High RPM Vibration 1991 GT - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 45 Old 04-11-2017, 11:22 PM Thread Starter
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High RPM Vibration 1991 GT

Had decent luck with advice here before so here it goes. I noticed a vibration in my shifter area at higher RPMs a while back and it was suggested to replace my harmonic balancer. I did so and it significantly helped my problem but did not resolve it completely. I can get to about 4-4,500 RPM before the vibration starts to become obvious. Still felt mostly in the shifter. The vibration is definitely RPM not speed based but does seem to be at least slightly worse under load as well. I do have concerns about the clutch with the car. Originally I assumed the cable was stretched but now thinking it could be more. The clutch likes to engage fully, and abruptly after shifting almost without lifting off the pedal at all. I do also have trouble getting into gears sometimes too. Not sure if those are purely stretched cable symptoms or could show other problems. Noticed today that at high RPM when I let off the gas there is a kind of buzzing vibration that sounds and feels very close to the shifter (Clutch area maybe as well). Car runs strong and smooth below 4K and I really want to push the car harder without feeling like I'll break something. Any advice is appreciated.

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post #2 of 45 Old 04-12-2017, 12:30 AM
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Vibration could be coming from the clutch or not. Stretched cable could definitely produce the symptoms you mentioned. If you have an adj clutch cable, its best to replace it with an oem non adj style and use a fire wall adj.
For the vibration, check the motor and trans mounts and the ujoints, esp the front one.


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post #3 of 45 Old 04-12-2017, 04:40 PM Thread Starter
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thanks for the reply. Replaced motor mounts with poly ones, trans with a rubber one, and new cross member and bushings for the trans as well. All to chase the vibration problem down. gotten better every step but not gone away yet. Does anymore know more about if these symptoms could be a clutch kit issue? I did hear a sound that sounded like a little header tick but I read that can be mistaken and it can be something with the clutch/flyhweel/TO/Pilot bearing. Really frustrating to chase the problem around.
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post #4 of 45 Old 04-12-2017, 04:43 PM Thread Starter
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Originally Posted by lunytuned View Post
Vibration could be coming from the clutch or not. Stretched cable could definitely produce the symptoms you mentioned. If you have an adj clutch cable, its best to replace it with an oem non adj style and use a fire wall adj.
For the vibration, check the motor and trans mounts and the ujoints, esp the front one.
Planning on checking the u-joints for sure. Just not getting why I would still feel some vibration in neutral
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post #5 of 45 Old 04-12-2017, 05:09 PM
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I second "u joints"

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post #6 of 45 Old 04-12-2017, 05:23 PM
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U joints, unbalanced drive shaft are the likely culprits. I've see a driveshaft with a small ding in it that caused that, it was either dropped once while it was out or something on the road just tapped a bit but it was enough.
Only thing that makes this odd is that you are saying it is not speed dependent, so if you are at 60 mph in 5th the car is smooth and no vibration but if you drop it to 3rd it starts vibrating because the Rpm came up?
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post #7 of 45 Old 04-12-2017, 05:28 PM Thread Starter
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U joints, unbalanced drive shaft are the likely culprits. I've seen a driveshaft with a small ding in it that caused that, it was either dropped once while it was out or something on the road just tapped a bit but it was enough.
The only thing that makes this odd is that you are saying it does not speed dependent, so if you are at 60 mph in 5th the car is smooth and no vibration but if you drop it to 3rd it starts vibrating because the Rpm came up?
In fifth, I may feel a tiny bit, an acceptable amount, but yes higher RPM is when I notice it much more. Even in neutral like I said there's some vibration. Under load and high RPM is the worst vibration. Cruising on the highway you'd think the car is near perfect.
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post #8 of 45 Old 04-12-2017, 10:31 PM
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I would inspect the driveshaft and u joints just because they are exposed but it sounds like you may have a clutch or balancer problem. You can pull the inspection cover off and have a look up there but chances are you won't see much unless it is painfully obvious.
Just to be perfectly clear, if you are in neutral and cruising at 60 you get nearly no vibration but in every gear at 4k rpm it starts? If that is the case it is definitely engine or something rotating with the engine related.
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post #9 of 45 Old 04-12-2017, 11:44 PM
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Are you sure it's rpm and not speed related? Go 70 on Highway and kick it out of gear. I had the same issue. Fine under 55 but by 65 car buzzed vibrated. I put in an aluminum drive shaft and new u joints. All gone. Never thought it would be the drive shaft.
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post #10 of 45 Old 04-13-2017, 01:05 PM Thread Starter
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Are you sure it's rpm and not speed related? Go 70 on Highway and kick it out of gear. I had the same issue. Fine under 55 but by 65 car buzzed vibrated. I put in an aluminum drive shaft and new u joints. All gone. Never thought it would be the drive shaft.
I can go as fast as I want in fifth and as long as the RPMs are below 4 I'm not gonna feel much vibration, maybe a little, but not much. Im going to give the U-joints a look this weekend hopefully and update when I know something. I was paranoid I ruined the motor or something but I have 40-50 psi on the oil pressure all the time and no metal shavings or anything funny in the oil so I believe its fine. After U-joints I'm going to verify fuel pressure and spark....want to try and avoid paying for shop time but who knows

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post #11 of 45 Old 04-13-2017, 05:09 PM
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Are you sure it's rpm and not speed related? Go 70 on Highway and kick it out of gear. I had the same issue. Fine under 55 but by 65 car buzzed vibrated. I put in an aluminum drive shaft and new u joints. All gone. Never thought it would be the drive shaft.
I can go as fast as I want in fifth and as long as the RPMs are below 4 I'm not gonna feel much vibration, maybe a little, but not much. Im going to give the U-joints a look this weekend hopefully and update when I know something. I was paranoid I ruined the motor or something but I have 40-50 psi on the oil pressure all the time and no metal shavings or anything funny in the oil so I believe its fine. After U-joints I'm going to verify fuel pressure and spark....want to try and avoid paying for shop time but who knows
Fork arm clutch problem maybe clutch cable. Buy a adjustable clutch cable set up. Factory self adjusting maybe shot.
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post #12 of 45 Old 04-13-2017, 05:39 PM
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I just went through this. I would rev the engine in neutral to 2500 with the clutch pedal in and out. I had vibes either way. The engine wasn't balanced properly. Damn machine shops!
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post #13 of 45 Old 04-13-2017, 06:11 PM
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Planning on checking the u-joints for sure. Just not getting why I would still feel some vibration in neutral
Well, the vibration you feel in neutral would def not be related to driveshaft lol. That could be in the clutch or as mentioned if this is a new/rebuilt engine, the balance could be off. You said a new harmonic balancer helped, was it a factory replacement or a performance unit?

Honestly, without more info, it's a guessing game really. What's the history of the car? When did the vibration begin or was it always there? New engine build? How old is the clutch, what brand? Ect ect...

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post #14 of 45 Old 04-13-2017, 06:12 PM
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I just went through this. I would rev the engine in neutral to 2500 with the clutch pedal in and out. I had vibes either way. The engine wasn't balanced properly. Damn machine shops!
Ugh, that sucks....

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post #15 of 45 Old 04-16-2017, 01:13 PM Thread Starter
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Well, the vibration you feel in neutral would def not be related to driveshaft lol. That could be in the clutch or as mentioned if this is a new/rebuilt engine, the balance could be off. You said a new harmonic balancer helped, was it a factory replacement or a performance unit?

Honestly, without more info, it's a guessing game really. What's the history of the car? When did the vibration begin or was it always there? New engine build? How old is the clutch, what brand? Ect ect...
Balancer was a Ford Performance OE style balancer. Car is mostly stock with 24lb injectors and a matched MAF. 3.73s, shorty headers, off road X and Flowmasters, basic stuff. Smog, EGR and A/C delete. The vibration wasn't triggered by any mod. Cars at about 140,000 and I was told it had an aftermarket clutch, no idea which. The vibration was always there a bit but has gotten worse the past few months. Balancer helped but still there. Internals of the Engine/Trans have not been touched. driveline looks to be stock and U-joints presumably as well. driving the car later today to see if I can describe better.
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post #16 of 45 Old 04-16-2017, 02:39 PM
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99% on the throwout bearing, probably damaged by driveline misalignment due to the aftermarket motor mounts.
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post #17 of 45 Old 04-16-2017, 03:10 PM
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99% on the throwout bearing, probably damaged by driveline misalignment due to the aftermarket motor mounts.
Driveline misalignment from aftermarket motor mounts would affect the TOB how?

Wait, what? (My kids say that when I say something ridiculous. )
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post #18 of 45 Old 04-16-2017, 03:12 PM Thread Starter
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[QUOTE=vertvert;17852490]Driveline misalignment from aftermarket motor mounts would affect the TOB how?

Wait, what? (My kids say that when I say something ridiculous. )[/QUOTE

could totally be a bad TO but don't think my motor mounts can cause that
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post #19 of 45 Old 04-16-2017, 06:17 PM
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Feeling the vibration through the shifter is key. The throwout bearing is bad. When you replace it, I bet it's visibly out of round.
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post #20 of 45 Old 04-16-2017, 06:50 PM Thread Starter
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Feeling the vibration through the shifter is key. The throwout bearing is bad. When you replace it, I bet it's visibly out of round.


Can a bad throw out make a noise on cold start as well?


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post #21 of 45 Old 04-16-2017, 07:11 PM
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Is the noise kind of a buzzing sound?
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post #22 of 45 Old 04-16-2017, 07:49 PM Thread Starter
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Is the noise kind of a buzzing sound?

Hard to describe... really doesn't sound like a Engine tick or knock like you might hear at cold start, just sounds like an extra noise from under the car kinda.... only for about 2 seconds on cold starts


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post #23 of 45 Old 04-16-2017, 07:52 PM Thread Starter
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Just took the car for a drive. Shifter starts to buzz around 3,500 no matter in gear or out, clutch in or out. Flywheel? It makes a buzzing vibration sound that can be felt through the shifter and even the car a little. It's not terrible but not good....


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post #24 of 45 Old 04-16-2017, 08:05 PM
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Yep, at least T-5's are light and throw out bearings are cheap. Harbor Freight sells a nifty tranny jack for $89...
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post #25 of 45 Old 04-16-2017, 08:09 PM Thread Starter
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Yep, at least T-5's are light and throw out bearings are cheap. Harbor Freight sells a nifty tranny jack for $89...


You saying flywheel or throwout? lol I'm gonna try to get a look Tuesday hopefully get this resolved soon.


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post #26 of 45 Old 04-16-2017, 08:22 PM
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Throwout bearing!
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post #27 of 45 Old 04-17-2017, 12:51 AM
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Driveline misalignment from aftermarket motor mounts would affect the TOB how?

Wait, what? (My kids say that when I say something ridiculous. )
Bet you hear that a lot! ...could not resist!!

vertvert think brickbrick!! Many aftermarket mm's ain't stock height (####'s all over the place). Take two plain ole bricks, stand up one behind the other, and stuff a fairly tight fitting rod through the holes and spin it at high speed... How far up you think you can move the front brick up w/o causin' a problem?

Sure, get a taller trans mount but then the not previously mentioned 3rd brick (rear) might be unhappy...and vibrate...just sayin...

Be shocked if the OP didn't need a TOB...especially now...that's ridiculous though!!
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post #28 of 45 Old 04-17-2017, 09:00 AM
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HMMM, I did help a buddy drop his engine in recently and he got new mounts and they fit like crap but we got them in there. His car is an AOD, you guys think that will cause a misalignment and problems? Sorry to hijack thread.
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post #29 of 45 Old 04-17-2017, 01:57 PM
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Originally Posted by vertvert View Post
Driveline misalignment from aftermarket motor mounts would affect the TOB how?

Wait, what? (My kids say that when I say something ridiculous. )
Bet you hear that a lot! ...could not resist!!

vertvert think brickbrick!! Many aftermarket mm's ain't stock height (####'s all over the place). Take two plain ole bricks, stand up one behind the other, and stuff a fairly tight fitting rod through the holes and spin it at high speed... How far up you think you can move the front brick up w/o causin' a problem?

Sure, get a taller trans mount but then the not previously mentioned 3rd brick (rear) might be unhappy...and vibrate...just sayin...

Be shocked if the OP didn't need a TOB...especially now...that's ridiculous though!!
How would aftermarket motor mounts cause a vibration in neutral?
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post #30 of 45 Old 04-17-2017, 08:19 PM
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[QUOTE=fasterthangas;17854010]How would aftermarket motor mounts cause a vibration in neutral?[/QUOTE what he said is that the misalignment of the drive train from uneven aftermarket mounts causes wear on the throw out bearing which will make noise when it is out of round.
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post #31 of 45 Old 04-17-2017, 08:29 PM
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[QUOTE=bwdz;17854546]
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Originally Posted by fasterthangas View Post
How would aftermarket motor mounts cause a vibration in neutral?[/QUOTE what he said is that the misalignment of the drive train from uneven aftermarket mounts causes wear on the throw out bearing which will make noise when it is out of round.
I must be missing something here. The tranny is bolted solid to the engine. They are as one. The engine can sit a bit higher on one side and not effect the throw out bearing. Correct?
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post #32 of 45 Old 04-18-2017, 12:23 PM Thread Starter
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Gonna have a transmission place I trust look at it. I will know something by the end of the week.
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post #33 of 45 Old 04-18-2017, 10:27 PM
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Bet you hear that a lot! ...could not resist!!

vertvert think brickbrick!! Many aftermarket mm's ain't stock height (####'s all over the place). Take two plain ole bricks, stand up one behind the other, and stuff a fairly tight fitting rod through the holes and spin it at high speed... How far up you think you can move the front brick up w/o causin' a problem?

Sure, get a taller trans mount but then the not previously mentioned 3rd brick (rear) might be unhappy...and vibrate...just sayin...

Be shocked if the OP didn't need a TOB...especially now...that's ridiculous though!!
I am sure driveline mis-alignment can cause vibrations. However your brick brick thing has no relation to a throw out bearing being damaged due to driveline misalignment. The only remote possibility of damaging the throw out bearing as you suggested would a totally screwed up indexing of the bell. Which is far fetched at best. Tell me how you think a highe or lower engine/trans/rear would misalign the front bearing retainer, which is where the TOB lives. No matter where the mounts are, the relationship between the eng/TOB doesn't change.

Op, good luck and let us know how you make out.
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post #34 of 45 Old 04-19-2017, 06:45 PM Thread Starter
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So the shop tends to think that the vibration could be caused by the mismatching of engine and transmission mounts. They don't think the trans/clutch is an issue. Going to get a poly trans mount and then after that, I'm looking at possibly a fuel delivery issue. I learned that would make sense since the vibration gets worse as the car warms up and the MAF and IAT sensors start sending data when the motor is at operating temp, something like that. Replacing the IAT, and Fuel Filter after the mount and going from there. Also going to check fuel pressure. Probably looking at hooking up a wideband to verify my suspicion.
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post #35 of 45 Old 04-19-2017, 06:56 PM
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So the shop tends to think that the vibration could be caused by the mismatching of engine and transmission mounts. They don't think the trans/clutch is an issue. Going to get a poly trans mount and then after that, I'm looking at possibly a fuel delivery issue. I learned that would make sense since the vibration gets worse as the car warms up and the MAF and IAT sensors start sending data when the motor is at operating temp, something like that. Replacing the IAT, and Fuel Filter after the mount and going from there. Also going to check fuel pressure. Probably looking at hooking up a wideband to verify my suspicion.
A misfire of any kind will cause vibration. The motor and tranny mounts only transfer the vibration that is already there. Soft mounts bandaid the source of the vibration. Poly mounts transfer more of the vibration. Neither causes vibration. You should have little to no vibration in a properly tuned and balanced engine. If the engine vibrates with the clutch pedal in and in neutral; the vibration is either the flywheel or engine or both. Check accessories for bad pulleys or bearings. Look at the plugs.

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