A propeller shaft is the main component that transfers the engine power from the transmission box to the differential. It’s a one-way communication barrel that transfers the torque or the power to the wheels through the differential. In this article, I will discuss the 4 common types of propeller shaft problems and their solutions.
Propeller Shaft Problems and Its Solutions
To extend the life of the drive line and especially, the lives of the universal joints and slip yokes(joints), two factors are significant- lubrication and alignment. Although it is limited in what you can do about lubrication when the universal joints are sealed, you should check them regularly for excessive end play and wear. If worn, they should be replaced, otherwise, the universal or slip yoke will cause vibration which could damage the transmission bearings and carrier bearings.
Lubricate the universal joints and slip yokes at regular intervals(about 50,000 km) with the recommended grease in such a way that all old grease is removed and new grease is visible at every bearing seal. To grease the slip joint, remove the dust cap. Then pump grease into the joint until new grease comes out of the dust cap end. Next, clean the joint, position the seal and washer; and then replace and firmly tighten the dust cap.
Alignment should be checked and measured when vibration or noise is reported. However, before commencing alignment procedures, make certain that the vibration does not originate elsewhere by testing and checking the entire drive-line suspension. Drive the vehicle to pinpoint the origin of the noise and the cause of the vibration may come from the carrier or transmission mountings. It may be that the emergency brakes were inadvertently applied. Maybe the brake down is out of balance, the suspension is damaged or worn, the torque ar or radius rods are worn or bent, the wheel assembly is out of balance or the tires are worn.
When noise and vibration occur regardless of road speed, the cause could be damaged or worn universal or slip yokes, loose flange nuts, or bent or distorted flanges or yokes which cause high propeller shaft runout, and high bearing friction. The slip yoke or universal joint bearing may be seized, the propeller shaft could be bent or damaged, or road tar may be sticking to the shaft. It is also possible that the balance weight could have broken off the propeller shaft tube. Any of the above could cause an unbalanced condition.
Angular alignment checks and adjustment.
Before checking the propeller shaft alignment, check the entire power train and suspension as outlined above, make any necessary repairs, and then again test drive the vehicle. If the vibration and noise persist, check alignment. The first step is to read the service manual to determine if the alignment checks are to be made under loaded or no-loaded conditions.
Next, drive the vehicle onto a level surface, that is, level from front to rear and from side to side. Do not jack up the axles to achieve the level. Next, check and, if necessary, inflate the tires to the operating pressure and record from the service manual the alignment and the maximum propeller shaft runout specifications.
Two-Joint Assembly Alignment.
To check the alignment of a two-joint assembly, first check the runout of the propeller shaft at the transmission end, at the center, and the carrier end. Thoroughly clean the exterior of the shaft tube at these points with emery cloth.
Attach a dial indicator so that you can measure the shaft runout at each point. If the runout at the transmission or carrier end is above specification indications are the universal joint or slip joint is worn, the flanges or yoke bores are distorted, or the flange nut is loose. The runout at both ends is within specification but the runout at the center of the propeller shaft is higher than specified, which indicates that the propeller shaft tube is bent.
If the runout is within specification, remove the front and rear universal joints to remove the propeller shaft; or when the bearing cups are held by lock plates, remove one lock plate from each joint. Next, clean and inspect the transmission flange and carrier flange for looseness and distortion. They have nicks and burrs which cannot be removed, or if they are twisted or bent, they must be replaced. Next, attach a dial indicator and measure the flange runout.
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With a protractor, measure the angle of the crankshaft. (This is done by placing the protractor on a horizontal, clean surface (cylinder head, cylinder block, or transmission). Centre the spirit bubble and read from the scale the degree the engine is tilted downward. Record the reading.
Next, repeat the same procedure on the carrier and record the measurement. If measurements of both the engine and carrier angles are within specification, which is, say 20^0, 30′ on the transmission, and – 2^0 15′ on the carrier, the drive line angles are within specification. If the transmission flang angle is greater than specified, lower the transmission or raise the front end of the engine.
If the angle increases, raise the transmission or lower the front end of the engine by employing shims, washers, or plates or by adjusting the mounting bolts. If the carrier angle is too great or too small, tilt the axle housing by installing a greater or smaller wedge between the spring and housing spring saddle.
measuring the Offset alignment (Parallelness of the flanges)
Alignment (Parallelness) of the flanges. Clamp a straight edge to the bottom of the frame rail between the transmission and carrier; and by using a large square, square the straight edge with the frame. Next, plumb the center of the rear axle spindle and the rear edge of the straight edge onto the ground, then measure the distance (Y) at each side between the points plumbed on the ground. They should be within 1.5 mm of each other. If they are not, check for worn shackles, broken center bolts, damaged or worn torque or radius arms, loose spring clamps, or a bent frame.
Next clamp a square bar [about 91.44 mm in length] to the flanges, or insert a round steel rod through the yoke bores and secure them so that the ends are an equal distance from the center of the transmission and pinion shaft. Then measure the distances on both sides of W and X. The two measurements should not vary by more than 1.5 mm. If they are within the 1.5 mm limit, the flanges are parallel. If not the transmission and or suspension must be moved to achieve parallelness. However, first, check the suspension for wear or broken or bent components and check the frame to determine if it is bent or twisted.
If the vibration persists after all these tests and adjustments have been made, you can assume the propeller shaft is out of dynamic balance.
Balancing the Propeller shaft problems
To check the dynamic balance of the propeller shaft, lift the rear axle so that the tires just clear the ground and then support the axle. With a piece of chalk, mark the front and rear end of the propeller shaft tube. Attach and position a wheel balancer pickup to the propeller shaft once at the transmission and then at the carrier and as close as possible to the universal joint. Start the engine, shift the transmission into high gear, and measure the balance condition of the propeller shaft. If the unbalanced point and weight are determined, clamp the required weight to the tube, use a radiator hose clamp, and recheck the balance condition of the propeller shaft.
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If you do not have wheel balancing equipment, you can check and dynamically balance the propeller shaft by the following method: with a hose clamp, clamp a weight (near the spline shaft) to the propeller shaft tube. Use (0.028 kg) weight for a large propeller shaft, or 0.014 kg weight for a small propeller shaft. With the tires off the ground, start the engine, place the transmission in high gear, and note the vibration of the propeller shaft. If the vibration has increased, “the added weight is in the wrong position, or too much weight was added.
Stop the engine and reposition or reduce the weight. These steps have to be repeated (by the trial and error method), that is, by repositioning the weight around the shaft until the least vibration is apparent. When the dynamic balance is achieved, weld the weight to the tube, but keep the weld to a minimum, otherwise it could cause an unbalanced condition.
You may be able to reduce propeller shaft vibration by disassembling the drive line and rotating one end of the shaft 180° from its phase position. Then reinstall the drive line and·test-drive the vehicle. If the vibration has not disappeared, return the propeller shaft to its original phase position and make a dynamic balance of the propeller shaft.
In a power transmission system, the propeller shaft is the main and important component that helps to transfer the power to the wheels. In a rear-wheel drive vehicle, the engine is mounted on the front and the differential or the drive system is mounted on the rear side. The propeller shaft or the drive shaft is the component that attaches these two shafts and transfers the power. So, maintaining and understanding the problems are so important to make the vehicle move on the road. So, please read every point of the article.