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Hydraulic jacks: pumps, valves and leaks

A hydraulic leveling system is one pump, a valve per jack and a cylinder at each corner. A jack that won't move is usually fluid, voltage or a valve. A jack that sinks is a leak, and if the ground is dry the leak is inside a cylinder or a valve.

The short version

What's in the system

Level Up runs a 12 V motor on a hydraulic pump with a reservoir, a valve manifold and a dual-polarity solenoid valve. On a 4-point fifth wheel the landing gear valve sits on the lead landing gear and the jack valves are on a 4-bank remote manifold. A pressure switch tells the controller the jacks are holding retracted.

On Lippert motorhome systems the pump builds to 2,150 psi, where the pressure switch opens. If holding pressure falls to about 1,500 psi, the jacks down alarm sounds. Power Gear's older systems use spring-return jacks: the pump extends them, a dump valve opens to retract, and the springs push the fluid home. HWH 625 pumps make 3,300 to 3,600 psi.

Lippert motorhome hose is 1/4 in ID rated 3,000 psi working, with size 4 O-ring face fittings. Equalizer says replace any hose that leaks at a crimp or along its length; don't repair it.

Fluid: type, level and condition

Filling with jacks or slides out overfills the tank, and it spills or keeps jacks from fully retracting when they come in. Power Gear lists an overfilled system as the cause when every jack won't retract fully.

SystemFluidLevel, everything retracted
Level Up fifth wheelATF meeting Dexron III or Mercon V, or a blend (factory fill Type A)Within 1/4 in of the fill spout lip, checked monthly
Lippert motorhome, Class CSame; not Type F, not Type E1/2 in from the top of the reservoir
Power GearType A ATF (Dexron III); Mercon V for big temperature swings; don't mix hydraulic fluid and ATFVertical pump within 1/4 in of the fill port lip; horizontal pump to the weep hole
EqualizerDexron ATFTop of the upper horizontal ridge on the reservoir

Manual retract

Every Lippert hydraulic system retracts the same way: open the valves, then spin the pump by hand with a drill on the motor coupler. The drill direction is not the same on every system, so check the label and watch the jack in the first second.

Disconnect or shield motor power before you put a drill on the coupler. When you're done, turn every override set screw fully counterclockwise to close it, without overtightening. An override left open is Lippert's listed cause of a jack that bleeds down.

HWH systems use manual release valves: small valve nuts no more than 4 1/2 turns counterclockwise, T-handle valves about 5 turns, and close them before you troubleshoot. Power Gear spring-return jacks have their own sheet (LCI's spring-return jack manual retract procedure, TIP 12001); get the one for that pump.

SystemOpen the valvesDrive the pumpTo retract
Level Up fifth wheel5/32 in hex, set screw clockwisePeel the motor label; 1/4 in hex bit in the couplerDrill forward (clockwise)
Level Up motorhome5/32 in hex, clockwiseRemove the cap; 1/2 in socket on the couplerDrill reverse (counterclockwise)
LCI 4-point Sprinter5/32 in hex clockwise on all 3 cartridge valves; unplug the directional valve harness1/2 in socket on the couplerCounterclockwise

Careful: The coach comes down as the valves open, so keep everyone clear of the jacks and from under the coach. Keep hands off a pressurized leak: fluid at these pressures can go through skin.

Drift, internal leaks and air

Lippert's motorhome guide lists the sources of lost holding pressure in order: a hose or fitting, an external jack leak, an internal jack bypass (failed seal), a manifold leak, and an internal pump or direction valve failure. Its fix for a bypassing jack is a new jack, and for a manifold bypassing internally, a new power unit. Equalizer's order is the same idea: external leaks, then the directional valve (override position, O-ring, backing ring), then cylinder drift or seal bypass.

Not every movement is a leak. Air gives popping, jerky retracts; Power Gear bleeds by running all jacks fully out and in 4 times with a few minutes between, checking fluid each time. Equalizer holds each jack in bypass for 10 to 15 seconds each way with 15 to 20 minute rests. Fluid also grows and shrinks with temperature, which is why HWH added a Store function to pull in jacks that creep out.

The swap test: cylinder or valve

Reservoir full, overrides closed, nothing wet, and one jack still sinks: you have two suspects, the piston seal inside that cylinder or the valve for that port. One swap tells you which.

  1. Level the coach on its jacks with weight on them and mark every rod at the wiper with a paint pen.
  2. Come back in an hour, or overnight. The rod that moved is your jack.
  3. Retract fully. At the manifold, swap that jack's hoses (both lines on a double-acting jack) with a neighbor's of the same size.
  4. Snug the fittings without overdoing it (HWH: an existing hose end gets snug plus 1/4 turn), bleed per the maker, re-level and re-mark.
  5. Drift follows the jack: the seal is bypassing, replace the jack. Drift stays with the manifold port: the valve or manifold is leaking.
  6. Put the hoses back where they belong and bleed again.

On the job

  1. Retract everything, then check fluid level and condition.
  2. Close every manual override set screw (fully counterclockwise on Lippert).
  3. Read voltage at the pump while it runs, and listen for it to build pressure and shut off.
  4. Look for wet hoses, fittings, cylinders and the manifold.
  5. Level on the jacks, mark the rods, and wait an hour or overnight.
  6. Swap the sinking jack's hoses with a neighbor at the manifold to split cylinder from valve.
  7. Bleed after any hose or cylinder work and check the marks again.

Numbers

Shop tip

Mark the rods before the customer leaves the coach overnight. A paint line at the wiper turns 'it sinks sometimes' into a measured number on one named jack.

Where this comes from

Try it on a service call

Put the lesson to work on a hands-on troubleshooting case.