Differential v/s Transaxle

[shadow83]

My son has a 1998 Grand Prix with a 3.8L. He called from college a few weeks ago and said that it was having trouble shifting. He said that when he got on the highway it would not upshift into the highest gear unless he let off of the accelerator. I thought that maybe it was a sensor or solenoid. He took it to his garage and the code said a shift drum was bad but that they would need to pull it to see if that was really the problem. It was only $160 to pull the tranny so he dropped it off. Today they called him and said that the differential was bad and needed replaced, that it was VERY difficult to get the axle out. They got the axle out but only after a lot of prying.

My problem is I can not see how a bad differential caused a shift problem. I am not real familiar with FWD cars but have a lot of experiance on RWD and the differential is just gears and has nothing to do with the tranny. I'm afraid that they cracked the housing trying to get the axle out and are just saying that it is bad as not to pay for it. Anyone's thoughts would be greatly appreciated.

In any event, it looks like a used transaxle can be purchased for around $600 and that would fix his problem.

[Sabrewings]

The differential would not cause the shift problem. They probably damaged it during the removal.

[Trannyman95]

The axle being hard to pry out should have nothing to do with the diff being bad. Some axles have snap rings that fit a little more tight than others and the axles can really be a bear to get out. IF the differential was bad I would ask to look at it and visually inspect the gears with your own eyes. If the gears dont have visable pits and chunks of the teeth missing then I would raise the BS flag that the diff is to blame for the shifting problems. If the gears look torn up and lots of metal missing than all of that debris will go into the trans filter or not and will eventually work its way up into the valve body and cause problems. $160 sounds dirt cheap to pull a trans and inspect it! Most shops want minimum $500-$800 to go that far or at least $500 to remove and install one of these transmissions. There is a thread on here where member SyntheticShield posted pics of his failed differential and you will clearly see the damage. If the diff was bad you would hear noise unquestionable as the differential is also called the Final Drive assembly and connects the power from the trans to the drive axles and will emit a lot of noise that is directly related to road speed.

[SyntheticShield]

Here is the thread:
http://www.grandprixforums.net/f21/c...nage-1638.html

[shadow83]

He called today and they are going to rebuild the tranny $2000!! He told me that they said a lot more yesterday than the differential was bad, there were many items that may have been bad (including the torque convertor) and that a rebuild was the best route to go. Personally I believe that they are just fixing everything that they can to make sure that they hit the real problem. I advised him and asked the questions that I would have and he likes the car and wants to keep it (even though the book value is only $4000). This is his decision and his first lesson in life with expenses. I just hope that the garage isn't ripping him off and does the rebuild right, but they have been fair in the past.

Thanks for the advice all. I just wish that he was at home here, I have a garage that I have been using for over 15 years for major things and I would trust them 100%.