Help With Violent Vibration

dark_viper42 · Oct 25, 2010

My wife's 2001 Mustang GT(140k) 5 speed, has started getting a bad vibration in any gear. It first started showing up anytime the car was holding a constant speed around 1600rpm. Was less noticeable under acceleration or deceleration. Could also hear a slight ticking noise.

Very quickly the vibration has turned violent. Seemed like it was a u joint going out at first, but after changing both of them its still there. Where should I go next?

Vibration happens in all gears including reverse.

I'm thinking broken motor/transmission mounts or the clutch? Looking for some help and direction.

Car is basically stock. Some exhaust work.

Thanks in advance,
Bret

Sonic04GT · Oct 25, 2010

Looks like you've already named my guesses, U-joints and motor mounts

wmburns · Oct 25, 2010

+1 on U-joints

trinity_gt · Oct 25, 2010

The vibration happens in all gears including reverse: Does it happen with the car motionless (i.e. trans in neutral) and revving the engine? If not, you can basically rule out the clutch & flywheel.

Motor mounts wouldn't really cause a "violent vibration". You might get some knocking and banging though.

You say holding speed at 1600RPM: Is the vibration occurring when the engine is at ~1600 in any gear? This is important because 1600 in first gear results in the driveshaft spinning much slower than 1600 in 5th gear. If the vibration is engine speed dependent (e.g. it happens at 1600 no matter the gear) then you're back to the clutch or flywheel I think.

If it's speed related then you might have a damaged driveshaft or have thrown a weight from it.

Has the clutch ever been replaced?

bmylez · Oct 25, 2010

dark_viper42 said:
Very quickly the vibration has turned violent. Seemed like it was a u joint going out at first, but after changing both of them its still there. Where should I go next?

wmburns said:
+1 on U-joints

Unless he put in busted, old U-joints, not sure how that could be it.

wmburns · Oct 25, 2010

Your right. Didn't read the part about having already replaced the U-joint. Gulity of not reading before typing.

Of course a vibration could be from an out of balance drive shaft. Did you index the drive shaft before removing it?

trinity_gt brings up some great points that can help narrow this down.

If the ticking noise changes with the engine RPM, think clutch forward.

If the ticking noise changes with the car's speed, it could still be rear-end related. Consider pulling the rear diff cover and inspecting the gear oil. Examine the diff sump looking for small bits of metal. Also check the condition of the ring/pinion teeth. Look for chips or other rough areas. If the carrier is removed, possible to inspect the wheel bearings and diff carrier bearings for wear. The bearing races must be smooth. The ends of the roller bearings must have rounded edges. If the ends are sharp, the bearing is worn out.

FWIIW, I had a rear end tick on my 2003 GT that turned out to be worn pinion bearings. The frequency of the tick varied with the car's speed. The intensity changed slightly going from power to coast or coast to power. IMO, it simply doesn't make sense to service just the pinion bearings. Install a rebuild kit.

Don't over look the role that motor mounts can play in a problem such as this. In addition to allowing more vibration to be transmitted inside the car, this also allows the motor to set lower in the K-member. This in turn changes the angle of the drive line thus affecting the U-joints.

Consider that the mounts are over 10 years old and may have lived a very hard life.

dark_viper42 · Oct 26, 2010

trinity_gt said:
The vibration happens in all gears including reverse: Does it happen with the car motionless (i.e. trans in neutral) and revving the engine? If not, you can basically rule out the clutch & flywheel.

Motor mounts wouldn't really cause a "violent vibration". You might get some knocking and banging though.

You say holding speed at 1600RPM: Is the vibration occurring when the engine is at ~1600 in any gear? This is important because 1600 in first gear results in the driveshaft spinning much slower than 1600 in 5th gear. If the vibration is engine speed dependent (e.g. it happens at 1600 no matter the gear) then you're back to the clutch or flywheel I think.

If it's speed related then you might have a damaged driveshaft or have thrown a weight from it.

Has the clutch ever been replaced?

With the car in neutral I don't get these vibrations at all. I have the rear end on stands right now and the vibration is coming in as soon as the drive shaft starts to spin. I tested R, 1st, and 2nd last night.

I first noticed the vibration is worst at 1600 rpm in any gear. It is not speed related.

Still has the original clutch.

dark_viper42 · Oct 26, 2010

wmburns said:
Your right. Didn't read the part about having already replaced the U-joint. Gulity of not reading before typing.

Of course a vibration could be from an out of balance drive shaft. Did you index the drive shaft before removing it?

trinity_gt brings up some great points that can help narrow this down.

If the ticking noise changes with the engine RPM, think clutch forward.

If the ticking noise changes with the car's speed, it could still be rear-end related. Consider pulling the rear diff cover and inspect the gear oil. Look for bits of metal. Also check the condition of the ring/pinion teeth. Look for chip or other rough areas. I the carrier is removed, possible to inspect the wheel bearings and diff carrier bearings for wear.

Don't over look the role that motor mounts can play in a problem such as this. In addition to allowing more vibration to be transmitted inside the car, this also allows the motor to set lower in the K-member. This in turn changes the angle of the drive line thus affecting the U-joints.

Consider that the mounts are over 10 years old and may have lived a very hard life.

I did index the drive shaft before removing and the vibration started before I had ever removed the drive shaft so I don't think my issue is there. Didn't see any places on the shaft that looked as if I had lost a balancing weight...

The ticking seemed to get louder with a change in rpm but the speed didn't seem to change. Best way I can think of to describe the sounds is a zip tie that keeps hitting something on every revolution. However as I said the speed of it hitting doesn't seem to change with different road speed or RPM.

Transmission mount looked fine while i was looking last night. Need to work on checking the motor mounts next. Any suggestions on best way to do this?

Also if it was a motor mount with the vibration happen in neutral?

N8Dogg98 · Oct 26, 2010

I have the same problem, same ticking noise, and same vibration at 1600 RPM. I recently had the clutch replaced, and am curious to find out what is causing this.

trinity_gt · Oct 26, 2010

dark_viper42 said:
With the car in neutral I don't get these vibrations at all. I have the rear end on stands right now and the vibration is coming in as soon as the drive shaft starts to spin. I tested R, 1st, and 2nd last night.

I first noticed the vibration is worst at 1600 rpm in any gear. It is not speed related.

Very puzzling how 1600 engine RPM is the magic number but you don't see the vibration in neutral...

Check the tailhousing bushing where the driveshaft enters the trans. Perhaps the bushing is blown out and the yoke is flopping around.

Check for looseness in the drive flange at the rear axle. Not the U-joints but the actual flange and pinion shaft of the rear axle.

95Vert383AOD · Oct 26, 2010

Maybe the computer is doing something funny at that rpm under load. Like pulling massive fuel/timing?

dark_viper42 · Oct 26, 2010

I wouldn't say that 1600 is the magic RPM. That's just where I first started noticing it.

With the rear end on stands the vibration starts as soon as the drive shaft starts to engage.

dark_viper42 · Oct 26, 2010

95Vert383AOD said:
Maybe the computer is doing something funny at that rpm under load. Like pulling massive fuel/timing?

Pretty sure its not computer related. Its somewhere in the power train.

dark_viper42 · Oct 26, 2010

trinity_gt said:
Very puzzling how 1600 engine RPM is the magic number but you don't see the vibration in neutral...

Check the tailhousing bushing where the driveshaft enters the trans. Perhaps the bushing is blown out and the yoke is flopping around.

Check for looseness in the drive flange at the rear axle. Not the U-joints but the actual flange and pinion shaft of the rear axle.

I don't get vibration at all in neutral. 1600 RPM is just where I noticed it most while driving down the road.

I checked the yoke after changing the u joints and there was no play. Did the same at the rear drive flange when i reattached the drive shaft.

I'm going to double check the motor mounts tonight. I don't think that is the problem but I might as well check. If those check out I'm thinking clutch or transmission....

N8Dogg98 · Oct 26, 2010

I notice my vibration worst in 3rd gear at 1600 RPM's... I don't know if it would be transmission related as it seems to happen in other gears, but 3rd gear at 1600 seems to be the worst.

dark_viper42 · Oct 26, 2010

N8Dogg98 said:
I notice my vibration worst in 3rd gear at 1600 RPM's... I don't know if it would be transmission related as it seems to happen in other gears, but 3rd gear at 1600 seems to be the worst.

And you get no vibration when you not in gear?

If you rolling along at 1600 RPM in 3rd gear and push the clutch in, does the vibration go away or change at all?

Are you driving your car while its like this?

N8Dogg98 · Oct 26, 2010

No vibration when not in gear and the u-joints are fine as I recently installed an aluminum D/S. The vibration goes away if I push the clutch in, and actually it's most noticeable in 3rd gear at 1600 RPM's if I apply light throttle to maintain speed or ever so slightly accelerate.

Yes I am driving my car when I notice it.

dark_viper42 · Oct 26, 2010

N8Dogg98 said:
No vibration when not in gear and the u-joints are fine as I recently installed an aluminum D/S. The vibration goes away if I push the clutch in, and actually it's most noticeable in 3rd gear at 1600 RPM's if I apply light throttle to maintain speed or ever so slightly accelerate.

Yes I am driving my car when I notice it.

Any vibrations when taking off?

N8Dogg98 · Oct 26, 2010

Hard to tell, but it is definitely most noticeable when holding a constant speed or accelerating lightly.. again the worst of it occurs around 1600 RPM's

fast97gt · Oct 26, 2010

ill shoot, what about the alignment of your trans in the tunnel, mine had an agressive vibe on take off and early in the rpms then mellowed out later. the cause was what seemed to be a good trans mount but had twisted under a load sometime while driving it, thus the trans looking from the rear forward it sat to the passenger side almost touching the sheet metal. i installed a new mount but with dismay, it was the same. i took the x-member off and notched the hole perpendicular to the the originals. doing this worked like it was made for it. i had no more vibes since.

Help With Violent Vibration

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