Thump Coming From The Underneath

[lexus082]

Seems to happen frequently when I am leaving work. Usually I will be going 40mph and then the light ahead will turn red and I apply the brake to slow down (with still a good distance before the light). As I am approaching the light with my foot lightly on the brake (for a few seconds) all of a sudden there's a loud single thump coming from the rear underside. It only does it once and it occurs when I am moving under 20mph if that helps and slowing down. Doesn't happen all the time.

Also, I can kind of re-create the "thump" (just not as loud) on purpose while at a steady speed of 40mph. I noticed that while coasting with my foot off the gas at 40 mph and then slighty tapping the gas only for a split second and then off again very quickly and repeated it there was a repeated thump coming from the same place rear underside each time I repeatedly tapped the gas pedal and then released just as quickly.

Does this sound like a mechanical problem or just a worn bushing? Anyone else have these symptoms/problems ever?

[jzz30]

diff mount/bushings?

[lexus082]

diff mount/bushings?

I called the lexus dealer and they said they had never changed out the rear diff. mount bushings before on any sc's and also never before had a request of having that done. They said it would be 10-12 hours of labor to change out the bushings.

After calling 4 lexus dealers I then explained my scenerio to another dealer and he said it could be the rear lower control arms. But he did mention something that I for some reason did not think about This "clunk" only happens when I am braking which also is when the weight of the car is shifting towards the front. I didn't notice anything worn out that would allow such play. It just feels like its in the drive train but maybe I just think that b/c I am used to driving and working on a fwd car.

[jzz30]

maybe it could be the rubber coupling for the driveshaft?

[lexus082]

maybe it could be the rubber coupling for the driveshaft?

Thanks for the help. I think replacing the transmission mount did wonders... :) When I tried to re-create the thumping noise all I heard was a slight increase of sound from the exhaust. I will have to keep driving to confirm that it completely eliminated that problem of the "rear end thump".

[lexus082]

maybe it could be the rubber coupling for the driveshaft?

Thanks for the help. I think replacing the transmission mount did wonders... :) When I tried to re-create the thumping noise all I heard was a slight increase of sound from the exhaust. I will have to keep driving to confirm that it completely eliminated that problem of the "rear end thump".

I can now confirm that it elimated my problem after driving it for two days.

[jzz30]

good to hear!

[rtd111]

....

I can now confirm that it elimated my problem after driving it for two days.

Can you tell us where you got the part, cost and how easy? Can you provide instructions?

[lexus082]

....

I can now confirm that it elimated my problem after driving it for two days.

Can you tell us where you got the part, cost and how easy? Can you provide instructions?

Got the part from dealer for 76.00 and its very easy to change the tranny mount on the LS400 and Sc400. There should be a write-up in the LS400 on how to replace the tranny mount.