Vibration/resonance on low rpm upshifts 91 C4
12-01-2013, 10:16 AM
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Track Day
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Vibration/resonance on low rpm upshifts 91 C4
When I'm upshifting my newly acquired 91 C4 I'm getting a vibration/resonance up to around 2000rpm-2100rpm and then it goes away. It sounds like it's coming from behind the passenger seat. Not to say that's actually the case. Sometimes there is no resonance. No resonance on downshifts. The engine was recently removed for service. I should add that it is 30 degrees F but it happens when the car oil temp is up to temp. Any ideas?
12-01-2013, 11:49 AM
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IHI KING!
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What is the condition of your engine mounts? Also, have you checked the exhaust for any loose panels or if its rubbing against anything?
Edit: What type of engine mounts do you have? Are they the originals, RS, Wevo, etc?
Edit: What type of engine mounts do you have? Are they the originals, RS, Wevo, etc?
Last edited by Rocket Rob; 12-02-2013 at 05:03 PM.
12-01-2013, 04:48 PM
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I have not checked either. I'm a newbie so forgive my 964 technical insolence. How would I check the condition of the motor mounts and what would I be looking for rubbing? The tranny and/or the motor? Thanks for the help I really appreciate it.
12-01-2013, 05:11 PM
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IHI KING!
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New to 964 maintenance? No worries. We all have been there.
How to check your engine mounts? See this thread
What to check for vibration? Check your exhaust heat shields at the cat. They can get loose and vibrate.
What can rub? Check the exhaust tail pipe is adjusted so that it doesn't touch anything. The tip has a ball joint with a clamp and if it touches the bumper, you may hear noise.
How to check your engine mounts? See this thread
What to check for vibration? Check your exhaust heat shields at the cat. They can get loose and vibrate.
What can rub? Check the exhaust tail pipe is adjusted so that it doesn't touch anything. The tip has a ball joint with a clamp and if it touches the bumper, you may hear noise.
12-01-2013, 05:47 PM
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12-02-2013, 10:49 AM
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I think what you're describing is normal and is exactly what the DMF was designed to address. Try shifting at 4k rpm instead, then move to 7k once the engine is warm 
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12-02-2013, 12:27 PM
#8
Interesting as I'm chasing an issue with what I would describe as an unusual metal rattly type noise. Hard to describe but like a load of ballbearing being turned in a metal drum which is when (anything more than gentle) accelerating around 1700-2500RPM in all the gears bar 1st (engine noise disguises it?).
Seems to emanate from behind me and if I had to guess it would be rear centre tunnel. There is no noise in neutral through the revs, all tinware looks solid so definitely mechanical which I'm thinking driveshaft, clutch?
Any ideas
Seems to emanate from behind me and if I had to guess it would be rear centre tunnel. There is no noise in neutral through the revs, all tinware looks solid so definitely mechanical which I'm thinking driveshaft, clutch?
Any ideas
12-02-2013, 03:41 PM
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12-02-2013, 03:47 PM
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Tom - Cheers. That's what a lot say about C4. It is a weird sound almost agricultural and if I had to guess the location I'd say in the area of gearbox.
