Universal Joint

Universal Joint (also called U-joint, Cardan joint) is a mechanical device that is a positive, mechanical connection between rotating shafts. Universal joints allow drive shafts to move up and down with the suspension while the shaft is moving so power can be transmitted when the drive shaft isn’t in a straight line between the transmission and drive wheels. They are widely used in drive shaft applications and situations where shaft force needs to transmitted through various angles.

U-joints can also be classified by their application: automotive, industrial, or mechanism.

Universal joints are capable of transmitting torque and rotational motion from one shaft to another when their axes are inclined to each other by some angle, which may constantly vary under working conditions. U-joints are incorporated in the of vehicle’s transmission system to perform three basic applications :

(a) Propeller shaft end joints between longitudinally front mounted gearbox and rear final drive axle.

(b) Rear axle drive shaft end joints between the sprung final drive and the unsprung rear wheel stub axle.

(c) Front axle drive shaft end joints between the sprung front mounted final drive and the unsprung front wheel steered stub axle.

Universal transmissions are commonly found in modern automobiles, which can transmit power between two shafts that are far apart and whose axis is not on the same centerline. The universal transmission device is mainly composed of the universal joint and the transmission shaft. According to the needs, the U-joint and the transmission shaft are mostly splined. The universal joints commonly used in automobiles include cross-shaft universal joints,Double universal joint and three-axis universal joints.

The cross-shaft universal joint

The cross-shaft universal joint is a variable speed universal joint widely used in automobiles, and the maximum angle of intersection between two adjacent shafts is allowed to be 15゜~20゜. The cross shaft universal joint is composed of a cross shaft, two universal joint forks and four needle bearings. The holes on the two universal joint forks are respectively sleeved on the two pairs of journals of the cross shaft.

In this way, when the driving shaft rotates, the driven shaft can rotate along with it, and it can also swing in any direction around the center of the cross shaft, so as to adapt to the simultaneous change of the angle and distance.

 A needle roller bearing is installed between the cross shaft journal and the universal joint fork hole, and the outer ring of the needle roller bearing is axially positioned by the snap ring.

In order to lubricate the bearing, the cross shaft is generally equipped with an oil nozzle and an oil path leads to the journal. Lubricating oil can be injected from the grease nozzle to the needle bearing of the cross shaft journal.

Features of the cross shaft universal joint

1): The structure is compact and reasonable. The structure design of the cross shaft universal joint shaft is very rigorous and compact, so the carrying capacity of the cross shaft type U-joint is very strong, and it is safe and reliable.

2): The cross shaft type universal joint shaft has a large load capacity. The torque that it can transmit is relatively large, so the cross-shaft universal coupling is more prominent in its matching range for mechanical equipment with restricted rotation diameter.

3) : The energy-saving characteristics of the cross shaft universal joints are remarkable, because the traditional efficiency of the universal coupling is high, generally up to 98%, which improves the work efficiency during the work, thereby achieving energy saving effect.

The cross-axis universal joint has many advantages, so it is widely used.

The Double universal joint


Double universal joint, this kind of U-joint belongs to constant velocity universal joint. Constant velocity universal joint is a universal joint where the rotational speed (angular velocity) of the driving shaft and the driven shaft are equal, that is, the driving shaft rotates at a constant angular speed, and the driven shaft is at a constant speed. Its simple and compact structure and good power transmission have greatly promoted the development of front-wheel drive vehicles.

When the universal joint fork swings within a certain angle range relative to the U-joint fork, the double-linked fork is also driven to deflect the corresponding angle, so that the angle difference between the center line of the two cross shafts and the axis of the two universal joint forks is small , So as to ensure that the angular velocities of the two shafts are approximately equal, and within the allowable range of the difference, the double-joint universal joint has quasi-constant velocity.

Its advantage is that it allows a maximum angle of 50° between the shafts and is simple in structure and reliable in work. It is often used in off-road vehicles. For example, the universal joint installed between the front drive shaft of the off-road vehicle and the front output shaft of the transfer case is a double joint of.

the three pin-type universal joint

the three pin-type universal joint, which is a quasi-constant speed U-joint evolved from a double universal joint.

It mainly consists of two eccentric shaft forks, two three pin shafts, six bearings and seals. The active eccentric shaft fork and the driven eccentric shaft fork are integrally formed with the inner and outer half shafts of the transaxle, respectively. The main and driven eccentric shaft forks are all eccentric forks, and the center line of the fork hole and the center line of the fork shaft are perpendicular to each other but do not intersect, and the two forks are connected by two three pin shafts.

The big pin end of the three pin type universal joint has a through hole, the center line coincides with the center line of the small end journal, and there are two journals on both sides of the big end, and the center line is perpendicular to the center line of the small end journal. Do not intersect. When assembled, the two fork holes of each eccentric shaft fork are matched with the big end two shafts of one of the three pins, and the small ends of the latter two pins are inserted into the bearing holes of the other end of the other end.

The biggest feature of the three-pin type universal joint is that it allows a larger angle between the two shafts to be connected, up to 45°. The steering axle with this U – joint allows the car to obtain a smaller turning radius and improve the maneuverability of the car.

Signs of a Bad or Failing Universal Joint

When U-Joints are worn or damaged they make squeaking noises that gain frequency with speed as well as vibrations when driving and other more serious symptoms. Finding the cause of the wear and choosing the right replacement U-Joint for your vehicle’s duties or activities can decrease the chance of premature wear and failure and increase the interval between replacements.

Here are some symptoms of a bad or failing universal joint you may notice:


If your driveshaft is out of balance, it’s often because of a defective universal joint. You will usually feel a vibration that increases in intensity as your vehicle’s speed increases.

This vibration means that the universal joint bearings have now worn enough to allow the driveshaft to move outside its normal rotational path, causing imbalance and vibration.

A vibration caused by wheel imbalance will have a consistent, steady vibration when the vehicle is in motion; a universal joint failure will cause vibration when both accelerating and decelerating but the vibration will stop when your vehicle is not moving, even if you gun the engine.

2.Squeaking noises.

Does your car squeak when it starts moving after kicking off the engine?  this noise is a tell-tale sign the bearing(s) in the u-joint are on the way out.

because the bearings on a universal joint tend to spin only in one direction, the grease can be forced out causing the bearing to become dry. Now, this greasing can be used up or evaporated over time. Each rotation of the driveshaft makes the bearings twist a little. So, dry bearings cause metal-to-metal contact, and excessive friction leads to squeaking noises and corrosion.

We recommend that Take your vehicle to your mechanic to have the bearings re-greased. Timely servicing will extend the lifespan of the joints and save the driveshaft from breaking down.

3.Transmission fluid leaking.

This fluid leaks for many reasons and bad universal joints are one of them.

The vibration noted above has now worn the transmission tailshaft bushing and damaged the transmission output shaft seal, which then leaks transmission fluid.

When this happens, thoroughly examine the transmission to find out the source of the leak and and the appropriate repair made.

The universal joints on a vehicle should last the life of the car or truck, but this is not always the case. There are a number of repair issues that can arise that can render the U-joints on your vehicle unusable.

Usually, you will be able to tell when this part of your car goes out due to the issues it will cause. If the universal joints on your car are not working properly, it can lead to the driveshaft not spinning. Without a fully functional driveshaft, you will not be able to drive the vehicle.

If the universal joints on your car need to be replaced, it is best to replace them in pairs in order to avoid further issues down the road. The more you are able to perform this type of preventative repair, the easier you will find it to keep your car running as intended.

How to Replace a U Joint

Worn universal joints, or U joints, can be a real aggravation. If not replaced, worn U-joints can come apart, spitting your driveshaft into the street (if you’re lucky—if you’re unlucky, it can result in a serious accident).

Replacing these joints is a fairly straightforward job, though it takes some prior experience. But follow these step-by-step instructions on how to change universal joints is will be easy.

1.Mark the shaft for reinstallation. Remove the U bolts, then slide the driveshaft forward into the transmission with a large screwdriver. It should slide forward enough to drop clear of the pinion yoke.

2.Remove the internal/external C-clips or press out the injected ring of polymer holding the U joints in place. For polymer, be prepared to use extreme pressure to remove the joints. Heat may be required, so have a heat gun or small Prestolite torch handy.

3.Press the universal joint out one side of the shaft. Remove the bearing cap and then press the joint and bearing cap out the other side. Handle the driveshaft carefully while doing this.

4.Stop to compare the old part and new part. Then, reinstall new joints by removing the bearing caps and needle bearings. Carefully twist the cap back and forth to remove.

5.Slip the universal joint cross into the driveshaft bearing loops. It takes a little perseverance to get the joint into position.

6.The new bearing caps are then pressed into the driveshaft with a universal joint press. Don’t be tempted to just make do using a bench vise—if you put even the slightest dent in the driveshaft, it can put it out of balance and then you’ll have a whole new set of problems. Make certain that the joint cross is aligned with the caps while pressing in place. Be careful not to allow bearings to shift. This is tricky, so be patient and take your time.

  1. After pressing in the new joints, the snap-ring C-clips are pushed in place by hand. The universal joint must be perfectly centered in the driveshaft to install the C-clips.

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