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Old 06-22-2013, 10:57 PM   #1
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Thunk from rear and swerve on hard acceleration

Hi, my first post here.
Like the title says, I have a loud thunk from my rear and the car swerves on hard acceleration. It's a '94 Z28. I feels like this; when it is punched hard, the rear end dips on the right side, there is a thunk or bang, and I must counter-steer to prevent me from going off the road. I checked all underneath and could find nothing obvious. I pried all the bushed joints, even pulled a couple off to make sure. I thought sure there must have been a bad bushing from the feel of the problem. Springs look and feel good. There are no witness marks anywhere. I checked all bolts and welds I could see or pry with a bar.
Does anybody have a clue as to what I'm missing? I thought from the way it feels that I would find something obvious. But no.
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Old 06-22-2013, 11:14 PM   #2
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Re: Thunk from rear and swerve on hard acceleration

Check your trans. mount and the torque arm mount at the trans. There are a couple of companies that make "Poly" replacement mounts for these.
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Old 06-23-2013, 01:21 AM   #3
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Re: Thunk from rear and swerve on hard acceleration

Thanks Z28SORR,
The track bar mounting looks fine and is stiff. I was going to check on the trans mount tomorrow. But I don't see how that could make the whole car shift around the way it does. Stranger things have happened before I suppose. It just "feels" like its related to rear end linkage somehow. But I'll check never the less. Thanks.
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Old 06-23-2013, 08:58 AM   #4
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Re: Thunk from rear and swerve on hard acceleration

I assume your bushing check included the bushings for the track bar (aka panhard bar)? Is it possible the right rear shock is bad, allowing the rear to dip excessively on sudden acceleration? As the right rear drops and the panhard rod rotates downward, it pushes the body of the car slightly to the right.

The sudden drop may also indicate a broken end link or worn bushings on the front or rear sway bar.

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Old 06-23-2013, 07:24 PM   #5
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Re: Thunk from rear and swerve on hard acceleration

Thanks Injuneer,
Yes, the traction bar and bushings look OK. I'm trying to remember which way I have to counter-steer. I seem to remember the rear dipping and shiftong to the left however, not the right. But my memory is failing me right now, and it is a real pain to get it off the stands to see. I will add however that it is a fairly violent thing. Not subtle at all.
Also, under normal driving, it handles just fine, with the exception of a constant pull to the right, which I put down to a front end alignment issue, and does not feel at all related to this. 'Course I could be wrong.

Last edited by BikerJim; 06-23-2013 at 07:31 PM.
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Old 06-25-2013, 11:22 AM   #6
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Re: Thunk from rear and swerve on hard acceleration

Do you have a stock panhard bar? Before I replaced mine, one day i got on it hard and the stock one flexed real bad and actually spun me out. Luckily I was on a back road with no one on it.

Just something else to check for.
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Old 06-25-2013, 09:40 PM   #7
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Re: Thunk from rear and swerve on hard acceleration

Is it possible he has a slipping/broken clutch cone in the rear axle? There is a procedure in the service manual describing a test of the limited slip axle operation using part of an axle remover tool and a torque wrench.
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Old 06-25-2013, 09:40 PM
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