When buying a used car rear end in New Hampshire, you should prioritize a thorough inspection for damage, verify compatibility, and confirm the part’s history. The condition of used parts is crucial since New Hampshire‘s “Lemon Law” does not cover used car rear ends and rear axles, leaving you with little legal recourse if a part is defective.

Before you buy

• Make sure the used axle is compatible:  By checking the axle ratio, mounting locations, axle width, and other details to make sure it matches the make, model, and year of your car. The ratio has an impact on your car’s fuel efficiency and performance.
• Check the source: Reputable auto salvage yards often inspect and offer some assurance on the condition of their parts, though used car rear ends in New Hampshire typically have no warranty. Avoid buying from unknown private sellers who cannot provide a full history.
• Get the vehicle’s history: If possible, ask about the history of the donor vehicle. An axle from a vehicle that was in a front-end collision may still be in good shape, but one from a rear-end accident is more likely to be damaged. 

Inspecting the axle

Visual inspection

• Look for damage: Check the axle housing for any cracks, large dents, or signs of collision damage. A bent axle is a big problem that can lead to strange vibrations and issues with steering.
• Examine seals: Look for fluid leaks at the differential gasket, pinion seal, and axle shaft seals. Fresh dirt mixed with oil is a telltale sign of a leaking seal. If you don’t fix a slow leak, it can eventually ruin the gears and bearings inside.
• Look for rust: Some surface rust is normal, but too much rust or corrosion on the differential cover or housing can weaken the axle. 

Mechanical inspection

• Listen for abnormal noises: Worn bearings or gears can produce distinctive sounds.
  • Howling or whining: Often points to worn-out ring and pinion gears or improper gear alignment. When you speed up or slow down, this sound might change.
  • Rumbling or whirring: Typically indicates worn carrier or pinion bearings. You can usually hear these sounds when you’re going faster than 20 mph.
  • Clunking or crunching: Can signal a serious issue like a chipped or broken gear tooth. A repeating clunking sound every few feet suggests a damaged ring gear.
• Check gear backlash: With the vehicle safely on jack stands, you can check the gear backlash (play) by rotating the driveshaft while holding one wheel still. Excessive play indicates worn ring and pinion gears or bad bearings.
• Test the differential type: To check for a limited-slip (posi) or open differential, jack up both rear wheels and spin one tire by hand.
  • Limited-slip/posi: The opposite wheel will spin in the same direction.
  • Open differential: The opposite wheel will spin in the opposite direction.
• Check the axle shafts: If you can, look for twists or galling on the axle shaft splines, which can mean that the vehicle has been used a lot or abused. 

After purchase and installation

• Replace fluids and seals: Even if the seller says the fluids are new, replace the differential fluid and seals upon installation. This allows you to inspect the old fluid for metal particles and ensure proper lubrication.
• Check the gear pattern: For expert-level confidence, a mechanic can check the gear wear pattern and backlash to ensure proper alignment before driving.

Adjust and align: After installation, get a wheel alignment that measures the thrust angle to ensure the axle is positioned correctly and avoid excessive universal joint wear.