TRANSMISSION INFORMATION FILE

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Torque Converter Clutch

Electronically-Controlled Trannys

TORQUE CONVERTER CLUTCH: MALFUNCTION SYMPTOMS, DIAGNOSTICS

[www.e-toolbox.com/application/8852/8852CH21_TORQUE_CONVERTER_CLUTCH_CONTROL.htm]

TORQUE CONVERTER CLUTCH CONTROL Electrical and Vacuum Controls
The torque converter clutch should apply when the engine has reached near normal operating temperature in order to handle the slight extra load and when the vehicle speed is high enough to allow the operation of the clutch to be smooth and the vehicle to be free of engine pulses.

NOTE: When the converter clutch is coupled to the engine, the engine pulses can be felt through the vehicle in the same manner as if equipped with a clutch and standard transmission. Engine condition, engine load and engine speed determines the severity of the pulsation.

The converter clutch should release when torque multiplication is needed in the converter, when coming to a stop, or when the mechanical connection would affect exhaust emissions during a coasting condition.

The typical electrical control components consist of the brake release switch, the low vacuum switch and the governor switch. Some vehicle models have a thermal vacuum switch, a relay valve and a delay valve. Diesel engines use a high vacuum switch in addition to certain above listed components. These various components control the flow of current to the apply valve solenoid. By controlling the current flow, these components activate or deactivate the solenoid, which in turn engages or disengages the transmission converter clutch, depending upon the driving conditions as mentioned previously. The components have the two basic circuits, electrical and vacuum.

Fig. 1: Using electrical and vacuum controls to operate the torque converter clutch

Fig. 2: Typical diesel engine vacuum and electrical schematic for the torque converter clutch

ELECTRICAL CURRENT FLOW

All of the components in the electrical circuit must be closed or grounded before the solenoid can open the hydraulic circuit to engage the converter clutch. The circuit begins at the fuse panel and flows to the brake switch and as long as the brake pedal is not depressed, the current will flow to the low vacuum switch on the gasoline engines and to the high vacuum switch on the diesel engines. These two switches open or close the circuit path to the solenoid, dependent upon the engine or pump vacuum. If the low vacuum switch is closed (high vacuum switch on diesel engines), the current continues to flow to the transmission case connector, into the solenoid and to the governor pressure switch. When the vehicle speed is approximately 35-50 mph (56-80 kph) , the governor switch grounds to activate the solenoid. The solenoid, in turn, opens a hydraulic circuit to the converter clutch assembly, engaging the unit.

It should be noted that external vacuum controls include the thermal vacuum valve, the relay valve, the delay valve, the low vacuum switch and a high vacuum switch (used on diesel engines). Keep in mind that all of the electrical or vacuum components may not be used on all engines, at the same time.

VACUUM FLOW

The vacuum relay valve works with the thermal vacuum valve to keep engine vacuum from reaching the low vacuum valve switch at low engine temperatures. This action prevents the clutch from engaging while the engine is still warming up. The delay valve slows the response of the low vacuum switch to changes in engine vacuum. This action prevents the low vacuum switch from causing the converter clutch to engage and disengage too rapidly. The low vacuum switch deactivates the converter clutch when engine vacuum drops to a specific low level during moderate acceleration just before a part-throttle transmission downshift. The low vacuum switch also deactivates the clutch while the vehicle is coasting because it receives no vacuum from its ported vacuum source.

The high vacuum switch, when on diesel engines, deactivates the converter clutch while the vehicle is coasting. The low vacuum switch on the diesel models only deactivates the converter clutch only during moderate acceleration, just prior to a part-throttle downshift. Because the diesel engine's vacuum source is a rotary pump, rather than taken from a carburetor port, diesel models require bath the high and the low vacuum switch to achieve the same results as the low vacuum switch on the gasoline models.

Fig. 3: Typical computer controlled clutch

Computer Controlled Converter Clutch

With the use of microcomputers governing the engine fuel and spark delivery, most manufacturers change the converter clutch electronic control to provide the grounding circuit for the solenoid valve through the microcomputer, rather than the governor pressure switch. Sensors are used in place of the formerly used switches and send signals back to the microcomputer to indicate if the engine is in its proper mode to accept the mechanical lock-up of the converter clutch.

Normally a coolant sensor, a throttle position sensor, an engine vacuum sensor and a vehicle speed sensor are used to signal the microcomputer when the converter clutch can be applied. Should a sensor indicate the need for the converter clutch to be deactivated, the grounding circuit to the transmission solenoid valve would be interrupted and the converter clutch would be released.

Hydraulic Converter Clutch

Numerous automatic transmissions rely upon hydraulic pressures to sense, determine when and to apply the converter clutch assembly. This type of automatic transmission unit is considered to be a self-contained unit with only the shift linkage, throttle cable or modulator valve being external. Specific valves, located within the valve body or oil pump housing, are caused to be moved when a sequence of events occur within the unit. For example, to engage the converter clutch, most all automatic transmissions require the gear ratio to be in the top gear before the converter clutch control valves can be placed in operation. The governor and throttle pressures must maintain specific fluid pressures at various points within the hydraulic circuits to aid in the engagement or disengagement of the converter clutch. In addition, check valves must properly seal and move to exhaust pressured fluid at the correct time to avoid "shudders" or "chuckles" during the initial application and engagement of the converter clutch.

Centrifugal Torque Converter Clutch

A torque converter was used that locks up mechanically without the use of electronics or hydraulic pressure. At specific input shaft speeds, brake-like shoes move outward from the rim of the turbine assembly, to engage the converter housing, locking the converter unit mechanically together for a 1:1 ratio. Slight slippage can occur at the low end of the rpm scale, but the greater the rpm, the tighter the lock-up. Again, it must be mentioned, that when the converter has locked-up, the vehicle may respond in the same manner as driving with a clutch and standard transmission. This is considered normal and does not indicate converter clutch or transmission problems. Keep in mind if engines are in need of tune-ups or repairs, the lock-up "shudder" or "chuckle" feeling may be greater.

Fig. 4: Exploded view of the centrifugal lock-up converter

Mechanical Converter Lock-Up

Another type of converter lock-up is the Ford Motor Company's AOD Automatic Overdrive transmission, which uses a direct drive input shaft splined to the damper assembly of the torque converter cover to the direct clutch, bypassing the torque converter reduction components. A second shaft encloses the direct drive input shaft and is coupled between the converter turbine and the reverse clutch or forward clutch, depending upon their applied phase. With this type of unit, when in third gear, the input shaft torque is split, 30% hydraulic and 70% mechanical. When in the overdrive or fourth gear, the input torque is completely mechanical and the transmission is locked mechanically to the engine.
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ELECTRONICALLY-CONTROLLED TRANSMISSIONS

[http://au.geocities.com/ozbrick850/at-driveline.html]
GM/generic Driveline info
XVI. Driveline

C. Electronically-Controlled Automatics

Yeah, I know. You're not particularly thrilled with the trend toward electronically-controlled automobiles. After all, you're MECHANICALLY inclined, right? You never imagined you'd be needing the skills of a computer technician. First, it was just ignition, which wasn't too bad. But then EFI and feedback carbs started to show up in big numbers along with computers that handle all the goings on under the hood from emission controls to the subject of this section, torque converter lockup. Now, we're getting smart suspensions, computerized anti-skid braking, digital dashboards, and chip-controlled shift points. Will it ever end?

Probably not. As Boss Kettering, the inventor of point and coil ignition and founder of Delco said many years ago, "Nothing is constant but change." There's no doubt that the transition from the mechanical age to the computer era is going to be difficult for everybody who works on cars. But, like it or not, it's happening, and if you're going to remain competent, you've got to bite the bullet and learn a lot of new stuff. Fortunately, the system that controls the clutch in GM torque converters is easier to understand than some other gee-whiz automotive wonders I can think of.

Rationale:
A torque converter is a wonderful thing. It allows a car to sit still while idling in gear, and, by a seemingly magical process, puts out more twisting power than is put into it.

In spite of its good qualities, it has one serious drawback: It slips, and that wastes fuel. With the automakers frantically trying to get mpg up, this characteristic couldn't be tolerated. Chrysler moved first. In '78, it introduced a converter with an internal clutch that locked up solid at cruising speed. But it was controlled hydraulically. The next logical step in the evolution of a more efficient transmission was a switch to electronic means of deciding when the clutch should be engaged, and the most prominent example of this is GM's TCC (Torque Converter Clutch) operated by the C-3 (Computer Command Control) system.

How do you translate a computer-generated electrical signal into a mechanical act? Easy, with a solenoid-operated valve. When the brain sends voltage, the solenoid moves a check ball in a fluid line that routes apply pressure to the clutch servo.

This simple component is easily accessible with the trans in the car. On transaxles, just remove the side cover. On regular automatics, pull the pan.

Considerations :
The ECM (Electronic Control Module) determines the best time to lock up the clutch on the basis of data it receives from various sensors and switches:

First, there's the VSS (Vehicle Speed Sensor) -- mph must be above a certain point before the TCC can be applied.

Since the engine should be warm, CTS (Coolant Temperature Sensor) input is considered too.

The clutch is supposed to disengage whenever the car is accelerating or decelerating at a particular rate, and the computer gets this info from the TPS (Throttle Position Sensor).

On some transmissions, a third or forth gear switch lets the ECM know what gear is currently engaged so it can vary the conditions under which it applies or releases the clutch, but the trans doesn't have to be in high for the clutch to engage (if you see three or four wires coming out of the TCC connector, the transmission has gear select switches).

Other controls don't go though the computer. One is a normally open third gear switch in series on the battery side of the TCC solenoid. It prevents lockup until third is engaged. Another, found on certain transmissions, is a 4-3 (four speed) or 3-2 (three speed) pulse switch that opens the TCC solenoid circuit momentarily during a downshift. Finally, there's the brake switch. When the driver puts his foot on the stop pedal, the switch opens, which breaks the circuit to the TCC.

Some don't like it:
As far as fuel efficiency is concerned, this system works great. But many motorists are annoyed or dismayed by the way it feels. They'll think their transmission is constantly shifting up and down as conditions lock and unlock the clutch, and they'll swear there's something wrong. Others will say their engines are misfiring. So, the first step in troubleshooting a complaint is to ascertain whether or not a problem does indeed exist. Take the car for a test drive and really concentrate on what's happening, then read the owner's manual or try another similar GM car to refresh your memory. Maybe the TCC is working as it's supposed to.

Right here I'd better caution you that this is an area where the old saying about a little bit of knowledge being a dangerous thing definitely applies. You might think it's a very clever idea to cure that annoying "hunting" condition by just disconnecting the TCC wire so the clutch never engages. It'll cost a little in mileage, but the trans will act just like a pre-fuel crisis unit, right? Unfortunately, no. On the 200 4R and the 700 R4, doing this can cause fourth gear to burn out and ruin the front pump. And it'll increase fluid temperature to the danger point on all models. Mileage will drop more than you'd expect too -- clutch-equipped converters slip a lot in the unlocked mode. GM has issued bulletins warning us never to run a car with the TCC disabled.

What about splicing a toggle switch into the wire that sends voltage to the TCC solenoid? No good either. You're risking all the same problems mentioned above whenever the switch is off.

Actual (as opposed to perceived) problems you may run into are a clutch that won't disengage -- of course, that'll stall the engine. If the clutch never locks up, the only thing you might notice is a considerable drop in fuel mileage (in fact, you may even prefer the way the car drives). If you're a little more sensitive to your vehicle, and it has a tach, you might also be worried when you see that the engine is turning 300 to 500 more rpm than it used to maintain the same speed. And you may be heading for a megadollar trans failure because of the overheating and lubrication problems that occur when that clutch doesn't work.

Preliminaries:
Before you start blaming the electronics for the trouble, make some preliminary checks, including fluid level, linkage adjustment, and the condition of vacuum lines. Since the engineers have given you self-diagnostics, you might as well use them. Find the ALDL (Assembly Line Diagnostic Link) under the dash (or on the odd duck such as the late lamented Fiero, in the console), turn the ignition on but don't start the engine, then connect terminal"B" of the connector to terminal "A" or a good ground. This will activate the self-criticism mode.

Code 12 (flash-pause-flash-flash) will be signalled by the "Check Engine" light three times, then any troubles the computer has recorded will be flashed out. A 24, which fingers the VSS circuit, is the trouble code most directly related to TCC function. But others suggest problems that can affect the system too: 14 or 15 for the CTP, 21 or 22 for the TPS, and 33 or 34 for the MAP sensor.

Of course, if you have one of those neat aftermarket C-3 scanners, you can read the trouble codes without having to count flashes, get a direct verdict on the VSS circuit, and compare how many rpm and mph relate to clutch on/off status.

VSS check:
When presented with a code 24, you should consult the logic-tree chart in the factory manual for the car in question, but the procedure for an average A-Car is typical:

1.Make sure the speedometer is working.

2.Raise the drive wheels, put the trans in Neutral, turn the ignition on, then connect a voltmeter between ECM terminal #16 and ground.

3.Rotate a drive wheel by hand. The meter reading should alternate between three and six volts.

4.If voltage varies, check the Park/Neutral circuit, then the TPS setting. If they're both okay, the ECM connection or the ECM itself is bad.

5.If there was no voltage variation while you turned the wheel, disconnect the VSS and measure the voltage between harness terminals "A" and "B," then "B" and "C."

6.If both readings are over six volts, check the VSS connections. If they're okay, replace the VSS.

7.If either of the voltage readings are low, you've found a poor connection, an open wire, or a faulty ECM.

Another thing worth doing before you come to any rash conclusions is a test of transmission fluid pressure. Tee a gauge into the return line from the cooler, attach a tach, disconnect the hose from the vacuum switch or sensor, raise the drive wheels, warm up the engine, run it in Drive until it shifts into high, hold 2,000 rpm, and check the gauge reading against specs. If there's not enough pressure, nothing's going to work properly even if the TCC components and controls are in fine shape.

Logical sequence
If nothing's wrong so far, it's time to look up the TCC system diagnosis chart in the proper manual. While I'm not going to squeeze the whole boring step-by-step into this section, I'll tell you how to start the sequence so you can get an idea of what's involved. First, warm up the engine and raise the drive wheels. Connect a test light from terminal "F" in the ALDL to ground, start the engine, put the trans in gear, and accelerate to 35 mph. The light will go on if the TCC is being sent a signal. Hold the throttle position and touch the brake. If the brake switch is okay, the light will go out. From there on, you'll have to follow the chart, which, I'm happy to say, is pretty easy.
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{http://www.quality-trans.com/faq/faq4.htm: "...temperature sensor that prevents the lockup portion of the torque converter from functioning before the transmission is up to operating temperature. ... If the pan is relatively clean, then the TCC (Torque Converter Clutch) solenoid is at fault and should be replaced.

In an emergency only, you can locate the wiring harness that routes to the transmission and disconnect it at the transmission. It is located on the front of the unit toward the driver's side on a front wheel drive and can be easily seen from the top. On a rear wheel drive transmission, the harness is on the driver's side of the transmission. Once the harness is disconnected, the torque converter clutch should not engage. The harness allows other functions to occur, and you will probably see a "check engine" light after it is unplugged. Do not continue to drive the vehicle in this condition. This is just to allow you to drive the vehicle long enough to have it repaired!

If the symptoms continue after the harness is disconnected, then there is a mechanical problem with the torque converter and/or transmission.]
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"...Occasionally, it will stall when I put it in reverse. Can you help? George
[ http://www.signonsandiego.com/marketplace/autocenter/archives/990712poorgas.html.]
Dear George: You first have to determine if the stalling is related to the engine or transmission. Idle speed is controlled by the computer. A stuck or faulty lock up toque converter clutch or solenoid can cause stalling, as can a lazy idle speed control motor, vacuum leaks, and especially an EGR valve opening too soon.

Dear Doctor: I own a 1990 Oldsmobile Silhouette 3.1-liter V6. The van has been trouble-free until now. After a 17 mile trip, as I was coming to a stop, the engine stalled out and then started right back up. As soon as I put the transmission in drive, the engine stalled out. I waited ten minutes, and started it back up and it was fine. I had it checked and there were no trouble codes in the computer. The stalling happened again, but this time I had to let the van cool down for 30 minutes. What's the problem? Larry

Dear Larry: Your van has a common GM transmission problem with the lock up torque converter or solenoid. A simple test is to unplug the electrical connector on the front of the transmission and do a road test. I see this problem regularly.
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{General: "...Generally speaking, transmissions that are computer shifted (most domestics since early 90¹s) will still utilize the factory shift timing, which is controlled by the onboard computer. This automatic shift function is not changed with the installation of the TransGo Performance Shift Kit®..."]

{general: 4T40E / 4T60E [In "TRANS SPORT" 3.8} / 4T80E - The transmissions above are 4 speed automatics that are computer controlled. The most common problems are: Your check engine light comes on. The transmission starts shifting erratically or not at all.

Make sure you or a shop runs a scanner on the vehicle. You want to see if a sensor has gone bad causing your problem. Always check your modulator line on the 4T60E transmission to see if there is fluid inside. If fluid is inside the line, then the modulator is no good.

These problems can be caused when the external sensors on the vehicle go bad. The input and output speed sensors, throttle position sensor or vehicle speed sensors need to be checked. Always run a scanner first to see if a sensor is causing your problem.

Always check the throttle pressure cable that goes from your transmission to your carburetor or throttle body depending on the configuration of your engine. This controls the shift points and sometimes the heat causes the little plastic connector that holds it on to become brittle and break, causing erratic shifting. Shift timing [on these different models... may be different on the Trans Sport] is controlled by a throttle pressure cable that connects from the transmission to the carburetor or throttle body, depending on the configuration of your engine. Check this cable first. Make sure the cable is not out of adjustment.
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The TCC solenoid is what actually causes the TCC to engage and disengage. When the TCC solenoid receives a signal from the ECM, it opens a passage in the valve body and hydraulic fluid applies the TCC. When the ECM signal stops, the solenoid closes the valve and pressure is vented causing the TCC to disengage. If the TCC fails to disengage when the vehicle comes to a stop, the engine will stall.

Before attempting to diagnose converter clutch electrical problems, mechanical checks such as linkage adjustments and oil level should be performed and corrected as needed.

Generally, if you unplug the TCC solenoid at the transmission and the symptoms go away, you have found the problem. But sometimes this can be misleading because you don't know for sure if it's a bad solenoid, dirt in the valve body or a bad signal from the ECM. The only way to know for certain is to follow the diagnostic procedure as outlined by General Motors. If you follow the test step by step you will be able to determine the exact cause of the problem.

Check For 12 Volts To Terminal A At Transmission.{Presumably at the solenoid- RJ]

Test #6 (Regular Method) Check for ground at terminal D at the transmission.

On Non-computer-controlled vehicles skip this test and go directly to cooler line pressure, or surge test.

Raise the vehicle on the lift so the driving wheels are off the ground.

Unplug the wires at the case and connect the alligator clip of your test light to terminal A.

Place the tip of your test light on terminal D.

Start the engine and bring to normal operating temperature.

Place the selector in Drive. (O.D. on four speed units).

Accelerate slowly to 60 mph and the tester should light.

If the tester does not light you have a computer system problem. Go to test # 7 (Regular Method).

Test #7 (Regular Method)

Ground the D wire at the transmission

Shave a little insulation from or pierce the D wire near the transmission connector. Reseal with silicon.

Connect one end of a jumper wire to the bare wire you just shaved or pierced.

Connect the other end of the jumper wire to ground.

Road test for lock-up (can be done on lift).

If you're not sure if lock-up occurred, then hold a steady speed of 60 mph (on the lift) and lightly touch and release the brake. You should feel lock-up disengage and re-engage.

Checking the Solenoid:

You will need an ANALOG ohmmeter and a 12-volt source for this test.

Connect the Black lead of your ohmmeter to the RED wire on the solenoid.

Connect the RED lead of your ohmmeter to the BLACK wire on the solenoid. If you have a one-wire solenoid then connect the RED lead of your ohmmeter to the solenoid body.

With the ohmmeter set at ohms times one (Rx1), the reading should be no less then 20 ohms, but not infinite.

Connect the RED lead of your ohmmeter to the RED wire on the solenoid and the Black lead to the Black wire or body (You're just switching your connections). The ohmmeter should read less than the reading in the first test.

Connect the solenoid to a 12-volt source. BE SURE TO OBSERVE PROPER POLARITY, if using a car battery.

With lung pressure (or very low pressure) try to blow through the solenoid. It should be sealed.

Disconnect the 12-volt source and you should now be able to blow through the solenoid.

Test #10

Checking Electrical Switches on Transmission

SWITCH TYPE: Single terminal normally open

PART#: 8642473

TEST: Connect one ohmmeter lead to the terminal of the switch and the other lead to the body of the switch. Ohmmeter should read infinite. Apply 60 psi of air to the switch and the ohmmeter should read 0.

SWITCH TYPE: Signal terminal normally closed

PART#: 8642569, 8634475

TEST: Connect one ohmmeter lead to the terminal of the switch and the other lead to the body of the switch. Ohmmeter should read 0. Apply 60 psi of air to the switch and the ohmmeter should read infinite.

SWITCH TYPE: Two terminal normally open

PART#: 8643710

TEST: Connect one ohmmeter lead to one terminal of the switch and the other lead to the other lead to the other terminal. Ohmmeter should read infinite. Apply 60 psi of air to the switch and the ohmmeter should read 0.
SWITCH TYPE: Two terminal normally closed PART#: 8642346 TEST: Connect one ohmmeter lead to one terminal of the switch and the other lead to the other terminal. Ohmmeter should read 0. Apply 60 psi of air to the switch and the ohmmeter should read infinite.

How To Replace Your Torque Converter Clutch Solenoid (GM)

How to repair a very common failure.

What you will need:

Combination Wrenches / A Socket Set / Torque Wrench / Screwdrivers / Tube of Silicone Sealer (GM P/N 12345282) / Red or Blue Loc-Tite® / Drain Pan / Jack / Jack stands / A New TCC / Transmission Fluid / J 28467-A Engine Support Fixture /




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[MOPAR TRANSMISSION FLUID - www.neons.org/faq/FAQ_ET.html "You *must* use type 7176 transmission fluid in all Chrysler-built automatic transmissions since the mid-70's. Dexron II and III are much more slippery than type 7176/ATF+3 and will cause shuddering during shifts. The latest version of the Mopar ATF is Mopar ATF+3 type 7176. It is more heat resistant than the prior ATF+2 formula.
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