4x4 and four-wheel drive

A-1 Transmission lists 4x4s among the vehicles the shop works on and transfer cases among its services. This page explains what a 4x4 drivetrain adds, the signs to watch for and what the shop needs to know when you call.

At a glance

• 4x4s and transfer cases are both on the shop's list
• A transfer case has its own fluid, separate from the transmission
• Noise in 4WD, a flashing 4WD light or no engagement are the usual symptoms
• Jeeps, pickups and SUVs with transfer cases are all 4x4s

What a transfer case does

In a four-wheel-drive vehicle the transmission sends power to a transfer case, which splits it between the front and rear axles. Many transfer cases also offer a low range, a set of reduction gears for crawling, towing a heavy load or pulling out of mud and snow. Wikipedia describes the main designs, from gear-driven to chain-driven, and the owner's manual for your vehicle says which one it has and what fluid it takes.

The transfer case is bolted behind the transmission and shares the vibration, heat and road debris that the rest of the drivetrain sees. Its fluid wears out like any other. Our transfer case guide goes into more detail.

Signs a 4x4 needs a look

• A 4WD light that flashes, stays on or will not come on
• The shift into four-wheel drive or low range does not engage, or pops back out
• A grind, clunk or whine that is there in 4WD and not in 2WD
• The vehicle binds or hops in tight turns on dry pavement
• Oil or fluid at the front or rear of the transmission

The 4WD noise or not engaging page covers what these usually point to, and the transfer case repair page says what the shop does first.

Winter and northern Nevada

The Reno normals show 25.7 F as the average December low and 5.2 inches of snow in each of December, January and February (NOAA 1991 to 2020), and the passes above Reno get more. Many owners of 4x4s use 4WD for the first time of the season on the first snowy morning, and a system that has sat unused for months is the one most likely to show a problem then. Using it briefly where the owner's manual allows, before the snow arrives, is a way to find out early.

4WD or AWD?

The two are not the same, and the care differs. A part-time 4WD system is selected by the driver and is meant for slippery surfaces, while an AWD system works automatically and may include clutches or couplings that need fluid service on their own schedule. The 4WD vs AWD guide explains the difference, and the manual lists the intervals for your vehicle.

See also the page on Jeep transmissions and transfer cases.