2000 buick lesabre occasional transmission thud

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I have a 2000 Lesabre with 133K miles. Had transmission serviced last week. No apparent problems detected by technician but I am getting an occasional thud sensation from transmission. Can happen accelerating from stop sign as well as on highway. No loss of power just know something's not right. Ideas? Thanks.

[Ralph50]

I had a thud feel. I looked under the hood gave the engine a quick press on accel lever and would see the engine go up and back down and I felt the thud go through the body. I replaced the motor mount that is behind the radiator and solved the issue. When I got the mount in my hands it was apparent how bad the mount was.

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thanks for the suggestion. was told a few months ago that the motor mount would need to be replaced soon. was it an expensive job? also, problem could be related to control arm assembly which is due to be replaced this weekend.

[maxwedge]

Ok, so you already knew there were issues, both can cause your symptoms.

[1955Joe]

My son described his 97 LeSabre, 130,000 miles, symptoms to me similar to yours. He had a slight thud after the initial acceleration and a slight thud when he let up off the gas. He did not tell me until after it was fixed the whole car would vibrate and that it scared him.

So we took the car in to have the transmission mount and 2 engine mounts replaced. The real problem was a front subframe bolt was no good and the vibration was that the body was coming off the frame.

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thanks for the advice. had the transmission/motor mount replaced. the one behind the radiator. also had the control arm assembly replaced on both sides. Still have a thud occur once or twice along ten mile commute...when driving car up incline. No change in RPMs when thud occurs.