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Old 09-10-2019, 08:42 PM
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Default Heavy knocking from rear when cornering hard

Last weekend I took the Trans Am to the road course for a performance driving school. One thing I noticed was that in a tight apex turns under hard throttle the rear would knock about pretty good - sounding like a floor jack was tumbling about in the trunk.

Any ideas on this? Car has Konis with composite springs and 5/8 sway bar.
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Old 09-10-2019, 08:48 PM
punkin punkin is offline
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Any chance one of the front spring mounts or even the pocket is broken?
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Old 09-10-2019, 08:50 PM
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no, they are fine
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Old 09-10-2019, 09:03 PM
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Does the car have over-axle pipes? Mine used to make a similar noise from time to time and discovered it was the pipes hitting the frame rails. Readjusted the pipes to give a bit more room between them and the frame rails.
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Old 09-10-2019, 09:19 PM
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yes, standard duals with transverse muffler.
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Old 09-11-2019, 09:09 AM
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Do you have poly control arm bushings? Years ago I had them and they made strange sounds when the car was put in demanding turns..

Funny, I'm about to go downstairs and remove my tail pipes and mufflers and install Walker #17197 mufflers without tail pipes because of all the weird noises they make.. These are big mufflers for trucks, I always liked the way those big 427 dump trucks sounded.
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Old 09-11-2019, 05:36 PM
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no, Firebirds have leafs in the back.

Issue found: axle housing must have jumped quite a bit as it hit both pipes, even the spring on the driver's side colored the exhaust pipe.

I will need to make a spacer for the upper bumper to limit travel a bit...




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Old 09-11-2019, 08:53 PM
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Interesting information. I have a similar problem and haven’t been able to find it. I swapped in both new leafs and did an 8.5 swap at the same time. Since then, when you goose the throttle from a stop I get a clunk somewhere behind me. This is especially prevalent if you are on an uphill incline. It will do it almost every time then.

I’ll check my exhaust at the frame rails too. I had been figuring it was the driveshaft hitting my x pipe. The exhaust was built to clearance with the old saggy springs. That said, I can’t find any actual evidence of this.
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Old 09-11-2019, 11:03 PM
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Had a feeling that was going to be the case.

If you look at most of the first gen f-bodies that run auto-x they pretty much all run dumps before the axle. There’s just not enough room back there for stock style pipes in any significant diameter.

You do also see a decent number of cars with the tail pipes ran under the axle instead of over it. I dislike that setup on a street car that can see rough pavement and potholes though.
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