Two-Post Lift, Rusted Sills and a Missing Powertrain
A 1,145 kg petrol hatchback comes in for clutch replacement on a two-post lift rated at 3,500 kg. The manual gives kerb axle loads of 690 kg front and 455 kg rear, and the centre of gravity sits 1.15 m behind the front bumper. With the car raised, the front arms are set at 0.60 m and the rear arms at 1.90 m from the bumper. The left sill seams are rusted, so a fitter moves that rear arm inboard onto the floor reinforcement, where the rubber pad contacts only about half its area; the right sill cover crushes as the lift rises. The engine and transaxle (185 kg, centred about 0.45 m from the bumper) are then removed and the bare body stays up for four hours. The mechanical locks are not engaged, a 2 L drain tray sits under the rear axle, and an air hose lies across the walkway. At 15:00 the body rocks visibly when the rear arm is knocked, and a trainee is working underneath.
1. The trainee argues the lift is safe because 1,145 kg is far below 3,500 kg. Using the figures given, assess the real load and stability situation and explain what the rating does not cover.
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Static load check
- Support base = 1.90 − 0.60 = 1.30 m. Unladen CG at 1.15 m gives rear-arm load = 1,145 × (1.15 − 0.60)/1.30 ≈ 484 kg and front-arm load ≈ 661 kg, roughly 330 kg per pad.
- After removing 185 kg at 0.45 m, the remaining 960 kg has its CG at (1,145 × 1.15 − 185 × 0.45)/960 ≈ 1.29 m, i.e. about 135 mm rearward of the original position. Rear arms now take ≈ 506 kg, front ≈ 454 kg.
What this proves and what it does not The numbers show the lift is nowhere near its rated capacity, so capacity is not the problem. The rating assumes four pads correctly seated on the manufacturer's lifting points, on sound structure, with the load roughly centred between them. Here: (a) one pad sits half-on a reinforcement over a rusted sill, so its share of the load is concentrated and can slip; (b) the CG has moved rearward, shortening the tipping margin to about 0.6 m; (c) the rocking shows a pad is not carrying load, so the body is effectively on three supports and the resultant is near a support edge; (d) with locks disengaged the body is held by hydraulics alone. Any one of these defeats the rating.
2. Rank the hazards in the bay and state what must be done before anyone goes back under the vehicle.
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Priority 1 – person under an unsecured load. The trainee must come out immediately and the vehicle must be lowered to the ground; nothing is inspected, adjusted or refitted while it is held only on hydraulics with a pad that is visibly not seating. This is a crush/fatality hazard and outranks everything else.
Priority 2 – unstable support. Do not 'tap the arm down'. Lower fully, inspect the arm pad, the reinforcement and both sills, and condemn or repair any rusted seam before re-lifting. A deformed sill is a structural finding, not a cosmetic one.
Priority 3 – housekeeping. The 2 L oil tray is a slip and fire risk directly under the work area and the air hose is a trip hazard across the only walkway; both are removed or relocated before the bay is re-used.
Priority 4 – procedure. No work at height until the lift is at working height with the mechanical locks engaged, the vehicle is shaken on the locks, and a second person has confirmed pad contact at all four points. Record the near-miss; the pattern (rusted sills plus powertrain removal) should become a written check on the job card.
3. Describe the correct re-lifting procedure, including pad placement, and what you would check after the powertrain is refitted.
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Re-lifting
- Repair or reject the rusted sill area first; if the maker's lift point is unsound, use the specified alternative points (usually the chassis rails) with the correct adapters, not the floor pan.
- Set both arms symmetrically so the pad centres sit on the designated points; the pad must contact full face, not on a seam, hose, fuel line or plastic cover.
- Raise slowly to just off the ground, shake the body, re-check all four pads, then raise to working height and engage the mechanical locks before anyone goes under.
- Support the front or rear with stands when a heavy assembly is removed, because the CG moves (here ≈135 mm rearward) and the four-pad assumption no longer holds.
After refitting Re-check pad contact with the powertrain back in, since the CG returns forward and the load distribution reverses; inspect the repaired sill and floor reinforcement for cracking; check that no hose or wiring was pinched by a pad; confirm the locks engage at both working heights; then lower fully, remove stands and re-check the vehicle on the ground.