Front Final Drive Noise and Metal in the Axle Oil

The oil sample and symptoms point strongly to the front left final drive, not the driveshaft or a tire. Iron at 380 ppm is very high for 300 hours of service, and chromium at 45 ppm is consistent with bearing races or gear surfaces wearing. Silicon at 12 ppm suggests some dirt ingress, which may have started the wear or be a result of the repair history. The 4 mm fuzz ball on the magnetic plug is visible metallic debris, not normal break-in fuzz.

The vibration beginning at 8–12 km/h under load and worsening in a left turn fits a planetary final drive or wheel bearing under load. In a left turn the left wheel slows and the differential and final drive components change their load path; a damaged bearing or gear tooth will often growl louder. The fact that the noise disappears in two-wheel drive and unloaded reduces the likelihood of a tire or driveshaft fault, and the universals and wheel bearings have already been checked.

I would still consider:

• Differential side gear or pinion bearing wear, though the noise is localized to one wheel.
• Axle shaft spline wear or a failing suspension joint, which can transmit vibration.
• Contaminated oil from a previous repair, which would make the sample less diagnostic.

The chromium and iron together make a bearing or gear failure in the left final drive the leading suspect.

I would drain the oil through a clean strainer and cut the filter, if fitted, to capture large particles. The magnetic plug debris should be examined under a light; shiny flakes suggest bearing material, while larger chunks suggest gear tooth spalling.

With the final drive removed:

• Inspect the planetary gears, sun gear, ring gear, and thrust washers for spalling, pitting, and discoloration.
• Check the bearings for roughness, cage damage, and heat discoloration. Spin them by hand and feel for tight spots.
• Measure gear backlash and bearing preload against the service specification. A loose or tight preload can explain the heat and wear pattern.
• Check the axle shaft splines and the final drive housing for cracks or fretting.
• Use dye penetrant on suspected gear teeth if a crack is not visible.
• Compare the left and right final drives; a difference in backlash or bearing drag is a strong clue.

If the gears are scored or the bearings have spun in the housing, individual bearings will not be enough. If the gears and housing are serviceable, a bearing and seal kit may be appropriate. I would not order the two-day parts until the unit is apart and the gear condition is known, because a remanufactured assembly may be the better choice once the core is inspected.

My recommendation is to stop operating the tractor until the front left final drive is inspected and repaired. A final drive with 380 ppm iron, 45 ppm chromium, and visible magnetic debris is already failing. Continuing to run it under tillage or grain-hauling load can turn a bearing replacement into a destroyed planetary, a cracked housing, or a wheel seizure. At 8–12 km/h with a loaded grain cart, a seizure or loss of drive on the front axle is a serious safety event, not just a breakdown.

The 600-acre harvest pressure is real, but the economics favor stopping. A remanufactured final drive in five days or a bearing and gear repair in two days is far cheaper than a catastrophic failure that damages the axle housing and leaves the tractor blocking the field. If the crop cannot wait, the better options are to rent a tractor, borrow a machine, or use another unit for hauling while this one is repaired.

If the owner insists on running, I would require a magnetic plug check after a short interval and limit the load, but I would not sign off on that as a repair. My release decision would be: repair first, then verify with a road test and a oil sample at 50 hours.