Rolling Jacks for 4-Post Lifts

What Rolling Jacks for 4-Post Lifts Do

A four-post lift carries the vehicle on its tires. That is fine for storage and under-car work, but useless the moment you need a wheel off. A rolling jack — also called a bridge jack or sliding jack — spans the two runways, rolls fore and aft to line up with the vehicle's lift points, and raises one end clear of the runway surface. That converts a parking or service four-post into a wheels-free lift for alignment, brake, axle and suspension work, which is exactly how the Katool KT-RJ60 lists its primary uses.

Rolling jacks are not floor jacks. They ride on the runways or on a cross-member frame, carry the load through adjustable pads set at the manufacturer's lift points, and stay put while the vehicle is up. Construction in this collection reflects that: welded and heavy-duty steel frames with powder-coated finishes on the Katool KT-RJ50, KT-RJ60 and KT-RJ70.

Manual vs. Air/Hydraulic Rolling Jacks

The main split in this collection is how the jack builds hydraulic pressure, and it drives both price and shop requirements.

• Manual pump. The AMGO J5H (5,000 lbs.) and J6H (6,000 lbs.) use a hand pump. No compressor, no air line, nothing to plumb — a reasonable fit for a home shop or a low-volume bay where the jack comes out a few times a week.
• Air/hydraulic. The AMGO J6A, RJ-8A, RJ-10A and RJ-20A and the Katool KT-RJ50 and KT-RJ60 are air-over-hydraulic. Both Katool models state that an external compressed air supply is required. The AMGO RJ-20A lists 0.8 MPa air pressure and an automatic pump. These are the ones to buy if you cycle the jack all day.
• Hydraulic. The Katool KT-RJ70 (7,000 lbs.) lists a high-pressure hydraulic pump and includes adjustable contact adapters.

Speed differences are smaller than buyers expect: both the AMGO J6H and the much larger RJ-20A list a 50-second lifting time. The real argument for air is operator effort over a full day, not seconds saved per lift.

Capacity: Sizing the Jack to the Work

Rate the jack against the heaviest end of the heaviest vehicle you service, and never against a number the four-post lift itself cannot support. Here is what this collection covers:

OSHA 1910.244(a) requires the rated load to be legibly and permanently marked on a jack and prohibits loading it beyond that rating, so treat the plate on the jack as the ceiling, not a starting point.

Fitment: Runway Spacing, Reach and Lift Compatibility

Capacity is the easy part. Fitment is where orders go wrong. The jack has to span your runways, so compare its support base width to your lift's runway spacing before ordering. The AMGO J6H lists a support base width of 33-7/8 in. to 52-13/16 in., arm pad reach of 33-1/16 in. to 53-7/16 in., overall width of 20-1/16 in. and a gross weight of 280 lbs. The RJ-20A is a far larger frame: 45-3/16 in. to 58-1/4 in. support base width, 45-1/4 in. to 66-1/8 in. arm pad reach and 25-1/2 in. overall width.

Katool publishes compatibility by lift model. The KT-RJ70 lists the KT-4H110, KT-4H950 and KT-4H850; the KT-RJ50 lists the KT-4H110 and KT-4H850; the KT-RJ60 lists Katool four-post lifts such as the KT-4H150. If you are shopping a rolling jack for an Extreme 4H950, the KT-RJ70 is the model in this collection that names that lift.

Minimum height decides whether the jack will slide under a low car at all. The J6H lists a minimum height of 8-7/16 in. and a minimum rubber pad height of 8-5/8 in.; the RJ-20A starts at 14-3/16 in. Maximum rise matters at the other end: the J6H reaches 17-3/4 in. without adapters and 20-1/4 in. with them, while the RJ-20A reaches 31 in. to 32-5/16 in., or 40 in. to 41-5/16 in. with adapters. Add the jack's rise to your lift's rise and the vehicle's height before you assume the ceiling clears.

Air Supply and Airline Kits

Air-over-hydraulic jacks are only as good as the air feeding them, and a four-post lift usually has no plumbing from the factory. The AMGO 40102 Air Line Kit is built for four-post lift pneumatic air supply and includes high-pressure air hoses, an adjustable regulator with pressure gauge, safety-rated quick-connect couplers and mounting hardware for the lift frame. The 40106 kit is listed for heavy-duty four-post lifts, and the PX004 kit covers scissor lifts. Running a dedicated regulated line to the lift beats dragging a hose across the bay every time the jack comes out, and it gives you a clean supply point for impact guns and other pneumatic tools.

Safety, Inspection and Maintenance

Rolling jacks fail in predictable ways: worn pads that let a vehicle walk, casters that bind, hoses that seep, and lift points chosen by guess. ANSI/ALI ALOIM is the standard covering operation, inspection and maintenance of automotive lifts, including periodic inspection by a qualified person, and ANSI/ALI ALCTV covers construction, testing and validation. The Automotive Lift Institute also publishes a Vehicle Lifting Points Guide for locating manufacturer-specified lift points, which is the single most useful reference for anyone new to bridge jacks.

Day to day: check hydraulic fluid level and hose condition, keep the rubber pads and any adapters intact and correctly seated, keep the runway surfaces clean so the casters roll and lock properly, and confirm the mechanical locks are engaged before anything goes under the vehicle. Never work under a load held only by hydraulic pressure.