Thread: Broken differential casing in the transmission?

I hope I have the right forum, and sorry for my long winded story, I'll try to keep it short

I have a 2002 Grand Prix SE that has 65k miles on it. Yes, you read that right, only 65k. Two years ago on Christmas Eve, my husband was at work and the car was parked outside when some kid in a giant truck decided to do backwards donuts in the parking lot. Why? Who knows, apparently that's what kids do these days. Anyway, he ended up backing into the Grand Prix and his trailer hitch hit the drivers side front tire at the top, causing a TON of damage. Luckily his insurance paid for all of our repairs, but it was in the shop for 27 days and we ended up needing a new shock, strut, control arm, and some cosmetic things like a rim and headlight. I think there may have been more internal repairs, but I honestly can't remember.

Anyway, fast forward to a few weeks ago, I noticed my car started making this humming noise that changes pitch depending on how fast I'm travelling. It doesn't change pitch when my RPM's change, so I didn't think it was related to the motor, I was thinking bad wheel bearing or something. I took it to the mechanic and he replaced the hub assembly, but it was still making the noise. So he started digging deeper and now he says that I need a new transmission. He told me he noticed that the shock and strut on that side were newer so when I told him that it had been hit a few years ago, he said he almost guarantees that's what caused the damage to the transmission.

What he said is basically that the differential casing inside the transmission is broken and there is a wheel bearing in it that has started to work it's way out, and the only way to fix it is to rebuild the transmission or buy a new one. He said more than likely when the kid hit my car, it shoved the transaxle into the transmission, which broke the differential casing.

I called the insurance company and they said it sounds like the transmission trouble is related to the original accident and they actually reopened out claim. We have to take it back to the shop who repaired it from the wreck and have them determine if it was caused by the accident. Well I called that shop and told them I would be bringing it in, but of course he said "Well I mean it's been two years, I don't know if I can say that's what caused it." So I'm afraid it's going to be a fight.

Basically before I take my car down to them, I wanted to see if anyone could explain this differential casing to me in a little more detail and get some opinions on whether getting hit like that could cause the damage? Yes I am a woman, but no I am not stupid so when I go to the shop I want to make sure they don't try to screw me over. I want to know what I'm talking about and I'm not having much luck finding information online.

Glad I could at least make you chuckle! He really was a 16 year old kid, and without going into all the drama, it took the police and his mother to get involved before he would even call State Farm to tell them that yes, he hit our stationary car.

Anyway, that's exactly why I wanted to ask before I take it to the shop. I had no idea where the differential casing is or what it actually does. He did say he checked my tranny fluid and there were no metal shavings in it, which I assume is good. Is there anything else that can cause a casing to break like that other than being struck? I mean even our mechanic said he couldn't believe there was anything wrong with the tranny with such low miles on the car. And I will say he can replace transmissions, but he's not a transmission specialist. He actually called a friend of his that owns a tranny shop and told him what he found to make sure he was right.

But yes, the damage was all to the drivers side. After he hit it, the tire was sitting at an angle, tilted in toward the engine at the top and wasn't driveable. I wish I had taken a picture.

I took the car in about a month ago because when it started making that humming noise, I thought it was a rotor because I did need my brakes replaced. That trip I got all new pads and two front rotors and a new wheel bearing on one of the back tires, but the noise didn't stop. You can't hear it when I'm a low speeds but once I hit about 30 miles an hour you can hear this constant mid-pitch humming noise. The faster I go the louder and higher pitch it gets. About 50 mph you can really hear it, even over the radio. So if it's weird that the casing is on the other side, any ideas what else could be making that noise? I'm not ruling out that the mechanic might be wrong and nothing is going on with the transmission!

Thanks for the info! And while I will say that I'm not an "aggressive" driver, buuuut I don't always obey the speed limit lol I try to take care of my car because I do love it and want to keep it in good shape as long as possible, so I try not to go too crazy.

The mechanic also showed me under my car, he grabbed the transaxle and was moving it around, like wiggling it, and he said "That's not supposed to do that." Is that true? And if it is true, would a broken differential and casing cause it or could it be something else?