Trannies 101

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Leroux Brothers, Inc.
1369 Glover Road
Barton, VT 05822

toll-free 1.800.420.4330
local 1.802.525.4330
fax 1.802.525.3116


Proud member
of the Barton Chamber
of Commerce. 

At Leroux Brothers, we know transmissions.  For years, we've been hard at work repairing, rebuilding and modifying transmissions to work better, and last longer.

An automatic transmission (we repair manual trannies as well) is one of the most complicated electro-mechanical devices on a modern vehicle.  Made up of literally hundreds of specialized components, an automatic transmission utilizes hydraulic pressure, electro-mechanical valve switching, sophisticated computer control and a series of clutch plates and gears to match your vehicle's engine power to every possible driving situation. 

Transmission on Bench

The panel above shows a light duty truck transmission, almost completely disassembled on one of our Transmission Lab benches:

Here is the Valve Body for the same tranmission:


A Torque Converter Tour

Below is a thorough pictoral essay on the function of the all-important TORQUE CONVERTER, with captions by Dale Leroux...


1. Here you have a complete torque converter, with a plastic cap protecting the transmission pump drive slots.


2.  Opening the unit reveals two halves, with the torque converter's PUMP on the right.


3. A closer image reveals the torque converter PUMP's vanes, which take the energy of the vehicle's motor and transfers it to the hydraulic fluid present inside the torque converter.


4.  On the other half of the converter, we now reveal the STATOR assembly, which sits onthe top of the TURBINE.  This part of the torque converter takes the energy OUT of the hydraulic fluid and transfers the energy onto the automatic transmission's INPUT or TURBINE SHAFT.


5.  This is the TURBINE. The vanes on the outer rims received fluid from the torque converter PUMP (see number 3 above) and transfer it to the center of the unit, the TURBINE SHAFT receptacle.


6.  This is the STATOR.  At low speeds, it redirects hydraulic fluid back to the torque converter PUMP. The torque converter utilizes centrifugal force to change it's hydraulic behavior.  At low engine speeds, hydraulic fluid is sent via the STATOR back to the the converter PUMP.  At high engine speeds, the STATOR revolves at the same rate as the entire torque converter.  It is important to remember that the center of the STATOR features a one way clutch.  This allows the STATOR to turn in only one direction, providing the automatic transmission with torque multiplication.


7.  A close up of the splines in the center of the STATOR.  These splines provide a positive contact surface for theSTATOR SHAFT, the part that anchors the torque converter to the tranmission case.


8.  Dale's fingers are around the heavy duty THRUST BEARING, the part of the torque converter that keeps the STATOR from being impelled into the torque converter PUMP.  (This is a very nasty occurence. When it happens, it ruins the torque converter and transmission almost simultaneously.)


9.   A revealing look at the DAMPER assembly, in the center of the LOCK UP plate.  The LOCK UP system allows the torque converter to become a mechanically "direct" link from the engine to the automatic transmission.  Up until the point that the LOCK UP system becomes engaged, the link between the engine and the automatic transmission is purely hydraulic, via the torque converter.


10.   The splines in the middle of the DAMPER assembly mate directly with the torque converter's TURBINE...


11.  Detail of DAMPER assembly splines


12.  Detail of FRICTION PLATE that makes contact when LOCK UP is achieved.


13.  Under LOCK UP, excess hydraulic fluid is vented out of this chamber back into the automatic transmission case through the center of the TURBINE SHAFT.


14.  The remaining hydraulic pressure clamps the LOCK UP PLATE to the torque converter cover, creating the near 1:1 friction lock up between engine crankshaft and automatic tranmission.

For more information, CLICK HERE to link to "HOW STUFF WORKS", Automatic Transmissions...

This is a 15 page tour de force, so be braced. Clicking the link will take you out of the Leroux Official Website, so you're on your own! (When you're done exploring, just close the new window to return to this page.)