The break-in procedure for a new rearend (or frontend) is a relatively simple task; however, it needs to be done correctly to ensure a long-lasting setup. The idea is to mate the ring, and pinion gear tooth surfaces together, which, if done improperly, can lead to premature gear wear – however, it's not as complicated as it sounds. Because the ring and pinion are machined separately at the factory, it's important to "introduce" these surfaces together by putting a load on the setup, letting it cool, then progressively adding more load (speed) until the gears are in sync with each other. This is easily achieved by simply "cruising" your vehicle at typical street speeds in specific steps. At Currie, we recommend the initial break-in to start by driving normally for 15-20 minutes (no bun outs, hard starts, or highway driving), then letting the vehicle rest for 30-minutes, never going over 50 miles without letting it cool. Towing and high speeds should also be avoided until after break-in (300-500 miles). Once this is achieved, we recommend you change the oil.
Drive normally on streets for approximately 15-20 minutes, stop, and then let the rearend cool down for 30-minutes. The process should be repeated 2-to-3 times. The oil should be changed at 500 miles, don't be alarmed if this first oil change comes out much darker than when it went in as the black phosphate coating is wearing off the gears, along with a minimal amount of steel from the bearings, gears, and differential wearing-in.
Drive at low-loads for a total of approximately 300 to 500 miles of mixed street driving (see above) and highway driving before towing any load.
Drag Race Vehicles
Due to the short duration use and low potential for heat build-up, it is only necessary to perform an initial run-in with the driven wheels off the ground, and the vehicle idling in high gear for approximately 15 minutes, and then allow the rearend to cool. Once this initial heat/cool cycle has been completed, many will further break in the gears with a quick burnout or even a short track run before changing to fresh gear oil.
For off-road vehicles such as Jeeps and trucks, the break-in procedure is the same as it is for street-driven vehicles. When breaking in new gears or axle assemblies on the trail, avoid sand washes, big whoops, and inclines as it can load the gears prematurely.
REM® Gear Polishing
The REM ISF® (Isotropic Superfinish) process uses a proprietary combination of vibratory finishing equipment and refinement chemicals to achieve a smooth micro-textured finish that reduces friction, improves oil retention, and increases gear durability. Additionally, REM polishing eliminates the need to perform the standard break-in procedure. However, a 500-mile oil change is still required to remove contaminants from the break-in of other components, such as the bearings and differential. REM polishing is available for an additional charge for all ring and pinion gear sets purchased from Currie.
As an alternative to the traditional break-in procedure, Currie offers a dyno break-in service for new or rebuilt 9-inch third members that go through our shop. The dyno brake-in procedure spins the third member in a fixtured rearend for 20 minutes to allow the unit to reach operating temperature, after which it's allowed to cool, completing the initial run-in of the gears and bearings. The dyno break-in service is available for a fee of $150 and can help save some time and ensure your third member is quiet.