DriveshaftThe shaft that brings the engine's turning force back from the gearbox. Also called the propeller shaft.
Drive pinionThe small gear on the end of the driveshaft. It turns the ring gear.
Ring gearThe large gear bolted to the differential case. The pinion turns it, and because it has more teeth, the drive is slowed and turned through a right angle.
Carrier (differential case)The case bolted to the ring gear, turning with it. It carries the differential pinions round.
Differential pinionsSmall gears on a shaft across the case. Going straight they do not spin; in a turn they spin, letting one side gear run faster than the other.
Side gearsThe gears on the inner ends of the axle shafts. The differential pinions turn them.
Axle shaftsThe shafts from the side gears out to the driving wheels.
How this list was compiled: Read 2026-09-27. (1) US Army, TM 9-8000, Principles of Automotive Vehicles (1985), chapter 29, paragraphs 29-1 and 29-2 and figure 29-2, https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 : the bevel drive pinion turns the drive ring gear and the differential case it is bolted to; the axle shafts are splined to the differential side gears; the differential pinions on their shaft do not turn about their own axis going straight, and let the outer wheel turn faster in a turn; the propeller shaft. (2) Wikipedia, Differential (mechanical device), Ring-and-pinion design, https://en.wikipedia.org/wiki/Differential_(mechanical_device) : a ring gear driven by a pinion connected to the transmission, turning the drive through 90 degrees and reducing the gear ratio; the output shafts (axles), drive gear, output gears, planetary gears, carrier, input gear and input shaft (driveshaft). Licence: own work
The drawing: Drawn for this site on 2026-10-05 by script from a small solid model of our own (bevel-gear geometry, real tooth counts). The arrangement was checked by eye against two public-domain plates on Wikimedia Commons: Differential (Manual of Driving and Maintenance).jpg, 1937, and Differential gear (PSF).png, Pearson Scott Foresman. Nothing traced. Licence: own work
How it works
These are the parts of a car's differential, the gears in the middle of a driven axle, seen from above with the front of the car at the bottom and the case cut open.
Read the full guide
Following the drive
The driveshaft turns the drive pinion, which turns the ring gear through a right angle. The ring gear is bolted to the carrier, so the carrier turns too, carrying the differential pinions round. They push the side gears, and the side gears turn the axle shafts.
Going round a corner
Straight ahead, the differential pinions do not spin, and both wheels turn at the same speed. In a turn the inner wheel slows, the pinions spin on their shaft, and the outer wheel turns faster.
Watch the differential pinions: going straight they stay still on their shaft; only in a turn do they spin.
Questions and answers
What does a differential do?
It passes the engine's turning force to the two driving wheels while letting them turn at different speeds, which they must do going round a corner.
What are the gears inside a differential called?
Two small differential pinions on a shaft across the case, and two side gears on the ends of the axle shafts. Some diagrams call them planetary gears and output gears.
Why does the ring gear have more teeth than the pinion?
So the drive is slowed down on its way to the wheels. The pair also turn the drive through a right angle, from the driveshaft to the axles.