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Technical

The simple mistake that can leave the CVT 7 unable to reverse

In this situation, a Nissan Sentra comes in with a CVT 7 transmission that can go into reverse but not drive. The unit was disassembled only to find a snapped off sun gear in the low clutch hub (figure 1). 

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After a new clutch hub was located, the unit was repaired and reassembled. Once it was installed in the vehicle, forward movement functioned as designed with a shift from the low clutch to the high clutch followed by TCC apply and the ratioing of the pulleys. But the problem was, now the vehicle couldn’t reverse. 

What went wrong? A simple mistake that can be made in assembling this transmission is to not properly index the reverse clutch piston retainer when placing it into the case, as shown in figure 2.

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This retainer has a feed hole that must be aligned to the cover. A feed pipe and tube seal fit into this cover to supply pressure to this clutch (figures 3 and 4).

If the piston retainer is not properly indexed (figure 5), the seal and feed pipe will sit on a sealed portion of the retainer blocking the pressure supply to the piston (figure 6)

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Tech-Speak-Jan-

There is a specific notch in the case where the tab on the reverse clutch piston retainer fits into as shown in figure 7. This positions the feed hole in this retainer (figure 8), to the cover (figure 9).

The tube seal will now crush up against the cover around the feed hole, allowing reverse pressure to flow through the pipe and into the back side of the apply piston, restoring reverse movement to the vehicle.

Click here to read more of Wayne Colonna’s Technically Speaking columns.

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