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By TCRA & TCRA Technical Committee

General Tips by TCRA & TCRA Technical Committee

It’s a System
The correct ATF is important

By Robert King
Senior Research Engineer
University of Dayton Research Institute

Torque converter clutches (TCC) have been around since the mid to late seventies. The primary purpose of the TCC is to assist with improving fuel economy by providing a mechanical lockup to the transmission. The secondary function is to provide torsional damping to the driveline. The original design only required the TCC to be either fully applied or released using inputs from the throttle position switch, speed of the vehicle and manifold absolute pressure sensor. Engagement only occurred above approximately 35 MPH while the vehicle was cruising in the final drive gear.

Over the past several years automotive manufacturers have increased the breadth of the engagement cycle using calibrated computer controls. This allows the TCC to be partially applied (slipping) at lower speeds and in different gears along with full lockup at cruising speeds which accounts for additional fuel economy. The newer computer controlled TCC systems present some formidable problems for the design engineers and system calibrators. New friction materials containing carbon particles or carbon weave were developed to provide the required performance and durability to survive in the elevated temperature environments. The computer controlled TCC requires automatic transmission fluids with special modifier packages to enhance the durability and performance of the latest generation friction materials.

Manufacturers have developed their own TCC systems which includes (in most cases) automatic transmission fluid specifically developed for their applications. Substituting alternate fluids for the recommended fluid may cause performance problems (chatter, reduced friction material torque capacity) and/or durability problems (reduced friction material life due to heat glazing and/or accelerated wear). The new systems are so smooth when working properly, their application is transparent to the driver. The owner of the vehicle may not be happy if after having his converter replaced he starts noticing the torque converter clutch engagements. Remember, the toque converter clutch is part of a system comprising of the friction material, automatic transmission fluid, and calibrated computer controls. Using the correct automatic transmission fluid may alleviate unnecessary converter replacements and unhappy customers.

Oil Cooler Pipes

If replacement of transmission steel tubing lines is required, use only double wrapped and brazed steel tubing meeting GM specification 123m equivivalent. Under no condition use copper or aluminum tubing to replace steek tubing. These materials do not have satisfactory fatigue durability to withstand normal vehicle vibrations. Steel tubing should be flared using the double flare method.

Cooler Line Flusing

In a major transmission failure, where particles of metal have been carried with the oil throughout the transmission, it will be necessary to flush out the oil cooler and connecting lines. Cooler flushing is essential to prevent a repeat failure of a transmission due to contaminated fluid. To flush the cooler and lines, use the following procedure:

  1. Remove transmission cooler lines at the transmission and allow cooler to drain.
  2. Prepare a commercial cleaning solution recommended for use with steel, copper, brass or copper nickel. (Commercial trademark products such as Oakite #77, Oakite #24, Oakite Railrod Cleaner, Pennsalt p-35, Permag #70, Permag #178 or equivalent, are good solutions for cleaning the oil passages.)
  3. Attach one cooler line to tool J-35944 or an equivalent device capable of circulating the cleaning solution at a pressure not to exceed 75 psig.
  4. Place a filter cloth or screen suitable for trapping foreign material over the remaining cooler line.
  5. Circulate the cleaning solution for 15 minutes or until the solution appears clean after having flowed through the cooler.
  6. Switch cooler lines and repeat step 5 to circulate the cleaning solution in the opposite direction.
    1. Note: If an abnormal amount of metal particle contamination is found at the filter cloth or screen during the above flushing procedure, the cooler should be replaced.
  7. Rinse the cooler with water (almost boiling) until the water comes out clean. After the rinsing operation, blow out the cooler with compressed air to dry.
  8. If the cooler is to be stored more than one day, it should be flushed with transmission fluid to prevent corrosion.

IF THE OIL COOLER IS NOT CLEAN, THE TRANSMISSION MAY EXPERIENCE PROBLEMS WITH STUCK VALVES AND PREMATURE FAILURE. To prevent this condition, it is necessary to do the following after installing the transmission.

  1. Install a temporary in-line filter in the cooler return line and attach the line to the transmission. Road test the vehicle for a few miles, TWENTY MINUTES MAXMIMUM. This filter will trap any contaminants that come out of the cooler and keep the transmission clean. After the test drive, remove the filter and install a compression union in its place. This procedure will prevent stuck valves and the filter can be reused.
  2. Before hooking the cooler return line to the transmission, hold a container under the line and start the vehicle for a few seconds, this will determine if there is adequate lube flow.


Checking Converter Clearance

What is stab depth? Stab depth is the total distance that the torque converter is pulled out of the transmission pump when the transmission has been bolted to the engine and the torque converter is pulled out of the pump to be bolted to the flex plate, flywheel or drive plate of the engine.

The stab depth distance must be set or maintained at the proper distance. Pump whine and no egagement of the pump gear drive lugs by the torque converter hub are problems caused by too much clearance.

Correctly setting the stab depth of the torque converter has become a very, very important procedure of the R & R process

To set the stab depth of the torque converter, first, bolt the tranmission and torque converter assembly to the engine as you normally would, being certain that the torque converter is engaged into the pump as far as possible.

Second, measure the distance from the torque converter mounting pad or bolt flange to the area of the flex late or flywheel that the torque converter will be pulled to when the mounting bolts are installed. The distance you have measured will be the distance the torque converter pump drive hub will be pulled out of the pump drive gear at final assembly.

Stab depth final dimensions should be as follows:

  1. THE TORQUE CONVERTER MUST BE PULLED OUT OF THE PUMP A MINIMUM OF 1/8 OF AN INCH. This gives necessary head room or expansion clearance during normal torque converter ballooning and flex.
  2. THE TORQUE CONVERTER MUST NOT BE PULLED OUT OF THE PUMP MORE THAN 1/4 OF AN INCH. If the torque converter is pulled out of the transmission more than 1/4 of an inch, you can experience a pump whine caused by the pump gear running too close to the crescent or actually rubbing the crescent, more than likely developing during initial start-up or after only limited number of miles. When you find the stab depth to be too close or not at least 1/8 of an inch, or course, you might be able to install another torque converter and possibly gain more clearance or headroom as needed. Save the torque converter you did not install for the next transmission because it, in all probability, will have a different stab depth clearance and may need a taller torque.
    When you find stab depth to be too great, either change torque converters to find a taller unit, or measure the distance with the torque converter fully stabbed into the transmission from the mounting pad to the flex plate and add shims or spacers (usually flat washers) to keep the distance of torque converter pull out less than 1/4 of an inch. When adding shims or washers, be sure to add the same amount to each mounting pad of the torque converter.
    The addition of spacers between the mounting pads and the flex plate may require the use of slightly longer mounting bolts with some application. be cetain when using this procedure, not to pull the torque converter pilot out of the engine crankshaft after a set of shims has been added or vibration and transmission pump damage could result.

**** The preceding information has been derived from a General Motors publication dated 1972 ****