99 bonneville wont go into 4th
So my moms 99 bonneville SE wont go into 4th. My dad tells me that it was having troubles recently going from third to 4th/over drive and then it just stopped going into 4th. From what he tells me he says it sounds like the car wants to go into 4th but it cant. I'm sortof the family mechanic and am going to end up fixing this whether it be installing a new tranny or rebuilding the current one. I have read the trouble shoot guide and will be looking into those issues when i get the chance but i also read about some issue with the 4th gear output shaft there it wasnt hardened from the factory so they go out I guess. I guess I'm wandering two things: first, what tends to be the most common reason for this; second, are there any places out there where i can download a service manual or some good tranny rebuild info. I should also mention the fluid level is fine and the fluid has been flushed and filter changed within the last 40k and the vehicle has around 180k on it.