Repair or replace the pump?

Sound housing → rebuild the rotating group; cracked/scored → replace.

Diagnose from photos?

Send nameplate + leak photos; we identify the pump and quote parts.

Which brands do you cover?

Kawasaki, Kayaba, Rexroth, Nachi and more — send the nameplate.

How to Diagnose an Excavator Hydraulic Pump Problem: The 4-Step Field Method

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Short answer: Confirm a main-pump problem with four steps: listen (whine/grinding under load), look (slow cycles, weak combined moves, foam or metal in the tank), test (main pressure and case-drain flow against spec), eliminate (pilot pressure, relief valve, suction leak — the cheap causes first). Only after those four do you order a pump or a parts repair.

The 4-step field method

Step	What to do	What it tells you
1. Listen	Run each function to relief, then combined moves	Squeal/whine that fades warm = suction leak or aeration; grinding = bearing/pistons inside
2. Look	Tank oil: foam, milky color, glitter; cycle times vs before	Foam = air in suction; milky = water (coolers/seals); glitter = internal damage. Already see milky oil? Check the water-in-oil guide
3. Test	Gauge at main test port: standby pressure, max pressure at relief, case-drain flow	Can't reach spec at relief = wear or relief valve; case drain above ~5–8% of pump flow = internal leakage, pump worn
4. Eliminate	Pilot pressure, relief valve setting, throttle/suction strainer, coupling	A stuck relief or weak pilot mimics a dead pump — the most common "wrong pump replaced" story

Symptoms vs likely cause

All functions slow, worse when hot → internal leakage increasing with oil temperature (pump wear, or oil too thin).
One function weak, others normal → that circuit's valve or cylinder, usually not the pump.
Noise follows oil level/warm-up → aeration: suction hose, strainer or shaft seal leaking air.
Boom drifts down with engine off → hold valves/cylinder seals, not the pump.

For the classic warning signs overview, see 7 signs your hydraulic pump is failing. When the pump is confirmed, we stock rotating groups, piston assemblies, liners, valve plates, drive shafts and seal kits for Kawasaki, Kayaba, Rexroth and Nachi pumps on CAT, Komatsu, Hitachi, Volvo and more — search by pump model.

Frequently asked questions

Repair the pump or replace the whole assembly?

If the housing and shaft are sound, a rotating-group rebuild with new parts is usually a fraction of a new pump. Cracked housing or scored shaft → replace.

Can you tell what is wrong from photos?

Partly — send the pump nameplate photo and the leaked part photo; we can identify the exact pump model and quote the internals.

Do you supply parts for my pump brand?

Kawasaki K3V/K5V, Kayaba, Rexroth A8VO/A11VO, Nachi and more. Send the nameplate number and we confirm fitment.

Pump confirmed faulty?

Send the pump nameplate photo — we quote rotating group, seals or full parts set.

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