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Diagnostic guide · Fontana, CA
Hydraulic Leak Diagnosis Guide
Hydraulic leaks are information. Where the oil appears, when it appears, and what the machine does while it leaks tells a practiced eye which component is failing and how far the damage has gone. This guide covers the leaks we diagnose daily at our Fontana shop — and the point where a leak stops being a seal job and becomes a rebuild.
Diagnostic guide · Fontana, CA
External leaks: read the location
Oil at a cylinder rod means the gland area — rod surface condition, gland fit and seal state, in that order of importance. Oil at fittings and hoses is usually mechanical: chafed hose, loose or damaged fitting faces, wrong flare or O-ring. Oil at a pump or motor shaft seal often means case pressure or a worn shaft surface, not just an old seal — replacing the seal without the cause schedules the same leak again.
Hydraulic Leak Diagnosis Guide · Fontana, CAInternal leaks: the machine tells on itself
No puddle, but the boom drifts, the bucket curls open, or the machine weakens as it warms up — that is internal bypass: cylinder piston seals, a worn valve spool, or pump wear passing oil where it does no work. A simple drift test and a flow/pressure check separate cylinder from valve from pump, which is why diagnosis comes before parts.
The contamination spiral is the part nobody budgets for: a wearing component sheds metal, the metal scores everything downstream, and a one-component failure becomes a system rebuild. Clean oil and early attention are the cheapest hydraulic insurance there is.
- Rod leak + scored rod = rebuild territory, not reseal
- Drift under load = cylinder piston seals or control valve bypass
- Weak when hot = pump wear or internal leakage growing with thin oil
- Foamy oil + whine = suction leak or cavitation at the pump inlet
- Metal in the filter = stop and inspect before the circuit spreads it
Our 8-step repair process
A clear path from the first call to a tested component or machine returned to work.
Inspection
Disassemble and evaluate the complete failure.
Photos & video
Document condition and findings for a clear repair conversation.
Repair quote
Define the recommended work and quote before proceeding.
Approval
Confirm scope, urgency and the practical path forward.
Manufacturing
Machine, weld, rebuild or reverse engineer required components.
Testing
Verify operation and workmanship before release.
Shipment
Return the completed component or equipment to service.
Frequently asked questions
Is it safe to run a machine with a hydraulic leak?
Small external seeps are a scheduling problem; active leaks, drift under load, or metal in the oil are stop-and-inspect problems. When in doubt, call and describe it — that conversation is free.
Why does my leak only show when the machine works hard?
Heat thins the oil and pressure opens marginal seals and fits. A leak that appears under load is diagnostic gold — it tells us exactly which circuit to test hot.
Related services
Emergency breakdown? Call the 24-hour rush line.
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