Graco GMAX II 3900 Lo-Boy is America’s favorite mid-range gas airless for good reason: a Honda 4 hp engine drives an Endurance Vortex pump that moves 1.25 GPM at a rock-steady 3300 psi. That’s enough muscle to run two guns or push thick elastomerics through a 0.036 tip without thinning. With 65 % more output than the GMAX 3400 yet 20 lb lighter than many competitors, the 3900 Lo-Boy strikes the sweet spot between portability and raw production.
Why Contractors Trust Genuine Graco GMAX II 3900 Parts
- Exact Tolerances ±2 µm rod finish: keeps packings alive far longer than knock-offs, so you spend weekends spraying, not wrenching.
- Full 3300 psi validation: every seat, seal and filter is burst-tested at the factory—cheap copies start weeping around 2500 psi.
- SmartControl 3.0 handshake: OEM pressure sensors plug-and-play with the board; generics can trigger “pressure error” shutdowns mid-job.
- Warranty : you get Graco’s equipment warranty.
Key Features & Specs
- Maximum Flow: 1.25 GPM (4.7 L min-¹) keeps two RAC X 517 tips fully fed.
- Working Pressure: 0-3300 psi via SmartControl 3.0—±1 % dead-band for glass-smooth patterns.
- Maximum Tip Size: 0.036 in (1 gun) or 0.023 in (dual gun) for high-solid acrylics.
- Engine: Honda GX120 4 hp, low-vibe, EPA-compliant, 95 dBA at full throttle.
- Weight: 61 kg (133 lb) Lo-Boy frame with wide pneumatic wheels for easy curb hops.
- Annual Duty Cycle: up to 500 gal per week—ideal for commercial repaint crews.
Cross-Fit Parts for a Multi-Brand Fleet
Stock one shelf and service half a dozen graco sprayers. The 3900’s Endurance Vortex pump shares seats, balls and graco paint sprayer filters with these popular rigs:
Heavy-Hitters
- GMAX II 7900—all RAC X guards, ¼ in BlueMax II hoses and MaxLife piston seals drop straight in.
- GMAX II 5900—ProConnect 2 lower swaps in under a minute; packings and filter cores match the 3900.
Electric Siblings
- 395 Graco Sprayer / Ultra 395 PC—share the 60-mesh Easy-Out filter and Contractor PC gun repair kit.
- 3400 GMAX—inlet strainers and rod seals are identical, letting you support entry-level rigs with pro-grade spares.
DIY & Handheld Crossover
- Graco TrueCoat 360 Electric TrueAirless Sprayer—RAC IV/V tips and 60-mesh inlet filters match our pro-series kits, perfect when you need a backup for touch-ups.
Top Accessories That Pay for Themselves
- Gas powered paint sprayers need clean fuel—add a 10 µm inline fuel filter to stave off carb rebuilds.
- Graco spray pump parts: the MaxLife rod/sleeve combo lasts 2× longer in abrasive roof coatings.
- Graco paint sprayer filters: 60-mesh for latex, 30-mesh for elastomeric—colour-coded end caps cut mistakes.
- Graco spray hose whip: a 3 ft × ¼ in whip trims wrist torque when cutting trim lines.
Pro-Level Maintenance Plan
40-Hour Rule: record engine hours and flush with mineral spirits nightly. Three minutes beats a Saturday carb clean.
500-Gallon Rule: rebuild the lower with an OEM kit and fresh Throat Seal Lubricant. A $120 kit saves a $600 pump rod.
Seasonal Rule: swap graco spray pump parts—inlet ball, seat and spring—before the big exterior rush and you’ll sail through summer break-downs.
Frequently Asked Questions
- What’s the biggest tip I can run on one gun?
- The 3900 Lo-Boy is rated to a 0.036 in tip at 3300 psi—perfect for block fillers or high-build roof primers.
- The pump casting is smaller, but packings, balls, seats and filter elements are identical—ideal for consolidating consumables.
- How is the 3900 different from a graco gmax 7900?
- The 7900 steps up to 2.2 GPM and a 6.5 hp Honda engine for four-gun work, but shares hoses, tip guards and MaxLife seals with the 3900.
- Are graco 3400 parts worth keeping?
- Absolutely. The 3400 uses the same inlet strainer, rod seal kit and ¼ in BlueMax hose—great for backup rigs or new hires.
Boost Uptime & Profit—Today
Add genuine Graco GMAX II 3900 Lo-Boy Series parts plus crossover kits for 395 units, graco 3400 parts and handheld TrueCoats—to your cart now. You’ll receive express shipping, and the confidence that comes from running 100 % OEM components.
