What is the Differential Output Seal?

Your vehicle’s engine produces power and transmits it in a straight line through the crankshaft into the transmission. The power that issues through the transmission is in the same straight line as the engine, yet somehow requires to change 180 degrees to power the wheels. The differential is a part in your vehicle that changes the direction of the propulsion from a longitudinal orientation to a lateral one, and it can also offer a fixed gear ratio change.

The differential has a pinion gear and side gears that rotate in fluid to solidly sends the power 180 degrees. Axle shafts run from the differential to each wheel in a couple different designs, yet each requires a way to contain the oil inside the differential assembly. The axle shaft runs through an output seal in the differential that lets the shaft to rotate without losing the lubricating oil inside. If the axle seal leaks and the fluid is lost, the differential won’t be properly lubricated and the gears and bearings can get overheated and seize, causing extensive damage and rendering your car unfit to drive.

Bear in mind:

  • A differential doesn’t have a dipstick to check fluid level in most cases. If there is a leak present, it is nearly impossible to know how much fluid is left.

How it is done:

  • The differential output seal is checked to confiem that it needs to be replaced. The vehicle is lifted and supported on jack stands.
  • The CV axle is taken out and defective differential output seal is removed using a seal removal tool.
  • The new differential output seal is mounted using a seal installer then the CV axle is reinstalled.
  • The differential is refilled and tested for leaks. The car is removed from the jack stands.
  • The car is road tested to ensure proper operation of the differential output seal.


The differential fluid needs replacement at regular intervals, usually around every 25,000 miles. Have the differential output seals checked for leaks at this time, and if during any other regular maintenance inspection an output shaft seal is found to be leaking, have it changed by one of our expert technicians.

What common signs indicate you may need to change the Differential Output Seal?

  • Fluid leaking onto the ground under your car
  • Loud whining or grinding noise that increases with speed heard when driving

How vital is this service?

The differential output seal is vital to the lubrication of the internal gears in the differential, though most leaks start out small. If you have just noticed or been notified of a small leak, you have some flexibility in timing to change it. If the differential leak is major, have it repaired soon to prevent additional internal damage.