Product Description
Superior-grade idler caster assembly for electric lift trucks, featuring an 8 inch by 4 inch high-impact polyurethane wheel (95A durometer) with cludg ball bearings. Assembly includes wheel, bearings, and axle in EZ compound format. Manufacturer part SU S684-XL-A, cross-reference SU684-XL-A / SU 684-XL-A. Compatible with Liftsplus.com electric lift truck castings requiring this size and design.
Specifications: 8.000 inch diameter x 4.000 inch width (8.000" x 4.000" | 8 x 4 wheel | 8 x 4 | 203.20mm x 101.60mm)
Specifications
Material & Construction
| Wheel Material | High-impact polyurethane compound |
| Bearing Housing Material | Machined steel |
Part Numbers
| Manufacturer Part Number | SU S684-XL-A |
| OEM Part Number | SU S684 |
| Cross-Reference Part Numbers | SU684-XL-A, SU 684-XL-A |
Wheel Dimensions
| Outside Diameter | 8 |
| Inside Diameter | 2.25 |
| Width Side to Side | 4 |
| Bore Depth | 0.63 |
| Bore Outside Diameter | 2.4404 |
Frequently Asked Questions
Q: What is the difference between the SU S684 and SU S684-XL-A idler caster assemblies?
A: The SU S684 is the base designation for an 8 inch diameter by 4 inch width idler caster assembly with 95A durometer polyurethane wheel. The SU S684-XL-A variant upgrades the compound to XL polyurethane with XL3 bonding technology, offering extended service life and superior durability. Both share the same core dimensions (8 inch diameter, 4 inch width) and bearing configuration. The XL-A designation indicates the assembly includes precision ball bearings and is pre-assembled in EZ compound format, ready for bolt-on installation. Choose the base S684 for standard duty, or select the S684-XL-A for high-cycle warehouse operations requiring extended wheel life.
Q: What is an idler caster, and where is the SU S684 installed on an electric lift truck?
A: An idler caster is a freely-rotating non-powered wheel assembly that supports the frame and improves steering and stability. Idler casters are typically mounted at the front or rear of the truck frame to provide directional support and reduce turning effort. The SU S684 (8 inch by 4 inch assembly) is used on larger-frame electric lift trucks. The assembly includes the wheel, bearing housing, ball bearings, and axle in one preassembled unit. Do not confuse idler wheels with load wheels; idler wheels support only frame weight, while load wheels support lifted cargo. Verify your truck design and consult the manual to confirm correct idler wheel size and mounting location.
Q: Are the cross-reference part numbers SU684-XL-A and SU 684-XL-A interchangeable, and what other part numbers reference the SU S684?
A: Yes, SU684-XL-A and SU 684-XL-A are the same part; the space in the second variant is a formatting variation. Both refer to the high-durability XL assembly version. The base designation SU S684 cross-references to SU S684-XL-A as the upgraded variant. Additional equivalent part numbers may exist in different manufacturer catalogs; contact your supplier for complete cross-reference documentation. When ordering, specify the exact part number including the dash and suffix (S684-XL-A) to ensure correct shipment. Omitting the suffix may result in shipment of the standard S684 instead of the XL-A variant.
Q: What is the installation process for the SU S684 preassembled caster assembly, and are any tools required?
A: The SU S684 is supplied fully assembled and requires only bolt-on installation to the truck frame. Park the truck on level ground and engage the emergency brake. Position the caster assembly against the mounting location on the frame. Align the bolt holes and slide bolts through the frame and caster housing. Tighten bolts with an appropriately sized wrench or socket (typically 3/8 inch or 1/2 inch) to the torque specification in your truck manual, usually 40 to 80 ft-lbs. Do not over-tighten, as this stresses the casting. Spin the wheel by hand to confirm free rotation. No bearing packing, greasing, or adjustment is required prior to installation for the EZ-format assembly, though you should inspect bearings every 500 hours during operation.
Q: How do I diagnose bearing failure in the SU S684 caster assembly?
A: A failed bearing produces grinding, squealing, or rumbling noises from the wheel area that increase with truck motion. Feel the bearing housing; a failed bearing may feel hot or very warm to the touch (warn: do not touch immediately after operation). Spin the wheel by hand; a defective bearing may resist rotation or produce grinding sounds. Watch for excessive side-to-side play in the wheel when grasped and wiggled. Inspect for grease leakage from the bearing seals or discoloration around the bearing housing. If you observe any of these symptoms, reduce operation to essential tasks only and schedule bearing replacement. Continued operation with failed bearings risks loss of wheel support and potential truck tip-over.
Q: What maintenance intervals and procedures apply to the SU S684-XL-A ball bearing assembly?
A: Inspect the SU S684-XL-A weekly for debris, noise, or play. Clean the wheel and housing monthly to prevent dirt accumulation. Repack ball bearings with appropriate multipurpose lithium grease every 500 operating hours or every 6 months, whichever comes first. Remove the caster from the truck, remove the axle bolt, slide the wheel off, and pack the bearing cavity 50 percent full with fresh grease. Reinstall the wheel, axle bolt, and reassemble the mounting. Check bearing preload by spinning the wheel; it should rotate freely with no resistance or grinding. Store the assembled caster indoors in a dry location when not in use. Do not store the assembly in wet environments, as moisture corrodes bearings and shortens service life.