Early JLG 40F Boom Lift: Insight & Technical Notes

[MikePhua]

The JLG 40F is an early-generation telescopic boom lift that enthusiasts and mechanics often refer to when dealing with legacy machines. Understanding its quirks can be tricky because JLG’s official support for this older model is limited, but peer‑to‑peer insights offer valuable clues. Here’s a detailed breakdown of what makes the 40F unique, common issues, and technical considerations.

Machine Origins and Context

• JLG Industries, founded in 1969, quickly became a leader in aerial work platforms, boom lifts, and scissor lifts. The 40F is part of its older straight boom line, built before the modern “Ultra” series.
  
• These “F series” machines are rare now — many were used, parked, or retired, so finding documentation and spare parts can be challenging.
  
• A 1979 auction video shows a 40F selling for just over $5,000, illustrating how these machines have depreciated over decades.
  

Structure, Controls & Components
From community reporting and hands‑on restoration experience:

• The 40F often uses Cutler/Hammer joystick controllers and Racine solenoid-type valves. These are simpler, older electrical-hydraulic components that remain relatively serviceable if you can find the right parts.
  
• It typically has dual joystick control: one for lift/swing, another for drive/steer. This reflects its early design philosophy and makes it somewhat intuitive to operate — though parts like wiring harnesses may be patched or spliced through decades of use.
  
• For descent safety, there is likely a manual descent valve integrated into the lift cylinders. If that hose degrades, the boom can drop — but due to a velocity fuse, it will descend at a controlled rate rather than free fall.
  
• One reported coil for the level control valve is ¾″ ID, held by a threaded nut, and is not always listed in later manuals — earlier editions or parts catalogs are more helpful.
  

Challenges with Documentation & Support

• Some users say JLG provides “no real support” for the E/F series: parts, diagrams, and service manuals are often missing or difficult to obtain.
  
• Because of this gap, people rely heavily on vintage manuals, PDF scans from other owners, or community-shared diagrams. A working parts or repair manual is gold in these situations.
  
• Electrical and hydraulic repairs often require reverse-engineering: users have reported splicing old wiring with newer harnesses, and each machine may have slightly different configurations depending on how it’s been maintained.
  

Safety & Operational Notes

• Even though it's an older model, the 40F's safety components — such as holding valves — are critical to ensure boom stability. Operators should confirm these are in working condition before lifting loads.
  
• Regular inspection of hoses, especially those related to the manual descent system, is essential to avoid failures that could lead to uncontrolled boom movement.
  

Parts & Reference Material

• A recommended resource is the JLG 40F Illustrated Parts Manual, which helps identify component numbers, diagrams, and replacement parts.
  
• If original wiring or coils are damaged, sourcing from salvage units or specialized parts suppliers is often necessary.
  

Technical Terms Explained

• Solenoid Valve: An electrically controlled valve used to direct hydraulic flow. On the 40F, these control boom lift and descent.
  
• Velocity Fuse: A safety device in hydraulic systems that restricts flow if oil escapes too quickly — used to prevent sudden free-fall of the boom.
  
• Manual Descent Valve: A backup or emergency valve allowing controlled lowering when the machine is not powered or a failure occurs.
  
• Control Coil: The electromagnetic coil in a solenoid valve; energizing it switches the valve state.
  

Summary & Advice
The JLG 40F may not be well supported by the manufacturer anymore, but it’s far from a lost cause. For anyone restoring or operating one: procure a parts manual, verify control components like solenoids and coils, maintain descent hoses, and respect its vintage design by being careful and thorough with maintenance. Community knowledge is invaluable for these early machines — tap into that, and you'll keep yours running safely and reliably.