By Glenn Goodspeed (April, 1999)
If you're hearing a clunking, grinding or threshing noise whenever you coast or downshift in your classic car, you should check the universal joints to see if they need replacing. U-joints are the cross-shaped devices that tie the driveshaft together and allow it to flex. The Volvo P1800 has three u-joints. To test them, raise the car securely, and lying underneath, grasp the driveshaft on either side of each u-joint and twist it this way and that. If there is any play in a u-joint, it must be replaced. If you put it off, the u-joint could come loose and chew up the yokes on the driveshaft before separating and leaving you on the road at an undetermined time and location.
Universal joints are inexpensive, but they can be stubborn to remove and tricky to replace. Do yourself a favor and plan ahead. Remove the driveshaft from the car before attempting to work on the u-joints. Because the driveshaft is balanced as a unit, mark the pieces so you'll be able to position them the same way when reassembling. Before replacing the u-joints, be sure they are oriented correctly. Nothing is more irritating than going to all the trouble of replacing u-joints and then finding you have to do the job over.
Removing the driveshaft in later model cars is straightforward. With the transmission in gear (or in park with an automatic), undo the flange bolts on the rear flange first. You may have to put the transmission in neutral and turn the driveshaft to make some of the flange bolts accessible. In earlier model cars, the front and rear u-joints are held to the transmission and rear axle yokes by u-bolts. When you have removed these u-bolts, wrap some tape around the front and rear u-joints to keep the caps from falling off while you maneuver the driveshaft out of its tunnel. Don't try to pull the shaft out entirely from the rear, because it may separate at the slide joint in the middle. Rather, put one hand on the forward part of the shaft and one on the rear and guide it out.
Once you have the driveshaft clear, spray the outer caps of all the u-joints with a penetrating oil like WD-40. Use a pair of inside snap ring pliers to remove the rings that hold the u-joint caps in the yokes. (These special pliers are available at good hardware stores.) With the snap rings out, clean the bores of the yokes with a wire brush.
Now comes the hard part. Place the driveshaft in a vise, being careful not to dent it. Using a hammer and cold chisel on the center of the u-joint, push one end cap out of the yoke. Depending on the age and condition of the parts, this may be difficult or extremely difficult. Take care not to damage the driveshaft. When you have one end out, turn the driveshaft over and use the same method to remove the opposite end.
Before replacing a u-joint, clean the yokes and smear a thin coat of chassis grease in the bores. If the u-joint has a grease nipple, use a grease gun to fill it with fresh grease. Hold the u-joint up to the driveshaft and position it so that the grease nipple is facing the driveshaft and is located in one of the hollow areas of the yoke. If you position it any other way, the grease nipple will contact the yoke and will be broken off.
When you are sure you have the correct position, carefully remove the upper and lower caps on the u-joint. Make sure none of the roller bearings stick to the u-joint, and that they are neatly aligned around the inside of the cap. Place the u-joint in the yoke from the inside and tap the lower cap into place from the outside. Turn the driveshaft over and tap the other cap into place. Always be aware that the roller bearings are free to move inside the cap, and position the u-joint to hold them in place when you are tapping the caps in.
When you install a new snap ring, it's a good idea to tap the end cap down a little bit first. That way, you can be sure the snap ring groove will be fully exposed. Once you have the first snap ring installed, turn the driveshaft over and install the opposite ring in the same manner, tapping the cap down first. When you have two opposite snap rings installed this way, you'll notice the u-joint may not rotate freely. To fix this, turn the driveshaft over again and tap on the center of the u-joint with the cold chisel to force the first end cap to seat against the snap ring.
Depending on the design of your driveshaft, you may have to use the same method to install the u-joints in the flanges. If you have the older style driveshaft that uses yokes on the transmission and rear axle rather than flanges, you're almost finished. Tape up the exposed u-joints and position the driveshaft in the car. Remove the tape, being careful not to remove the end caps, and install the u-bolts that hold the u-joints to the yokes. If the u-joints seem too wide to fit in the yokes, check inside the exposed end caps for roller bearings that may have fallen out of place.