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Failure Analysis Of Four Supporting Devices Of Typical Case Wd615 (E2-3a)
Graphic Explanation Of Steyr Typical Accident Case Analysis Series

Analysis Of Common Faults Of Fast Rt-11509 Series Transmission


Vibration usually originates from other parts of the driveline, but its effect is reflected in the transmission. Drivers can usually feel or hear vibration, but they do not necessarily know that sometimes vibration can cause damage to the transmission.

1) Some problems of transmission caused by driveline vibration.

(1) The gear rattles when idling

(2) Worn splines of gears and shafts,

(3) The synchronizer pin is damaged or loose,

(4) Noise,

(5) Bearing wear

(6) The rear oil seal leaks oil repeatedly,

(7) Screws, brackets and mounting points are continuously loosened,

(8) Input shaft spline worn,

(9) The universal joint is worn (although it is not a fault of the transmission, it is one of the signs of vibration).

2) Main causes of vibration

(1) The propeller shaft is unbalanced,

(2) Wheel or drum imbalance,

(3) The engine does not work smoothly,

(4) Damaged or worn engine mount,


(5) The suspension is worn.

Out Of Gear And Skip Gear

1) Main transmission

When moving the engagement teeth to mesh with the main shaft gear, the matching teeth must be parallel. If the engagement teeth have taper or have been worn, they will tend to separate during rotation, which will cause out of gear under certain conditions.

The main transmission is out of gear due to:

(1) The transmission is not concentric with the guide bearing in the engine flywheel;

(2) During gear shifting, the gears collide violently, causing wear on the end face of the engagement teeth,

(3) The engagement teeth are worn into a cone,

(4) The pressure on the positioning steel ball of the shift fork shaft is insufficient due to the weakening or damage of the locking spring

(5) The positioning groove of the shift fork shaft is excessively worn,

(6) Improper adjustment of the connecting rod of the remote shift control mechanism causes the gear and engagement teeth to not mesh in full length,

(7) When the car is pulled with full power or decelerated under load, it often occurs out of gear.

Causes of main transmission skip:

When the force on the shift fork shaft is enough to overcome the pressure of the locking spring, a gear jump will be generated to move the engagement teeth to the neutral position.

(1) When the car is driving on an uneven road, too long and too heavy speed change will swing like a pendulum. The shaking of the speed change lever will overcome the pressure of the locking spring and cause gear jump;

(2) When mechanical remote control is adopted and the control device is installed on the frame, the relative movement between the engine transmission assembly and the frame will cause gear jump. The wear and damage of the engine suspension will increase the possibility of gear jump in this case.

2) Auxiliary box

The shift out of the auxiliary box may be caused by wear of the engagement teeth, taper or non full-length engagement. The reasons for these defects are shift impact and normal wear after long-term use.

The vibration caused by improper installation of transmission shaft and insufficient pressure of air circuit system will also cause out of gear.

In the auxiliary transmission, gear skipping usually occurs on the high-speed gear pair. When shifting into the high-speed gear, if the torque interruption time is not long enough, the sliding engagement teeth may not have enough time to complete the shift action, and the torque acts on the gear again. At this time, the partially engaged engagement teeth will jump out of the high-speed gear. Due to the torque acting on the gear, the engagement teeth of the matching gear will also be damaged.

Hard Shifting

The force required to shift with the gear lever is different, but if the force required is too large, it will lead to the dissatisfaction of the driver.

The shift difficulty mostly occurs on the long-distance shoving device used in flat cars. Therefore, when checking the causes of the transmission shift difficulty, the connecting rod of the remote control device must be checked first. The problems in the connecting rod are caused by the wear, bite, improper adjustment of the connecting fork, bushing and ball joint, poor joint lubrication or mechanical obstacles restricting the free movement of the rod

In order to determine whether the shift difficulty is caused by the transmission itself, it is necessary to remove the transmission fork or connecting rod from the top of the transmission, and then move the shift block with a crowbar or screwdriver to engage it into each gear. If the shift fork shaft can slide easily, it indicates that the fault exists in the connecting rod. On the contrary, the fault is inside the transmission. If it is internal, it is generally caused by the following reasons:

(1) The splines of the sliding engagement teeth bite on the main shaft. This is caused by the twisting of the main shaft, the bending of the shift fork or the bending of the main shaft spline.

(2) The shift fork shaft bites in the housing. This is caused by the rupture of the housing, the excessive tightening torque of the locking screw of the shift block, the bending of the shift fork shaft and the bulge on the surface of the shift fork shaft.

The surface bulge may occur on both sides of the interlocking steel ball groove of the shift fork shaft. This phenomenon is easy to occur when the shift lever is in the position of moving two shift fork shafts at the same time. If this situation occurs repeatedly, the bulge surface will become larger and larger until it hinders the free movement of the shift fork shaft. The bulge on the surface of the shift fork shaft can be polished off with sandpaper, but when the shift fork shaft is bent, it must be replaced.

If it is difficult to shift only first gear and reverse gear, the movement of the locating pin may be blocked, which is caused by burr on the locating pin or over tightening of the spring preload screw plug of the locating pin. When the locating pin has been pressed into the groove of the shift fork shaft, screw the spring preload screw plug to the end, and then return it for 1 / 4 to 1 / 2 turn.

Shifting difficulty cannot be confused with shifting impact. Shifting impact is caused by trying to shift before the engaging gear sleeve (sliding sleeve) is synchronized with the main shaft gear


The long-term operating temperature of the transmission shall never exceed 121 ℃. If it exceeds this temperature, the lubricating oil will deteriorate and the service life of the transmission will be affected.

Due to the friction of moving parts, the transmission will generate a certain amount of heat. The normal working temperature is about 38-40 ℃ higher than the ambient temperature. The heat is emitted through the transmission housing. If the heat dissipation is not normal, it will cause overheating

Before looking for the cause of overheating, the transmission oil temperature must be checked, and the lubricating oil temperature sensor used for testing shall be used to ensure that the reading of the oil thermometer is correct. Generally, overheating is caused by the following reasons.

(1) Improper lubrication. The oil level is too low or high, the oil grade is wrong, or the working angle of the transmission exceeds 12 °

(2) The driving speed is usually below 32 km / h·

(3) The engine speed is too high,

(4) As the transmission is enclosed between the frame, floor, fuel tank and mounting bracket or large bumper assembly, the airflow around the transmission is blocked

(5) Engine exhaust system too close to transmission I

(6) The ambient temperature is too high,

(7) Overload and overspeed.

In some cases, an external lubricating oil cooling device can be used to solve the problem of overheating


The transmission has certain noise under normal operation. However, if the noise is too loud or abnormal, such as roaring, screaming, etc., it indicates that there are some problems with the transmission. These noises may be caused by the transmission itself, or they may be transmitted from other parts of the vehicle to the transmission and amplified by it.

1) Transmission noise

(1) Knocking sound

① The bulge on the tooth surface of the internal gear of the transmission can be identified by the bright spot after the strong grinding of the tooth surface. Generally speaking, this noise is more significant when the gear is under load. Therefore, when a gear is engaged, it will produce noise, indicating that there is a problem with the gear of this gear. Tooth surface bulge is caused by improper machining or assembly. This uplift can be smoothed by oilstone or hand reef wheel.

② If the ball or roller of the bearing is damaged and the raceway produces pitting and falling off, noise will be generated at low speed of each gear.

③ If cracks appear after the gear is subjected to impact load or when the gear is pressed on the shaft during assembly, knocking sound will be generated at low speed and screaming sound will be generated at high speed.


(2) Scream

① Caused by normal wear of the gear. This also includes pitting after long-term use. Screams before damage,

② Caused by improper gear pairing. This can be identified by uneven wear on the tooth surface,

③ After bearing preloading, the axial radial clearance is too small.

(3) Roar

Caused by tooth alignment error. Incorrect alignment of teeth when the transmission is reassembled, or incorrect alignment of teeth caused by the rotation of the gear on the intermediate shaft. In both cases, pitch error will occur.

(4) Click

The axial clearance of the intermediate shaft and the main shaft bearing is too large. When the torque changes direction, the axial clearance of the intermediate shaft bearing is too large, resulting in a clicking sound. If the radial clearance of the intermediate shaft bearing is too large, the center distance of the shaft will increase, so the load acts on the tooth top, which may also cause the fracture of the tooth

2) Transmission noise caused by other parts of the vehicle

(1) The engine does not run smoothly at idle speed

(2) Engine operating noise,

(3) The spring or damping block of the clutch driven plate loses its damping effect due to wear or fracture,

(4) The propeller shaft is unbalanced,

(5) The working angles of the universal joints are not equal,

(6) Cardan spider worn,

(7) Loose or worn middle support bearing of transmission shaft,

(8) The tooth surfaces of the drive axle crown wheel and pinion are worn or pitted. The rear axle bearing is damaged,

(9) Wheel imbalance:

(10) The leaf spring lifting lug bearing is worn,

(11) The riding bolt is loose,


(12) The brake drum is warped or unbalanced.

Gear And Shaft Failure

1) Impact

Gear impact during gear shifting is a common problem of asynchronous transmission. The damage caused by slight impact is not large. The real damage is due to the violent impact caused by engaging the gear long before synchronization is reached. This may cause the material on the end face of the engagement teeth to fall.

The main causes of impact are as follows:

(1) Improper shift operation. The driver is not familiar with the position of each column or the variation range of engine speed between gears.

(2) When starting with first gear or reverse gear, impact may occur due to insufficient clutch separation clearance or incomplete clutch separation. This is because in this case, the transmission intermediate shaft and main shaft gear continue to rotate after depressing the clutch pedal, and the engaging teeth do not rotate at this time. When they are combined forcibly, there will be impact.

(3) After the clutch is disengaged, due to inertia, the intermediate shaft and main shaft gear usually stop rotating after 3 ~ 5 seconds. Before the main shaft gear stops rotating, trying to mesh the engagement teeth with it will cause impact. If the transmission does not have clutch brake or intermediate shaft brake, stop for a few seconds after pressing the clutch pedal before starting the shift.

2) Gear damage

(1) Normal wear

Due to the relative sliding of gear teeth in the meshing process, the gears will be worn. This normal wear of the tooth surface is stable and slow. All kinds of bad service conditions will accelerate the wear of tooth surface and shorten the service life of gear. These service conditions and the resulting damage will be discussed below.

(2) Broken tooth

Tooth breakage is a serious form of gear damage. Moreover, tooth fragments will cause serious damage to other parts when they are installed through gear transmission. Tooth fracture is caused by serious impact load. Under the action of heavy load, the phenomenon that the gear teeth break after only short-term operation is called impact fracture.

The pressure side of the broken section is humped. The more the working cycles of the gear, the smaller the hump. The fracture after many working cycles under mild or medium overload or after many small impact loads is called fatigue fracture. The fracture surface of fatigue fracture is beach like, which is caused by the gradual expansion of the crack under the repeated action of a load that is enough to expand the crack but can not break the whole gear tooth at the same time. When the remaining unbroken part of the tooth cannot bear the load, it will break.

(3) Pitting and peeling

The gear will gradually produce pitting and peeling after long-term overload operation. This kind of tooth surface damage will also occur if the lubricating oil with wrong brand or unclean lubricating oil is used. If these gears continue to work, fatigue fracture will occur.

(4) Scratch and bond

Scratches and sticking are caused by direct metal to metal contact of the mating gear. The relative sliding of the metal surface will produce high temperature, which will soften the metal on the tooth surface. This softened metal will bond in the meshing process. Adhesion is an early manifestation of scratch. At this time, considerable metal particles have been torn off the tooth surface. The scratch can be identified by the raised stripes up and down the tooth surface.

The main causes of scratch and adhesion are poor lubricating oil or temporary lack of lubricating oil

(5) Abrasive wear

Lubricating oil containing impurities such as abrasive powder will become an abrasive. Abrasive wear is the result of this kind of grinding. The use of extreme pressure lubricants with too much activity will also produce this result.

This wear can be identified by grinding the smooth tooth surface and spots along the transverse direction of the tooth surface.

(6) Manufacturing defect

Gears with machining marks sometimes need to be replaced or regarded as defective parts. However, such machining defects will not cause gear damage.

(1) Hobbing trace

Cutting marks or stripes formed during rough cutting of gear teeth. The hobbing marks on the tooth surface can be eliminated by shaving, but most of the hobbing marks on the tooth root will be retained, even on the severely worn teeth.

(2) Shaving marks

After shaving, obvious diagonal marks will be left on the tooth surface of the tooth (the scratch marks are close to the vertical line). Most shaving marks will disappear during the normal operation of the gear.

(3) Crimping

Crimping or shaving burr is the convex part formed at the top of the gear tooth during machining. These convex parts do not hinder the normal operation of the gear.

4) Gear rattle at idle speed

In the design, the main shaft gear has a certain axial clearance on the main shaft so that the gear can rotate freely on the shaft. The clearance can be adjusted with shims. The unstable operation of the engine at idle speed will produce vibration, causing the main shaft gear to collide with the matching gear and make a rattling sound. This situation can generally be solved by improving the idle performance of the engine. When the transmission has been used for a long time, the gasket needs to be replaced in order to keep the axial clearance of the gear within the tolerance range.

5) Twisting and breaking of spindle

When the stress on the transmission main shaft is greater than the design stress, the shaft will break and twist. The reasons for breaking and twisting are as follows:

(1) incorrect gear shifting method,

(2) when starting, the gear in the main transmission or auxiliary transmission is too high,

(3) drag violently,

(4) attempt to start the vehicle when the brake is not released,

(5) the operating conditions of the transmission do not meet the design requirements;

(6) when reversing, the rear of the car collides with other things,

(7) the adjustable saddle is improperly installed.

The transmission spindle, like the gear, may break due to fatigue or impact. Breaking may cause distortion first.

Bearing Failure

1) Fatigue

Bearing fatigue is characterized by bearing raceway spalling. This is due to the reduction of particle strength of bearing steel, which causes particles to peel off from the raceway. The bearing surface behind stripping is rough, which will produce noise and vibration.

When the bearing reaches its expected life under normal load and working conditions, normal fatigue damage will occur. This form of damage can be predicted. It is due to the damage of metal under the continuous action of load.

After the bearing hole in the transmission is re sleeved, if the size of the bearing hole is too small or out of round, early fatigue damage may occur. Special care should also be taken when re boring holes in the housing. After boring the hole on the shell, the installation error of the shaft will be caused, which will also cause the early fatigue damage of the bearing. Therefore, the accuracy of boring equipment should be relatively high.

2) Poor lubrication

Bearing damage caused by poor lubrication is characterized by discoloration of bearing parts and peeling of raceway, or cage damage. The reason for bearing damage is not only that the oil level is too low, but also that the lubricating oil contains impurities, the grade is inappropriate and the lubricating oil with different grades is mixed.

In order to prevent such damage, the proper oil level shall be maintained in the transmission, the recommended lubricating oil brand and grade shall be adopted, and the oil shall be changed on schedule

3) Indentation

Indentation refers to the small gap at the shoulder or bottom of the bearing raceway. It may be caused by improper installation or disassembly methods of the bearing. If it is supported on one race of the bearing, knocking or pressing the other race will cause indentation. When hitting the bearing with a hammer or chisel, in addition to indentation, it may also cause damage to the dust cover, cage and retaining ring. The above damage can be avoided by using the correct tools such as puller.

4) Micro vibration wear

Due to vibration, machining strips on the bearing hole will be rolled out on the outer ring of the bearing. This effect is called micro vibration wear. Bearings subject to micro vibration wear are often mistakenly diagnosed as the above stripes caused by the rotation of the bearing in the hole. The bearing outer ring will rotate in the hole only under extreme conditions

5) Pollution damage

Contamination and damage of the bearing caused by dirt entering the transmission housing or impurities entering the bearing during maintenance and storage.

The pollution and damage of bearings are mostly manifested in raceways: nicks, scratches or pits on rolling balls or rollers, and rust or corrosion of bearing parts. In addition, if the lubricating oil contains very fine particles (such as abrasive powder), or the extremely active extreme pressure lubricating oil is used, the bearing parts will also be ground

When the transmission is normally ventilated, impurities often enter the transmission. Therefore, it is necessary to replace the lubricating oil of the transmission according to the specified cycle to reduce the pollution and damage of the bearing.

6) The inner and outer rings are not concentric

If the input shaft is not aligned with the guide bearing hole in the flywheel when installing the transmission, the positioning bearing on the input shaft may be out of center with the inner and outer rings. At this time, the roller cage and dust cover may be damaged.

When looking for the cause of non concentricity, first check the coaxiality between the clutch housing and mounting surface and the guide bearing, and check whether there are sundries mixed in and whether the installation position is correct.

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