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New Gear Set Break In: Break In Or Break Down

Posted in How To: Transmission Drivetrain on July 1, 2012
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Grenaded ring-and-pinion gears aren’t only expensive, but they can leave you stranded, complicating an already frustrating breakdown. Regearing a 4x4 typically costs in excess of $1,200, yet we see people making the same mistakes all the time when it comes to breaking them in. The longevity of your gearset is directly proportional to the care taken to break them in, so here is how to do it right.

The first 100 miles are critical. New gears need several heat cycles in them before they are ready for primetime. One of the biggest mistakes we see is guys who pick up their newly regeared 4x4 from the shop and immediately hit the freeway for the ride home. We know, because we’ve done it too and understand that it is sometimes unavoidable.

If you do have to travel by highway, make sure you vary your speeds and don’t exceed 60 mph. After 20-30 minutes, pull over and take a break. Be sure the vehicle is parked and the gears are allowed to cool down to the point when you can hold your hand on the diff cover for a while. This cycle should be repeated a couple of times, and a complete cool-down of the gears overnight is welcomed.

The next milestone is at 500 miles, and before you reach it, care should be taken to avoid hard starts, high shock loads, sustained high speeds, and any towing. As soon as the 500-mile mark is met, the differential should be drained, the diff cover removed, and the gears inspected for any abnormal wear or chipping. If everything looks good, you can reinstall the cover and fill up the differential with fresh fluid. At this point you are ready to resume normal use.

At 500 miles your diffs should go through a complete cover-off inspection to check the wear pattern, bearings, and gear teeth.

It is important to note that a bad break-in doesn’t always manifest itself immediately, which is why a cover-off inspection is important. Ignoring this break-in procedure could mean a flatbed ride back to the shop when you least expect it, as well as a corresponding lightening of your wallet.

Once the gears are broken in, it is easy for them to be forgotten, but differentials need regular service too. It is important to replace the gear oil after a water crossing deeper than your hubs. At minimum once a year, change the oil and perform a cover-off inspection. These steps will ensure that your bearings will have a long, happy life and that your gears will provide you with years of service.

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