S-708/PRO Lever Action Grease Gun

Frequently Asked Questions: Lever Action Grease Gun

What features should I look for in a lever grease gun?

Four features separate professional lever guns from commodity guns: pressure rating, head construction, accessory kit and cartridge compatibility. On the S-708/PRO: 6,000 PSI (413 bar) working pressure suitable for standard automotive, agricultural and light-industrial service, precision-machined head with rolled-thread barrel, premium accessory kit (rigid steel extension, 12" flex hose, hydraulic coupler) included, and the standard 57.15 mm barrel accepting 14 oz. (400 g) cartridges across all major markets. The Pro tier adds a rubber sleeve on the barrel for slip-resistant grip and tighter quality-control inspection. The underlying platform is shared with the base S-708.

What is a lever action grease gun?

A lever action grease gun is a hand-operated grease dispenser that uses a long pivoting handle to develop grease-dispensing pressure via mechanical advantage. The S-708/PRO's lever design delivers 40:1 pressure ratio . Operator input force is multiplied 40 times at the coupler output, so 150 PSI of lever-arm input produces 6,000 PSI at the fitting. The long lever arm trades one-handed convenience (pistol grip territory) for sustained pressure development and grease-per-stroke volume. Lever action is the workhorse category for agricultural, fleet and industrial service because the pressure and volume per pump comfortably clear typical zerk fittings without operator fatigue during extended multi-fitting rounds.

How does a lever action grease gun work?

The S-708/PRO's lever moves a piston inside the head assembly on each pump. The piston compresses grease from the reservoir through a non-return valve and out through the coupler at 6,000 PSI. Mechanism: the follower spring pushes grease from the reservoir through the piston intake on each upstroke. The downstroke drives the compressed grease through the non-return valve (preventing backflow) and out through the flexible hose or rigid extension at the coupler. The 40:1 pressure ratio is set by the lever geometry and piston area. It is fixed and does not vary with operator technique. Each stroke delivers a measured 1 gram of grease at full 6,000 PSI at the coupler.

Does the S-708/PRO accept 14 oz. grease cartridges?

Yes. The S-708/PRO uses the 57.15 mm standard barrel that accepts 14 oz. (400 g) cartridges . The global standard cartridge size stocked across North America, Europe, Asia and most export markets. Loading: retract and lock the plunger rod, unscrew the barrel, peel the metal pull-tab off the cartridge nose, insert nose-first, peel the plastic bottom seal, screw the barrel back on, release the plunger rod. The 400 g cartridge takes about 3 grams of supplementary bulk if topped-off to use the full reservoir capacity. For Australian and NZ 450 g cartridge markets, the wider-barrel S-710 family is the correct pick.

How do you load a lever action grease gun?

Load the S-708/PRO from either a 14 oz. Cartridge or bulk pail in six steps for cartridge fill, seven steps for bulk fill. Cartridge fill. Retract and lock the plunger rod. Next, unscrew the barrel from the head. Then, peel the metal pull-tab off the cartridge nose. After that, insert nose-first into the barrel. From there, peel the plastic seal off the bottom and screw the head back onto the barrel. Finally, release the plunger rod. Bulk fill: (1-2) same. Then, dip the barrel into a grease pail and pack firmly with a scoop to avoid air voids, (4-7) screw the head on, release the plunger, crack the head a quarter turn, pump 3-5 strokes to bleed air, retighten.

How do you prime a lever action grease gun after loading?

Prime the S-708/PRO in four steps after every reload. Ensure the head is screwed snug against the barrel. Next, crack the head a quarter turn to open the bleed path. Then, with the coupler disconnected, pump the lever through 3-5 full strokes to purge air from the reservoir. After that, retighten the head once grease flows from the head seam without air bubbles. For 14 oz. Cartridge fill with pre-packed grease the priming cycle is shorter than bulk-fill priming because cartridges have no internal air voids. Bulk fill from a pail typically needs 5-8 strokes because manual packing leaves some air pockets. Never prime against a connected fitting. Air must escape at the head, not into a bearing.

What causes air lock in a lever grease gun?

Air lock has three causes on the S-708/PRO. Incomplete bulk-fill packing leaving voids in the reservoir. Next, swapping cartridges mid-partial-fill so air fills the space above the new cartridge. Then, leaving the plunger rod retracted-and-locked so the follower spring is disengaged and grease settles away from the head. Air is not compressible the way the follower-spring mechanism is designed to handle. Trapped air compresses before grease moves, preventing the non-return valve from opening. Cure: retract and lock the plunger rod, crack the head a quarter turn to open the bleed path, release the plunger rod so the follower spring compresses the grease column, pump 3-5 strokes until grease flows from the head seam without bubbles, retighten the head.

How do you release trapped air from a lever action grease gun?

Release trapped air on the S-708/PRO in five steps. Retract the plunger rod fully and lock it into the side slot. Next, crack the head a quarter turn to open the bleed path. Then, release the plunger rod so the follower spring compresses the grease column. After that, pump the lever through 3-5 full strokes while holding the gun with the head tilted slightly upward. From there, retighten the head once grease flows from the head seam without bubbles. The tilt helps trapped air rise to the head where it can escape through the bleed gap. If air keeps trapping after three cycles, inspect for incomplete bulk-fill packing or swap the cartridge (sometimes a defective cartridge has internal voids from manufacturing).

What PPE should I wear when using a lever grease gun?

Mandatory PPE at 6,000 PSI (413 bar): wraparound safety glasses, nitrile chemical-resistant gloves, closed-toe work boots and long-sleeve protective clothing. Safety rules: never point the coupler or flex hose at any body part, keep the lever-hand behind the coupler head, inspect the flex hose before each use for cracks or bulges, never test grease flow by pressing the coupler against skin or fabric. The S-708/PRO at 6,000 PSI operates below the 7,000 PSI threshold above which amputation risk from grease injection injury rises sharply. Even so, any suspected injection injury is a surgical emergency requiring immediate hospital treatment. The Pro tier's rubber-sleeve grip reduces slip-drop injury risk but does not change injection-injury safety procedures.

What is the pressure ratio of a lever action grease gun?

The S-708/PRO has a 40:1 pressure ratio. Every 150 PSI of operator input force on the lever produces 6,000 PSI at the coupler output. Pressure ratio is a fixed mechanical property of the lever geometry and piston area. The 40:1 ratio is the industry premium tier for lever grease guns. Lower ratios (15-20:1) are typical on pistol-grip guns and cannot develop the pressure needed to clear crusted zerk fittings on heavy equipment. The S-708/PRO is aimed at standard automotive and light-industrial service where 6,000 PSI is sufficient. For heavy-duty fitting clearing in construction and mining environments where zerks sit crusted, step up to 10,000+ PSI guns like the S-724DC or S-707.

How much grease does a lever action grease gun deliver per pump?

The S-708/PRO delivers 1 gram per stroke, or 1 ounce per 28 full-lever strokes. A full 14 oz. (400 g) cartridge delivers 400 strokes before needing reload. For service planning: a 20-gram fitting shot needs 20 lever strokes, a 15-fitting light vehicle service needs 300 strokes, a single 14 oz. cartridge covers 1-2 vehicles per fill. Stroke-count planning works precisely because output is constant across the full reservoir. The first stroke after reload and the last stroke before empty both deliver 1 gram at full 6,000 PSI. For higher-volume per-stroke output at lower pressure, high-volume lever designs are an alternative. Most professional service uses the standard 1-gram-per-stroke architecture.

Can I mix different types of grease in one lever grease gun?

No. Mixing grease chemistries in the same gun causes thickener separation that can damage downstream bearings. Lithium complex, calcium sulphonate, aluminium complex and polyurea thickeners all use different chemistry. Combining them forms slurry that blocks seals. To change grease types in the S-708/PRO: empty the reservoir completely, unscrew the head, wipe the barrel interior with solvent-dampened lint-free rag, solvent-clean the head internals and non-return valve, reassemble with the new grease and prime per the procedure. Best practice for workshops running multiple grease types: dedicate one S-708/PRO per grease chemistry and label each gun with chemistry and NLGI grade on visible tape. The Pro tier's colored rubber sleeve can serve as visible grease-type identifier.

How often should I clean my lever action grease gun?

For regular professional workshop use (2-5 reloads per shift), deep-clean the S-708/PRO every 6 months. For occasional service (few reloads per week), annual cleaning suffices. Cleaning procedure: depressurize by retracting the plunger rod and pressing the bleeder valve, empty the reservoir through the coupler, unscrew the head, wipe the barrel interior with solvent-dampened lint-free rag, solvent-clean the head internals and non-return valve, inspect the plunger rod seal for circumferential wear, reassemble with fresh grease lightly applied to seals. Replace the plunger seal every 12-18 months of daily use from the STAR spare-parts kit. Never use WD-40 as a flush solvent. It leaves residue that contaminates fresh grease.

Should I store my lever grease gun horizontally or vertically?

Store the S-708/PRO horizontally with the plunger rod disengaged for any period over a week with grease loaded. Oil bleed (base oil separating from grease thickener) happens faster when the gun stands vertically because gravity drives oil settling toward the bottom. Horizontal storage minimizes settling. Releasing the plunger rod from the side-slot lock lets the follower spring keep the grease column compressed against the head, which also reduces oil bleed compared with a disengaged-spring configuration. For storage over 30 days: drain the reservoir completely, wipe the barrel interior with solvent, reassemble with the plunger seal lightly greased, store dry at 10-30°C away from direct sun.

Why won't my lever action grease gun pump grease?

A non-pumping S-708/PRO has four root causes ranked by frequency. Air lock in the reservoir. Next, stuck or hardened grease blocking the non-return valve. Then, plunger stuck in the barrel from dried grease or worn seal. After that, disengaged plunger rod not pressing the follower against the grease column. Diagnostic sequence: verify the plunger rod is engaged and pressing. Bleed air per the trapped-air procedure. Disconnect the coupler and pump into open air to check flow at the head. If no flow, unscrew the head and inspect the non-return valve for contamination. Clear hardened grease with a solvent flush. Never continue pumping against a blocked gun since trapped pressure can damage seals.

What is the difference between standard and heavy duty lever grease guns?

Standard lever grease guns like the S-708/PRO operate at 6,000 PSI. Heavy-duty lever grease guns like the S-707 and S-724DC operate at 10,000-12,000 PSI with reinforced construction. Differences: standard guns use stamped-steel or basic die cast heads with 0.035" barrel walls. Heavy-duty guns use CNC-machined aluminium die cast or forged-steel heads with 0.049" (1.2 mm) barrel walls. Standard guns handle 90 percent of typical automotive and light-fleet service. Heavy-duty guns add pressure margin for mining, construction and outdoor-contaminated fittings. Weight: standard guns are 200-400 grams lighter than heavy-duty equivalents. Pick standard for workshop and standard-fleet service. Step up to heavy-duty only when your service includes regular outdoor-equipment fittings that develop crust.

What type of grease should I use for tractor loader pins and bushings?

For tractor loader pins and bushings, NLGI #2 moly-fortified EP (extreme pressure) grease is the standard. Lithium complex NLGI #2 is an acceptable alternative. The S-708/PRO handles all standard tractor-service greases: lithium complex, calcium sulphonate, aluminium complex, polyurea, moly-fortified EP and synthetic PAO-based. Across NLGI 1, 2 and 3 grades. For loader pin service specifically, moly-fortified EP provides additional shock-load protection. For marine and coastal service, calcium sulphonate resists water washout. For high-temperature applications (near exhaust or hydraulic systems), aluminium complex or polyurea. Never mix chemistries. Dedicate one S-708/PRO per grease type if the workshop runs multiple.