One of the more common repairs needed for many Corvettes is axleshaft u-joint replacement. In IRS cars, Corvette axleshaft u-joints constantly change drive angles as the suspension traverses bumps and dips in the road while the driveshaft angle remains constant. Another factor weighing heavy on the u-joints is the load created because of the '63-'96 Corvettes rear-suspension design. Axle shafts are the pivot point for the suspension since there are no upper control arms to keep the rear-wheel position in check. The negative rear-wheel camber alignment keeps pressure on the axle shaft and u-joints, while the lower camber struts keep the alignment adjustment correct.
Typically, u-joints do their job for many miles with minimal maintenance and, in most cases, none at all. Considering that the u-joints handle thrust load, drive-angle movement, and vehicle-load torque, it's amazing they can live for 75,000-125,000 miles and, in some cases, more than that. Usually, u-joints will start to tighten up from lubricant loss even though they have grease fittings, but really, how often are they serviced?
A tell-tale audible sound of impending u-joint failure in a Corvette is a clicking noise from the rear axle during cornering because the axleshafts rotate at different speeds, thus loading one side more than the other. Visual signs of failure are rust trails or rust stains at the u-joint cups. The clicking eventually leads to banging when shifting gears and eventually total u-joint failure that will effect the rear-wheel alignment. Either way, it's time to replace the u-joints whenever the rust stains are evident or this type of noise starts. It's also recommended that all u-joints in the suspension should be replaced at the same time since most u-joints will begin to fail on the same car at the same time.
Choosing what type of replacement u-joints you will use depends on the abuse or lack thereof that you may put them through. The strongest u-joints manufactured have no grease fittings (with no drilled passages for the grease to flow through), which equates to a solid cross-section for superior strength. The downside of this design is not being able to grease them, but with today's synthetic chassis lubricants, the nongrease-type joints should last many miles. We have installed greasable u-joints for many years of service in a Corvette that will be driven few miles annually. The serviceable fittings allow you to push out the moisture laden grease when they are serviced.
Whether you're working on a '63 or a '96 Corvette, the objective of this article is the same: removing the axleshafts and replacing the u-joints. Of course, the '84-'96 Corvettes have aluminum axleshafts, and the u-joints are easier to replace because of the softer material, but the concept is the same. Removing the axleshaft requires lifting the rear of the car and supporting the frame in front of the '63-'82 trailing arms (or spindle rods on the '84-'96 Corvettes). Remember, we mentioned earlier the axleshafts are part of the suspension alignment. When the rear suspension hangs freely, the axleshafts are unloaded. You can remove the axleshafts out of a '63-'82 Corvettes without loosening or removing any other suspension components. It's a good idea to support the trailing arm during disassembly to avoid a surprise when the trailing arm moves quickly. In some cases, you will have to support the trailing arm to reinstall the axleshaft.
The '84-'96 Corvettes are a little different because they usually don't have as much movement in the rear suspension, and removing the axleshaft out of the suspension takes some additional finesse. If you have a helper (highly suggested) during the job, they can apply some outward pressure to the spindle knuckle while the axleshaft is pulled up and out of the inner differential yoke. The axleshaft is then moved inward enough to allow the outer end to pass by the spindle knuckle.