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Low throttle/speed rumble.

 
Old 10-22-2018, 10:29 PM
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Speedtoys
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Default Low throttle/speed rumble.

87 S4
The car has always, across now two transmissions, the current one being GB rebuilt entirely, and now the entire combustion system is all brand new, and all cyl compression numbers are known good too.

Leaving a light with liiiight throttle, theres a Rrrrrrrrrrrrrrr rumble/vibration in the car. Or if you apply light throttle in 1400-1800 rpm, you can feel the same thing.

Not convinced it goes away past 1800, but other things mask it, and if you leave a stop with more than really light throttle, it appears to go away too.

Ideas?

Both half shafts are also replaced.

TT is only 25k old from Porsche.

How does a bad torque converter feel?
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Old 10-22-2018, 10:32 PM
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motor mounts good?
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Old 10-22-2018, 10:36 PM
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37k miles old, 2006, Porsche.

Ive felt bad ones, this isnt it..plus you drove it a fair amount last week too.
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Old 10-22-2018, 10:49 PM
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Originally Posted by Speedtoys View Post
87 S4
The car has always, across now two transmissions, the current one being GB rebuilt entirely, and now the entire combustion system is all brand new, and all cyl compression numbers are known good too.

Leaving a light with liiiight throttle, theres a Rrrrrrrrrrrrrrr rumble/vibration in the car. Or if you apply light throttle in 1400-1800 rpm, you can feel the same thing.

Not convinced it goes away past 1800, but other things mask it, and if you leave a stop with more than really light throttle, it appears to go away too.

Ideas?

Both half shafts are also replaced.

TT is only 25k old from Porsche.

How does a bad torque converter feel?
I've "chased" this vibration for years....on many different 928's. From what I can tell, all 5.0 928s have an inherent vibration at 1400-1800 rpms. It's very subtle, but always there.
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Old 10-22-2018, 10:59 PM
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Originally Posted by GregBBRD View Post
I've "chased" this vibration for years....on many different 928's. From what I can tell, all 5.0 928s have an inherent vibration at 1400-1800 rpms. It's very subtle, but always there.
All three of my manual S4's have a low-speed/load rumbling vibration at around 1500-1700rpm - which I put down to harmonics. I just drive around it - i.e. don't use 5th gear below 50mph etc. I've not driven an auto to know whether they have the same issue (only drove auto's years ago when shopping for 1st 928 and I wasn't educated on 928's back then)
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Old 10-22-2018, 11:00 PM
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Originally Posted by GregBBRD View Post
I've "chased" this vibration for years....on many different 928's. From what I can tell, all 5.0 928s have an inherent vibration at 1400-1800 rpms. It's very subtle, but always there.

Ok..cool, I guess im at that point..solve enough issues, and things like this become noticeable.
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Old 10-23-2018, 05:10 AM
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Jeff,

Another way of looking at the issue is "why did they fit hydraulic mounts". My guess is that they found a vibration they wanted to suppress- maybe the one you are experiencing? Some folks are more sensitive to such than others. The classic sign of engine mount failure is vibration at 1400 and 2800 rpms- note the order of magnitude. When I had problems with my flexplate clamp slipping 20 years ago it was a dead give away with vibration at 3050 rpms. I dare say that not all examples behave identically- rather some variation thereof and some will be more pronounced than others.

Bottom line- the thing was never intended to be driven at 1500 rpms.
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Old 10-23-2018, 09:42 AM
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Originally Posted by GregBBRD View Post
I've "chased" this vibration for years....on many different 928's. From what I can tell, all 5.0 928s have an inherent vibration at 1400-1800 rpms. It's very subtle, but always there.

Same, and it's annoying as hell. A '90 GT I've been chasing down for years is by far the worst one and a '90 S4 that is more recent. Literally everything that can be done has been done on both. My '88 has had a slight vibration its entire time I've had it and the best reduction was due to the GB Dampener.
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Old 10-23-2018, 10:15 AM
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You can add my 86.5 manual to this club. Comforting to know others have chased it to no avail because my approach has been to keep the revs high and wait for the day it changes and worry about it then. Transaxle/Torque tube combination presents many opportunities for vibrations in my view. I wonder if the "rope drive" in the 1961 Pontiac Tempest (Popular Science September 1960) which had a curved torque tube to kill vibrations, would have worked here.
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Old 10-23-2018, 11:52 PM
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Finally! A vibration I don't have (or maybe just don't notice)!
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Old 10-24-2018, 11:50 PM
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My '88SE does it. My '90GT doesn't ?????????????
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Old 10-25-2018, 12:05 AM
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They all do that. At least all the 6 or 7 I've driven do it. Ok, so maybe not all.
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