How to Replace a Rolling Jack Cylinder

A rolling jack is the air-over-hydraulic jack that sits between the runways on a 4-post alignment lift and picks the vehicle off the runway so wheels can come off. The cylinder is the actuator that lifts the arms. It fails from side-load fatigue, a blown rod seal, or a bent rod after somebody let a car settle sideways onto a jack that was still air-loaded. When the jack will not lift, or it lifts slowly and the reservoir is not low, the cylinder or its seal pack is the answer. Knowing how to replace a rolling jack cylinder is mostly a battle with rusted-in cylinder pins — the hydraulics are simple; the pins are what turn a two-hour job into an all-day one.

Tools and prep

Have ready: an oxy-acetylene or propane torch for seized pins, a porta-power for a stuck arm stop bolt, a punch and hammer, e-clip pliers, sandpaper, anti-seize, metal caps for the hose and port, the correct fluid, and the replacement cylinder. Make the jack safe first: raise the rolling jack to nearly max height and set it on its locks, hold the lowering valve for 10 seconds, then disconnect the airline. Never let a car settle onto a rolling jack that is not fully lowered or fully locked — side-load from a shifting vehicle is what bends jack cylinder rods in the first place.

Step-by-step: how to replace a rolling jack cylinder

1. With the jack on its locks, pressure bled, and the airline off, remove the jack from the 4-post runways or the pit. Raise it on the shop floor to a comfortable working height.
2. Extend the arm that the rollers attach to so you can reach the lower cylinder pin. Remove the arm stop bolt if the jack has one. If it is rusted solid, heat it and press with a porta-power; if that fails, either cut an access hole in the frame that matches the existing pin-access hole, or replace the jack.
3. Remove the stop bolts on the top of the rolling jack. Slide the top of the jack off the slide blocks and set it aside.
4. Remove the hydraulic hose. Cap and plug the hose and the cylinder port so nothing gets in. Pull the e-clips off both the upper and lower cylinder pins.
5. Drive out the lower cylinder pin and clean it up. This pin is often rusted in and may need heat, or the pump may have to come off to clear it. Sometimes the pin has to be cut out and replaced.
6. Drive out the upper cylinder pin the same way and clean it up.
7. Set the new cylinder in place. Install the lower pin — anti-seize the pin and the bore. Install the upper pin the same way. Reinstall both e-clips.
8. Remove the caps from the cylinder and hose, install the hydraulic fitting, and reconnect the hose.
9. Check the slide blocks — if worn, replace them now while the jack top is off. Reinstall the top of the jack and its stop bolts.
10. Adjust the arms to the correct width for the runways. Put the jack back in the pit or on the 4-post runways.
11. Top off the oil and reconnect air. Cycle the jack up and down, lower onto its lock, and drop all the way down. Look for leaks.

Fluid and oil

Most rolling jack pumps run ISO-32 hydraulic oil. Rolling jacks with an air bleeder screw on the reservoir need it loose during operation — if the bleeder is closed, the jack will not lift. Defer to the jack’s manual for the exact fill; top off with the arms all the way down.

How to tell it’s time to replace

Replace the cylinder when the rod is bent, when it weeps past the rod seal, or when the jack lifts slowly or not at all with the reservoir full. While the jack is out, inspect the cylinder pins — if you cut one out, plan on replacing both; the slide blocks, since the jack top rides on them and worn blocks make the top cock and bind; the rollers, which must roll freely with no flat spots and the adjustment arm moving in and out; the mechanical locks on the jack itself, which must move freely and not be rounded off; and the reservoir cap and pump fittings — clean them so a fresh leak is visible. Understanding how to replace a rolling jack cylinder includes replacing both pins as a pair once one has been cut.

Safety

Never let a car settle onto a rolling jack that is not fully lowered or fully locked — side-load from a shifting vehicle bends jack cylinder rods, which is what put you here. Bleed the lowering valve for 10 seconds and disconnect the airline before you touch a pin. When you know how to replace a rolling jack cylinder, the finish is a full cycle onto the lock and back down with your eyes on the rod and the fittings for leaks before the jack goes back under a vehicle.

Common mistakes and how we avoid them

The pins are the whole battle. The most common mistake with how to replace a rolling jack cylinder is trying to muscle out a rusted cylinder pin cold — it will not move, and you will round the end. Heat it, and if one pin has to be cut out, plan on replacing both, because the second is rarely far behind. The second mistake is reinstalling the pins dry; anti-seize the pin and the bore so the next tech is not fighting the same rust you just did.

The third miss is the one that sends jacks to the shop in the first place: letting a vehicle settle onto a jack that is not fully lowered or fully locked. Side-load bends the rod, and a bent rod is exactly the failure you are now repairing. Before the jack goes back under a car, cycle it fully onto the lock and back down with your eyes on the rod and the fittings. Knowing how to replace a rolling jack cylinder also means checking the slide blocks and the mechanical locks while the top is off, so the jack goes back solid.

We do this every week — how to replace a rolling jack cylinder is a job our field techs run in customer shops across the region, not a procedure we read out of a manual. If you get partway in and something does not match what you see, or a part looks wrong before you commit to it, call us at 800-674-9302 and we will walk it with you. When you are ready to order, find the exact parts for your lift in our parts lookup so you get the right fit the first time and finish the job in one trip.