Trailer Suspension Equalizer Rocker Casting? Send your drawing to sales@cnsandcasting.com or WhatsApp +86 137 7712 4360 for a fast RFQ response from Ningbo Ruican.
