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Author
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Topic: Harmonic Vibration
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 02-24-2002 11:23 AM
   
Hi guys, sorry I haven't posted for so long-kids, work you know the story��I'm really puzzled by a problem that I'm having with my 69 Cobra Jet. When the car was returned to me in 1999 after a complete restoration/rebuild of the engine, engine bay, front and rear suspension, there was a noticeable vibration, which seemed to permeate down through the driveshaft. It was a sound that the car never had before. I contacted the fellow that rebuilt the engine and he took the car back to have another look. He determined that it was the clutch fan causing the problem and sure enough it seemed to take care of about 80% of the problem. The remaining vibration/sound he really couldn��t figure it out and it wasn��t noticeable enough for me to make a big issue out of it, although things like that due tend to drive me nuts. Anyway, over the past two years I��ve driven the car and you can faintly hear/feel the sound/vibration especially around 40-50 mph. Believe it or not, it actually increases in frequency when you let OFF the gas. My problem is that I just replaced the original torque converter with a TCI unit stall unit, and the vibration is REALLY back. This problem is really baffling my mechanic. He��s called TCI, reinstalled the unit again, although he swears it was done right the first time. We decided to replace the clutch fan with a flex fan and that actually did seem to take a little of the vibration away. We��ve twisted and reinstalled the driveshaft several times and all the original weights seem to be in place. He also made sure the muffler system was not touching the body of the car. If I speed up to 60 and drop the car in neutral there is no vibration. However, the whirring sound/vibration seems to really come on strong as the speed increases. In fact, at high speed my C-6 shifter and car really starts to intermittently shake-it��s not constant shaking but does increase with speed and when I let off the gas. A little background to aid you in your suggestions. When the car was restored the engine was balanced, the entire rear-end was rebuilt to concours condition. About the only items that weren��t replaced was the driveshaft and transmission, which I hadn��t had a problem with before the rebuild. There is a slight leak out of the front corner of the transmission pan-passenger side, but I��m not sure that would have any bearing on the problem. Thoughts?
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beachbum
Gearhead Posts: 142
From: Florida
Registered: Oct 2001
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posted 02-24-2002 12:34 PM
I had a vibration in my 1968, 289, C4 and replaced the transmission mount.
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johnmustang
Gearhead Posts: 4088
From: Vancouver Island , British Columbia , Canada
Registered: Nov 2001
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posted 02-24-2002 02:07 PM
Just throwing some thoughts out for you , but , did you balance your crank shaft? re-check your drive shaft for balance, check your rear end , as well as , your rear axle bearings. How are the brakes on the car ? Check out your shocks , and , I know it sounds stupid , but , you could have a bad or improperly balanced , harmonic balancer. Good luck  JOHN ------------------
65 2+2 FASTBACK
68 COUPE
87 TAURUS WAGON
98 F150 XLT TRITON V8 4.6, 4 WHEEL DRIVE
Member:Vancouver Island Mustang Association
M&M #1710
MyPhotoPage
MY TRUCK
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 02-24-2002 03:00 PM
quote:
Originally posted by johnmustang:
Just throwing some thoughts out for you , but , did you balance your crank shaft? re-check your drive shaft for balance, check your rear end , as well as , your rear axle bearings. How are the brakes on the car ? Check out your shocks , and , I know it sounds stupid , but , you could have a bad or improperly balanced , harmonic balancer. Good luck JOHN
John: The crankshaft was balanced with the engine. However I did not rebalance the driveshaft, although it appeared that the weights were still on the tube. Brakes are almost new, so is the axle bearings and shocks-the car doesn't make the sound/vibration when its coasting.thanks for your thoughts along with beachbum's reply! Bud
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1trickpony
Gearhead Posts: 107
From: Escondido, Ca
Registered: Oct 2001
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posted 02-24-2002 04:54 PM
ok, so it isn't wheel weights as that would vibrate in Neutral. Only things I can think of are that the driveshaft needs rebalancing or you have a u-joint that is tight and actually binding a little bit. With the driveshaft off can you move both u-joints throughout their range of motion?------------------
1969 "S" code Mach1
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johnmustang
Gearhead Posts: 4088
From: Vancouver Island , British Columbia , Canada
Registered: Nov 2001
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posted 02-24-2002 05:03 PM
quote:
Originally posted by BBrazinski:
[QUOTE]Originally posted by johnmustang:
[b] Just throwing some thoughts out for you , but , did you balance your crank shaft? re-check your drive shaft for balance, check your rear end , as well as , your rear axle bearings. How are the brakes on the car ? Check out your shocks , and , I know it sounds stupid , but , you could have a bad or improperly balanced , harmonic balancer. Good luck JOHN
John: The crankshaft was balanced with the engine. However I did not rebalance the driveshaft, although it appeared that the weights were still on the tube. Brakes are almost new, so is the axle bearings and shocks-the car doesn't make the sound/vibration when its coasting.thanks for your thoughts along with beachbum's reply! Bud [/B][/QUOTE] O.K. so now you have narrowed down to the drive train , if you have no vibration while in neutral and coasting , that means that you have taken the load off of the drive train , so that is where your problem is , but , I am sure you are aware of that already. JOHN ------------------
65 2+2 FASTBACK
68 COUPE
87 TAURUS WAGON
98 F150 XLT TRITON V8 4.6, 4 WHEEL DRIVE
Member:Vancouver Island Mustang Association
M&M #1710
MyPhotoPage
MY TRUCK
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 02-24-2002 08:29 PM
The U joints are also new, but that is still a good suggestion to try. I'm thinking it might be the driveshaft.
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65driver
Gearhead Posts: 101
From: Syracuse, NY, USA
Registered: Feb 2000
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posted 02-25-2002 07:23 PM
I have the exact same problem. It started after I changed the transmission and the Torque convertor. The funy thing is, the convertor is a TCI, just like yours. I've checked everything, and get the same results as you - however, I noticed that while parked, if I bring the revs up, I get a slight vibration at about 2100 rpms. I figure the only thing moving that is new is the convertor. while driving, I have the same as you, vibration at about 40, then back at 50, then REALLY back about 70 + (anything over 4000rpms and the vibration is brutal). I had to park it for the winter, and because I spent so much time farting around to fix it and got nowhere, I was pretty po'ed too!. But I'm almost convinced its the convertor, even though its new. Or somehow I ruined a u-joint when I changed the tranny. But it still does not explain the vibration while parked. Just wanted to share my experience.
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 02-25-2002 09:06 PM
Ummmm. Your vibration sure sounds about the same as mine. I didn't replace the transmission and even prior to the TCI unit, my car was experiencing a slight vibration. However, since putting in the TCI unit, it really is shaking. My mechanic ordered a new transmission mount based upon beachbums suggestion. As we work through this problem I will keep you posted as to what seems to be working.take care
BUD
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johnmustang
Gearhead Posts: 4088
From: Vancouver Island , British Columbia , Canada
Registered: Nov 2001
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posted 02-25-2002 09:29 PM
Tranny input shaft ? This sounds stupid , but , is your radiator properly installed , and , tightened down properly. Would not hurt to check your flex plate. This problem of yours is keeping me awake at night , I hate it when there is a problem I can not fix or help fix. JOHN ------------------
65 2+2 FASTBACK
68 COUPE
87 TAURUS WAGON
98 F150 XLT TRITON V8 4.6, 4 WHEEL DRIVE
Member:Vancouver Island Mustang Association
M&M #1710
MyPhotoPage
MY TRUCK
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 02-26-2002 04:07 PM
quote:
Originally posted by johnmustang:
Tranny input shaft ? This sounds stupid , but , is your radiator properly installed , and , tightened down properly. Would not hurt to check your flex plate. This problem of yours is keeping me awake at night , I hate it when there is a problem I can not fix or help fix. JOHN
John: I appreciate your concern, but don't lose sleep over it! I'm sharing your suggestions with my mechanic. He'll probably address each one at a time. I'll let you know what develops. However, if you do think of something else, let me know. take care, Bud
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SteveLaRiviere
Administrator Posts: 32655
From: Saco, Maine
Registered: May 99
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posted 02-26-2002 04:17 PM
quote:
Originally posted by johnmustang:
Tranny input shaft?
We had a guy here a while ago that traced a real persistant vibration to a bad tailshaft bushing. He replaced just about everything else until he found that.  ------------------
'70 Mustang Mach 1 M code 351C 4V/FMX/3.25 open
'72 Mustang Sprint Coupe 351C 4V/FMX/4.30 Trac Lok
'94 F-150 XL 5.8L/E4OD/3.55 Limited Slip
'97 Probe GTS 2.5L DOHC
MCA Member # 47773
I once asked a man: "Who art thou, that ye may pass judgment upon others?" Then he added $75 to my fine...
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Hemikiller
Gearhead Posts: 339
From: Clinton, CT
Registered: Feb 2002
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posted 02-26-2002 06:23 PM
Wow, we've now blamed every possible system in the car guys...LOL. Sorry to be so crass, but I'll bet next week's paycheck you've got a bad u-joint. I used to have fights with the owner of the garage I worked at over driveshaft vibrations. I won every time, Always a bad u-joint.
Do this simple test.
Accelerate to the 40-50 mph range, just normal acceleration. When you feel the vibration, let off the gas entirely. If the vibration changes in pitch or goes away, you've probably got a bad u-joint.
If you rapidly let on and off the gas, and you hear a clunk, or the vibration changes, bad u-joint.
Also, place your hand on the tranny tunnel, behing the console, when you get the vibe. If you feel a vibration (d-shaft vibrations are rhythmic, like a wave) in the floor, probably driveshaft.
A quick check for a bad joint without pulling the shaft:
Jack up the rear so you can get under the car. Put the trans in neutral, and grab the driveshaft. Now stick a finger in between each of the 4 "corners" of the u-joint, one at a time obviously,touching both of the yokes, and rotate and wiggle the shaft in all directions, nice and easy. If you feel ANY change in pressure on your finger, or any movement at all, the joint is bad. I mean ANY movement AT ALL. Do both ends of the shaft like this.
Also, a real common problem with some mechanics is they overtighten the rear u-joint straps to the point that they crush the cap and bearings inside, ruining the new joint. If you remove the shaft, rotate the joints through their range of movement very slowly, if you feel ANY change in drag,an easy or tight spot, it's bad. A tell tale mark on the joint will be "imprints" of the needle bearings in the u-joint bearing surface. Any mark that is inconsistant with freshly machined or polished metal signals a bad joint.
U-joints are very finicky, either you install them correctly the first time, or you'll be replacing it over and over 'til you get it right. How do I know? I tossed a shaft in my '71 Mach at 70, made a real mess out of the underside of the car. Since then I've become a bit anal about my driveshafts and am very attuned to the vibrations they make.
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Ryan Wilke
Gearhead Posts: 1368
From: Stanton, Michigan 49707
Registered: Oct 2000
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posted 02-26-2002 06:26 PM
...are the front and rear U-joints in 'phase' with each other?
I had that problem once (but I can't recall if it vibrated while coasting or not)...
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 02-26-2002 08:46 PM
quote:
Originally posted by Ryan Wilke:
...are the front and rear U-joints in 'phase' with each other?
I had that problem once (but I can't recall if it vibrated while coasting or not)...
WOW, Once again some great ideas that I'll pass onto my mechanic to check out. HEMIKILLER you mentioned about "accelerating to the 40-50 mph range, just normal acceleration. When you feel the vibration, let off the gas entirely. If the vibration changes in pitch or goes away, you've probably got a bad u-joint". Well the vibration is very strong around that speed and when I let off the gas the sound and vibration increases in frequency, although I don't ever remember hearing a "clunk". However, your comment about the tranny tunnel vibration is the most accurate description of what I feel is happening. The tunnel, stick shift, back seat vibrate just "like a wave", especially as I pick up speed. Given the fact that the C-6 and driveshaft are the only two components of the drivetrain that haven't been replaced, I hope that it's just the driveshaft. take care, Bud
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RonnieT
Gearhead Posts: 540
From: Port Allen, La. 70767
Registered: Jun 99
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posted 02-26-2002 10:38 PM
I have the same problem with my 69 MACh that you describe Bud, I will be watching this thread closely to see what you find. I haven't got a chance to look at mine good yet. My wife's 2000 daily driver had a very similar vibration that turned out to be a bad rear wheel bearing, but the vibration did not change if you popped it out of gear. ------------------
Ronnie
69 mach1 351W-4V
70 Torino GT 351C-4v with a "shaker"
Mustangs and More Member #23
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Hemikiller
Gearhead Posts: 339
From: Clinton, CT
Registered: Feb 2002
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posted 02-26-2002 11:31 PM
Bud:
One thing I forgot to mention, check to make sure all of the retaining clips are in place in the bores of the driveshaft yokes, and that the rear joint is centered in the yoke. There should be a locating tang in the bore where the cap sits, or there should be a clip on the bearing cap itself. Without one or both of these present, this would cause exactly the problem you describe. I'd follow up on the previous suggestion about the tailshaft bushing as well. I've seen toploaders that had the bushing spinning in the bore, although it didn't cause any vibe I could feel.
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thedave66
Gearhead Posts: 244
From: mountain home, idaho
Registered: Sep 2001
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posted 02-27-2002 01:46 AM
don't know if it helps any but a couple years back I had an axle bearing go out. For the life of me I could not figure out where this odd noise was coming from, the only way I could describe it was an oblong rolling sound. Finally figured it out when I was pulling into a parking lot and it went snap. Don't know if it helps but hey, bad advice is my specialty dave
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1trickpony
Gearhead Posts: 107
From: Escondido, Ca
Registered: Oct 2001
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posted 02-27-2002 02:54 AM
Are your frames tied?
Another thought I was having is your motor mounts. If they are wearing out they may flex enough at high sustained rev/acceleration and your engine may be touching the shocktower, especially if you have the wrap around supports most BB cars have.That could be the wave effect .. travelling from front to back...
I know the vibration you are talking about.I have felt it and it is scary feeling..------------------
1969 "S" code Mach1
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 03-02-2002 09:12 PM
OK well here is some news from the harmonic vibration front. After taking Beachbums suggestion and installing the new transmission mount "nearly" all of the vibration is gone! A slight bit still exists but it's hardly noticeable based upon a quick drive, just prior to rain/sleet storm hitting our area. There was also a multitude of other things my friend/mechanic did and I asked him to email these to me so that I could post them later.take care and thanks to all of you for your help/suggestions. Bud
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BBrazinski
Gearhead Posts: 52
From: Ridgway, PA, USA
Registered: Jun 99
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posted 03-24-2002 08:55 PM
I thought I'd just bring you up to date on my continuing saga of trying to cure the vibration problem in my cobra jet. The good news is the suggestion that Beachbum made of replacing the transmission motor mount made a considerable difference. The bad news is it still didn't completely cure the problem. So I decided to buy a new driveshaft along with front/rear U-joints. I drove the car today and guess what, it still has a vibration. It's like a deep base sound coming in waves from a powerful speaker. I could feel the vibration in the steering wheel. What is puzzling is after I drove the car about ten miles to get it warmed up, I ran it hard doing a couple quick accelartions and high speed runs on an open, lightly traveled road. I swear the car seemed a little bit better afterwards. Any thoughts? Bud
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V8 Thumper
Gearhead Posts: 3267
From: Orange, Ca. United States of America
Registered: Dec 2001
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posted 03-24-2002 10:06 PM
If the 'vibration' is more noticable under deceleration, I'd suspect the u-joints. Do you hear a 'clunk' when you drop it into gear? Incorrect gear lash in the rear end will howl under deceleration also... I wonder if they put the flex plate back on in the proper position for balance... I can't see a fan clutch shaking the whole car  Is it worse after the car sits for a few days? In a cold climate, those tires may take a while to get round again.
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