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Old 03-14-2004, 07:53 PM   #1
mikew968
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Default rear thumping noise

I am getting a thumping from the rear of the car upon heavy acceleration in a straight line or in a hard right turn. I have looked things over pretty well and am having no luck. Any thoughts

Mike
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Old 03-14-2004, 08:53 PM   #2
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Could be CV's, but in my 944 this turned out to be rear wheel bearings at 160k miles. Would show up when that side was loaded, even slightly, and dissappear when it was unloaded. For example, heading down an open freeway, slight turn right gave whooshing/thumping noise... Straight or slight turn left made it go away.

Hope this helps.
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Old 03-14-2004, 09:47 PM   #3
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Dave:

That is the one item that is hard to check. I am not having any problems in normal driving. It is when I really get on it that I have a problem. It is definately a thumping noise like the TA is bouncing up and down. My mechanic removed the TA mount and it is good and solid.

Thanks for the reply, Mike
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Old 03-14-2004, 10:12 PM   #4
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How many miles on your car? Are your shocks decent? One more thing to check would be the engine mounts. It could be that under high torque, the twist of the motor is pulling on a bad motor mount.
Start the car and open your hood. Give it throttle via the throttle linkage by hand and see how much your engine moves and if you hear the same sound.
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Old 03-15-2004, 02:07 PM   #5
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Mike,
my car was doing the same thing, under hard acceleration you get a thumping right under your butt, it turned out to be the resonator (middle muffler) hitting the torque tube tunnel, i put up with it for a very long time then took it to an exhaust shop where it was straightend to give more clearence, i think youll find that yours will be the same.

Scott
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Old 03-15-2004, 10:51 PM   #6
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968turbo
The shocks are new and I jsut removed and checked. I did just what you recommended on the engine and see very little movement.

Scott:
How did you figure the cause?
This thumping is only under very heavy acceleration and if you back off a little it goes away. It only happens when the driveline/suspenion is highly torqued and only straight away or right turns not on left turns.

Thanks, Mike
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Old 03-17-2004, 04:45 PM   #7
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Mike,
jack the car up slide under and give the resonator (middle muffler) a good push up if it hits the body you will find your problem, What is happening is that when you load up the engine it will move on the mounts slightly which in turn moves the exhaust closer to the body of the car. I'll bet that the exhaust is slightly bent (maybe from hitting speed humps).

Scott
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Old 03-17-2004, 05:14 PM   #8
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Sounds like CV joints are a good candidate to check out. I had mine replaced at 160K miles when I had my 944. This is quite a common repair at these miles. It's no big deal as rebuilt axles are available for a couple of hundred per side if you send in the cores. Alternatively you can replace just the CV joints yourself and many do. It's messy though. I found that the clicking would come and go over extended periods. Say a couple of weeks of no clicking followed by a few days of clicking. Mine was a daily driver.

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Old 03-21-2004, 01:31 PM   #9
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Scott:

My mechanic adjusted the entire exhaust and felt things were better. But, under hard acceleration there is a thump-thump-thump-thump noise. It is not a single thump but a series of thumps. The thumping feels liike it is coming through the seat. The shifter is "jumping" to the same "beat". We are going to take the exhaust off Monday night and see if anything changes.

Mike
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Old 03-23-2004, 11:09 PM   #10
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Scott you were spot on. The resonator was rotating enough were the engine torqued that it wqs very close to a brace under the torque tube. Then anytime there was some wheel hop under very hard acceleration it would band the brace. Very easy to see with the exhaust off.

By the way the car felt much more responsive with the rsonator and exhaust removed. Is this my imagination or could it be? Is there power to be gained from removing the cat?

Thanks for all the imput!!!


Mike
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Old 03-23-2004, 11:09 PM
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