Essential Parts and Restoration Insights for a 1975 Caterpillar 988 Wheel Loader

[MikePhua]

Overview of the 1975 Cat 988
The 1975 Caterpillar 988 is a classic large wheel loader, powered by a C18-series diesel engine paired with a planetary transmission and heavy-duty axles. Built to move earth and aggregate in quarries, mining, and construction, these machines require careful sourcing of components due to their age and evolving part catalogs. Keeping one running means relying on a combination of genuine Cat parts, aftermarket kits, and refurbished components.
Key Parts Commonly Needed
Owners and restorers of 1975‑series 988 loaders typically seek the following critical parts for maintenance and restoration:

• Engine components (pistons, rings, bearings, gaskets)
  
• Transmission parts (clutch packs, seals, planet gears)
  
• Hydraulic pump and valve components
  
• Cylinder seal kits (lift, tilt, steering)
  
• Brake system components (discs, seals, axles)
  
• Bearings and bushings for loader linkage and axles
  
• Alternator and electrical parts
  
• Cooling system elements (radiator, hoses, fan clutch)
  

Seal kits for lift cylinder, bucket tilt cylinder, steering cylinder, and hydraulic pump are widely available for serial numbers 87A1-up and above . Comprehensive parts manuals for the 988 series—covering assembly breakdowns and part numbers—are available via Cat dealer catalogs and third-party title sellers dating back to April 1975 (e.g. serial 87A6832 and up) .
Restoration Focus: Cylinder Seals and Hydraulic Integrity
A core restoration task is replacing hydraulic cylinder seals before fluid contamination or rod scratching occurs. Typical seal kits include:

• Lift cylinder seal kit (rod ~3¼″, bore ~7¼″ or 8¼″)
  
• Bucket tilt cylinder seal kits (rod ~2½″ or 2¾″, bore ~6½″)
  
• Steering cylinder seal kit (rod ~2¼″, bore ~5″)
  
• Hydraulic pump seal kit (pump # 7J0592)
  

These kits typically cost $50–$250 depending on application and supplier .
Diagnostic and Parts Acquisition Stories
A restoration crew once inherited a 988 from the mid-1970s with visible oil leaks from lift and tilt cylinders. After installing seal kits and flushing the hydraulic system, the loader regained lift height and respond‑time. The improvement was notable enough that the rebuilt machine passed all load‑test cycles without a leak.
In another case, the operator discovered worn bushings in the loader linkage causing misalignment and uneven bucket travel. Using a parts manual, they ordered exact Cat bushings, pressed them in, and greased them with zerks for future maintenance.
Sourcing Documents and Parts Guidance
Parts books from 1975—such as the April 1975 catalog covering serials 87A6832 through 87A6868-up—provide exploded views of engine, transmission, frame, drivetrain, and attachments. These manuals help identify part numbers accurately, avoiding ordering mismatches and downtime .
Caterpillar and aftermarket suppliers provide parts reference guides suited to the 988H and older models, allowing restorers to cross-reference newer part numbers or equivalent substitutes when exact original components are unavailable .
Parts Checklist for Restoration or Ongoing Maintenance
Essential wear‐and‐replace parts for a 1975 988 include:

• Engine overhaul kit (rings, bearings, gaskets)
  
• Torque converter seals and filters
  
• Lift cylinder seal kit
  
• Tilt cylinder seal kit
  
• Steering cylinder seal kit
  
• Hydraulic pump seal kit
  
• Alternator, starter relay, clutch linings
  
• Transmission clutch packs and gaskets
  
• Brake discs, axle seals
  
• Loader linkage bushings and pins
  
• Radiator hoses, fan clutch belt
  

Terminology Clarification
Understanding common terms aids accurate communication and ordering:

• Rod/Bore Sizes: Crystal-clear identification for cylinder dimensions.
  
• Serial Number Reference: Parts differ by machine serial; many kits fit only 87A1‑up or 87A6832‑up machines.
  
• Exploded Parts View: Visual diagrams in manual showing assemblies.
  
• Seal Kit: Package containing O‑rings, seals, backup rings specifically sized for a hydraulic cylinder or pump.
  
• Clutch Pack: Transmission or torque converter plates that transfer power via friction surfaces.
  

Maintenance Tips for Longevity

• Change hydraulic fluid and filters after seal replacement.
  
• Keep cylinders clean and capped when not in use.
  
• Grease linkage pins with periodic lubrication.
  
• Match bolts and torque specs to original values from parts manuals.
  
• Retain old parts as pattern references for future sourcing.
  

Field Anecdote: The Time‑Capsule Loader
One restoration shop received a 988 that had sat untended since the early 1980s. Original seal kits were sold out, but by referencing the 1975 parts book, they sourced correct seals for the lift and tilt cylinders. Once cleaned and reassembled, the loader moved under its own hydraulics for the first time in decades. The shop crew took care to preserve original serial plates and tagged all replaced parts for historical accuracy.
Conclusion
Restoring or maintaining a 1975 Caterpillar 988 loader is a process rooted in accurate parts identification, access to vintage manuals, and careful assembly. Seal kits for cylinders, clutch and transmission components, engine overhaul kits, and linkage wear parts are essential. By leveraging detailed parts books and trusted suppliers, technicians and enthusiasts can return these classic machines to reliable operation and preserve their heritage for years to come.