Vibration at Speed
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Intermediate
Joined: Oct 2012
Posts: 34
Likes: 2
From: Boston, MA
Vibration at Speed
87 S4 -AT 45K miles.
Vibates under acceleration from about 70 to 80 MPH.
Feels like driveline rather than tires (which I've had balanced twice) because it abates somewhat when I back off on the throttle.
Could use some help!
Many thanks
Vibates under acceleration from about 70 to 80 MPH.
Feels like driveline rather than tires (which I've had balanced twice) because it abates somewhat when I back off on the throttle.
Could use some help!
Many thanks
Former Vendor
Joined: Feb 2004
Posts: 2,139
Likes: 2
Hi Tom,
As Jeff said, it might be your torque tube (TT) bearings.
This sounds like a classic problem when one or more bearings (usually the front one) have moved a bit for where they should be.
Suggest you get under the car, drop your lower bell housing and measure how far down the TT the front bearing is from the edge. If it is more than 15 inches toward the transmission, it has moved too much and the drive shaft is no longer supported correctly causing it to vibrate under load.
There have also been cases when the front bearing has walked out of the TT and is hanging on the drive shaft at the front. This will cause the same vibration problem.
HTH,
As Jeff said, it might be your torque tube (TT) bearings.
This sounds like a classic problem when one or more bearings (usually the front one) have moved a bit for where they should be.
Suggest you get under the car, drop your lower bell housing and measure how far down the TT the front bearing is from the edge. If it is more than 15 inches toward the transmission, it has moved too much and the drive shaft is no longer supported correctly causing it to vibrate under load.
There have also been cases when the front bearing has walked out of the TT and is hanging on the drive shaft at the front. This will cause the same vibration problem.
HTH,
Former Vendor
Joined: Feb 2004
Posts: 2,139
Likes: 2
Hi Tom,
Again, this might be your TT bearings, or it might not.
If the vibration is only between 70-80 MPH, it might also be a wheel balance problem, even if you had the balance checked.
Usually a bad TT vibration under load problem has a wider MPH range when vibrations occur.
Good luck with your search,
Again, this might be your TT bearings, or it might not.
If the vibration is only between 70-80 MPH, it might also be a wheel balance problem, even if you had the balance checked.
Usually a bad TT vibration under load problem has a wider MPH range when vibrations occur.
Good luck with your search,
Under the Lift
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From: Buckeye, AZ
Tom wrote to me and I told him my tale of woe with a seemingly identical ROAD SPEED related vibration felt through the body of the car (not steering wheel) that I still have not resolved. Because it is road speed related, not engine speed related, TT bearings don't seem likely to be the source of the problem. You should feel a TT or TC bearing related vibration just revving the motor in Park or Neutral over a wide RPM range, as Constantine added. I hope I'm wrong, but I can't see how.
It would seem it must be in the rear rotating mass, axles on out, but repeated balancing, new wheels and tires, swapping axles, and the vibration persists. Checked over all the suspension bolts and bushings. Checked wheel bearings as well. Nicole Mossinger has the same vibration, and despite having Greg Brown work on it at least briefly, the vibration persists in her case as well.
Mine actually started soon after I replaced the tranny mounts. The original ones were not completely collapsed. Maybe should have left well enough alone. The new mounts look fine and I have readjusted them several times thinking perhaps I had introduced some stress to the drivetrain. No effect.
A while back I had my car on a dyno and felt no vibration. Isn't that peculiar. That would argue that it is not rear rotating mass.
It's been several years and the vibration is unchanged. It's a bit variable. Sometimes not there at all, but only briefly, like one time into that speed range may seem totally smooth, the next time the car shakes. That's why I suspected a loose suspension bushing that might only start to oscillate under some road conditions, but I haven't found anything.
Anyway, Tom, give us as many clues as you can about just how the vibration presents and how it feels and how it varies and maybe we can finally find the likely source for you, me and Nicole.
It would seem it must be in the rear rotating mass, axles on out, but repeated balancing, new wheels and tires, swapping axles, and the vibration persists. Checked over all the suspension bolts and bushings. Checked wheel bearings as well. Nicole Mossinger has the same vibration, and despite having Greg Brown work on it at least briefly, the vibration persists in her case as well.
Mine actually started soon after I replaced the tranny mounts. The original ones were not completely collapsed. Maybe should have left well enough alone. The new mounts look fine and I have readjusted them several times thinking perhaps I had introduced some stress to the drivetrain. No effect.
A while back I had my car on a dyno and felt no vibration. Isn't that peculiar. That would argue that it is not rear rotating mass.
It's been several years and the vibration is unchanged. It's a bit variable. Sometimes not there at all, but only briefly, like one time into that speed range may seem totally smooth, the next time the car shakes. That's why I suspected a loose suspension bushing that might only start to oscillate under some road conditions, but I haven't found anything.
Anyway, Tom, give us as many clues as you can about just how the vibration presents and how it feels and how it varies and maybe we can finally find the likely source for you, me and Nicole.
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From: Oman
Because it is road speed related, not engine speed related, TT bearings don't seem likely to be the source of the problem. You should feel a TT or TC bearing related vibration just revving the motor in Park or Neutral over a wide RPM range, as Constantine added. I hope I'm wrong, but I can't see how.
Logic, mileage and "too much common sense" may be working against you wrt your specific problem.
I have read your thread about your vibes- I cannot remember what you have done and what not extensive as the list must be- but as you have nigh on 300k miles on an 87 with the original TT bearings [?] and a great resource like yourself cannot isolate the problem then I would be thinking very strongly in terms of the TT bearings.
Logic may tell you otherwise but statistics tell me time to change them. If you have and it did not solve your problem then fair enough. Remember, these things are spinning at high rpms and given the power they are transmitting [and in your case have well transmitted] I might reasonably expect different characteristics under load than in the no load condition and I have no rational explanation as to why it would not manifest itself on a dyno albeit there are somewhat different dynamic conditions in play [the chassis is not being effected by air blast currents on a dyno]. Remember flat out the wind is hitting the car with a resistance force of 300 bhp there or thereabouts!
Have you actually pulled the tube and removed the bearings for inspection? Is it possible the rubber bearing cradle has hardened/degraded with age even though the bearing races themselves may still be mechanically OK?
Every vibration has a reason and unless and until the TT is categorically eliminated it would remain a candidate for suspicion on my car. I think they should be on the suspect list for the OP's problem.
I know you wil have given your problem many hours of thought/attention and hope you do not mind me rattling your chain a bit on this one. Apologies if I have missed something.
Regards
Fred
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Instructor
Joined: May 2011
Posts: 132
Likes: 1
From: San Francisco
I'm having VERY similar symptoms... Also between 70 and 80, then smooths out around 90's. Don't know how she handles beyond 100. But tempted to find out when I drive down to Sharktoberfest on i5...
Under the Lift
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A torn boot!! Hard to belive that could imbalance the axle that much unless perhaps all the grease had packed into one side of the boot. Even then, it's hard to believe. My CV boots were fine until a few months ago. Now, I have a split one. I'll be replacing them soon.
Fred, I said the same thing to Tom - you gotta be careful that you don't get so hemmed in by logic that you don't find the solution.
You know I had the TT out and found a broken damper. Replaced that (thanks to Rob Edwards). Tried to get the bearings out to replace them but even a 3 lb sledge would not budge the carriers. I spun the shaft. It had no play, was firm and did not freewheel or make any noise. Bad TT bearing make noise or at least vibrate with engine RPM. My car is smooth all the way to 75 regardless of whether it is 2nd, 3rd or 4th gear, and the vibration has not changed at all in several years. That's just too much evidence against TT (or wheel) bearings. If they had come out, I would have replaced them. If I concede your point, I'll have to get a ram to push them out. Some people push the shaft out and then used threaded rod with washers and nuts to pull out the bearings and carriers. I beat the crap out of my shaft and it would not budge. I may just get a rebuilt TT from 928 Intl. I don't know, I just wish I had some other indication that was the source.
Fred, I said the same thing to Tom - you gotta be careful that you don't get so hemmed in by logic that you don't find the solution.
You know I had the TT out and found a broken damper. Replaced that (thanks to Rob Edwards). Tried to get the bearings out to replace them but even a 3 lb sledge would not budge the carriers. I spun the shaft. It had no play, was firm and did not freewheel or make any noise. Bad TT bearing make noise or at least vibrate with engine RPM. My car is smooth all the way to 75 regardless of whether it is 2nd, 3rd or 4th gear, and the vibration has not changed at all in several years. That's just too much evidence against TT (or wheel) bearings. If they had come out, I would have replaced them. If I concede your point, I'll have to get a ram to push them out. Some people push the shaft out and then used threaded rod with washers and nuts to pull out the bearings and carriers. I beat the crap out of my shaft and it would not budge. I may just get a rebuilt TT from 928 Intl. I don't know, I just wish I had some other indication that was the source.
Pro
Joined: Jan 2012
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From: Scottsdale, AZ
All four boots were torn at the CV joints. They must have unbalanced the half shafts at speed. But she's smooth all the way up now. Had same effect when I rebuilt the shafts on my 86 944na a few years ago. It doesn't take but a few ounces spinning around at that speed. Think of what a out of balance rim does. If your vibration is speed related and not rpm then I would say its not the torque tube. Otherwise you could replicate the vibration simply by revving the engine. On our cars the main shaft spins at engine speed not road speed. The only things that spin at road speed are the final drive, half shafts, hubs and wheels. A simple test for you would be to see what rpm your vibration occurs at and rev the engine in neutral at same rpm.
Under the Lift
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From: Buckeye, AZ
OK, thanks. Perhaps my axles are out of balance and I just can't tell that by examining them. These are 8 year old rebuilt axles that seem firm and straight. Only one boot is torn. I'll get to them soon. If it proves true, you may be due for a reward.
And it occurred to me that perhaps the reason I felt nothing on the dyno is that the suspension is tightly strapped down.
And it occurred to me that perhaps the reason I felt nothing on the dyno is that the suspension is tightly strapped down.
Instructor
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From: San Francisco
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From: Oman
Whereas half shafts could be out of balance, I do not buy into the theory of such being caused by the boots tearing. It is not like rim balancing where the out of balance mass is acting at a significant radius.
Bill- remember the words of Spock- "when you eliminate the obvious that is all that remains". In your situation, with your talents and capacilities, if you intend to keep the car for another zillion miles then I would go for Constantine's bearing kit knowing that it is a sound technical investment for years to come and if the base problem is not cured it is not a waste of money rather it would be good pre-emptive maintenance.
Could the fact that you [a 928 superhero] struggled to get the shaft [bearings?] out of the TT assembly be a clue here?
It may be worth restating that when I had my original problems with the flexplate coupling slipping 3mm on my late S4 back in 1999 just after I joined the tank the result was a very distinct narrow band vibration at exactly 3050 rpm or roughly 140 kph [85 mph?] - a very nice cruising speed- it annoyed the hell out of me. This tells me these systems are very fickle and such happened because of a bit of pre-load. Something was shaking un-naturally but exactly what I guess I will never really know. Take the pre-load off- it dissappeared- two weeks later without fail it would be back. Earl and a bottle of loctite 260 helped me cure than one [to this day].
Regards
Fred
Bill- remember the words of Spock- "when you eliminate the obvious that is all that remains". In your situation, with your talents and capacilities, if you intend to keep the car for another zillion miles then I would go for Constantine's bearing kit knowing that it is a sound technical investment for years to come and if the base problem is not cured it is not a waste of money rather it would be good pre-emptive maintenance.
Could the fact that you [a 928 superhero] struggled to get the shaft [bearings?] out of the TT assembly be a clue here?
It may be worth restating that when I had my original problems with the flexplate coupling slipping 3mm on my late S4 back in 1999 just after I joined the tank the result was a very distinct narrow band vibration at exactly 3050 rpm or roughly 140 kph [85 mph?] - a very nice cruising speed- it annoyed the hell out of me. This tells me these systems are very fickle and such happened because of a bit of pre-load. Something was shaking un-naturally but exactly what I guess I will never really know. Take the pre-load off- it dissappeared- two weeks later without fail it would be back. Earl and a bottle of loctite 260 helped me cure than one [to this day].
Regards
Fred