Spider gears are primetime players inside the differential. Also known as satellite gears, spider gears rotate around the side gears in the differential carrier. Side gears may also be referred to as axle gears or planetary gears. To spot spider gears look for the gears with the cross-pin shaft going through them.
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What Gears Do
The diff’s array of spider and side gears take the rotational energy from the driveshaft and help redirect it outwards to the axles and on to the tires. More importantly, they also play a key role in allowing the tires to rotate smoothly at different speeds when the vehicle is turning.
Gears In Trouble
Broken spider gears will make a grinding or banging sound when the vehicle is turning because the difference in wheel speeds causes the chatter. You usually won’t hear them when traveling in a straight line because the spider gears remain motionless within the carrier in this instance. But, if they are bad enough, compromised spider gears will make noise even when going straight. When you hear a loud differential think of metal flakes being formed and circulated throughout the unit, usually damaging the vulnerable bearings first. So, noise means trouble.
In some cases, the damage may not be the gears themselves. When the spider gears are in motion they rotate on the cross-pin shaft, especially when the vehicle is turning a corner. But there are situations that can cause over spinning and the result can be a heat-scored cross-pin shaft. A common scenario is getting stuck in the mud or snow and free spinning your wheels trying to break free. When this happens, the spider gears can rotate on the cross-pin shaft so quickly that the differential oil is slung away, resulting in metal-on-metal wear. In extreme cases the cross-pin shaft and the gear get so hot that they melt each other, sometimes to the point where they weld themselves together. Damage such as this can not only damage the spider gear set, but also destroy the carrier and ring and pinion gear set.
Spider Gear Replacement
When replacing spider gears you are, in fact, replacing both the spider gears and the side gears. Over the miles these gears mesh and wear in unison, so dropping in new spider gears with the original side gears can cause an imbalance. Yukon Gear & Axle and USA Standard Gear spider gear kits include two side gears, two pinion gears, a cross pin shaft, a roll pin, and thrust washers. Installation is relatively straightforward. For a more in-depth look, view the accompanying installation video from our YouTube channel.
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