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9/07/2017 1:08 PM  #1

Driveline/engine vibration a question for MS and anyone else

MS --I am very intrigued by your comments about the range of engine/transmission angles that you have tried. Particularly your feeling that the vibration did not change regardless of the angle tried. I am trying to make a decision on whether or not to cut my tunnel and raise the transmission. I feel that I might have had two problems simultaneously. One the Driveline angles and two a vibration in the engine. I believe that the driveline angle is usable and within the range of proper u joint operation however it is somewhat reversed from the factory angles. My transmission angle is 3.5 down and my driveshaft is approximately level and the pinion is pointing up towards the transmission almost equal and opposite angles. My concern is that upon acceleration the pinion might climb out of the range of proper u joint operation. The vibration seems to go away at speed when the clutch is depressed which now points to pressure plate on forward. The vibration now seems to be in the range of 4000 to 5400 rpm with it now mellowing out at 5500. This occurs with the transmission in neutral regardless of whether the clutch is depressed or not. What do you think? Would you go to the trouble of hacking up the car just to match the factory specs when it might not be that critical?


9/07/2017 2:39 PM  #2

Re: Driveline/engine vibration a question for MS and anyone else

Usually a bad angle condition will get worse on hard acceleration.
Can you produce the vibration condition sitting still in neutral revving the engine to typical rpm where you experience the vibration?

I have chased a harmonic vibration for many years. It has not changed although every single component on the car has been changed multiple times. Except the body.
My next step is a section of flexible exhaust tubing right behind the header collectors.  The car even had same vibe with very mild 302 and c-4 trans using stock mounts.

Money you enjoy wasting is NOT wasted money... unless your wife finds out.

9/07/2017 4:23 PM  #3

Re: Driveline/engine vibration a question for MS and anyone else

Yes, the vibration occurs with the car in neutral sitting still. You have an interesting thought about the flexible exhaust behind the collectors. I am drifting away from the concept of hacking up the tunnel. After reading that you've tried a range of greater than 3* down to 1* with no apparent effect it makes me wonder if it would be worth the effort. The fact that I can take her up to 70 and depress the clutch and the vibration goes away reaffirms, at least in my mind, that it is not driveline related. Do you know if there is anything about the 347 that would make it more likely to be  vibration prone than any of the other Ford engines? It would help if I were a little better at determining whether the vibration is mechanical or a resonance issue.

     Thread Starter

9/07/2017 7:12 PM  #4

Re: Driveline/engine vibration a question for MS and anyone else

Before cutting the floor try dropping the tailshaft of the tans and see if the issue gets worse.  If so then you may be on to something with moving it higher.  If not you saved yourself cutting up the car.

When there are potentially two things wrong my advice is always to attack them one at a time.  Trying to address two problems makes it impossible to know which thing you did made the difference.  Its like running at the drag strip.  Bump timing until it slows down, then back it off to the fastest setting.  THEN start screwing with the jets in the carb.  Otherwise you just end up chasing your tail. 


9/07/2017 7:52 PM  #5

Re: Driveline/engine vibration a question for MS and anyone else

All very good points. The transmission was raised up as much as it will go because of the belief that the TKO600 is a taller transmission and we are trying to fit it into the space that a toploader would go. The tunnel on the 66 is not as accommodating as the later models. When I installed the 9" rear I noticed the vibration. Now if you made me put my hand on a Bible and swear that it wasn't there with the 8",I can't say 100%.When I purchased the car it came with the 347 and the TKO600 already installed as per Keisler's instructions. I was able to get it up in the tunnel a bit more. After further modification to the Keisler template it is now as far up into the stock tunnel as it can go without hitting the chassis. The transmission itself is a Keisler modified unit that has had some of the top section machined off. I believe that it was called a "Perfect Fit" kit. When I started with this the tailshaft angle was somewhere in the neighborhood of 4* or so. Maybe it isn't as big a concern, I have seen posts where people describe 5 and 6 degree angles and don't complain about vibration. I reasoned that if a person could duplicate the factory angles there shouldn't be a problem. Does anyone know the dimensional differences between the toploader and the TKO600?

     Thread Starter

9/08/2017 12:30 PM  #6

Re: Driveline/engine vibration a question for MS and anyone else

If you have a smart phone you can download a free app called Tremec Toolbox.  One of the features in this "toolbox" is a driveline angle finder that uses your smartphone to take a reading on the engine, the driveshaft, and the rear end and then tells you if your angles are in spec or not.
It's how I finally got my angles right.  Of course, even with the angles correct I still had a vibration until I added the T5 counter weight.

For what it's worth my vibration was different than yours... I had no vibration in neutral... so yours may be more engine related, where mine was more transmission/rear end related.


9/08/2017 4:48 PM  #7

Re: Driveline/engine vibration a question for MS and anyone else

Seems you have already determined the vibration to be forward of the driveshaft.  Does the vibration remain the same with trans in neutral with the clutch in or out.  Clutch in would seem to eliminate clutch disk and tranny.  Check all accessory pulleys (alternator, water pump, a/c, p/s, etc). Check harmonic balancer.  If all is well on the front of the motor, you will have to check the balance of the flywheel and pressure plate combination.  Only thing left after that is the basic engine build itself.  Not likely it is a mechanical fan with a bent blade.  You guys seem to favor electric fans these days.  Besides, I have found seriously bent blades in the past that did not produce noticeable vibrations.

Classic cars are full of surprises and almost none of them are good ones!

9/08/2017 6:20 PM  #8

Re: Driveline/engine vibration a question for MS and anyone else

Al-I believe that I have been dealing with 2 separate issues that overlapped at the same approximate rpm. When I took the car up to 70 plus and depressed the clutch the car smoothed out. Was this due to the engine returning to idle,  or did it smooth out because I finally hit the correct pinion angle with my shims, or was it a combination of both? My desire to correct the tailshaft angle was directly related to the postings that I have read and the common sense of matching the factory angles. If I indeed need to remove the transmission in order to check my clutch and pressure plate for balance it seems logical that this would be the time to raise the tunnel in order to get the transmission up higher in the chassis. The real question is whether attaining this "perfect angle" is really even necessary. My angle now is a bit less than 4*and might actually be closer to 3*.I do however know that with the transmission in neutral and the car sitting still I do get a vibration that does not seem to change with the clutch in or out. The vibration that I'm now describing is either engine related or a resonance issue. MS stated that he has changed almost everything on his car multiple times without a solution.  I have now removed the balancer and front pulley and have taken them into a shop to have them checked. I have also noticed that the vibration seems to lessen with the front(air conditioning) belt removed. This belt drives only the compressor through a single idler. This occurs even without the ac running. The crank pulley is an older style cast pulley that is a little over 2 pounds heavier than the stamped welded version. I am hoping that the machine shop tells me that it is slightly out of balance. I did run the engine momentarily without any drive belts connected and it still vibrated. The vibration occurs from about 4000 to 5400 or so with it apparently smoothing out above that speed. I purchased this car back in 2012 about 80% restored, or at least I thought it was. I have since had to redo most of the work and replace and upgrade many components. I have made most of the suspension upgrades that most people do and literally almost every component on this car has been changed or upgraded. The one nice thing about that is that I rarely get my hands dirty when I work on it. The not so nice feature is that I've spent 99% of the time working on it. I don't even have enough break in miles logged to really see what it will do after having Liberty's go through the transmission and the rear end replaced

     Thread Starter

9/09/2017 1:55 AM  #9

Re: Driveline/engine vibration a question for MS and anyone else

Well that pretty much leaves the flywheel, pressure plate.  In my unexperienced opinion, 5,000+ rpm is an unlikely place for harmonic vibrations, though.
Keep us posted.

Classic cars are full of surprises and almost none of them are good ones!

9/09/2017 12:59 PM  #10

Re: Driveline/engine vibration a question for MS and anyone else

Brad and I have been discussing this off-line but I thought it would be better to add a few cents here.  I may be using some big words so be warned.

First, in the world of rotating machinery we do not use the term "resonant harmonics" when describing vibration issues.  If you are dealing with a violin or guitar string that is very uniform and symmetric you can describe the fundamental natural frequency of the string and some possible harmonics of that natural frequency as "resonant harmonics".  In rotating machinery, a harmonic is simply a multiple of some fundamental frequency and a resonance is resonance.  It is extremely unlikely that the second bending natural frequency of an exhaust system would be exactly 2 times the first bend mode/natural frequency, for example.  I cannot think of any situation where I have encountered a resonant harmonic in a machine.  Resonance is a condition where a natural frequency of a structure or system is excited by a forcing frequency that is close to or exactly matches a natural frequency.  A bell has many natural frequencies but the bell will not ring or "resonate" unless it is struck or excited.  The conditions that affect natural frequencies are mass, stiffness, and damping (damping affects the total response more that than the natural frequency).  So, when ever you change any of these parameters, you can end up getting into a resonance condition when you have not had issues in the past.  An automobile has many many natural frequencies which include the entire body structure, the suspension, the drive train to the frame, etc. so there is always a chance that you will have forces that are very close to these frequencies  But resonance takes two things - a natural frequency, and a force.  When forces can be brought down to very low levels there will not be enough energy to excite a natural frequency and therefore no resonance.  Tires are a great example.  When you have a tire that is out of balance, it will produce a force at a frequency equal to the rotating speed of the tire.  The unbalance forces increase at a square of the change in speed.   This means that the forces acting on the spindle will increase by a factor of 4 between 20 mph and 40 mph.  This is why you may not feel the effects of unbalance until you hit 50 or 60 mph and the higher the frequency, the greater the likelihood that you will find a natural frequency.  Natural frequency behavior will often show up as a sensitivity to a particular speed or engine rpm.  As you approach a natural frequency, the vibration amplitude will increase at a greater rate than the unbalance forces.  The peak amplitude of vibration will occur when the forcing frequency matches the natural frequency.  As you increase in speed or rpm above the natural frequency the vibration levels will drop.  For a bell, the width or range of the natural frequency "affected zone" is very narrow - low damping shows sensitivity over a narrow range of maybe plus or minus 2 to 5%.  Systems that have high damping will have a lower overall amplification but the resonant zone may increase to plus or minus 20%.  For example, if the suspected range is between 4000 to 5400 rpm, this would tend to indicate that whatever is resonance has relatively high damping such as motor mounts.  If you have ever backyard mechanic tested a crank to see if is cracked you are actual seeing these principles in action.  If you properly support a good crank and strike it, it will ring at a very high frequency and ring for a long period of time - this is a lightly damped system.  If the crank is cracked, the stiffness is reduced, the natural frequency is reduced, and the movement of material at the crack increases damping.  The result is a dull thud rather than a sharp and long ring.  In the case of real world vibration it is important to remember that it takes two things to have resonance - a natural frequency and a force.  In many cases, it is best to try to eliminate the force if possible.  In some cases where force cannot be controlled adequately counter measures such as tuned absorbers may be used to limit the amount of vibration that is felt or experienced.  The masses that are attached to the back end of a transmission or to the nose of the pinion are examples of these countermeasures.  Remove one of them and you may understand why they are there.  In some cases, you may not feel any difference and this may be due to manufacturing tolerances where the countermeasures are designed to handle the worst-case scenario of the stack up of tolerances.

Now on to Brad's problem.  As suggested in an earlier post you are trying to troubleshoot two things at once and what is needed to fix one will not fix the other.  I suspect based on what you have described that you have an engine balance issue.  Yes, there is a speed sensitivity but if the engine was smooth you probably would not have a potential resonance problem.  Based on our discussions and your observations this is what I would suggest that you do.

1.  Un-pin the motor mount.  While putting a bolt through the mount might protect the mount from tearing, you may be short-circuiting the damping properties of the mount which will lead to greater transmission of energy into the body/frame where it can be felt.  There is a possibility that the balance and assembly of the motor is OK and you are just perceiving unusual vibration because of the transmission of the engine vibration that would normally be isolated.  If it was my car and I had acquired an old project I would simply replace the mounts.  The elastiomers in a mount harden over time which has a combined effect of increasing the stiffness and therefore also increasing the natural frequencies of the motor on the mounts.  Additionally, the damping effectiveness of the mount is decreased.  Mounts are relatively cheap so unless they are new, I would replace them.  If they are poly mounts, I would replace them with stock rubber mounts at least through the testing period.  We are in troubleshooting mode and what we do here may not be what we end up with.

2.  After freeing up the mount(s), use a floor jack with a block of wood or a rubber pad and lift carefully under the pan and then under the transmission to ensure that there is some freedom of movement before anythingmakes hard contact (or any contact) with the frame or body (yes I know the Mustang doesn't have a frame).   Check on top of the transmission and around the exhaust system.  This is also a good time to put the jack under the exhaust system at several locations to ensure that it is free to move on its mounts and that it is not hard-mounted somewhere along its path.

3.  For the first driving test, you need a fairly flat section of road.  You need to test the car in 2nd through at least 4th gear.  Get up to speed in second gear (about 3000 rpm) and then gradually increase the engine speed to take you through the suspected problem engine rpm range.  Do no accelerate heavily during these test as we want to observe the engine when it is not straining at the mounts and where pinion angle may be an issue.

4.  Repeat this test in 3rd gear and see if the problem follows engine rpm or vehicle speed.  Verify if the problem rpm range is the same as second gear.  I am not sure of your final drive ratio but try the same test in 4th gear.  I assume that in 5th you would be in excess of legal speeds but you should learn enough in 2nd, 3rd, and 4th.  If the problem follows engine rpm and not speed then the focus needs to be on the engine.

Report your results.

If the mystery 347 came with the car (i.e., you didn't purchase it yourself) you cannot assume that anything is right until it can be proven to be right.  If you look at a number of the crank/rod/piston kits that are available, one option from many suppliers is "balanced" or "not balanced".  The price on the "not balanced" components is attractive and some budget-minded crate motor builders may just buy the unbalanced pieces and hope for the best.  I am having a 347 built and we bought the unbalanced assembly because my engine builder has found that even the "balanced" assemblies are mediocre to poor in some cases.  There are two types of unbalance that we are dealing with in an engine - rotating and reciprocating.  If I was able to take vibration readings on your engine it is fairly easy to tell the difference between the two.  When you are testing by seat of the pants you will likely not be able to determine which of the two is the problem (if not both).  As suggested, the crank pulley seemed suspicious to me.  Due to its mass, the fact that is is overhung outside of the front bearing, and its age, it could be a/the source of unbalance.  The different behavior with different balancers is interesting and a little suspicious.  Unless you have an unusual crank kit the 347's use a 28 oz-in crank and the flywheel and damper have to match.  Talking to others that have ended up with 50 oz-in flywheels by mistake, the car could not be driven so I don't think you have a 28 versus 50 issue.  I have heard of issues with the damper that you got with the motor and my engine guy does not use or recommend them.

As suggested by Al, that leaves the flywheel and pressure plate.  From my hot rod Volkswagens in my college years to any other performance motor I have worked with over the years I always have the flywheel and pressure plate balanced as an assembly.  If the history of what was and what was not balanced in your motor is unknown, I would be very tempted to pull the transmission and bellhousing and balance the flywheel assembly.  This may not be the problem but right now you do not know that it is or is not the problem.  While you are in there you can confirm the engagement of the transmission into the pilot bearing and it is not a bad idea to confirm that the bellhousing is concentric to the crank.

If the vibration levels subside after balancing then move on to the drive angles but first make sure that the motor is right.  Unfortunately, there is a possibility that the reciprocating or rotating assembly is out of balance internally which cannot be corrected with the flywheel or damper/balancer,

Just a little more on harmonics (an not harmonic resonances).  A harmonic is simply an exact multiple of a fundamental frequency.  For example, in a driveshaft when there is misalignment of the u-joints, a vibration force will be produced twice for every revolution of the shaft.  We tend to describe this as a harmonic of driveshaft speed.  In an engine, when you have a reciprocating unbalance (rods and/or pistons) a vibration force is produced at 2 times rpm because there are two motions of the piston for each revolution of the crank.  This is also described as a harmonic.  Noe of these are harmonic resonances, they are simply harmonics.  Can you have a natural frequency that is excited by one of these harmonic forces - yes but I will stop for now.

To summarize - replace the mounts, check for any binding or contact, test the car in 2nd, 3rd, and 4th, and report your findings.  Sorry for then length of a post but sometimes complicated subjects require a little more detail.


9/09/2017 2:54 PM  #11

Re: Driveline/engine vibration a question for MS and anyone else

Gary,I am waiting for the machine shop to finish checking my cast pulley and harmonic balancer. I am prepared to replace the balancer based on what I have read regardless of their results. What brand/type are you using on your 347?When I get the engine back together and the car off the stands I will do the road tests and report the findings. I am greatly appreciative of your time and knowledge and am fascinated with the physics behind this. Feel free to go into whatever depth you wish on this issue, it is a great read.-Brad

     Thread Starter

9/09/2017 3:37 PM  #12

Re: Driveline/engine vibration a question for MS and anyone else

He is using a Dayco Powerbond - this is close to the part number  .  I don't have the detailed parts list with me but I am pretty sure this is the one we ended up with.  All builders have their preferences and this is what he currently recommends.

There are several variants on bolt pattern and balance.  I am using a March serpentine setup.  You have to be careful with the pulley mounting surface dimension/distance because these have changed and you could push your pulleys out of alignment.  It sounds like you are running 289 pulleys so match accordingly.


9/09/2017 3:42 PM  #13

Re: Driveline/engine vibration a question for MS and anyone else

Dazzling!!!  Me and my dictionary are still sorting through this info.

Classic cars are full of surprises and almost none of them are good ones!

9/09/2017 6:24 PM  #14

Re: Driveline/engine vibration a question for MS and anyone else

2X.... I guess what GP said, or just good at what I have done....... But there's still a 302 still running around here that we throw together one afternoon..... All we needed was one more piston to fill the hole. So checking the archives, all we could find was this 289 piston,  but it kept hitting the crank when we turned it..... We die grinded A bunch off the skirt till it cleared......, and it never vibrated....To be very honest,  the only engine I ever had balance,  is the red car, and it shakes a bit at times, and I still get speeding awards 30 some thousand miles later. So is a little shaking a bad thing??? Not till my FILLING come loose.........time to bed, and good nite........RED


9/10/2017 1:38 PM  #15

Re: Driveline/engine vibration a question for MS and anyone else

What clutch assy are you running ? I have a Center Force Dual Friction clutch in mine and found that the centrifical weights were slipping off to one side at high RPM's and causing a terrible vibration, doing some research I found many complaints of this happening, I removed the weights and that got rid of that vibration, still fighting driveline vibrations tho.

The amount of fun is directly proportionate to the damage done.

Board footera

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