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The 2-4 brake issue

Friday, January 2, 2015 - 09:00
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The main Powertrain Pro article in the June issue of Motor Age featured Mazda’s RX8 RC4A-EL transmission. In an outline issued by Mazda regarding this transmission, to improve shift quality they chose to utilize a clutch plate assembly as a holding clutch (brake) for second and fourth gears (figure 1). According to the outline, one of the benefits of this design is that it has optimum control at low oil temperatures. Given the fact that this clutch brake assembly is the “shifting core” of the transmission, apparent efforts were made to provide the cleanest shift possible. The “shifting core” of this transmission meaning it plays a role in each and every shift.

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But there was another item they added to this assembly which was not mentioned (and rightfully so), since it has nothing to do with shift quality. With this assembly being a brake, the steel plates are lugged to the case. When the piston compresses the assembly, the rotating friction plates are sandwiched into the stationary steel plates which ultimately prevent rotation of the front sun gear. The times this brake assembly is released (1st and 3rd gears); the steel plates can rattle in the case. To prevent this aggravating noise for the driver, tension springs were designed (figure 2) to be fitted between the lugs and the case. Since these units are not visiting the shops with a great deal of frequency, duringdisassembly theses tension springs may fall out before you are aware they exist. And then you wonder where they should go.

A careful look inside the transmission and you will notice the basic design of the tension springs embossed into the case above the lug slots, to identify their proper positioning (figures 3 and 4).  There are a total of 3 spaced approximately every 120° centering the steel plates away from the case. After a few steel plates and friction plates are installed, these tension springs can be pushed into place followed by the remaining plates.

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