HELP, Vibration I cant get around! - Vintage Mustang Forums
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post #1 of 29 (permalink) Old 02-21-2019, 08:00 PM Thread Starter
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HELP, Vibration I cant get around!

hey there, this may be a long story but I am trying to get to the bottom of a vibration that's coming at about 4k RPM I cannot pinpoint.

Here is my current setup
331 stroker SCAT internals
4 speed
28oz flywheel

I replaced the clutch last spring and ever since then I have been having a vibration coming through the car at 4k rpm, in ANY gear. here is is caveat it ONLY happens under load when driving, i can sit in the driveway with clutch in or out and rev it to 6k and nothing, clutch engaged and in gear sitting in driveway... still nothing. while driving in EVERY gear it vibrates at 4k.

I called the shop and they recommended i bring it in and they pulled the trans and we took the flywheel back to the machine shop that balanced and built my motor. it was a few oz off and was re balanced. ok good so far. to be safe we also balanced the tires and had the driveshaft balanced ( which was 3oz off) my speculation at this point would be that it should be 100% better and the issue resolved. we also noticed the crankshaft end play was waaay off at 16 thousandths of total movement ( sue to the vibrations) so we pulled the oil pan and replaced this e as well which are now set at .7 thousandths which is pretty much perfect! ok good. while it was there i had a set of new leaf springs and shocks i decided to install while we were at it. everything should be set and good by now..

got the car back and still.. vibrates at 4k it does however drive waaay smoother from the parts we installed but the vibration still comes in and i am not ready to replace the main bearings again. i am ready to sell this thing its making me so irritated.

the machine shop informed me if we had the original flywheel we could match it and it would be perfect, either way the new one that is balanced is set at 28oz where it should be. im beginning to speculate it may be something else at this point. I do have black widow exhaust installed and those mufflers are LOUD right when the vibration comes in. could this be a cause of this? a misfire? pinyon? trans and motor mounts ?? ( those were replaced but the original 1965 replacement rubber ones)

has anyone experienced anything like this before?
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post #2 of 29 (permalink) Old 02-21-2019, 08:09 PM
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My first guess would be torque from the engine is twisting it on the engine mounts and transmission mount causing contact between the engine and chassis or exhaust and chassis.

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post #3 of 29 (permalink) Old 02-21-2019, 08:26 PM Thread Starter
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Quote:
Originally Posted by Woodchuck View Post
My first guess would be torque from the engine is twisting it on the engine mounts and transmission mount causing contact between the engine and chassis or exhaust and chassis.
that is not a bad theory actually. do you think it would still happen while the car is not driving tho?
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post #4 of 29 (permalink) Old 02-21-2019, 09:32 PM
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Ideally, the flywheel is balanced first, then the clutch is bolted up and the combo is balanced. Mating position is marked so it goes back together in the same position. Given that it started after the new clutch, I would suspect this. I recently had this done with a new good quality clutch and the clutch did need balancing.

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post #5 of 29 (permalink) Old 02-21-2019, 09:59 PM
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If the vibration is "coming through the car" my suspicion is that it's probably not mechanical. You'd feel it coming through the shifter or the steering wheel. What Mr. Chuck said makes sense. I'd look at the exhaust system front to back, especially in the rear where the pipes come pretty close to the fuel tank. Driver side (from memory) is pretty tight with aftermarket exhaust.
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post #6 of 29 (permalink) Old 02-21-2019, 11:03 PM
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When you test it in the driveway, I assume the rear tires are off the ground and the suspension is unloaded. Is it possible that when the suspension is loaded there is something making contact? Im no expert, but I play one on the ole interwebs. I hope you find it!

1966 GT 2+2 - 347, Edelbrock carb, Tremec TKO 600 5 speed, 9 rear and a bunch of other cool stuff.
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post #7 of 29 (permalink) Old 02-22-2019, 03:19 AM Thread Starter
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The flywheel and clutch being matched during the build was my biggest fear. The machine shop told me they had it balanced all together with clutch assembly as stated above. When we brought it back and gave them the whole assembly and marked it where it was before we gave it back for them to balance. He said if we had the origional flywheel then we can match it then viola, fixed. He said the only way to get it perfect would be to take the motor apart and basically do it all over again. However stated he was 100% that they use 28oz and basically just make sure there good. Just like he did when we sent it back to him.

So it’s either something in the body of the car like driveshaft pinion related, exhaust, rear end (which was rebuilt about 2000 mikes ago with Yukon internals, track lock 3.25 ratio) or the brand new motor is coming out that has 1500 mikes in it. I really wish I would have just replaced the clutch when I did all this in the first place. The clutch was “good” at that point tho and had life left in it.

The clutch is a cheapo auto zone made in China as well, as I confirmed with the shop that replaced it that I had it back to. However if it’s balanced with the machine shop it balanced right?!

Another shop I chatted with assumes it’s the rear end.. but we’ll see. Im gonna get under the car and check the exhaust tomorrow
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post #8 of 29 (permalink) Old 02-22-2019, 07:43 AM
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While you are under there check your transmission tail shaft bushing.

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post #9 of 29 (permalink) Old 02-22-2019, 06:31 PM Thread Starter
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no when tested in the driveway the car is not lifted at all.
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post #10 of 29 (permalink) Old 02-22-2019, 06:35 PM Thread Starter
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thank you!
i just checked the back where the exhaust is running and you are right it is very close to the gas tank on drivers side. i would "assume" it would buzz/rattle from metal on metal contact but ive been wrong before haha

I have not gotten under the whole car yet or checked trans tail shaft mounts or bushings
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post #11 of 29 (permalink) Old 02-22-2019, 06:56 PM
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Drewsky, what kind of harmonic balancer are you running? If it's OEM type, sometimes the weight ring can slip, and it won't do much good. Also, is yours 28 oz to match the flywheel?

Hope this doesn't sound too basic, but if your car only shakes when it's moving, then it's something in the driveline. Don't rule out tires either; I wouldn't trust most shops these days to balance their receipts at the end of day, much less get the tires right.

I had a problem with a pulley on my 5.0 one time, and the vibration was enough to damage my balancer so that it wobbled on the crank just a little. Nasty little hard-to-find issue.

Good luck!
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post #12 of 29 (permalink) Old 02-22-2019, 10:34 PM
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Drewsky, what kind of harmonic balancer are you running? If it's OEM type, sometimes the weight ring can slip, and it won't do much good. Also, is yours 28 oz to match the flywheel?
This is a good point. I'm thinking a driveline-related vibration would have more to do with MPH than it would with RPM, but the balancer would be a factor in RPM

Hope this doesn't sound too basic, but if your car only shakes when it's moving, then it's something in the driveline. Don't rule out tires either; I wouldn't trust most shops these days to balance their receipts at the end of day, much less get the tires right.
Here I'd disagree. Tires causing vibration would relate to MPH, not RPM.

I had a problem with a pulley on my 5.0 one time, and the vibration was enough to damage my balancer so that it wobbled on the crank just a little. Nasty little hard-to-find issue.
Also another good point... and also RPM related.

Good luck!

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post #13 of 29 (permalink) Old 02-23-2019, 03:38 AM Thread Starter
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Thanks for the replies!
So I took the mustang out for a dive this afternoon with a fresh mind. I only have driven the car once since I left the shop and noticed the vibration at 4K was still prevalent. The car drives great besides the obvious bibreauims coming through. To be more clear on what’s going on I payed special attention to when and where it was happening. So when back in the driveway the car DOES seem to be a bit shaky even sitting still when reving it up. It comes through the shifter but not really the steering wheel, it’s a hopped up motor with a semi medium grade radical cam and aluminum heads.. so on and so forth. It seems to come thru louder and more prevalent at 3k plus and gradually more and more till 4K. Now back to main story, it’s much more noticeable under load when driving. I can live with a little shaky ness and mild vibes at idle and even a tiny bit while driving but this seems like it will cause damage (like it already did to crank bearings). It seems like I keep going back to the flywheel needing to be balanced to the origional which was trashed a year ago OR motor/ trans mounts. I know the 66 motor mounts were much improved over the 65’s and to be honestly would pray this would be the simple fix to this. However it didn’t do this before the clutch install so it’s either that or because if the new clutch became more noticeable or possibly driveshaft/pinyon angle?

Another point, before the clutch install and no vibration at 4K when driving I ALWAYS had a little vibration/shakyness thru my hurst shifter but just imagined that just being the nature of the beast in the setup I have in a 50 year old hit rod.
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post #14 of 29 (permalink) Old 02-23-2019, 07:50 AM
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First, you need to separate whether it is an engine vibration or a drive train vib. When you go through the gears, is the vibration tagged to the RPMs in every gear or 3-4k in a particular gear? SInce its in every gear, I would rule out drive train angles, u joints etc. Since it appears to be by RPM, then start cheap. Inspect teh exhaust especially back at the gas tank for evidence of contact where ever it is close to any solid object. Since the exhaust is solidly connected to the motor, its gonna twist with the motor and well you get the picture. You can wedge a peice of wood in place to see if ends the noise. I run dual duals out the back and its tight next to the gas tank. Took me a while to rework the mount and frankly a BHF on the tank to get a little extra room to end that problem. Start at the back and work your way forward methodically inspecting with a mirror and good light on both sides as applicable. Don't forget the cross over and header clearance at the shock towers, clutch Z bar assembly and steering box.

Next, is the vib a function of torque? Does it happen at 3-4k regardless of how much throttle you are giving e.g. neutral throttle at 70 or only when on-throttle? If its a function of torque, could be a bad motor mount from too much HP for stock mounts. Once you rip a mount your done, needs replacement and of course, when you are torquing hard, one side will lift till something hits something. I used to have to chain my motor ~400hp to the frame from the head before I went to custom motor mounts, others "pin" the lift side of stock mounts. Could be once you had a good clutch, you did a burnout or power run enjoying the benefits of a clutch that finally works and ripped a motor mount with all your new found power. Put the car in gear with the hood open and let the clutch out while on the brakes heel-toing the throttle. If you see the motor lifting on one side - its a motor mount - it will be noticeable.

Finally, I would get it up on a lift with someone in the car and run it to replicate the noise whilst I was underneath with a BFScrewdriver wedged between the bone outside your ear and different places on the car - listening around to identify where the vibe is coming from. I do not like the fact that the thrust bearing was shot on a new motor. Are you sure you have the right pilot bearing and it wasn't farcled on installation? Loose INput bearing on the transmission...

Good Luck
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Last edited by dobrostang; 02-23-2019 at 07:55 AM.
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post #15 of 29 (permalink) Old 02-23-2019, 11:29 AM
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Quote:
Originally Posted by FrankieThe69Kid View Post
Frankie, by 'driveline' I really meant all the bits and pieces getting power to the ground, which only come into play when your car's moving.

That would include tires.

Whatever this problem is, it's RPM related in one way or another! Trying to isolate whether it's an engine-only problem, or something after the transmission (including tires) is the first step. But I can see that you get that. =)
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