Thread: Clunk or grinding sound when shift into reverse

First, the car drives great and shifting is very smooth. But,

When I had a cold start and shift into reverse, I can hear a grinding kind or clunk sound. It does this when the car is cold. When the car is warm, the grinding goes away but I still hear kind of a clunk. The clunk is much weaker though. I can only hear it inside the car. I try to listen the sound with the window open, I can hardly hear anything from outside. Also, when shift into reverse, I can feel a impact as if something in the front end hit the car and try to push it back. I can feel the same impact when shift into drive but the impact is much weaker. And there is no sound shifting into drive.

I looked at the engine when shifting. When shifting to reverse, the engine moves a little bit. When shift into drive, engine does not move at all. When I put the car in park and give gas, the engine does not move at all. The car idles very smooth, no shake or vibration when I give gas.

I am wondering if this is normal. I found people say that the reverse is not synchronized so it will be a little rough than shifting to drive. So I am just asking if this kind of thing is normal. Maybe I am just too paranoid.

Thanks very much for your help!

Thanks! I was suspecting the motor mount. But the car is so smooth when I drove it and the engine does not move that much when I shift into reverse. Engine does not move when shift into drive. So I am not leaning towards a bad mount. But I will get it checked out soon.

Also, the sound is like grinding when car is cold. I can also hear a slight grinding kind sound when shift out of reverse when the car is cold. When the car is warm, shifting out of reverse has no sound at all.

So besides the sound, is the kind of impact I feel normal? Thanks!!!!

Yes, I have checked the fluid level several times and it is correct. The transmission fluid and filter is changed by dropping the pan about 2k miles ago but the sound exist before changing the fluid. Transmission feels the same after changing fluid so I haven't doubt the fluid change.

The car is completely stock. No modification. All parts in the car are OEM, except wiper blade......

Just to clarify, the sound happens when I shift into reverse and no noise when I am moving either forward or backward. It is just sound when I shift. No sound when I am moving.

Thanks a lot for your help!

Thanks a lot! I should include the car model in the initial post. It is a 2005 Pontiac Grand Prix Base model with 90000 miles now. The car is completely stock without any modification.

You are absolutely right. When I drive, I can feel the car changing gear. Since the impact is normal, I will not worry about it. It makes sense when the transmission grab gear and try to push the car forward or backward.

The grinding kind of sound somehow makes me a little nervous. The magnitude of "impact" or "push feel" is pretty similar when the car is cold or warm. I cannot think of a reason how the grinding happens only when the fluid is cold. If fluid is cold and it is thicker, it should somehow provide more "cushion".

Maybe it has something to do with the fluid flow or fluid pressure inside transmission?

Thanks! Hmmm....It seems like I should get the transmission and engine mount checked out first. How much does it cost you to replace the engine mount and transmission mount? Since my current situation does not affect my driving, I might just live with it if it is expensive.

check drive shaft U joint cups

Replaced tranny mount today and the clunk when reversing went away. Bought mount from Rockauto for less than $30

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Just following up my original post. I went to a local shop and the mechanic checked it today. They said it is due to "weak engine and tranny mount". The way they check is that they rev up the engine with brake pressed while shifting to D and R. They told me it is normal tear and wear to the rubber in the mount. The mounts are a little weak but they are still OK. They just get normal wear over time. I asked them if I need to change them. They say I am good to go. They can change it if I want but he suggest me not to do it now.

Just replace them. Top mounts might be fine but not lower mounts

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now isnt that what i originally said it was

Haha, you are right! I should learn more about diagnosing car problems.

Originally Posted by iRideGTP

Just replace them. Top mounts might be fine but not lower mounts

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Thanks! I have two shops checking it and they both suggest no need to change now. Since I am a student and don't have much extra money, I guess I will just live with the initial clunk when it is cold. Since the car drives fine, I will just leave as it is now.

Thanks very much for your advice!

I was close with u jount cups