Aircraft Jack Maintenance Guide: How to Test, Refill & Repair Hydraulic Jacks

March 6, 2026

Proper aircraft jack maintenance is essential for safe and efficient aircraft servicing. Whether you're an A&P mechanic, aircraft owner, or maintenance shop, keeping your hydraulic aircraft jacks in top condition prevents downtime, improves safety, and extends equipment life.

In this guide, we’ll walk through how to test, refill, troubleshoot, and repair aircraft jacks using proven procedures.

Why Aircraft Jack Maintenance Matters

Hydraulic aircraft jacks are critical for:

Aircraft lifting and inspections
Landing gear maintenance
Tire, brake, and gear servicing

If a jack is not properly maintained, it can lead to:

Incomplete lift height
Unsafe lifting conditions
Hydraulic failure during use

Routine maintenance ensures your jack performs reliably when it matters most.

How to Check Aircraft Jack Oil Level

One of the simplest, and most important, maintenance steps is checking the hydraulic oil level.

Quick Test Method:

Pump the unloaded jack to its maximum height
Observe performance:

If oil level is correct:

Jack reaches full extension
Pumping becomes more difficult near the top (you’ll feel resistance)

If oil level is low:

Jack will NOT reach full extension
Pumping feels easier
Ram stops short of full height

This quick test helps diagnose low oil without disassembly.

How to Refill a Hydraulic Aircraft Jack

If your jack is low on oil, follow these steps carefully:

Step-by-Step Refill Process:

Stand the jack upright on its base
Remove the rubber fill plug carefully
Lay the jack on its side with the fill hole facing up
Add hydraulic jack oil using a small funnel
Periodically stand the jack upright and pump to test oil level

Important Tip:

Approximately 1 ounce of oil = ~1 inch of lift gain
Do NOT overfill

Once full, reinstall the plug securely

Always test the jack after refilling to confirm full extension.

What Type of Oil Should You Use?

Most aircraft jacks require standard hydraulic jack oil.

Acceptable Alternatives:

Mineral oil
Non-detergent motor oil (if hydraulic oil is unavailable)

Always verify compatibility with your specific jack model.

Common Problem: Jack Only Lifts on One Stroke

If your aircraft jack only lifts on one pump stroke, you’re likely dealing with an air lock.

Why This Happens:

Air enters the hydraulic system
Common in new jacks or after transport (stored horizontally)

How to Remove Air from a Hydraulic Jack (Burping the Jack)

Method 1 (Quick Fix):

Pump the jack up a few inches
Open the release valve
Push the ram down manually
Listen for air release (“burping”)
Retest

Method 2 (If Problem Persists):

Place jack on the floor
Open the valve
Manually pull the ram to full extension
Push the ram back down fully
Repeat and retest

This process forces trapped air out of the system and restores normal operation. Click here to watch the process of burping a jack.

Hydraulic Jack Leak Repair Guide

Leaks are one of the most common issues in aircraft jacks. Identifying the source is key to proper repair.

1. Leaking Pump Piston Shaft

Fix:

Do NOT drain the oil
Access piston by removing rocker assembly pins
Replace worn seals
Reinstall and test

Be careful not to damage new seals during reinstallation.

2. Leaking or Worn Control Valve Seal

Fix:

Position jack to move oil away from valve
Remove control valve pin
Extract and replace seal
Clean chamber and reinstall components

Do not over-insert the new seal, it can block oil flow.

3. Worn Ram Seals or Leaking Housing

This is a more advanced repair.

Fix:

Drain the oil
Disassemble gland and ram assembly
Replace seals, including:
- O-rings
- Support seals
- Housing seals
Reassemble, refill, and test

Note: Some seals are directional, install correctly to avoid failure. Click here to watch the disassembly and reassembly of your jack for complete re-sealing instructions.

Best Practices for Aircraft Jack Maintenance

To keep your hydraulic jacks operating safely:

Regularly check oil levels
Test for full extension before use
Inspect for leaks or seal wear
Store jacks properly (vertical when possible)
Address air lock issues immediately

Preventative maintenance is far easier than full repair.

When Should You Service or Repair Your Jack?

You should service your aircraft jack if:

It won’t reach full height
Pumping feels inconsistent
Oil leaks are visible
It only lifts on one stroke
Performance has changed over time

Don’t ignore small issues, they often lead to bigger failures.

Final Thoughts: Keep Your Aircraft Jack Mission-Ready

Your aircraft jack is a critical piece of ground support equipment. If it fails, it can delay maintenance, or worse, create unsafe working conditions.

By regularly testing, refilling, and maintaining your hydraulic jack, you ensure: