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?
Only the serious automotive...
Only the serious automotive connoisseur could love the tired, rusty underside of this Corvette.
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.
1-A U-joints need to be replaced...
1-A U-joints need to be replaced and can become quite corroded over time.
1-B This one is way past its...
1-BThis one is way past its useful life.
2 Once we got the axleshaft...
2 Once we got the axleshaft out, we realized how lucky the owner had been since the u-joint retaining clip was never seated in the groove properly. From the look of things, the minimal use of the Corvette lets corrosion take over and seals the u-joint cup in place.
3 Although this is not the...
3 Although this is not the preferred way and looks crude with careful hammer blows, the u-joint can be disassembled effectively. The wedge of the heavy hammer is placed on the weld where the tube and u-joint trunnion meet. Sometimes this is the only way to get stubborn u-joints out because of the shock load the hammer delivers.
4 Then there's always the...
4 Then there's always the one joint that just won't come loose. We're applying heat to the trunnion while the vise applies pressure to the joint itself. A FEW WORDS OF CAUTION: if the u-joint has a grease fitting, remove it to allow pressure relief as heat builds if it has no fitting. Beware that as pressure builds a small explosion can occur. The ensuing pop can blow the caps off and cause injury if they're not contained.
5 Now that the u-joint cups...
5 Now that the u-joint cups are pushed out on each side of the trunnion, we grab the cup in the vise and tap upward to release the cup from the trunnion. The cups are usually easy to get out at this point, and the dead blow hammer applies enough pressure for final removal without axleshaft-tube damage.
6 This is the preferred way...
6 This is the preferred way to remove the u-joints with our u-joint/ball joint press. The cost of the press can be prohibitive for one time or occasional use at $300. The press will remove the most stubborn u-joints where a bench vise will break if the same load is applied.
7 One problem we have found...
7 One problem we have found when dealing with tight or corroded u-joints is the axle flange trunnion gets bent. As you push on one corroded cup, it bends the trunnion together during removal, making it difficult to get the u-joint cup retaining clips in place. This trunnion is bent .025 on both sides, so we will need to replace it or fix it.
8 As '63-'82 original Corvette...
8 As '63-'82 original Corvette pieces become harder and harder to locate, we find ourselves trying to reuse the original pieces if possible. We found we could use our press to apply reverse pressure on the trunnion, thus straightening the trunnion out. This is one of those easy-does-it fixes. You have to apply enough pressure to go beyond perfectly straight so when the pressure is released, the trunnion is flat. The good part is you can sneak up on it, applying a little more pressure each time until the desired effect is achieved.
9 This is not the preferred...
9 This is not the preferred way to install the u-joint cups, but very effective. The cross is placed in the trunnion, and the caps are carefully tapped into place. We're holding the cross up into the cup so the needle bearings won't come out and be damaged. The cross must be held up into position while the shaft is turned over to install the other cup.
10 Now comes the tricky part-you...
10 Now comes the tricky part-you need to keep focused on the position of the cross until the other cup is in place. We place the cup in the shaft, then pull the cross up into the cup to be installed. The cross is then centered to keep the needle bearings in place until the cup is tapped into position.
11 The large drift is used...
11 The large drift is used to tap the cup beyond the top of the trunnion to avoid snap-ring groove damage. never tap the cups with the hammer or you'll pay the price later as the snap ring won't fit in the groove or, worse yet, the outer edge of the groove can be broken off. We make a habit of moving the cross back and forth into each cup before using the drift to fully seat the cups to make sure the cross sits against the cups' seal surface.
12 The preferred way to install...
12 The preferred way to install the new u-joints is with the press used for disassembly. The trick with the press is to make sure the tool is sitting flat on the trunnion, and the cup is going in straight. If the cup quits moving, back off as the cup is cocked; if you try to go further, the trunnion will be bent.
13 Hold onto the clip while...
13 Hold onto the clip while you're squeezing it to install it or it may knock out a tooth if it gets loose. Don't squeeze the retaining clip any more than necessary, or it will lose its spring retention and can come out. If we installed the cups correctly and the needle bearings stayed in place, the snap ring should go in place. If the snap ring doesn't go in, the trunnion is bent or a needle bearing has fallen out and is in the bottom of the cup.
14 We always make sure the...
14 We always make sure the snap ring is seated in the groove fully. If the clip won't go in with light force, you may want to take the joint apart and check the needle bearings for placement. If you try to hammer the cap with the biggest hammer in the toolbox, the needle bearings will be crushed.
15 We're using the dead blow...
15 We're using the dead blow hammer to free up the cups from assembly. The u-joint should rotate with minimal effort once the snap rings are in place. Give it a few whacks on one side, then roll the shaft over and give it a few more whacks. The dead-blow hammer won't distort the snap-ring groove but will seat the cups.
16 The vise is used to keep...
16 The vise is used to keep the cups in place while we pump some synthetic chassis grease into the new u-joints. Rotate the shaft on the joint to allow the grease to be dispersed throughout the joint. Grease should come out all four cups. If not, debris or a needle bearing may be obstructing the grease flow. Either way, make sure the grease flows out of all four cups even if the joint has to come apart.
17 It never hurts to torque...
17 It never hurts to torque the retention bolts to 75 lb-ft at the spindle flange. We always clean the threads at the flange to make sure the bolts are properly tightened. We're now ready to go for a testdrive, which is why we spent our Saturday afternoon under the shark after all.