Odd Vibration with most likely transmission-S4 any ideas?
08-14-2019, 07:02 PM
#46
Rennlist Member
Hi Dr Bob,
Not to hijack this thread, but for the rest of us with stock engines and original crank dampers, like my US ‘83 for instance with a much lower horsepower rating, is the damper something you would recommend be prophylactically replaced at this point in the absence of any other symptoms short of a teardown to examine bearings?
Cheers
Rick
Not to hijack this thread, but for the rest of us with stock engines and original crank dampers, like my US ‘83 for instance with a much lower horsepower rating, is the damper something you would recommend be prophylactically replaced at this point in the absence of any other symptoms short of a teardown to examine bearings?
Cheers
Rick
Yes, the HP doesn't matter..the rubber is likely separating already, or may have nearly completely.
08-19-2019, 06:23 PM
#47
Rennlist Member
Thread Starter
Good information. all things we have all discussed but I never gave it much thought, due to things always being as smooth as silk. yes, that damper is original and that might be the issue. it sill has a tight fit but the rubber component has to be in question due to age.. i wouldn't think it's part of the "load" or "HP" values, due to the acceleration rates changing in every gear and that should vary the effects of vibration due to harmonics. I would think this would be a problem, if I noticed the issue at ONLY WOT, and a particular gear, but I don't. its any moderate throttle under load... in other words, 5000 to 6000rpm under moderate load, say 200hp to 350hp.. if the TT was going bad (bearings) would I be able to feel the vibration or roughness in spinning the shaft in neutral? it felt smooth and ive heard bad TT shafts before. really noise in sound and in feel. what about the TT shaft getting more runout? I guess I could have measured this, but it sure didn't look like it as I attached the coupler in a few different angles and it slipped on in the same tight way with mutlple angle attemps. I also thought I would see a clutch disc torn up, as that was , in my mind, the most likely cause.. but they looked pretty good. full thickness. im thinking its the torque tube bearings at this point if I was to guess. changing the front damper is certainly not a bad idea and could be the issue too. any way of checking that?? is it just the hardening of the rubber that makes it fail?
08-19-2019, 06:28 PM
#48
Rennlist Member
The driveshaft in the TT, will not vibrate (the same or at all) without load. Load is adding torsional stress to it, so it -wants- to deform/bend a little bit, and if the bearings/damper are not in the right place/shrunken/etc the shaft will ring/vibrate.
Im chasing the same thing, and if I have a hard braking or accel event, it will slide things in there and for a day or to until the next "event" the on-power highway hammering/vibration will 90% go away with things in "a better place" in the TT.
Im chasing the same thing, and if I have a hard braking or accel event, it will slide things in there and for a day or to until the next "event" the on-power highway hammering/vibration will 90% go away with things in "a better place" in the TT.
08-19-2019, 08:38 PM
#49
Rennlist Member
Thread Starter
The driveshaft in the TT, will not vibrate (the same or at all) without load. Load is adding torsional stress to it, so it -wants- to deform/bend a little bit, and if the bearings/damper are not in the right place/shrunken/etc the shaft will ring/vibrate.
Im chasing the same thing, and if I have a hard braking or accel event, it will slide things in there and for a day or to until the next "event" the on-power highway hammering/vibration will 90% go away with things in "a better place" in the TT.
Im chasing the same thing, and if I have a hard braking or accel event, it will slide things in there and for a day or to until the next "event" the on-power highway hammering/vibration will 90% go away with things in "a better place" in the TT.
08-20-2019, 09:08 AM
#50
Hi Mark,
Would like to make a suggestion to just pull out the TT and have it rebuilt.
It has more than likely exceeded it's useful life, especially with your racing efforts you have put it through.
This way you can check the run out of the drive shaft and look for any other possible causes of your vibrations.
You will also get a fresh TT with which to continue your racing.
Cheers,
Constantine
Would like to make a suggestion to just pull out the TT and have it rebuilt.
It has more than likely exceeded it's useful life, especially with your racing efforts you have put it through.
This way you can check the run out of the drive shaft and look for any other possible causes of your vibrations.
You will also get a fresh TT with which to continue your racing.
Cheers,
Constantine
08-20-2019, 02:35 PM
#51
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
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^^^^ What he said ^^^^
The carriers for the bearings and the spacers between bearing and driveshaft are critical to keeping the driveshaft straight in the tube. Twisting the shaft (related to torque applied) tries to bend it too. If/when the shaft does bend even slightly, it will whip and be noisy at particular speeds. In a perfect world there's well-dampened bearing and support at the right place to manage that bending. Good reasons to look hard at Constantine's super bearings. New better rubber carriers for the bearings, plus new sleeves for the driveshaft.
Remember that the driveshaft itself can easily be considered a wear part, especially if it's subjected to extreme twisting and bending as yours is. A driveshaft vibration occurs when the supports can't keep the shaft coaxial to the tube. By the time you feel the vibrations it means the shaft itself has been distorting even more than original. That accelerates fatigue damage. Your typical "run it until it breaks" philosophy might be OK here. Just plan to replace the torque tube bearings, the pilot and throwout bearings, and the front bearings in the gearbox. The transmitted vibrations will eventually snap the input shaft on the transmission too. Good thing those transmission parts are plentiful and cheap!
The carriers for the bearings and the spacers between bearing and driveshaft are critical to keeping the driveshaft straight in the tube. Twisting the shaft (related to torque applied) tries to bend it too. If/when the shaft does bend even slightly, it will whip and be noisy at particular speeds. In a perfect world there's well-dampened bearing and support at the right place to manage that bending. Good reasons to look hard at Constantine's super bearings. New better rubber carriers for the bearings, plus new sleeves for the driveshaft.
Remember that the driveshaft itself can easily be considered a wear part, especially if it's subjected to extreme twisting and bending as yours is. A driveshaft vibration occurs when the supports can't keep the shaft coaxial to the tube. By the time you feel the vibrations it means the shaft itself has been distorting even more than original. That accelerates fatigue damage. Your typical "run it until it breaks" philosophy might be OK here. Just plan to replace the torque tube bearings, the pilot and throwout bearings, and the front bearings in the gearbox. The transmitted vibrations will eventually snap the input shaft on the transmission too. Good thing those transmission parts are plentiful and cheap!
08-20-2019, 02:52 PM
#52
Rennlist Member
^^^^ What he said ^^^^
The carriers for the bearings and the spacers between bearing and driveshaft are critical to keeping the driveshaft straight in the tube. Twisting the shaft (related to torque applied) tries to bend it too. If/when the shaft does bend even slightly, it will whip and be noisy at particular speeds. In a perfect world there's well-dampened bearing and support at the right place to manage that bending. Good reasons to look hard at Constantine's super bearings. New better rubber carriers for the bearings, plus new sleeves for the driveshaft.
Remember that the driveshaft itself can easily be considered a wear part, especially if it's subjected to extreme twisting and bending as yours is. A driveshaft vibration occurs when the supports can't keep the shaft coaxial to the tube. By the time you feel the vibrations it means the shaft itself has been distorting even more than original. That accelerates fatigue damage. Your typical "run it until it breaks" philosophy might be OK here. Just plan to replace the torque tube bearings, the pilot and throwout bearings, and the front bearings in the gearbox. The transmitted vibrations will eventually snap the input shaft on the transmission too. Good thing those transmission parts are plentiful and cheap!
The carriers for the bearings and the spacers between bearing and driveshaft are critical to keeping the driveshaft straight in the tube. Twisting the shaft (related to torque applied) tries to bend it too. If/when the shaft does bend even slightly, it will whip and be noisy at particular speeds. In a perfect world there's well-dampened bearing and support at the right place to manage that bending. Good reasons to look hard at Constantine's super bearings. New better rubber carriers for the bearings, plus new sleeves for the driveshaft.
Remember that the driveshaft itself can easily be considered a wear part, especially if it's subjected to extreme twisting and bending as yours is. A driveshaft vibration occurs when the supports can't keep the shaft coaxial to the tube. By the time you feel the vibrations it means the shaft itself has been distorting even more than original. That accelerates fatigue damage. Your typical "run it until it breaks" philosophy might be OK here. Just plan to replace the torque tube bearings, the pilot and throwout bearings, and the front bearings in the gearbox. The transmitted vibrations will eventually snap the input shaft on the transmission too. Good thing those transmission parts are plentiful and cheap!
Dropping the trans will suck. (S4 auto).
08-30-2019, 02:38 AM
#53
Rennlist Member
Thread Starter
good advice!! Well, what ever I did , made the vibration get slightly better and more intermittent, so I will probably change the TT after this season 2 more races. It makes sense that it is the culprit. pilot bearing was nice. TOB I recently changed a few years ago and it looked and felt good.. The TT being a little twisted or out of round seems like a logical assessment.
car is still running SO awesome too. Power same as when I first dynode it, over 10 years ago!! and over 120 racing hours.
thanks for the inputs...….. ill see how it works this weekend and then maybe even change it before the last race
regards,
MK
car is still running SO awesome too. Power same as when I first dynode it, over 10 years ago!! and over 120 racing hours.
thanks for the inputs...….. ill see how it works this weekend and then maybe even change it before the last race
regards,
MK