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Technical

Common failures on the GM AW55-50SN

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GM’s AW55-50SN, otherwise known as the AF33 transmission (figure 1, above), is known for its placement in vehicles including the Chevrolet Equinox and Captiva, the Pontiac Torrent and the Saturn Vue. Versions of this transmission can also be found in SAAB, Volvo and Nissan vehicles. This unit began being produced in 2000 and ended production in 2015.

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One of the most common failures in this transmission is case wear, located where the output gear assembly mounts (see figures 2 and 3).

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Figure 2.
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Figure 3.

The damage this causes to the bushings also causes a loss of cooler pressure. There are companies which can restore the integrity of the case by machining and installing a sleeve in the wear area. During the rebuild, all new bushings are installed restoring geartrain centerline and cooler circuit. 

Once the transmission is installed and road-tested, it becomes quite disheartening to have a noise problem after making such extensive repairs; not to mention the time and cost that went into making these repairs to give the customer a quality rebuild.

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What can be easily overlooked that is that the cause of this noise is pinion wear with the planet carrier assembly. Simply looking at the pinion shaft will not reveal the problem (see figures 4 and 5).

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Figure 4.
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Figure 5.

The close-up view of one of the pinion shafts looks normal. But, when the pinon gear is rocked by hand, it will become obvious of how badly the pinion shaft has worn into the carrier. Figure 6 shows the wear seen with this pinion shaft.

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Figure 6.

This is the cause of the unwanted noise after going to great lengths in providing a quality repair for the customer; something you don’t want to miss the first time you rebuild this transmission. 

Read more columns from our Shift Pointers series here.

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