Q: Overdrive not working

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My overdrive is not working.

Greetings! You have a 4T65E transmission. A transmission used in the Pontiac Montana and Pontiac Aztek by GM for about 10 years. About 4 years into production they started receiving complaints about no overdrive and no fourth gear. It was caused by worn splines on the fourth gear shaft.  The shaft not only controls fourth gear but overdrive as well. They ended up fixing the issue by producing the later transmissions with strengthened fourth gear shafts. Replacing the shaft will usually do the trick. The shaft is available for purchase individually but it will require installment by a transmission’s specialist or a full service shop.

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