120 mph harmonic roar/ vibration- SOLVED!
07-23-2016, 12:58 PM
#1
120 mph harmonic roar/ vibration- SOLVED! I have read, read and read and for the sake of not hijacking a thread or resurrecting an old thread, I will just start my own and get some alternative ideas.
1995 Trans Am Automatic, stock.
From day one I have had vibration issues. 70-80 mph then 120 mph and higher.
Here's what I've done:
New wheels
Balanced drive shaft with new u joints
New Bilstein shocks and Moog springs rear
New rear wheel bearings, rotors, pads
Transmission serviced as well as rear end checked out. All was well
New poly bushings all the way around. End links, sway bars, upper, lower control arms.
New front hub/ bearing assembly, rotors, pads
New front spring/ shocks or struts ( I hear it called different things.
Now with all that 0-110 is smooth. Once I get up to 120mph I get a rear sounding roar that has a harmonic rhythm to it. It causes enough vibration to slow me down. Not in the steering wheel but in the seats.
I've had the yoke bearings and related checked and all was well.
I'm leaning toward tires, as they were bought from a member here but they were practically new.
I've read repeated threads on this angle issue with the driveshaft. That's sort of confusing to me.
Is there anything glaringly obvious I could be missing? I've got to be getting in the short rows of figuring this out.
One final thought that I haven't read........ Hub- centric rings?
Any input is appreciated.
Thanks guys
SMOOVE
1995 Trans Am Automatic, stock.
From day one I have had vibration issues. 70-80 mph then 120 mph and higher.
Here's what I've done:
New wheels
Balanced drive shaft with new u joints
New Bilstein shocks and Moog springs rear
New rear wheel bearings, rotors, pads
Transmission serviced as well as rear end checked out. All was well
New poly bushings all the way around. End links, sway bars, upper, lower control arms.
New front hub/ bearing assembly, rotors, pads
New front spring/ shocks or struts ( I hear it called different things.
Now with all that 0-110 is smooth. Once I get up to 120mph I get a rear sounding roar that has a harmonic rhythm to it. It causes enough vibration to slow me down. Not in the steering wheel but in the seats.
I've had the yoke bearings and related checked and all was well.
I'm leaning toward tires, as they were bought from a member here but they were practically new.
I've read repeated threads on this angle issue with the driveshaft. That's sort of confusing to me.
Is there anything glaringly obvious I could be missing? I've got to be getting in the short rows of figuring this out.
One final thought that I haven't read........ Hub- centric rings?
Any input is appreciated.
Thanks guys
SMOOVE
Last edited by Smoove; 08-18-2016 at 05:09 PM. Reason: Change in status
07-25-2016, 07:56 AM
#8
Tracking down such a thing could get time consuming and expensive. You'd either have to send all the parts out to get checked and re-balanced or take a whack-a-mole strategy.
Strapping a cheap GoPro under the car may be the fastest and most inexpensive way to find out what's going on.
Strapping a cheap GoPro under the car may be the fastest and most inexpensive way to find out what's going on.
07-25-2016, 09:50 AM
#10
Per y2k_ta's comment, I assume you are renting track time for these high speed runs. If not - that's definitely not safe.
Putting the car on jack stands would probably be more safe - but could the vibrations could shake you off the stands? If the car fell, there would probably be less people damage than an accident on the road at 120 mph, but definitely a good bit of car damage.
If you aren't on a track, I think a dyno would be the best place to do this testing. That would also quickly confirm that the problem is in the rear part of the car.
That being said, I would think your drive shaft is a pretty good guess at the issue. Wheel balance issues manifest themselves from 55-70 mph and the fact that you have a "Balanced drive shaft with new u joints" raises suspicion. I recall reading threads over the years about drive shafts that weren't all that well balanced - or they were balanced just fine for normal road conditions.
Putting the car on jack stands would probably be more safe - but could the vibrations could shake you off the stands? If the car fell, there would probably be less people damage than an accident on the road at 120 mph, but definitely a good bit of car damage.
If you aren't on a track, I think a dyno would be the best place to do this testing. That would also quickly confirm that the problem is in the rear part of the car.
That being said, I would think your drive shaft is a pretty good guess at the issue. Wheel balance issues manifest themselves from 55-70 mph and the fact that you have a "Balanced drive shaft with new u joints" raises suspicion. I recall reading threads over the years about drive shafts that weren't all that well balanced - or they were balanced just fine for normal road conditions.
07-25-2016, 12:04 PM
#11
Of course I'm not renting track time. I have no tracks for that in my neck of the woods. 2 mile stretch of lonely 4 lane highway. No traffic so no more unsafe than me doing it on a rented track. Either way it's me that gets injured.
I'm going to swing by my mechanic who builds and drags cars and get his input. He did the tranny/ rear end service inspection.
The hub centric theory I had I believe is a dead end as I got my hands on my wheel specs and the wheel and hub on my car are both listed as 70.3, non-the-less I'm gonna pop off a wheel and measure for elimination purposes.
The driveshaft focus has me interested as the harmonic rhythm , in my minds eye , feels like it could be related. The go pro attempt is a good thought. I may go that route then start seeing how close a dyno shop may be for me.
I think I could come out of that knowing for sure what area the issue is coming from. I will continue to update.
Thanks for your time
I'm going to swing by my mechanic who builds and drags cars and get his input. He did the tranny/ rear end service inspection.
The hub centric theory I had I believe is a dead end as I got my hands on my wheel specs and the wheel and hub on my car are both listed as 70.3, non-the-less I'm gonna pop off a wheel and measure for elimination purposes.
The driveshaft focus has me interested as the harmonic rhythm , in my minds eye , feels like it could be related. The go pro attempt is a good thought. I may go that route then start seeing how close a dyno shop may be for me.
I think I could come out of that knowing for sure what area the issue is coming from. I will continue to update.
Thanks for your time
07-25-2016, 01:57 PM
#12
On The Tree
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If it feels like a harmonic rhythm it can really only be those things that are spinning while driving.
Next question is would you consider it a fast frequency or slow? If fast it's likely trans/driveshaft related, if slow it's likely axle/wheel/tire related.
A few other things you can do to test items is drive at 80 to get the vibration then let off the gas and see if it stays there, if so hen shift to neutral and see if it stays there. If it's still there after that then the third time cruise at speed throw it in neutral and shut the engine off.
Next question is would you consider it a fast frequency or slow? If fast it's likely trans/driveshaft related, if slow it's likely axle/wheel/tire related.
A few other things you can do to test items is drive at 80 to get the vibration then let off the gas and see if it stays there, if so hen shift to neutral and see if it stays there. If it's still there after that then the third time cruise at speed throw it in neutral and shut the engine off.
Last edited by 67Lark; 07-25-2016 at 02:03 PM.
07-25-2016, 04:18 PM
#13
I would have to say the frequency is fast as far as the rhythm of the harmonic.
0-100 is butter, I have no vibration at all. Around 115 it starts and is full bore at 120. Not shaking and shimmying like it's coming apart but just the consistant , come and go come and go rhythm of the vibration. It's there and constant, the rhythm is harder to softer kinda like 1 Mississippi 1 Mississippi 1 Mississippi tempo.
My mechanic wants me to get a new driveshaft or have them build one. He also uses a go pro under his drag car. So definently gonna go the go pro route since it's free and at least see what I can see first. It would be awesome if I could pinpoint it that way.
I will keep updating.
Thanks for the time and advice even though this has been discussed at length on every board out there. I just find mine unique in the speed at which it comes in.
Thanks again
SMOOVE
0-100 is butter, I have no vibration at all. Around 115 it starts and is full bore at 120. Not shaking and shimmying like it's coming apart but just the consistant , come and go come and go rhythm of the vibration. It's there and constant, the rhythm is harder to softer kinda like 1 Mississippi 1 Mississippi 1 Mississippi tempo.
My mechanic wants me to get a new driveshaft or have them build one. He also uses a go pro under his drag car. So definently gonna go the go pro route since it's free and at least see what I can see first. It would be awesome if I could pinpoint it that way.
I will keep updating.
Thanks for the time and advice even though this has been discussed at length on every board out there. I just find mine unique in the speed at which it comes in.
Thanks again
SMOOVE
07-25-2016, 05:08 PM
#15
152,000
I had the rear axle "serviced" and I myself have had the cover off twice and pulled and yanked looking for slack and wear. Not really knowing what to look for. ALL the work I've done that I mentioned in my first post was my first time relying only on this forum and YouTube to get things done so I don't really know what to look for. I only know there was no up and down play or side to side play grabbing the drive shaft itself and trying to find slack. The only play at all was a very small amount when I rotated the driveshaft forward and reverse or grabbed a tire and rotated it forward and reverse. I don't know how much is too much but it didn't seem more than what I've seen in videos or read about.
But who knows, this is my first rodeo in this area.
My next course of action is the go pro camera run and see what I can see and if possible will post that video here if it's possible to do so.
Again thanks for the feedback
Btw- the axle bearings at the wheel are new.
I had the rear axle "serviced" and I myself have had the cover off twice and pulled and yanked looking for slack and wear. Not really knowing what to look for. ALL the work I've done that I mentioned in my first post was my first time relying only on this forum and YouTube to get things done so I don't really know what to look for. I only know there was no up and down play or side to side play grabbing the drive shaft itself and trying to find slack. The only play at all was a very small amount when I rotated the driveshaft forward and reverse or grabbed a tire and rotated it forward and reverse. I don't know how much is too much but it didn't seem more than what I've seen in videos or read about.
But who knows, this is my first rodeo in this area.
My next course of action is the go pro camera run and see what I can see and if possible will post that video here if it's possible to do so.
Again thanks for the feedback
Btw- the axle bearings at the wheel are new.
07-26-2016, 01:47 AM
#18
Staging Lane
Join Date: May 2016
Location: Edmonton, AB, Canada
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OP, I can't offer much. Lots more knowledge in here then I can offer.
However, any time I have had an unexplained vibration in our cars the first thing I do is get the tires Road Force balanced. In my situation, it is the cheapest and easiest way to start trouble shooting - a good starting point.
I have done it on 3 cars, two with success. One it didn't work on and I still have a high speed vibration but at least I eliminated the possibilities of it being a tire/balance/rim issue before I look into other things.
However, any time I have had an unexplained vibration in our cars the first thing I do is get the tires Road Force balanced. In my situation, it is the cheapest and easiest way to start trouble shooting - a good starting point.
I have done it on 3 cars, two with success. One it didn't work on and I still have a high speed vibration but at least I eliminated the possibilities of it being a tire/balance/rim issue before I look into other things.
07-30-2016, 06:16 PM
#20
Quick update for this...... Got my GoPro hooked up and did some high speed runs. The only way I can figure how to post it is upload it to YouTube the post the link in here , so bare with me. It's a slow process but I think I got good info.