Low throttle/speed rumble.
10-22-2018, 10:29 PM
#1
Rennlist Member
Thread Starter
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?
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?
10-22-2018, 10:49 PM
#4
Rennlist
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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?
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?
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
10-22-2018, 10:59 PM
#5
Nordschleife Master
10-23-2018, 05:10 AM
#7
Rennlist Member
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.
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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10-23-2018, 09:42 AM
#8
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.
10-23-2018, 10:15 AM
#9
Rennlist Member
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.
10-25-2018, 12:05 AM
#12
Archive Gatekeeper
Rennlist Member
Rennlist Member
They all do that. At least all the 6 or 7 I've driven do it. Ok, so maybe not all.