This manual provides information about the clutch and the automatic transmission, enabling you to understand the operation of these units, to diagnose problems, and to prescribe corrective action.
When you have completed this manual, you will be able to do the following:
It is important to briefly review the purpose of the clutch and also the various types of clutches. The clutch permits the operator to couple and uncouple the engine and transmission. When the clutch is in the coupling (or normal running) position, power flows through it from the engine to the transmission. If the transmission is in gear, power flows through to the vehicle wheels, so the vehicle moves. Essentially, the clutch enables the operator to uncouple the engine temporarily, so the gears can be shifted from one forward gear position to another or into reverse or neutral. The flow of power must be interrupted before the gears are shifted; otherwise, gear shifting is extremely difficult if not impossible.
The clutch assembly (Figure 1) contains a friction disc, or driven plate, about a foot in diameter. It also contains a spring arrangement and a pressure plate for pressing the disc tightly against the face of the flywheel. The friction disc is splined to the clutch shaft. The splines consist of two sets of teeth: an internal set on the hub of the friction disc and a matching external set on the clutch shaft. They permit the friction disc to slide back and forth along the shaft but force the disc and the shaft to rotate together.
Figure 1 - Single disc clutch.
The flywheel, attached to the end of the engine crankshaft, rotates when the engine is running. When the clutch is engaged in the coupling position, the friction disc is held tightly against the flywheel by the pressure plate springs so that it rotates with the flywheel. This rotary motion is carried through the friction disc and clutch shaft to the transmission.
To disengage (or uncouple) the clutch, the clutch operator presses the clutch pedal down. This causes the clutch fork to pivot so the clutch release bearing is forced inward. As the release bearing is moved inward, it operates the pressure plate release levers (Figure 2). The release levers take up the spring pressure and lift the pressure plate away from the friction disc. The friction disc is no longer pressed against the flywheel face, and the engine can run independently of the power train. Releasing the clutch pedal permits the clutch fork to disengage the release bearing, so the springs will again cause the pressure plate to force the friction disc against the flywheel face to rotate together.
Figure 2 - Clutch operation.
There are two types of clutch operating systems: mechanical and hydraulic. The mechanical system is the most common and uses a rod type of linkage (Figure 3); other mechanical systems use a flexible type of cable (Figure 4). These systems are normally found in automotive applications. The hydraulic operating system (Figure 5) moves the release lever by hydraulic pressure. Depressing the clutch pedal creates pressure in the clutch master cylinder, actuating the slave cylinder which, in turn, moves the release arm and disengages the clutch.
Figure 3 - Clutch linkage.
Figure 4- Clutch cable
Figure 5 - Hydraulic clutch.
Hydraulic types of clutch operating systems are normally found in heavy construction equipment where extreme pressure is required to operate the clutch.
Most automotive and construction equipment clutches work on the same principle and are similar in construction. The differences are mainly in pressure plate assemblies, linkages, and overall size.
Of the different types of clutch assemblies, the one that was shown in Figure 1 is known as the plate clutch. The plate clutch is a simple clutch with two plates and one disc, clamped between the two plates. Another type (Figure 6) is the double-disc clutch. The driving members of the single-disc clutch consist of the flywheel and driving (pressure) plate. The driven member consists of a single disc splined to the clutch shaft and faced on both sides with friction material. When the clutch is fully engaged, the driven disc is firmly clamped between the flywheel and the driving plate by the pressure of the pressure plate springs, and a direct, nonslipping connection between the driving and driven members of the clutch is formed. In this position, the driven disc rotates the clutch shaft to which it is splined. The clutch shaft is connected to the driving wheels through the power train.
Figure 6 - Double-disc clutch.
The double-disc clutch is substantially the same as the single-disc clutch described in the section above, except that an additional driven disc and intermediate driving plate are added.
The information given in this section is general and may be applied to nearly every type of clutch you are likely to encounter. Refer to the manufacturer's repair manuals for problems not listed here.
The most common symptoms of clutch malfunctions are dragging, slipping, and noise. Improper adjustment is one condition that leads to clutch problems. You should always adjust the clutch according to the manufacturer's specifications. An improperly adjusted clutch can cause clutch slippage and hard shifting.
This condition results when the clutch disc does not completely disengage from the flywheel or pressure plate when the clutch pedal is depressed. As a result, the clutch disc tends to continue turning with the engine and attempts to drive the transmission.
Dragging may be caused by any of the following conditions:
To correct clutch dragging, adjust the free travel. Make this adjustment according to the manufacturer's specifications. If the problem is not corrected with this adjustment, you may need to remove the clutch for repairs or replacement.
Because of heat generation, slipping of the clutch (while it is engaged) can severely damage the clutch disc facings. The contact surfaces on the pressure plate and the flywheel may also be damaged. If a clutch is allowed to continue to slip, complete clutch failure may result. Clutch slipping is most obvious when you are just starting out from a dead stop or upon sudden acceleration in a low gear. Slipping will be very noticeable in a vehicle with a heavy load.
Causes of clutch slippage include incorrect clutch pedal free travel, binding in the clutch linkage, and "riding the clutch." If the free travel is insufficient, there is a tendency for the release bearing to contact the release levers, even though the operator's foot is off the clutch pedal. As a result, the clutch disc may not be clamped tightly between the flywheel and the pressure plate. Readjustment of the pedal free travel will solve this problem. If you do not adjust the free travel at once, the release bearing, as well as the clutch disc, will wear rapidly.
If a binding condition exists in the clutch linkage, the pedal will be reluctant to return when it is released. So again, you may encounter clutch slippage. To solve this problem, "free up" the linkage that is binding by simply lubricating or aligning the clutch linkage. If this fails to correct the problem, you may have to remove the clutch for further inspection and repair.
"Riding the clutch" is an operator problem whereby the operator steadily drives with a foot on the clutch pedal. As a result, the pedal may be partially depressed and cause clutch slippage. If this form of operator abuse is suspected, contact the transportation supervisor. The problem should be corrected through proper operator training.
Occasionally, you may encounter a clutch that grabs or chatters, no matter how evenly or gradually you try to engage it. If the linkage operates satisfactorily and the engine and clutch mountings are not loose, you may have to remove the clutch assembly from the vehicle to cure the trouble. The probable causes are loose, glazed, oily, or greasy disc facings; binding of the disc on the clutch shaft; broken or otherwise defective pressure plate springs; or a broken or otherwise defective pressure plate.
A careful inspection of all clutch parts should reveal any defective items. In any case, replace any damaged parts and rebuild the clutch as specified by the manufacturer. In most cases, it is best that you install the clutch as a unit, which includes replacing the clutch disc, pressure plate, release bearing, and pilot bearing, and resurfacing the flywheel. Replacing the complete assembly prevents the need for rework.
A noisy clutch may be caused by a number of conditions. Most of these conditions can be corrected only after you have removed the assembly from the vehicle. Start your inspection by noting whether or not the noise occurs when the clutch is engaged or disengaged. Do this with the engine idling since the noise is likely to be most apparent at this time.
To begin with, when you have the clutch disengaged, you may discover that the noise coming from the clutch is due to lack of lubrication or to defects in the assembly. For instance, a dry or binding release bearing is likely to squeal when it is placed in operation. If it does, you will usually need to replace the bearing. On some vehicles, however, provisions are made for lubricating this bearing. If so, you can generally lubricate or replace the bearing without removing the clutch assembly. Still, you may need to remove the transmission and the lower cover from the flywheel housing to get to the bearing. It usually pays for you to go a little further and inspect the entire clutch assembly if you must remove the transmission for any reason.
Noise may also come from a worn or dry pilot bearing. Such a bearing tends to "whine" when it is out of grease. This noise usually occurs when the vehicle is stationary with the engine running, the transmission in gear, and the clutch disengaged. To remedy this, replace the bearing and make sure it is properly lubricated if it is not a prepacked bearing.
Other clutch noises may occur when you have the clutch disengaged. Any one of several conditions can be responsible for noisy operation. For example, the clutch disc may be loose on the transmission shaft (disc hub loose on shaft splines). If this is the case, depending on the amount of wear, you may have to replace the input shaft and the clutch disc. Another condition involving noise and necessitating disc replacement is loose or weak torsional springs surrounding the disc hub. You may also find that the antirattle springs on the pressure plate assembly are weak and require replacement. A hose or misaligned transmission will cause noisy clutch operation. You can easily correct this by loosening the transmission, shifting it into proper alignment, and retightening it.
Movement felt on the clutch pedal or operating lever when the clutch is being disengaged is called clutch pedal pulsation. These pulsations are noticeable when slight pressure is applied to the clutch pedal. This is an indication of trouble that could result in serious damage if not immediately corrected. Several conditions could cause these pulsations.
One condition that can cause this vibration is misalignment of the engine and transmission. If the engine and transmission are not in line, detach the transmission and remove the clutch assembly. Check the clutch housing alignment with the engine and crankshaft. At the same time, check the flywheel for wobble. A bent crankshaft flange or an improperly seated flywheel produces clutch pedal pulsations. After the flywheel is properly seated, check it using a dial indicator. If the crankshaft flange is bent, the crankshaft must be remachined or replaced.
Other causes of clutch pedal pulsations include uneven release lever adjustments, a warped pressure plate, or a warped clutch disc. If the clutch disc or pressure plate is warped, it should be replaced.
It would be impractical to list every possible clutch problem and its remedy for repair in this training manual. Consult the manufacturer's operation and repair manual before making adjustments to any clutch system.
|Test Your Knowledge
1. A hydraulic type of clutch release mechanism is normally found on heavy construction equipment for which of the following reasons?
- To Table of Contents -
Automatic transmissions (Figure 7) are found in all types of automotive and construction equipment. The purpose of the automatic transmission is the same as standard transmissions-to match the load requirements of a vehicle to the power and speed of the engine. Changing the gear ratio automatically is controlled by throttle position, shift control lever position, and vehicle speed. It relieves the operator of the responsibility of selecting the best possible gear ratio for each condition and makes driving easier and safer.
Figure 7 - Automatic transmission.
Many different models of automatic transmissions are manufactured today. Automotive applications usually have three speeds forward and one reverse. More recently the automotive industry has added a lockup clutch to the torque converter, and on some models, an overdrive gear. Automatic transmissions for material handling and construction equipment will normally have a lower gear ratio, be considerably larger, and may have over six speeds forward and more than one reverse gear.
Whatever the case and regardless of design or construction, all automatic transmissions have the following six basic systems that enable them to function:
In automatic transmissions, these systems all serve the same purposes. For this reason, we will only discuss one type of automatic transmission in this manual. If you want information on a specific type, use the manufacturer's maintenance and repair manual for that unit.
The TH400 Hydramatic transmission was a stout and versatile transmission; however, it lacked any real fuel economy. With a three-speed gear set, it couldnot keep up with the demands of the rising fuel prices. Along came some new additions to the transmission world: the 4L60/4L80, 4L80E, and the Allison. These transmissions were based off the ever popular TH400, but had a kick overdrive.
The 4L80E (Figure 8) is a truck automatic transmission that was introduced by GM in the early 1990s. It basically uses many of the same internal components as the TH400 but has an overdrive fourth gear and uses electronics to control shift points and firmness.
Figure 8 - 4L80E automatic transmission.
Roughly 75 percent of the 4L80Es internal parts are interchangeable with a TH400, and the bellhousing bolt pattern and flexplate are the same as the 400, so it bolts up to big- or small-blocks just like normal.
Planetary gears are used in the automatic transmission as a basic means of multiplying the torque from the engine. The name is derived from the physical arrangement of the gears. They are always in mesh and thus cannot "clash" like other gears that go in and out of mesh. The gears are designed so that several teeth are in mesh or in contact at one time. This distributes the forces over several teeth at one time for greater strength. Because the shafts generally used with planetary gear trains can be arranged on the same centerline, a compact system can be obtained.
A planetary gear train consists of a center or sun gear, an internal or ring gear, and a planetary carrier assembly, which includes and supports the smaller planet gears or pinions (Figure 9). A planetary gearset can be used to increase speed, increase torque, reverse the direction of rotation, or function as a coupling for direct drive. Increasing the torque is known as operating in reduction because there is always a decrease in the speed of the output member proportional to the increase in the output of torque. This means that with a constant input speed, the output torque increases as the output speed decreases.
Figure 9 - Planetary gearset operation.
Reduction can be obtained in several ways. In a simple reduction, the sun gear is held stationary, and the power is applied to the internal gear in a clockwise direction. The planetary pinions rotate in a clockwise direction and "walk" around the stationary sun gear, thus rotating the carrier assembly clockwise in reduction (Figure 9, View A).
Direct drive results when any two members of the planetary gear train rotate in the same direction at the same speed, as shown in Figure 9, View B. In this condition, the pinions do not rotate on their pins but act as wedges to lock the entire unit together as one rotating assembly.
To obtain reverse, restrain the carrier from turning freely and power is applied to either the sun or the internal gear. This causes the planet pinions to act as idlers, thus driving the output member in the opposite direction (Figure 9, View C). In both cases, the output member is turning in the opposite direction of the input member.
The automatic transmission is coupled to the engine through a torque converter. The torque converter is used with the automatic transmission because it does not have to be manually disengaged by the operator each time the vehicle is stopped. The cushioning effect of the fluid coupling within the torque converter allows for shifting without interruption of engine torque application.
The torque converter serves two primary functions. First, it acts as a fluid coupling to connect engine power smoothly through oil to the transmission gear train. Second, it multiplies the torque from the engine when additional performance is desired.
The torque converter, as shown in Figure 10, consists of the pump (driving member), the turbine (driven or output member), and the stator (reaction member). The converter cover is welded (some maybe bolted) to the pump to seal all three members in an oil- filled housing. The converter cover is bolted to the engine flex-plate, which is bolted directly to the engine crankshaft. The converter pump is, therefore, mechanically connected to the engine and turns at engine speed whenever the engine is operating.
Figure 10 - Torque converter.
Figure 11 - Torque converter operation.
When the engine is running and the converter pump is spinning (Figure 11), it acts as a centrifugal pump, picking up oil at the center and discharging this oil at its rim between the blades. The shape of the converter pump shells and blades causes this oil to leave the pump, spinning in a clockwise direction toward the blades of the turbine. As the oil strikes the turbine blades, it imparts a force to the turbine, causing it to turn. When the engine is idling and the converter is not spinning fast, the force of the oil is not great enough to turn the turbine with any efficiency. This allows the vehicle to stand in gear with the engine idling. As the throttle is opened and the pump speed is increased, the force of the oil increases and the engine power is more efficiently transmitted to the turbine member and the gear train. After the oil has imparted its force to the turbine, the oil follows the contour of the turbine shell and blades so that it leaves the center section of the turbine spinning counterclockwise.
Because the turbine member has absorbed the force required to reverse the direction of the clockwise spinning of oil, it now has greater force than is being delivered by the engine. The process of multiplying engine torque through the converter has begun. If the counterclockwise spinning oil was allowed to continue to the section of the pump member, the oil would strike the blades of the pump in a direction that would hinder its rotation and cancel any gains obtained in torque. To prevent this, a stator assembly is added.
The stator is located between the pump and the turbine and is mounted on a one-way or roller clutch, which allows it to rotate clockwise but not counterclockwise. The purpose of the stator is to redirect the oil returning from the turbine and change its direction of rotation back to that of the pump member. The energy of the oil is then used to assist the engine in turning the pump. This increases the force of the oil, driving the turbine, and as a result, multiplying the torque. The force of the oil flowing from the turbine to the blades of the stator tends to rotate the stator counterclockwise, but the one way roller clutch prevents this from happening.
With the engine operating at full throttle, the transmission in gear and the vehicle standing still, the torque converter is capable of multiplying engine torque by approximately 2:1. As turbine and vehicle speed increase, the direction of the oil leaving the turbine changes. The oil flows against the rear side of the stator vanes in a clockwise direction. Since the stator is now impeding the smooth flow of oil, its roller clutch automatically releases, and the stator revolves freely on its shaft. Once the stator becomes inactive, there is no further multiplication of engine torque within the converter. At this point, the converter is merely acting as a fluid coupling as both the converter pump and the turbine are turning at the same speed or at a 1:1 ratio.
The hydraulic system has five basic functions:
A hydraulic system requires a source of clean hydraulic fluid and a pump to pressurize the fluid. The oil is drawn through the strainer from the transmission sump. The pump drive gear is geared or keyed to the driven member of the torque converter; therefore, whenever the engine is in operation, the pump is functioning. As the pump drive gear rotates, it rotates the pump-driven gear, causing the oil to be lifted from the sump into the oil pump. As the pump gears turn, oil is carried past the crescent section of the pump. Beyond the crescent, the gear teeth begin to come together again, forcing the oil out of the pump and into the hydraulic system under pressure. At this point, the oil is delivered to the pressure control system.
When the shift lever is in park and the engine is running, the pump is turning and therefore supplying pressure to the main pressure regulator. The main regulator consists of the regulator valve and a boost valve. There is a pressure regulator spring installed between the two valves.
Line pressure also passes through the manual valve and the low overrun valve and applies the low and reverse clutch. The low and reverse clutch has no effect when the transmission is in park.
Line pressure is also sent to the actuator fell limit (AFL) valve. The AFL valve limits the amount of pressure in the pressure control, and shift solenoids feed circuits because the excess pressure can damage the solenoids.
AFL oil pressure is also delivered to the shift valves and solenoids. The Electronic Control Module (ECM) energizes both solenoids in park. AFL oil from the accumulator limit valve cannot exit through the solenoids and pushes the shift valves to the left.
Since the solenoids are not supplied with drive oil, they cannot apply any holding members.
The main pressure regulator also directs some oil to the torque converter clutch valve. The torque converter clutch valve is in the released position at this time. The oil flows through the release and apply sides of the converter clutch plate, and the converter is unlocked.
In neutral with the engine running, the flow of oil is much like it is when the transmission is in park. AFL oil is sent to the pressure control solenoid and continues to regulate line pressure but has no effect on the shift valves.
In neutral, the manual valve is positioned to cut off the oil flow to the low reverse clutch piston, and no holding members are applied in neutral.
When the transmission is placed in drive with the vehicle not moving, line oil is sent to the forward clutch piston and engages the forward clutch. This oil is called D4 oil. Under normal conditions, the number 12 check ball seals the oil passage, forcing the D4 oil to travel through the smaller orifice next to it. This will engage a smoother, more gentle shift.
If the engine is at a high RPM when shifted into drive, the pressure control solenoid will raise line pressure. This will cause the D4 oil to be higher than normal, opening the forward abuse valve. When this valve is open, D4 oil is sent directly to the forward clutch piston, bypassing the orifice and check ball assembly. The forward abuse valve prevents clutch plate damage by quickly applying the clutch.
D4 oil is also directed to the accumulator valve, which fills and pressurizes the 1-2 and 3-4 accumulators. This oil is also delivered to one of the pressure switches in the pressure switch assembly. This normally open switch closes when it is pressurized to tell the ECM that the transmission is in drive.
When the ECM decides the transmission is to be shifted into second gear, it de- energizes the 1-2 shift selonoid. Since this solenoid is normally open, oil exits through the solenoid when it is de-energized. Spring pressure pushes the 1-2 shift valve to the right and allows D4 oil to pass through the valve and applies the 2-4 band servo. This oil pressure, called 2nd oil, applies the band and shifts the transmission into second gear. The number 8 check ball is used to restrict 2nd oil pressure to the servo and cushions the shift. Pressure is also now available at the 3-2 downshift valve.
The 2-3 shift solenoid is a normally open solenoid, and oil exits through the valve when it is de-energized. AFL oil pushes the 2-3 shift valve and 2-3 shuttle valve to the right. 2nd oil can now pass through the 2-3 shift valve. This oil is now called 3-4 SIG oil after it passes through the 2-3 shift valve. In addition to applying and releasing holding members, 3-4 SIG oil goes to the 3-2 downshift valve, 3-2 control valve, and 3-4 shift valve for later use.
To apply the clutch, the 3-4 SIG oil passes through a check ball and orifice number 4. The number 4 check ball and orifice restricts oil flow to the clutch piston to cushion the shift.This oil is now named 3-4 CL (CL is for clutch) oil after it passes through the number 4 check ball orifice. 3-4 CL oil is also sent to the 3-2 downshift valve and the 3-2 control vavle for use during 3-2 downshifts.
With the 3-4 clutch applied by 3-4 CL oil and band released by 3rd ACC oil, the transmission is now in third gear.
When enough speed is attained and other sensor inputs are correct, the ECM decides that the transmission should be shifted into fourth gear. The ECM energizes the 1-2 shift solenoid, sealing the exhaust passage in the solenoid. The 2-3 shift solenoid remains de-energized.
With the 1-2 shift solenoid back on, AFL oil pressure can build up on the right side of the 1-2 shift valve through the orifice above the valve. Once through the orifice, the oil is renamed SIG A oil.
The extra oil supplied by the 2-3 shuttle valve assits the spring and keeps the 1-2 shift valve from moving. The AFL oil, renamed the SIG A oil, builds up to its full value and moves the 3-4 shift valve.
With the 3-4 oil shift valve in the upshifted position, 3-4 SIG oil, renamed 4th SIG oil in this circuit only, pushes the 3-4 relay and 4-3 sequence valves to the right. This allows 2nd oil to charge the 3-4 circuit that sends oil to the outer side of the servo. The outer side of the servo is an apply area that helps the 2nd clutch oil overcome release oil and spring pressure and reapply the band. Some 3-4 SIG oil is diverted to the 3-4 accumulator to improve shift feel. This is renamed 3-4 ACC oil.
Automatic transmission service can be easily divided into the following three parts: preventive maintenance, troubleshooting, and major overhaul. Before you perform any maintenance or repairs on an automatic transmission, consult the maintenance manual for instructions and proper specifications.
Normal preventive maintenance includes:
The operator is responsible for first echelon (operator's) maintenance. The operator should be trained not only to know to look for the proper fluid level, but also to know how to look for discoloration of the fluid and debris on the dipstick.
Fluid levels in automatic transmissions are most commonly checked at operating temperature. This is important to know, since the level of the fluid may vary as much as three quarters of an inch between hot and cold.
The fluid should be either reddish or clear. The color varies due to the type of fluid. (For example, construction equipment using OE-10 will be clear). A burnt smell or brown coloration of the fluid is a sign of overheated oil from extra heavy use or slipping bands or clutch packs. The vehicle should be sent to the shop for further inspection.
Not all transmission fluids are the same. Before you add fluid, check the manufacturer's recommendations first. The use of the wrong fluid will lead to early internal parts failure and costly overhaul.
Overfilling the transmission can result in the fluid foaming and the fluid being driven out through the vent tube. The air that is trapped in the fluid is drawn into the hydraulic system by the pump and distributed to all parts of the transmission. This situation will cause air to be in the transmission in place of fluid and in turn cause slow application and burning of clutch plates and facings. Slippage occurs, heat results, and failure of the transmission follows.
Another possible, but remote, problem is water, indicated by the fluid having a "milky" appearance. A damaged fluid cooling tube in the radiator (automotive) or a damaged oil cooler (construction) could be the problem. The remedy is simple. Pressure-test the suspected components and perform any required repairs. After repairs have been performed, flush and refill the transmission with clean, fresh fluid.
The types of linkages found on an automatic transmission are gearshift selection and throttle kickdown. The system can be a cable or a series of rods and levers. These systems do not normally present a problem, and preventive maintenance usually involves only a visual inspection and lubrication of the pivot points of linkages or the cable. When adjusting these linkages, you should strictly adhere to the manufacturer's specifications.
If an automatic transmission is being used in severe service, the manufacturer may suggest periodic band adjustment, as shown in Figure 12. Always adjust lockup bands to the manufacturer's specifications. Adjust the bands by loosening the locknut and tightening down the adjusting screw to a specified value. Back off the band adjusting screw with a specified number of turns and tighten down the locking nut.
Figure 12 - Band adjustment.
Not all bands are adjustable. Always check the manufacturer's service manual before any servicing of the transmission.
Perform fluid replacement according to the manufacturer's recommendations. These recommendations vary considerably for different makes and models. Before you change automatic transmission fluid, always read the service manual first.
Service intervals depend on the type of use the vehicle receives. In the NCF, because of the operating environment, more than a few of the vehicles are subjected to severe service. Severe service includes the following: hot and dusty conditions, constant stop- and-go driving (taxi service), trailer towing, constant heavy hauling, and around-the- clock operations (contingency). Any CESE operating in these conditions should have its automatic transmission fluid and filter changed on a regular schedule, based on the manufacturer's specifications for severe service. Ensure the vehicle is on level ground or a lift, and let the oil drain into a proper catchment device.
The draining of the transmission can be accomplished in one of the following three ways:
Oil drained from automatic transmissions contains heavy metals and is considered hazardous waste and should be disposed of according to local instructions.
Once the oil is drained, remove the pan completely for cleaning by paying close attention to any debris in the bottom of the pan. The presence of a high amount of metal particles may indicate serious internal problems. Clean the pan, and set it aside.
All automatic transmissions have a filter or screen attached to the valve body. The screen is cleanable, whereas the filter is a disposable type and should always be replaced when removed. Screens and filters are retained in different ways: with retaining screws, with metal retaining clamps, or with O-rings made of neoprene. Clean the screen with solvent and use low-pressure air to blow-dry it. Do not use rags to wipe the screen dry, as they tend to leave lint behind that will be ingested into the hydraulic system of the transmission. If the screen is damaged or is abnormally hard to clean, replace it.
Draining the oil from the pan of the transmission does not remove all of the oil-draining the oil from the torque converter completes the process. To do this, remove the torque converter cover and remove the drain plug, if so equipped. For a torque converter with- out a drain plug, special draining instructions may be found in the manufacturer's service manual. Before performing this operation, clear it with your shop supervisor.
Reinstall the transmission oil pan, the oil plug, and the fill tube. Fill the transmission with the fluid prescribed by the manufacturer to the proper level. With the brakes applied, start the engine and let it idle for a couple of minutes. Move the gear selector through all gear ranges several times, allowing the fluid to flow through the entire hydraulic system to release any trapped air. Return the selector lever to park or neutral and recheck the fluid level. Bring the fluid to the proper level. Run the vehicle until operating temperature is reached, checking for leaks. Also, recheck the fluid and adjust the level as necessary.
Overfilling an automatic transmission will cause foaming of the fluid. This condition prevents the internal working parts from being properly lubricated, causing slow actuation of the clutches and bands. Eventually, burning of the clutches and bands results. Do NOT overfill an automatic transmission.
Good troubleshooting practices save a lot of time and money for the Navy. If you know what you are doing when you troubleshoot an automatic transmission, you should be able to pinpoint the problem before you remove it from the vehicle. In some cases, you may be able to make the repairs without removing the transmission.
Before troubleshooting the transmission, make sure the engine is in good running condition. An engine that is not operating properly will not allow the transmission to function normally.
A malfunction may have more than one probable cause. Complete all the tests and inspections for each cause to find the correct cause.
Keep in mind that it is impossible to list each and every malfunction and its possible corrective action in this training manual. Below is a seven-step process that will enable you to quickly isolate some problems.
The first step when troubleshooting a transmission problem is to verify the problem. Begin by asking the operator to describe what the vehicle is doing. Remember that the operator may not be a mechanic so they might misinterpret the symptoms.
Now it is time to check the fluid level and road test the equipment. Once you have determined what the problem is, proceed to the next step.
Check the simple things first. You have already checked for appropriate fluid levels. Also check to see if the transmission is overheating, or if the fluid is burnt.
If there is a shifting problem, check to see if the linkage is bent, broken, or out of adjustment. Check for loose electrical connectors. Check to see if the vacuum modulator has become disconnected.
If you are checking an electronically controlled transmission, see if you can get a trouble code from the ECM.
Using you knowledge of transmissions, determine if the problem is due to the mechanical system, the hydraulic system, or the electrical system.
This step takes the most time. You need to check each system and look at the major parts involved. Start with the easiest tests first, then move on from there.Once you have discovered the problem, you can go on to the next step.
At this point, you want to review what the problem was and determine if this is a stand alone problem or if it has evolved because of something else that is wrong.
If your testing causes you to come back to the same problem as above, you have more than likely discovered the problem.
In this step, you will need to make the necessary repairs to the transmission.
In this step, you will need to recheck the transmission. Give it another road test. Be sure to fully evaluate the transmission and be sure to pay attention to what you fixed to make sure that the problem no longer exists.
Because of the complexity of automatic transmissions, the need for special tools, and personnel skills, in overhauling these major components is usually done at a Construction Equipment Department located at a Construction Battalion Center.
Overhaul of automatic transmissions is not a job for an inexperienced person. If the job must be performed in the field, it is recommended that only a highly capable mechanic be assigned to this type of work.
Before proceeding with automatic transmission disassembly or reassembly, get the applicable repair instructions and have them on hand. Read this information carefully and completely! Incorrect disassembly procedures can lead to severe parts damage, causing unnecessary equipment downtime.
Have a workplace away from the main CM shop. A dust-free air-conditioned room is the best, but this is not always available. Obtain the cleanest work space possible! Have on hand any special tools needed for the job, such as snap ring pliers, torque wrenches, or special pullers. It is also a good idea to have an air compressor available for test purposes and for blowdrying individual parts. The steps listed below are common procedures listed for a generic automatic transmission and may not follow the type you are working on.
Compressed air used for cleaning purposes should not exceed 30 psi. Wear goggles and other appropriate protective equipment when you use compressed air.
Figure 13 - Checking input shaft endplay.
Figure 14 - Checking output shaft endplay.
Figure 15 - Transmission in a cradle.
The type of debris found in the bottom of the oil pan is indicative of the type of internal damage you may find in the transmission.
Figure 16 - Removing oil pump seal.
Figure 17 - Removing oil pump.
Now that the external parts have been removed you can start removing the internal components, such as the input shaft, bands, clutch packs, planetary gearsets, and output shaft.
Be sure to save all thrust washers, as they come out with these parts
Some clutch packs are held in place by a snap ring, located on the sun gear inside the input shell. This snap ring must be removed before the clutch pack and other internal parts can be removed.
Figure 18 - Transmission center support.
Many servos and accumulators are under strong spring pressure. Always consult the service manual before removing any retaining bolts or rings.
With the major components removed, the transmission case is ready to be thoroughly cleaned out and inspected for wear or damage.
All assemblies that have been removed from the transmission should be disassembled, inspected, and rebuilt to the manufacturer's specifications. Always replace seals and gaskets before reassembly. Look for any worn thrust washers and replace them as required.
Check the condition and proper operation of all vacuum or electronic devices connected to the unit. The automotive type of torque converter is usually a welded unit and can only be flushed out, usually with solvent, and pressure tested. If this type of torque converter proves to be the problem, replace it. Because of size and expense, construction equipment torque converters are made to be disassembled and repaired.
Remember, the instructions for disassembly given here are for description only; they do not apply to any one type of transmission. The information is only to give you an idea of the complexities involved in automatic transmission overhaul, not to make you an expert in this field. Be sure to check the transmission serial numbers to ensure you are getting the correct overhaul parts.
Aside from size and weight, construction equipment automatic transmissions are the same in many respects as automotive automatic transmissions and only specific instructions for that particular unit will be different. For these "specific" instructions, go to your technical library and check out the correct repair manual.
|Test Your Knowledge
2. The automatic transmission of a vehicle matches power and speed to what factor?
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In this manual, you learned how to troubleshoot problems with the clutch systems and how the automatic transmission works. In addition you learned preventive maintenance on the automatic transmission, how to troubleshoot it, and basic guidelines on how to overhaul it. The power flow to the drive wheels is something a construction mechanic needs to understand to enable you to properly troubleshoot and diagnose equipment. When you have mastered the knowledge of these systems, you will become a better mechanic.
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1. The pressure plate of a clutch assembly is held tightly against the flywheel by what means?
2. A flexible cable clutch release mechanism is most commonly used with what type of equipment?
3. Which of the following symptoms is common to clutch malfunction?
4. Clutch slippage is most noticeable during which of the following conditions?
5. When you notice insufficient clutch pedal free travel, you should check which of the following items?
6. Which of the following practices is recommended to correct a stiff clutch pedal?
7. When the clutch is being uncoupled, a series of slight movements (pulsations) can be felt on the clutch pedal. The trouble indicated may be caused by which of the following conditions?
8. In automatic transmissions, gears are designed so that several teeth are in contact with one another at one time. This design is used for which of the following reasons?
9. When torque is increased during the operation of a planetary transmission, what will happen to the output speed?
10. Your holding the sun gear stationary and applying power to the internal gear in a clockwise direction will produce what result in gearing?
11. What results when two members of a planetary gearset rotate together?
12. What means or device within the torque converter allows for shifting without interruption of engine torque application?
13. In an automotive application, the converter cover is normally attached to the engine by what means?
14. (True or False) When the engine is running, the converter pump is operational.
15. In addition to giving off a burnt smell, overheated transmission fluid will turn what color?
16. Air trapped in the hydraulic system of an automatic transmission will cause which of the following problems?
17. Water mixed with automatic transmission fluid will turn the fluid what color?
18. (True or False) Rags are an acceptable item to dry a screen in an automatic transmission.
19. Which of the following methods should you use to remove air trapped in a transmission hydraulic system?
20. What would most likely cause the fluid in an automatic transmission to foam?
21. During overhaul, the incorrect disassembly of an automatic transmission may cause what result?
22. During an automatic transmission overhaul, an air compressor is used for which of the following purposes?
23. When you disassemble an automatic transmission, you must remove what component before removing the valve body?
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