Vibration after torque tube bearing job
03-28-2018, 11:59 AM
#17
Rennlist Member
Thread Starter
Join Date: Aug 2014
Location: Adirondack Mountains, New York
Posts: 2,420
Received 318 Likes
on
166 Posts
Can you elaborate? They look OK... the engine is sitting up high, no metal-to-metal short circuiting.
I'm not re-positioning the flex plate today - access is not as easy as I thought it might be, but I think the heat shields can be loosened and spread apart enough. Does the WSM call for maintaining the original registration, or was Dwayne just being cautious?
The vibration occurs in neutral, so we can rule out anything beyond the TC. While doing that test I sensed that the engine may be running a little rough. Didn't notice any lack of power out on the road yesterday. Reality or perception? Damn, vibration problems are nasty.
I'm not re-positioning the flex plate today - access is not as easy as I thought it might be, but I think the heat shields can be loosened and spread apart enough. Does the WSM call for maintaining the original registration, or was Dwayne just being cautious?
The vibration occurs in neutral, so we can rule out anything beyond the TC. While doing that test I sensed that the engine may be running a little rough. Didn't notice any lack of power out on the road yesterday. Reality or perception? Damn, vibration problems are nasty.
03-28-2018, 01:18 PM
#19
Former Sponsor
Got everything buttoned up this morning and got out on a test drive. All went well (and the noise that led me to do this difficult job has gone away.) It's really quite something that the car stills runs after being so severely messed with by someone like me.
But there is a vibration between 2050 and 2200 RPM. In all gears? I should have explored that question better, but I think so.
Dwayne did something I didn't - mark the position of the rear flex plate relative to the torque converter so it could be re-installed the same way - important if they are jointly balanced. So, I had only a 33% chance of getting it right. I believe it will be easy to move them to another position (50% chance of success) and one more if necessary.
I put in a Constantine rebuilt TT, and added his clamp, too. I didn't unbolt the front flex plate. The half-shafts were unbolted, of course. I suppose that the wheels are now in a different position could be the cause, too. Oh - I put in new rear brake rotors. Damn - vibration problems are nasty.
Thoughts?
But there is a vibration between 2050 and 2200 RPM. In all gears? I should have explored that question better, but I think so.
Dwayne did something I didn't - mark the position of the rear flex plate relative to the torque converter so it could be re-installed the same way - important if they are jointly balanced. So, I had only a 33% chance of getting it right. I believe it will be easy to move them to another position (50% chance of success) and one more if necessary.
I put in a Constantine rebuilt TT, and added his clamp, too. I didn't unbolt the front flex plate. The half-shafts were unbolted, of course. I suppose that the wheels are now in a different position could be the cause, too. Oh - I put in new rear brake rotors. Damn - vibration problems are nasty.
Thoughts?
I really like Costantine's products. Great stuff!
That being said, I do not agree with his arbitrary decision to remove the harmonic absortion weight from the torque tubes. Porsche spent a small fortune studying the dynamics of the torque tubes, calculating the mass and the position of this harmonic absorber. (And this mass changed with differemt models of the 928.) To think that one can simply remove this device, without any scientific testing of the results, has never seemed to be the correct approach, to me.
The 944 GTRs used the 928 torque tubes....without the additional harmonic absorber (to save weight). Cracked and completely broken torque tubes was the result....harmonics are very destructive. A review of the problem resulted in the addition of the proper harmonic absorber, for this application.
I'm not saying that your vibration is from a harmonic. However, your problem is exactly in the rpm range where the 1st harmonic "wave" occurs....and I wouldn't ignore the possibility.
03-28-2018, 02:21 PM
#20
Rennlist Member
Thread Starter
Join Date: Aug 2014
Location: Adirondack Mountains, New York
Posts: 2,420
Received 318 Likes
on
166 Posts
I really appreciate everyone weighing in on this subject.
There's a very good reason normal driveshafts are made of large diameter tubing - diameter provides stiffness, which drives vibration frequencies upwards. The idea is to get the first mode frequency up above all potential excitation frequencies. In jet engines, part of the strategy is to have different numbers of airfoils in neighboring stages. "Loose" attachments are also part of the strategy to provide frictional damping. I recall a development engine turbine blade failure caused by an unexpectedly large third-mode torsional vibration mode. Managing vibrations is a huge and somewhat uncertain task in designing rotating equipment.
Constantine's practice of adding a bearing while removing the dampener must work, usually; he's adding stiffness and dampening, both, perhaps exactly at the anti-nodes. Or maybe not quite - the stiffness of the couplers makes it difficult to figure out where they are. If they're tight, it's good for stiffness - but maybe not for damping. Difficult problem.
Between the engine, the engine mounts, the TT and shaft, etc. etc. we're dealing with a pretty complex system here. It seems there are certain excitatory frequencies in the operating range. Whether the vibrations they induce get damped adequately is very difficult to predict in real systems.
But good news: I went out again and my previous Level 4 vibration is down to a 2.5. I'm going to at least pretend that this dampening business is taking some time to settle in. OK, I should mention that I jammed two tongue depressors in the vertical gap along one of the transmission mounts - just an experiment to stiffen up that bit of the system. I should go see if they're still there. If they are, I'll order some OEM tongue depressors from Roger.
There's a very good reason normal driveshafts are made of large diameter tubing - diameter provides stiffness, which drives vibration frequencies upwards. The idea is to get the first mode frequency up above all potential excitation frequencies. In jet engines, part of the strategy is to have different numbers of airfoils in neighboring stages. "Loose" attachments are also part of the strategy to provide frictional damping. I recall a development engine turbine blade failure caused by an unexpectedly large third-mode torsional vibration mode. Managing vibrations is a huge and somewhat uncertain task in designing rotating equipment.
Constantine's practice of adding a bearing while removing the dampener must work, usually; he's adding stiffness and dampening, both, perhaps exactly at the anti-nodes. Or maybe not quite - the stiffness of the couplers makes it difficult to figure out where they are. If they're tight, it's good for stiffness - but maybe not for damping. Difficult problem.
Between the engine, the engine mounts, the TT and shaft, etc. etc. we're dealing with a pretty complex system here. It seems there are certain excitatory frequencies in the operating range. Whether the vibrations they induce get damped adequately is very difficult to predict in real systems.
But good news: I went out again and my previous Level 4 vibration is down to a 2.5. I'm going to at least pretend that this dampening business is taking some time to settle in. OK, I should mention that I jammed two tongue depressors in the vertical gap along one of the transmission mounts - just an experiment to stiffen up that bit of the system. I should go see if they're still there. If they are, I'll order some OEM tongue depressors from Roger.
03-28-2018, 04:20 PM
#21
Very doubtful that the rear flex plate and torque convertor are balanced together. That would be extremely difficult in a production situation, where the two pieces come from two separate sources and down two separate assembly processes.
I really like Costantine's products. Great stuff!
That being said, I do not agree with his arbitrary decision to remove the harmonic absortion weight from the torque tubes. Porsche spent a small fortune studying the dynamics of the torque tubes, calculating the mass and the position of this harmonic absorber. (And this mass changed with differemt models of the 928.) To think that one can simply remove this device, without any scientific testing of the results, has never seemed to be the correct approach, to me.
The 944 GTRs used the 928 torque tubes....without the additional harmonic absorber (to save weight). Cracked and completely broken torque tubes was the result....harmonics are very destructive. A review of the problem resulted in the addition of the proper harmonic absorber, for this application.
I'm not saying that your vibration is from a harmonic. However, your problem is exactly in the rpm range where the 1st harmonic "wave" occurs....and I wouldn't ignore the possibility.
I really like Costantine's products. Great stuff!
That being said, I do not agree with his arbitrary decision to remove the harmonic absortion weight from the torque tubes. Porsche spent a small fortune studying the dynamics of the torque tubes, calculating the mass and the position of this harmonic absorber. (And this mass changed with differemt models of the 928.) To think that one can simply remove this device, without any scientific testing of the results, has never seemed to be the correct approach, to me.
The 944 GTRs used the 928 torque tubes....without the additional harmonic absorber (to save weight). Cracked and completely broken torque tubes was the result....harmonics are very destructive. A review of the problem resulted in the addition of the proper harmonic absorber, for this application.
I'm not saying that your vibration is from a harmonic. However, your problem is exactly in the rpm range where the 1st harmonic "wave" occurs....and I wouldn't ignore the possibility.
So Greg, guessing you 've had a lot of customer complaints over the years about harmonic vibrations tearing apart their 928s after the installation of the Super Bearings? If you have, this is in direct conflict with what we have heard from our customers and you never raised them to us before.
Is this raised concern of yours about the harmonic balancer due to us not going along with your twisty, micro-cracking, drive shaft theory of TBF? Or is it because you are making new vibration dampeners?
The decision to address the harmonic balancer problems found in 928 TTs through re-designing our Super Bearings was carefully weighed against the research we had done into the TT drive lines and they work as designed.
The 944GTRs are a different animal when it comes to harmonics due to their 4 cylinder engines which have horrible harmonics that need to be mitigated. That's why Porsche borrowed and paid for counter rotating engine shaft technology from Mitsubishi for their 944 engines to help calm them down.
The 928SE variants also were not given a harmonic balancers from Porsche to decrease weight. No issues.
Whatever...
03-28-2018, 05:33 PM
#22
Addict
Rennlist Member
Rennlist Member
Join Date: Oct 2003
Location: Gone. On the Open Road
Posts: 16,496
Received 1,638 Likes
on
1,069 Posts
Gentlemen, let's keep this civil. Both of you have high regard for each other's products. I certainly have high regard for both of you and your products. I will suggest that design concerns can be discussed privately in a phone conversation.
On topic, I achieved a passing grade in Physics of Waves and Vibrations last century. I remember enough of that class to not be concerned about the replacement of a big weight in the middle of a spinning loaded shaft by a bearing. In our application the differences in system behavior will be in the margin.
On topic, I achieved a passing grade in Physics of Waves and Vibrations last century. I remember enough of that class to not be concerned about the replacement of a big weight in the middle of a spinning loaded shaft by a bearing. In our application the differences in system behavior will be in the margin.
03-28-2018, 06:46 PM
#23
I'm sweating bullets over this. My 84 had a rattling noise and a vibration over the entire rpm range. I have my TT at black sea now. Replacing the trans mounts and motor mounts. After all that work to have a existing problem remain scares the hell out of me.
03-28-2018, 06:58 PM
#24
Thanks Dave.
Problem is this, as our current President loves saying, is "fake news." Greg is just sticking it in for one of the two reasons above. If he really ever had a concern about what we were doing with the Super Bearing line, one would think he would have called me and discussed these concerns. Never ever happened after all these years, strange don't you think?
Vibrations in cars, especially aging 928s, are very hard to identify and I have spent my share of time trying to help 928 (and 944) owners with these issues. Sometimes I do help, other times it can't be diagnosed. And usually this was after I've talked them out of buying the Super Bearings to fix their vibration issue since they were at the end of their rope trying to fix it by other means.
No worries, products from Black Sea R&D will continue to be sold to those who want them and believe in them. However to those who expressed interest in buying this company, this is a sobering reality you must contend with since some seem to enjoy in it.
Problem is this, as our current President loves saying, is "fake news." Greg is just sticking it in for one of the two reasons above. If he really ever had a concern about what we were doing with the Super Bearing line, one would think he would have called me and discussed these concerns. Never ever happened after all these years, strange don't you think?
Vibrations in cars, especially aging 928s, are very hard to identify and I have spent my share of time trying to help 928 (and 944) owners with these issues. Sometimes I do help, other times it can't be diagnosed. And usually this was after I've talked them out of buying the Super Bearings to fix their vibration issue since they were at the end of their rope trying to fix it by other means.
No worries, products from Black Sea R&D will continue to be sold to those who want them and believe in them. However to those who expressed interest in buying this company, this is a sobering reality you must contend with since some seem to enjoy in it.
03-28-2018, 07:02 PM
#25
We'll send the tube back to you with all your original parts this week, no worries. We will pull it from our coaters and send it back to you free!
Then you can get a rebuilt unit from another vendor like 928 Intl.
And Greg's job is done...
Cheers,
Constantine
03-28-2018, 07:16 PM
#26
Hi Mike,
We'll send the tube back to you with all your original parts this week, no worries. We will pull it from our coaters and send it back to you free!
Then you can get a rebuilt unit from another vendor like 928 Intl.
And Greg's job is done...
Cheers,
Constantine
We'll send the tube back to you with all your original parts this week, no worries. We will pull it from our coaters and send it back to you free!
Then you can get a rebuilt unit from another vendor like 928 Intl.
And Greg's job is done...
Cheers,
Constantine
03-28-2018, 07:22 PM
#27
Team Owner
you will be very happy with Black Sea R&Ds workmanship and the parts they produce.
They also will install a new Cranberry colored Greg Brown driveshaft into the fresh TT and bearings
They also will install a new Cranberry colored Greg Brown driveshaft into the fresh TT and bearings
Last edited by Mrmerlin; 03-28-2018 at 07:57 PM.
03-28-2018, 07:48 PM
#28
I was commenting about the original PO's problems and happened to post just after Greg's post about the dampener. Constantine misunderstood my post thinking I was complaining he just called me and we got it straightened out. He's a straight up guy.
03-28-2018, 08:07 PM
#29
Thanks Stan and Mike!
Obviously took Mike's post out of context and work is continuing as scheduled.
Obviously took Mike's post out of context and work is continuing as scheduled.