Vibration troubleshooting

Discussion in 'Troubleshooting & Diagnosis' started by 1970_Z28_503, Mar 14, 2019.

  1. 1970_Z28_503

    1970_Z28_503 Member

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    Forgive the long post.

    So I have been chasing a vibration in my car since the day I bought it a few years ago and I think I am losing my mind. The day I bought the car was raining and I didn't do a very long test drive which was super bad on me. Anyway, Once I got it home and got to drive it I noticed this vibration and have since sunk a lot of time and a lot of money trying to chase it down. I am at my wit's end and looking for some help.

    The car has a 350 in that was rebuilt about 7000 miles ago. It was installed by a prior owner and built by a local shop but didn't come with any info on the build. it has a 650 street avenger holly and MSD ignition mated to an M22 Muncie 4 speed.

    The vibration presented at around 2.5-3k and went away at 3500 RPM which happens to be right in my cruising speed of 60-65 indicated, so super annoying. This vibration is there with the clutch in or out and felt in every gear as I go thru them but most noticeable in 3 and 4 but with a close ration M22 you don't spend a lot of time in that RPM range. When on the road it shakes the car both up and down in that RPM range but is smooth as glass on either side. When I run the car up to the RPM range in the garage I feel it but it's not as noticeable.

    My first thought was that it was speed related as that's when I noticed it at first. So one of the first things I did was have all the wheels checked out and rebalanced and that did help a small amount. Tires are old and need replacing but that doesn't seem to be the issue as I can push the clutch in and drop the RPMs at speed and the vibration goes away completely.

    Next, I had the ring and pinion changed out along with new U-Joints and rebalanced driveshaft as it was clear that the ring and pinion was shot, I thought well that has to be the cause. And again I was disappointed as it was a little better but that vibration was still there. About this time I had figured out that it wasn't speed related but RPM and really started to dig into possibilities and solutions, looking over dozens of other peoples post about their vibration issues hoping to find a reason for mine. I started by trying some easier things like changing out the old motor mounts to the correct ones and that seemed to help but that cursed vibration was still there. I pulled the belt's off and ran it and no change. I pulled plug wires one at a time at RPM to check if I had a misfire or something and it wasn't that either. I checked all the front in steering components and they all look good.

    I was super frustrated at that point and wanted to sell the car and then found the rear subframe rails needed some attention and wouldn't sell the car like that. So I had both rear subframes repaired and added new springs, plus all new hardware and new shocks all the way around (Hotchkis). That certainly helped the ride and seemed to help the vibration a little but it was still there. One odd thing that would happen was every once in a while that vibration seemed to disappear completely for a few hours on a drive and then would come right back the next time I drove it. It didn't happen all the time but often enough that I was perplexed at what could be happing that would cause that to come and go like that. It was never for long and I kind of convinced myself it was me just becoming used to it and not noticing it as much.

    I finally had enough and had the transmission pulled by a local shop and found a centerforce clutch in there that had the weights shifted. I had read so many posts about people chasing vibrations that I knew that was a known issue and so when we found that I was positive that had to be it. So they pulled the flywheel and had it resurfaced, checked the pilot bushing and that seemed ok then installed a new RAM clutch w/ new throwout bearing and put it all back together. At the same time, I had also all the body bushing replaced (Solid) and the front subframe mounting holes in the frames fixed as there was rust present and the holes were too big. Drove the car for a short spin after the clutch replacment and the vibration was gone at 3-3500 and I was elated. Had some headers installed at the same time so was waiting on the new exhaust system to be installed before I really test drove it. Well once the exhaust was in I finally got to take it on a proper test ride and it was awesome until I got above around 4000 RPM and that vibration was back with a vengeance tapering off around 4500 -5000 rpm just as before only at 1000 RPM higher.

    crappy Video I know but you can see and hear the vibration when I go over 4k and the car smoothes out at 5k. It's really noticeable when I drop it back down and cruise at 4k as the vibration is gone and the car is super smooth. (.)

    We are now thinking about trying to balance the flywheel to the pressure plate but I am looking for any other suggestions on what could be causing this as I am out of ideas and if we drop the trans again I don't want to leave any stones unturned. I was thinking about a new Flywheel as the original is still in the car? Pilot bushing or starting to dig into the engine rotating assembly and balance as a possibility. But that is one that I am not sure I would bother with as I do have the numbers matching block I plan on rebuilding at some point.

    Anyway, I am very open to suggestions at this point so let me know if you have had a similar situation you were able to resolve as I am willing to try almost anything at this point.

    One bright spot is the car drives and handles amazingly at this point and I am not sure I would have gone through so much so fast if I wasn't chasing this vibration so I guess that's a positive.
     
  2. xten

    xten Veteran Member

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    Balancer on motor? Indexing bell housing? I was thinking output shaft bushing on M-22, but that would be speed related, not RPM...
     
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  3. czizza

    czizza Veteran Member

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    My motor mount bracket had two bolts full out and the third one loosen up. I know I know I tighten them up when I put the engine together but I must have not ...

    Jack up the motor and see if the bracket moves or if you have another issue.

    The vibration was awful.
     
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  4. 1970_Z28_503

    1970_Z28_503 Member

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    Been thinking it might be balancer but it visually looks good.
     
  5. COPO

    COPO Veteran Member Lifetime Gold Member

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    I've got a M22 in my 70 Z28 and when I went with a roller rebuild after losing 2 solid lifter cams, before the 2nd cam lost a lobe after 8700 mi, I had the orig nodular flywheel resurfaced and balanced. No problems before or after. When I had my engine rebuilt after that with a roller cam, I had the flywheel balanced with the clutch and marked for my assembly. No problems again and I mean all the way up to 6500 rpm.

    When I rebuilt my M22, my rear tail bushing and seal were not leaking, so I left good alone.

    - my balancer is still the orig and the car has over 150,000 mi on it
    - my body bushings are still orig to the car
    - car is never driven in the winter
    - my bell housing has never been indexed and I've owned the car since 1981
    - my driveshaft has not been balanced
    - I like to grab the tire in both hands and pull in and out to make sure there isn't a lot of slop while the tire is off the ground. So that's why I torque the front wheel bearings when I do brakes/rotor work.

    If I were you I would check the following or have repaired.
    - rotate driveshaft 180*
    - balance tires
    - are wheels true?
    - balance driveshaft
    - never use a Centerforce clutch with the weights and wires
    - balance flywheel then balance flywheel with clutch disc
    - use only bronze oil pregnated crank bushing, don't go roller or it'll wear out your Muncie input shaft
    - put the wheels/tires with the least balance weights on the front
    - front wheel bearings should be torqued to 12 ft lbs then....

    From the Camaro Supplement manual.
    When you spin the rotor, torque the nut to 12 lbs ft. Then backoff the nut one flat and insert cotter pin. If the slot and pin hole do not line up, back off the nut an additional 1/2 flat or less as req'd to insert the cotter pin.
     
    Last edited: Mar 14, 2019
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  6. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

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    You probably checked this when you did the rear end and u joints, but...

    Did you replace the yoke on the differential?

    Mine is slightly splayed out and there's a bit of slop between the u-joint ends and yoke. (End to end on the yoke side of the u-joint.)

    It gives me a 50-60 Hz vibration a few MPH on either side of 65.
    (I've never checked for vibration at the next harmonic. 130 MPH :eek: )

    I need to get a new ring/pinion along with replacing the yoke.
    (This gear set has always has always been noisy and I've put 50K miles on it so it's probably impossible to set up correctly anymore.)

    Oh... Mine seems to disappear at random times too.
    Like when the u-joint happens to settle perfectly in the balanced spot and stays there until some dip, bump or steering maneuver causes it to slip into an out-of-balance position again.

    It's easy to check.
    Grab the driveshaft near the rear u-joint and see if you can muscle any end-to-end movement across the yoke connection.

    Took me a long time to figure out the cause of mine.
    I've attempted to shim it in place for a pretty good improvement but I'll never get it perfect with this yoke.
     
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  7. cadillac_al

    cadillac_al Veteran Member

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    It does seem to be rpm related as you said. I would test this a little more to be certain but it sounds like you already have. If you get rolling down the highway at 70 or so and push in the clutch, the rpm's drop and the vibration goes away right? Then if you bring the rpm's back up the vibration comes back? It has to be in the engine. Usually an eingine built by a local shop should be satisfactory but you never know. They could have been training a new employee or they got interrupted during an important step. Shit happens. I think if I was 100% sure it is rpm related then I would start dreaming of an engine swap.

    I would probably do a little trouble shooting on the current engine first. I would check compression on all 8 cylinders. I would double check the valve lash and make sure they are all opening the same. It may have a cam starting to go bad but not popping through the carb yet. If that all looks good I would be thinking about another engine. I might even try that vibrating engine in another vehicle. Good luck.
     
  8. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    it can't be both
     
  9. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    add a washer to one of the crank pulley bolts, if that doesnt work try the next one, then the next
     
  10. 1970_Z28_503

    1970_Z28_503 Member

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    What I was trying to relate is that the vibration is there in the RPM range I feel it at when I am at speed or sitting still with the clutch in or out as long as I stay in that range. Tested this again yesterday, I had the car on the freeway in the RPM range I feel it at and I pushed the clutch in and the vibration was still there as long as I kept the RPMs up once it dipped below that RPM range it went away.
     

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