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The heart of the matter

An automatic transmission relies on its heart — the filter, pump and related seals — for quality performance
Tuesday, March 22, 2016 - 06:00
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It is no secret that having a good working heart is a necessary element towards enjoying quality of life. The same is true for an automatic transmission. The quality of the filter, pump and related seals are critical to the proper operation of the transmission and its length of life. Its veins reach out to apply clutches and brakes as well as lubrication and cooling circuits. A failure with the pressure circuit is no doubt an undesirable event.

An interesting aspect to pumps is the design manufacturers choose to use in their transmission. This couldn’t be anymore evident than with GM and Ford in their joint venture to build a six speed front wheel drive transmission. As mentioned in a previous Powertrain Pro article called “The Twists and Turns in Keeping Up with the Changes,” GM went with a crescent style pump while Ford went with a gerotor pump.  GM has a long history of using both a crescent style pump and a variable displacement vane pump (VDVP). Ford has had a history of using crescent style pumps too, but gerotor style pumps as well. The article mentioned that gerotor style pumps are less expensive to manufacture than crescent style pumps and can package nicely in a small diameter space. The same is true with “compact vane type pumps,” which have become widely used in a variety of applications.

The positive displacement rotary vane pump has history as far back as the late 1800s. The variable displacement vane pump showed up about a half-century later. The first time I ever saw a rotary vane motor was in my impact wrench back in the early 70s.

Today we are seeing this style of pump being referred to as a “twin-pipe-vane pump” or “twin-stroke vane pump.” General Motors uses this style pump in their new 8L90 transmission (figure 1), which they call a “Binary Displacement Vane Type Pump.” 

Figure 1
Figure 2

There are several advantages for using this style pump. Its compact size allows it to be positioned in an “off-axis” location. An “on-axis” style pump is typically located in the front of the transmission. The torque converter can then be used as an input drive member of the pump. This style set-up however, extends the length of the transmission.

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An off-axis pump provides the manufacturer with the freedom to locate the pump in such a way so as to save on the length of the transmission. With the 8L90, this pump is an integral part of the valve body inside the main case. When the pan is removed, the main filter inserts directly into this pump (figure 2). The pump is chain driven (figure 3) by the torque converter which lugs to the pump drive gear called a Drive Sprocket (figure 4). When the valve body is lifted off of the transmission, the pump can be unbolted and removed from the housing (figure 5). Immediately you will discover three critical seals; a beaded pump gasket (pump cover to the valve body pump housing), a fluid passage sleeve (sits in the pump suction [bypass] circuit), and the pump seal (between the pump pressure plate and valve body pump housing).

Figure 3
Figure 4
Figure 5
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