A jack that will not lift or will not hold is rarely a broken jack. In practice most cases come down to four things: the release valve, the oil level, air in the circuit, and dirt on a valve seat. Only after those does it make sense to replace seals. This guide goes through the checks in the order we give to distributors’ service teams, with a table to diagnose the symptom first.
Safety first
- Never work under a jack you are testing, and never repair a jack under load. Lower it fully and remove it from the vehicle.
- Wear eye protection: hydraulic oil under pressure can spray from a failed seal.
- Clean the outside of the jack before opening anything, so dirt does not get into the oil.
- After any repair, test the jack with no load first, then with a load well within its rating.
Quick diagnosis
| Symptom | Likely causes | Fix |
|---|---|---|
| Pumps, but the ram does not rise | Release valve open; oil very low; air; dirty inlet check valve | Fixes 1, 2, 3 and 4 |
| Lifts only part of the way | Oil low; air; the load is at the stroke limit | Fixes 2 and 3; check the maximum height |
| Lifts without load, stops under load | Load above the rating; worn pump seal; air | Check the rating; Fix 3; Fix 5 |
| Sinks slowly under load | Dirt on the release-valve seat; worn ram seal; leaking check valve | Fixes 1, 4 and 5 |
| Drops suddenly | Release valve opened, or a failed seal | Stop using it; Fixes 4 and 5 or replace |
| Spongy handle, jerky lift | Air in the circuit | Fixes 2 and 3 |
| Oil leaks at the ram | Worn or damaged ram seal; scored ram | Fix 5; replace if the ram is scored |
| Oil leaks at the filler plug or vent | Overfilled; plug seal damaged; stored on its side | Correct the level; replace the plug |
| Will not lower, or lowers slowly | Valve not opened far enough; dry or bent linkage (floor jack); cold, thick oil | Open the valve; clean and lubricate; correct oil |
Fix 1: Close the release valve properly
A release valve half a turn open looks closed and returns every pump stroke to the reservoir. Turn it clockwise until it is snug. On bottle jacks use the slotted end of the handle; on most floor jacks, twist the handle itself clockwise. Do not force it: an overtightened valve damages its seat and then leaks.
Fix 2: Check and top up the oil
Lower the ram fully, stand the jack upright (bottle jack) or level (floor jack), remove the filler plug and check that the oil reaches the bottom edge of the hole. Top up with hydraulic jack oil only, never motor oil or brake fluid. Our hydraulic jack oil guide shows the right grade and the full procedure.
Fix 3: Bleed the air out
Open the release valve, remove the filler plug and pump the handle six to eight full strokes. Close the valve, refit the plug, then raise the empty ram to full height and lower it again two or three times. Air collects in the pump chamber after low oil, a refill or storage on the jack’s side, and it is the most common cause of a spongy or partial lift.
Fix 4: Flush and clean the valves
A particle of dirt on the ball seat of the release valve or a check valve lets oil escape back to the reservoir, so the jack creeps down.
- Flush first. With no load, open the release valve and pump the handle quickly ten to fifteen times. The flow often clears a loose particle. Close the valve and test.
- Clean the release valve if it still sinks: unscrew the release valve completely, catch any ball or spring it holds, wipe the valve tip and seat with a lint-free cloth and clean jack oil, and refit it hand-tight.
- Change contaminated oil. If the oil is dark or gritty, drain it, flush and refill; otherwise the dirt comes back.
Leave the overload valve alone. It is a separate spring-loaded valve, set and sealed at the factory; turning it changes the capacity at which the jack stops lifting.
Fix 5: Replace the seals
If the jack still sinks under load, will not lift under load or leaks at the ram, the seals are worn. A seal kit contains the ram seal, the pump plunger seal and the O-rings and back-up rings for that model. Replacing them means removing the ram and the pump plunger, so it is a bench job for someone with the model’s service sheet:
- Drain the oil and note the order of the parts as they come out.
- Inspect the ram and cylinder bore: scoring, pitting or rust on the chrome means the new seals will fail quickly, and the jack should be replaced.
- Fit the new seals lubricated with clean jack oil, without twisting them.
- Reassemble, refill, bleed, and test with no load, then with a load within the rating.
JackMaker stocks seal kits, pump units and release valves for every catalogue model; quote the model number on the rating label when you order.
Floor jack problems
- Saddle will not lower fully: clean and lubricate the lift-arm pivots and the linkage; check the return springs.
- Handle will not open the release valve: the handle yoke or the valve coupling is worn or misaligned; check the pin that connects them.
- Jack will not roll or veers: clean and lubricate the casters and replace flat-spotted wheels. A floor jack must roll freely while it lifts.
- Frame or arm bent, welds cracked: do not repair. Replace the jack.
When to replace the jack instead
- The ram is bent, scored or pitted
- The body, cylinder or frame is cracked, or a weld has failed
- The jack has dropped a load, been overloaded or taken a shock load
- It still sinks after new seals and clean oil
- The capacity label is missing or unreadable
Maintenance that prevents most problems
| Task | How often |
|---|---|
| Look for leaks, damage and a clean ram | Before each use |
| Check the oil level, ram fully lowered | Every 3 months in workshop use |
| Lubricate wheels, pivots and linkage (floor jacks) | Every 3 months |
| Bleed the air | After refilling or transport on the side |
| Change the oil | Once a year in workshop use, or when dark or milky |
For distributors: after-sales that keeps warranty claims down
Many warranty claims turn out to be wrong oil, air or dirt rather than defects. Print the checks above in your manual, keep a few seal kits for your best-selling models in stock, and train counter staff to ask two questions first: “Is the release valve fully closed?” and “Has it been topped up with anything other than jack oil?” JackMaker jacks carry a 36-month warranty, and seal kits, pump units and release valves are stocked for every model.
Compare our hydraulic bottle jacks, floor jacks and air hydraulic jacks, or contact us about spare parts.