2nd Gen 4Runner Axles & Differentials: What You Actually Have
What's under your truck
The 1990–1995 4Runner uses a solid rear axle with an 8-inch ring gear, and it is genuinely one of the strong points of the platform. Toyota's 8-inch rear has a deserved reputation for taking abuse well beyond what the rest of the drivetrain will tolerate.
The front is a different story by design. These trucks use a torsion-bar Independent Front Suspension with a 7.5-inch front differential. IFS gives up some articulation and ultimate strength compared to a solid front axle, and it buys you noticeably better on-road manners in exchange. For a truck that spends most of its life on pavement getting to the trail, that was the right trade.
Worth knowing if you shop for parts: the 1986–1995 4Runners share this torsion-bar IFS layout with the mini-trucks of the same era, which widens your parts pool considerably.
You almost certainly have open differentials
Second gen 4Runners did not come from the factory with a limited-slip or a locker in either end. If yours is unmodified, both differentials are open, which means power follows the path of least resistance — lift a rear tire on an obstacle and that tire spins while the one with grip does nothing.
Here is the two-minute check. Safely jack up both rear wheels off the ground with the transmission in neutral, and spin one wheel by hand. If the opposite wheel turns the opposite direction, you have an open differential. If it turns the same direction, something is in there — a limited-slip or a locker. An electric locker would also show an actuator on the outside of the housing.
This is worth doing before you buy traction parts, because plenty of trucks have had work done that the seller never mentioned.
Traction options, honestly compared
Limited-slip differential. A helical or gear-type LSD like an Eaton TrueTrac transfers torque to the wheel with grip without any driver input and behaves normally on the street. It is the option most people are happiest with long term, particularly on a truck that daily drives.
Lunchbox lockers. These drop into the existing carrier and cost considerably less. They also make themselves known on pavement — clicking, banging on tight turns, and unpredictable behavior in the wet. Owners who do a lot of city driving, and especially those with automatics, frequently end up regretting them. If your truck is a dedicated trail rig, that calculus changes.
Selectable lockers. Best of both worlds and priced accordingly. Open on the street, fully locked when you flip the switch.
Before spending money on traction, be honest about whether traction is your actual limitation. On most 2nd gens, tires and suspension travel produce a bigger real-world improvement — our off-road build guide covers the order that works.
Noises that mean something
Groaning, clunking, or clicking from the rear that changes with load or turning deserves investigation. It might be the differential, but on this platform it is more often u-joints or the carrier bearing — both cheaper and easier. Our driveline vibration guide walks the diagnosis.
A howl that rises and falls with vehicle speed, unchanged by throttle, usually means a wheel bearing. A howl that changes with throttle on and off points at gear mesh in the differential.
Whatever it is, check the differential fluid while you are under there. Gear oil that is dark, gritty, or low is cheap to fix and expensive to ignore.
Sorting the stance? We build the complete 3" lift kit for the 90–95 trucks — shipped from Delaware.
