Does My Car Have Universal Joints?
Most cars and trucks that are rear-wheel drive, all wheel drive and four-wheel drive have universal joints.
Where Are Universal Joints Located?
Universal joints are located at the ends of the drive shaft. The drive shaft goes into the rear differential, and right between them is where the universal joint is. If you follow that drive shaft all the way to the front, where the drive shaft meets the transmission or transfer case, you can see another u-joint.
- On a four-wheel drive, coming out of the transfer case, you might have another u joint. It could be a CV joint at constant velocity joints a little bit different. Go forward and follow the front drive shaft to the front differential, you will see another u joint.
- On Jeeps, trucks, and SUVs with a solid front axle, you can find u-joints behind each front wheel.
- On some rear-wheel-drive cars, the rear axle shafts have u-joints as well.
So now you know all the different locations that u-joints could be found in your vehicle, but what’s the point of them? Why are u joints even used?
What Are Universal Joints Used For?
While u joints might be small, they’re actually pretty important. They allow the drive shaft to come in at an angle and they also allow to move up and down, and inside the side with the suspension. Without a u-joint, the drive shaft would have to be directly in line with the differential and it wouldn’t be allowed to move side to side, or up or down. A really good example of how all these works is using a universal joint extension which you use to remove hard-to-reach nuts and bolts. Without the universal joint, the socket can’t move it can only spin at that fixed point. If you add the universal joint extension, now the socket could spin and move up and down and side-to-side. U-joints allows the driveshaft and axles to move around with the suspension.
What Causes The U-Joints To Wear Out
- Universal joints have four caps that spin smoothly on needle bearings. At the end of each cap is a rubber boot which prevents dirt and debris from getting in there and damaging the needle bearings. Now, over time what happens is those rubber caps wear out, and then dirt and debris get in there and damage the needle bearings.
- Another thing is over time the grease that’s in these caps dries up and washes away, so the needle bearings run dry and you can notice at the end of the u-joint all grooves in the trunnion from those needle bearings.
Symptoms Of Bad Universal Joints
- The first symptom is a ”clunk” sound when you go from reverse to drive or drive to reverse. That ‘clunk’ comes from the u-joint when the drive shaft changes directions.
- The second symptom happens while you’re driving and it’s a rhythmic click, squeak, or grind that increases in speed the faster you go, and sometimes at higher speeds that noise might go away completely.
- The third and final symptom is if you feel a vibration under your seat. That’s an indication that your you joints are worn out. For a better visual, put a cup of water in the car which will give you a really good idea of how much vibration there actually is. Your drive shaft can be spinning over 3,000 rpms at highway speeds, so even if your u-joint is a little bit worn out, it is going to cause a vibration.
So, those are the most common symptoms of a bad u-joint. You might only have one of those symptoms, and the problem is those symptoms are similar to other car problems. You might have for example a vibration could be an unbalanced wheel, or a squeaking noise could be bad brakes. So in order to find out for sure that your u-joints are bad, you need to go under the truck and inspect them.
Visual Inspection Of Bad U-Joints
- First, do a visual inspection. You want to make sure that the retaining clips are in place and the u-joint isn’t pushed in or pushed outward.
- Next, you want to check the rubber boots on the caps and make sure they’re not damaged. If you see that the rubbers are dry, rotted and separated from the cat, probably because dirt and water got in there, causing those bearings to wear out and is making that noise you heard.
- And finally, grab the drive shaft and shake it side to side, and up and down. The drive shaft shouldn’t budge. There should be no play or movement at all. Sometimes using just your hands isn’t enough to move a bad u-joint, so try using a pry or screwdriver at different spots and at different angles. If you get even a little bit of motion, you need to replace your u-joints.
Not Replacing U-Joints Can Cause Other Problems
- You don’t want to be driving around on bad u joints. It could cause other more serious and dangerous problems. If that bad u-joint fails it could cause the drive shaft to disconnect and come flying out as you’re driving.
- Also, all those vibrations that you feel could damage the seal inside the differential and the seal in your transfer case, or transmission which could cause it to leak out fluid.
Types Of Universal Joints
- The first option is whether or not the u-joint is greasable. On the greasable u-joints, you can see a zerk fitting that goes into the u-joint and allows you to grease all four caps by connecting a grease gun. The benefit of being able to grease your u-joint is when the u-joints get old and the grease comes out, or there are dirt and debris that gets in, you could add the grease. The grease could force all that dirt and debris out, and you’ll have some new grease in your bearing caps which could make it last longer. There are two different styles. One that could be greased from the middle and then the one that could be greased on the end cap. I like the end cap better because it’s a lot easier to reach the end cap when it’s installed in the vehicle.
- The benefit of a non-greasable u-joint is that there’s no grease channel in it. They could last up to 150,000 miles.
Besides grease ability, the next thing to consider is the string. You have the OEM strength and then you have the high strength u-joints. If you are a daily driver, the OEM strength is perfect. If you have a drift car or an off-road vehicle, it’s better to use a high strength.