Description

JLG 3394RT, 4394RT 2008 Service Manual

You’re in the shop with a JLG 3394RT that won’t hold platform height. You’ve checked the hydraulic lines, but you’re guessing on the cylinder drift spec. That’s where this 2008 Service Manual pays for itself. 228 pages of factory-verified data, not some reprint from a third party. I’ve been an ASE Master tech for 28 years, and I’ve learned the hard way that skipping the factory torque chart costs you parts and time. This manual is the real deal.

Before you touch a wrench, you need Section A – Maintenance Safety Precautions. That’s not fluff; it’s the difference between a safe job and a hydraulic line bursting in your face. The manual explicitly states: “Modification of the machine without approval by JLG Industries Inc. is a safety violation.” That matters when you’re working on a lift that can kill someone if the platform drops.

Specifications: What Section 1 Gives You

Section 1 covers 1.1 through 1.14. You get specs for engines, tires, machine dimensions, pressure settings, and serial number locations. Need cylinder specs? That’s subsection 1.9. The manual lists Cylinder bore diameters, rod diameters, and stroke lengths – not approximations. If you’re rebuilding a lift cylinder, you need those numbers. Also includes 1.14 Torque Charts – these aren’t generic bolt torque tables; they’re specific to JLG fasteners. I’ve seen guys strip bolts on the drive hub because they used a generic chart. Don’t be that guy.

Torque Charts: Why Page 1.14 Matters

Flip to the torque charts in the 1.14 subsection. The factory gives you foot-pounds for every bolt grade and size used on the 3394RT and 4394RT. Hydraulic line fittings, wheel lugs, engine mounts – all there. If you’re replacing the integrated torque/drive hub (Section 3.4), the torque values for the disconnect mechanism are critical. I keep a printed copy of this page taped to my toolbox.

Cylinder Drift Test: Section 2.4 – Don’t Skip It

Section 2.4 covers the cylinder drift test – both platform drift and cylinder drift. The procedure is clear: cycle the controls, measure drop over time, compare to spec. If you’re troubleshooting a slow bleed-down on a 4394RT, this is where you start. The manual also gives you pins and composite bearing repair guidelines in 2.5. That saves you from replacing an entire scissor arm assembly when all you need is a new bushing.

Audience Fit: Is This for You?

This manual is for anyone who owns, rents, or services a JLG 3394RT or 4394RT built prior to S/N 0200191606. If you’re a shop owner in San Antonio like me, you buy this once and put it on the shelf for every boom lift that rolls in. Home garage enthusiasts? Only if you’ve got a scissor lift in your backyard and you know how to use a torque wrench. Beginners – listen: you need this because the safety warnings are written for the guy who’s never bled a hydro line. Section A.C says “Remove all rings, watches and jewelry when performing any maintenance.” That’s basic, but I’ve seen a wedding ring get caught in a drive chain. Don’t learn that way.

Source Validity: OEM vs Aftermarket – Not the Same

I’ve used aftermarket manuals that had torque specs off by 15%. That’s a leak waiting to happen. This is an original OEM document from JLG, published October 6, 2008. 228 pages, written by the engineers who designed the machine. The OCR excerpt at the start of the manual warns you about hydraulic system pressures – those warnings are missing from most aftermarket reprints. If you’re charging a customer for a repair, your liability goes down when you use factory data. That’s why I link to Manual Transmission only when I need a specific procedure outside this manual – for everything within the scissor lift, this is the only source I trust.

7 Systems Covered in the Chassis & Scissor Arms Section

Section 3 goes deep: leveling jacks, power deck, generator, lift, drive. There are calibration procedures for elevation sensors and joysticks. The dual fuel/LPG system (3.5) covers changing from gasoline to LP gas – something you appreciate when the propane regulator builds up oil. You also get the GM engine dual fuel system (3.12) with electric lock off and EPR assembly. If you’re swapping a fuel filter on a 4394RT, you need the propane fuel system pressure relief steps from 1.13. That’s a safety step most generic manuals skip.

The manual has 228 pages – that’s 228 pages of factory spec, not filler. Every page has a purpose. The preventive maintenance schedule in 2.6 tells you when to inspect pins, bearings, hydraulic oil. If you follow that schedule, the machine lives longer. I’ve seen fleets that use this manual have half the downtime of shops that guess.

FAQ

Does this manual cover the 4394RT model as well as the 3394RT?

Yes. The manual covers both the JLG 3394RT and JLG 4394RT models manufactured prior to S/N 0200191606 (excluding specific serial numbers listed). Same torque charts, same cylinder specs.

What years are covered?

This is the 2008 service manual edition. It applies to machines built up to the serial cutoff. For later revisions, check the JLG 3394RT 4394RT 2014 Parts Catalog for parts and the JLG 3394RT, 4394RT 2014 Operators Manual – Factory Safety & Specs for updated safety instructions.

Does it include wiring diagrams?

Section 3 covers engine electrical system maintenance and diagnostics for Ford EFI and GM engines. For full wiring schematics, you’ll want the 2014 parts catalog linked above. The service manual focuses on procedures and torque specs.

Where can I find the torque values for the cylinder rod gland nut?

Turn to Section 1.14 – Torque Charts. The cylinder specifications in 1.9 give you the dimensions, and the torque charts list the fastener torque for each bolt grade. If you need the assembly procedure for the integrated torque/drive hub, see Section 3.4. For other JLG machines, consider the JLG RS10 2013 Service Manual – Factory Specs & Diagnostics.

If you want external info on manual transmissions (not covered in this manual), check Manual Transmission for general principles. But for the JLG 3394RT or 4394RT, this is the only source you need.

You’ve got a machine that needs service. Stop second-guessing the specs. Access the Factory Manual and get the exact torque values, cylinder drift procedures, and safety warnings that will keep you – and your customers – safe.