4 Post Seal Replacement Guide

4 Post Seal Replacement Guide [PDF LINK CLICK HERE]

The piston which is connected to the rod has pressure seals (and guide spacer, O rings) which prevents oil from passing the piston.

• When fully lowered, piston is at the gland end, there is minimal oil in cylinder, mostly air.
• When fully raised, the piston is at the bottom of the cylinder, there is minimal air in cylinder mostly oil.

The gland cap has seals in it, that effectively prevent dust and other debris from entering the casing and pressure seals to stop oil leaking, when under pressure.

The gland cap is held into the casing with threads. The gland cap will have an O-ring installed on the threaded part again to stop oil leakage.

When oil pressure is applied on the side of the piston, between gland cap and piston it pushes the piston and rod in, causing the lift operation. The side of the piston to pump end of lift during normal operation has air with in it, which is expelled through a bleed hole near the cross beam. If the pressure seal on the piston leaks the oil will sit on the front of the piston which will be pushed out thru the bleed hole once enough oil has passed by the piston to reach the bleed hole. During normal operation there is oil between the piston and gland nut.

If the cylinder is leaking oil, it will be from the pressure seal on the piston passing oil from the oil side of the piston to the air side on the piston. It is unlikely to be the gland cap.

To replace the seals:

1. Position the lift a good working height on safety latches and put in extra blocks under runways as backup
2. Disconnect oil line from pump assembly and place into clean container (to collect oil from later steps)
3. Disconnect cables from rod (note how the cables are locked in, on the rod for later). Ideally, clamp the 2 x cable plates together so cables can’t fall out loose.
4. Remove the nut from the rod, to allow the cables to hang on the ground.
5. Extend the rod fully out of cylinder to remove oil, this will flow back to the container from previous steps.
6. Maybe use rachet straps if hard to move.
7. Push rod back in or support the rod to avoid to much load (bending) on rod.
8. Remove the gland cap using C hook spanner (o ring can be tight).
9. Pull rod out.
10. Replace seals on piston and gland, noting which way the seal was installed.
11. Reverse procedure to re-install.

We normally have seal kits for Happ 4 post lifts. The seals are also available at most seal shops.