Drivetrain Direct - What to Do When Your Rearend Craps Out

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Let’s say that one day the plumbing is broken and after a few hours of fiddling around, you finally figure that you’ll need a few things from the hardware store. The task of snaking unknown contents out of the drain awaits and is about as pleasant as porta-jons in the desert. Feeling frustrated and hurried, you hop in your truck and go. Short shifting, revving, wheeling out, and basically taking out your frustrations on your truck. Then all of a sudden a big whapam followed by a mild grinding noise emits from the rear axles. Something’s wrong and you might want to stop at the auto parts store since you just blew out the differential. The rearend of a truck takes a lot of abuse. As a rule, factory units are stout and last a long time under normal use and maintenance. There is a point in time when everything fails, even the best GM has to offer. So how do you tell when the bearings and differential are shot? What do you do if they are? And what’s the logic behind gear ratios and differential units? Relax and read on.

It’s important to understand the inner workings of the differential unit to get a feel for what goes bad in them. The big hunk o’ gears inside the rearend redirects power from the driveshaft to the wheels and as such is under an enormous amount of stress. The parts that are subject to wear include bearing journals, bearing races, axleshafts, spider gears, and the ring-and-pinion.

The function of the differential and gears dictates that they rub against each other under high pressure and load and have to maintain structural integrity. In other words, the components have to have immense torsional strength to resist twisting off and also must have surfaces capable of withstanding wear. To achieve this, the parts of the differential are hardened.

After the gears are cut and shaped, they are flash-hardened. This process leaves the inner portion of the gear metal relatively soft so it can resist and absorb torsional stress. The outer metal (about 1/64 inch thick) is hardened for good friction-wear characteristics. Over time, the outer hardened layer wears thin and the inner soft metal is exposed. When this happens, the gear faces are wearing on the soft inner metal which is not as resistant to friction. The result is increased temperatures due to friction and excessive gear wear. The symptom of a worn-out rearend is any unusual noise coming from the rear axles, such as grinding, whirring, or clacking. So pop the cover and start to look at things. We contacted Drivetrain Direct with our rearend dilemma. The chief mechanic, Martin, recommended that we bring a rearend unit in and he’d show us the rest. Drivetrain Direct is one of the industry leaders in rearend components and carries parts for any make and model truck. As Martin pulled apart the rearend, it became obvious to us what was wrong.