New Owner Learning Curve

[MikePhua]

A recent buy of a John Deere 35 ZTS mini excavator turned out to be a uniquely instructive experience. The new operator acquired this used compact machine, clocking around 6,000 hours, at an appealing price well below what newer alternatives typically fetch. Initial usage—moving gravel and light lifting—went smoothly. But after a brief idle period, the hydraulic functions behaved erratically: control sticks would lose response for seconds, only to regain function when another stick was nudged. It wasn’t a single stuck cylinder or joystick—it felt like mysterious power games with hydraulics.

Machine Background and Capabilities
The John Deere 35 ZTS is a zero-tail-swing compact excavator built between the early 2000s and 2021 . Weighing approximately 7,782 lb (3.53 t), it houses a liquid-cooled Isuzu diesel engine (model 3LD1) delivering around 29 hp at 2,450 rpm .
Its hydraulic system features a variable-displacement design with two piston pumps plus one gear pump. Total piston pump flow is around 11 gpm, with auxiliary hydraulic flow hitting 22 gpm . Traveling at about 2.8 mph and retaining low ground pressure of about 4.5 psi, it is well-suited to farm and landscaping work . Zero tail swing and full-rotation capability make it excellent in tight spaces .

Pilot Enable Switch and Hydraulic Fluid Clues
A key discovery was the left-arm safety lock, or “pilot enable” switch, which had been previously held in place by a bungee cord—clearly a workaround for a sticky or imprecise mechanism. That jittery safety switch likely interrupted hydraulic pilot control intermittently. Once held firmly, hydraulic oddities mostly vanished.
Simultaneously, the hydraulic fluid level was found to be slightly low—about two-thirds of tank capacity (~7 gal total). The original sight glass had been removed, leaving only plugged holes. Adding approximately two gallons of clean hydraulic oil, using a custom dipstick, helped stabilize flow and responsiveness.

Terminology Explained
• Pilot enable switch A safety interlock in the operator’s armrest that enables hydraulic controls only when properly engaged. A faulty switch can interrupt pilot signals and cause jerky operation.
• Sight glass A transparency in the hydraulic tank used for visually checking oil level. Without it, dipsticks risk contamination and imprecise reading.
• Zero tail swing (ZTS) Design where the tail of the excavator doesn’t extend beyond its tracks during rotation—ideal for working in confined spaces.
• Variable-displacement piston pumps Hydraulic pumps that adjust output flow based on demand, enhancing efficiency and performance.

Recommendations for Reliable Operation

• Restore the sight glass assembly (part number 8050296 with washers) to enable quick visual checks and reduce contamination risk.
  
• Repair or replace the safety switch assembly, ensuring firm contact and eliminating reliance on temporary fixes like bungees.
  
• Maintain hydraulic fluid at proper level, especially vital in variable-displacement systems; aim for mid-sight-glass or recommended fill line.
  
• Perform regular hydraulic filter maintenance—remove and inspect filters for debris, changing as needed, ideally every 500-1,000 hours.
  
• Verify main hydraulic pressure—if attachments such as the front blade feel underpowered, inspect pressure and flow parameters, potentially adjusting pump swash plate or checking for internal wear.
  
• Refer to the control pattern selector—the 35 ZTS features a dial allowing switching between backhoe and excavator control layouts, enabling operator comfort and consistency .
  

A Farmer's Tale of Success
A novice operator likened the machine’s behavior to a reluctant horse not wanting to move—until someone noticed the bungee holding the safety switch. Once replaced and fluid topped up, the little beast performed faithfully. Today, it’s the operator’s go-to for orchard stone digging and casual farm tasks. Maintenance is now prioritized, and though occasional pay-as-you-fix moments persist, the machine has earned its keep—and respect.

Summary
The John Deere 35 ZTS is a capable, nimble compact excavator, ideally suited for light farm, landscaping, and small-construction tasks. Initial hydraulic glitches were traced back to two simple yet critical issues: a loose pilot-enable switch and low hydraulic fluid without a proper viewing gauge. Fixing both instantly transformed erratic jerks into smooth, responsive hydraulics. With a restored sight glass, solid safety switch, fluid checks, and attention to hydraulic pressure, this machine will serve reliably for years of quiet, effective service around the farm.