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Torque Converter is fluid-filled case that contains a set of
turbines - there is an input turbine that is driven by the
engine, an output turbine that connected to the transmission's
input shaft, and a stator turbine between them that directs
and controls the flow of the fluid. |
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At a certain input
RPM, the torque converter will reach its maximum fluid flow.
Below this input RPM, there is poor hydraulic
"coupling" between the input turbine and the output
turbine - there is a lot of "slippage". Above this
input RPM there is a hydraulic "lockup" - there is
almost no slippage between the input turbine and the output
turbine. This certain input RPM is called the "stall
speed" of the converter. This property of a torque
converter allows an engine to rev-up to a speed where it
begins to make significant power (commonly referred to as
"torque multiplication") before being put under a
heavy load. The stall speed of a torque converter needs to be
carefully matched to the torque curve of the engine it will be
used with. A high-performance or race engine, which makes
power only at high RPM, needs a torque converter that has a
very high stall speed.
You cannot check the stall speed of a torque converter by
pulling the transmission into gear, holding a vehicle with the
brakes and adding power -- the drive-wheels will begin to spin
long before you reach full-power. The proper way to check the
stall speed is to make a standing-start, abrupt,
foot-to-the-floor acceleration run and note the RPM shown on
the tach at the instant the vehicle begins to move. This test
actually measures "flash stall", but this is usually
very close to the true stall speed of the converter. Also,
this test is only valid if the tires do not begin to spin and
if the engine can develop sufficient torque to actually reach
the rated stall speed. If the tires spin, the apparent stall
speed will be high. If the engine does not develop sufficient
torque for the converter, the apparent stall speed will be
low.
Some torque converters have an internal, hydraulically
operated "lockup clutch" in them. At some preset
point, the transmission will cause this converter lockup
clutch to engage in order to mechanically lock the input
turbine and the output turbine together. This improves the
vehicles efficiency a bit because the slight slippage between
the input turbine and the output turbine is eliminated. As a
side benefit, some "engine braking" is also
available when you take your foot off the accelerator.
The internal parts of the turbines are manufactured from
formed sheet metal vanes and machined rings. In most
"stock" quality torque converters, the assembly of
these parts is primarily accomplished by interlocking
mechanical means. In high quality, heavy-duty and high
performance torque converters, the turbine assemblies are
completely welded or furnace brazed together to provide for a
stronger and more robust unit.
As with the rest of the transmission, excessive heat and
contamination is what will kill a torque converter. Since the
fluid in the torque converter is ATF supplied by the
transmission, wear particles and/or bits and pieces of a
blown-up transmission will end up in the converter, thereby
destroying it. Changing the ATF at regular intervals and
installing an external transmission cooler will lead to
maximum torque converter life. If an in-radiator transmission
cooler fails, ATF contamination with engine coolant will
destroy a lockup torque converter.
© 2008 Level 10 Products
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(973) 827-1000 - 3670 RT. 94 -
Hardyston, NJ - info@levelten.com
Hours M-F 7AM - 8PM / Sat 7AM - Noon
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