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iTrader: (2)

I have a 98 GS300, 156K miles. Well maintained and all service is current. Every once in a while, not often at all, when I am traveling at a steady speed around 40-55mph, if I do a quick but slight acceleration and then release the pedal I hear and feel this drop or thunk coming from the rear. The acceleration is not even enough to downshift. Has anyone heard of or experienced this?

99Aristo

iTrader: (19)

I have been experiencing something similar to this also....thought it was a transmission mount at first but that wasn't it. Checked the rubber mounts at the rear diff and they all seemed good also. Anyway, take a look at those first and go from there. Best of luck to ya.

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iTrader: (2)

Thanks for that glad to know Im not the only one experiencing this strange issue. My mechanic is a master lexus tech and he also said it could be the rear diff rubber mounts. But you say yours are ok and still experience this. I wonder what this could be?

BCP43002

Does it happen when you drive in reverse and then drive forward?

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iTrader: (2)

No only when driving forward

BCP43002

Can we eliminate anything in the trunk moving around and spare tire firmly in place?

ThomasGS4

iTrader: (19)

There's no way it's the spare tire moving about. Keep in mind that we're talking about a stock '98 GS3 slightly accelerating.


It's most likely a differential issue like others have mentioned previously.

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iTrader: (2)

Not the spare and trunk is empty. Not sure if this means anything but I have noticed it also when driving in the rain. Im in southern california and it doesnt rain much but I do remember it more often in rain on the freeway.

I will have to look into the diff issue others mention..

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iTrader: (2)

In some of the other threads this issue was reported as possibly being caused by the motor mounts. I talked to my mechanic and I guess he told me a few months ago that my mounts need to be replaced. So I will have them changed and report back

YviE

iTrader: (3)

If it's the engines mounts, I think you would also be hearing the noise when accelerating from a stop, or when reversing.

Gunbelt

Did you figure out what the problem was? I have a GS430 and the same problem you have described has just started to come back after going away for months. I am going to get an Optima battery tomorrow and see if that is the culprit. I have heard a bad battery can cause problems.

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iTrader: (2)

Yes I believe it was the motor mounts. I replaced all three and the problem has not returned. Examining the old mounts they where pretty jacked up too.