New 408/727 Vibrations

Small Block Mopar Engine

  1. JD Erisman

    JD Erisman FABO Gold Member FABO Gold Member

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    I wasn’t sure where to post this issue, it could potentially cover many different areas. I am having a vibration problem in my ‘67 notchback Barracuda that is getting worse, bad enough that on the highway, hard acceleration, the 3,000-4,000 RPM and up it is causing the steering wheel to grossly vibrate. About 200 miles ago I had a 408 short block assembly put together and shipped to me, I have only one local machine shop, owned and operated by meth addicts so I will never use them and having this reputable shop build it was my best option. They balanced it (now internal balance), all forged internals, main cap stud girdle, timing chain tensioner; I installed Trick Flow 190 heads, Edelbrock Pro Flow 4 EFI, B&M flexplate and a Fluidamper (for the first time), both for an internal balanced small block Mopar, I’m using adjustable rockers (for the first time), Hughes 228/232 hydraulic flat tappet cam and Mopar performance lifters, custom length Smith Brothers push rods, I have a Dynamic Converters 9” converter with 3,000 stall, and I installed Mancini racing Mag Mount engine mounts (another first time). 8 3/4 rear with 3.55 Sure Grip. Installed a stock Mopar engine-to-tranny brace on the driver’s side (first time ever using those), passenger side wouldn’t fit due to TTI headers. I installed 15x10 Wheel Vintiques steel wheels and 265/50/15 tires in the back, checked for clearance. This is only the 7th or 8th engine build I’ve done, first time having a shop build me a short block, but I’ve never had a vibration issue. I feel it at practically all RPMs, but it’s getting worse, especially at higher RPMs, and in all three gears. I’ve also noticed the exhaust “sound” is not like any of my other small block Mopars, it’s just off but I cannot explain it and whether it’s related to the vibration I cannot see how unless the issue is somehow related to the internals. When I did the engine break-in I followed Hughes guidelines then I drove the car slowly around my neighborhood. For the first 30-60 seconds, maybe more, it seemed OK but I could feel the vibration slightly. Then I heard a loud thunk, thunk, thunk... that increased with RPM/speed (in both first and second gear). The thunk, thunk went away before I could circle back home, about a five minute total drive time. I checked the pulley alignment again, just because the Fluidamper is thicker than stock to make sure the damper was seated all the way in, it was. I again checked the flexplate to converter bolts, all tight (when I installed the converter originally I made sure it was seated all the way in). I checked the lug nuts, tires for rub marks, tranny mount, bell housing bolts, and engine mounts. The only thing I can see that looks different or appeared “wrong” was the driver’s side engine mount; it looks squished on the forward side (I’ll try and post a picture of it). I cannot see how most of the parts I’ve put on could cause such a strong vibration and the engine would have to have been put together really incorrectly, I think, to cause so much vibration, and I doubt they built the short block incorrectly. One issue came up when I installed the motor: I’ve never had such a hard time lining up the mounts to the K-member, it took hours to get the engine installed, I eventually had to drop the tranny down and backwards then still had some difficulty getting the engine in and I could not get the drivers side mount stud to sit any higher than the very bottom of the K-member mounting slot, which caused me to shim that side twice as thick as my previous 360, to clear the headers. Before I start tearing everything apart I’m hoping I’ve described it enough to get some ideas or input from all of you, thanks for any help. B587A337-79DE-412E-8DC4-7ADF48525B06.jpeg
     
  2. yellow rose

    yellow rose Overnight Sensation FABO Gold Member

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    If you put it in neutral while driving and let the RPM drop does the shake go away?
     
  3. JD Erisman

    JD Erisman FABO Gold Member FABO Gold Member

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    No, it’s still there but not as strong. Thank you for asking.
     
  4. CFD244

    CFD244 Well-Known Member

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    Any chance the U joint/yoke alignment may be off? Sounds like you really had/have a lot of tension on the engine/transmission assembly to get the mounts tightened up.
     
  5. JD Erisman

    JD Erisman FABO Gold Member FABO Gold Member

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    I thought of the joints since I did have to pull the driveshaft when I moved the tranny but everything seems ok at that end.
     
  6. jay27

    jay27 Well-Known Member

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    Do you have a poly transmission mount?
     
  7. JD Erisman

    JD Erisman FABO Gold Member FABO Gold Member

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    I do have a poly transmission mount but I was using that before this build without issues. I am guessing the thunk, thunk, thunk noise I heard near the beginning of the very first drive after the engine build has something to do with it but I cannot figure out what that noise was but it sounded like something was banging the floor of the car, but there is no sign of that happening.
     
  8. jay27

    jay27 Well-Known Member

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    Does the engine vibrate at idle?
    Does it start to vibrate with rpm as you rev it up while parked?
    Are the headers touching the body anywhere?
     
  9. jay27

    jay27 Well-Known Member

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    I would check the headers and exhaust are not touching any body , steering etc and then put rubber mounts back on it to see what changes
     
  10. JD Erisman

    JD Erisman FABO Gold Member FABO Gold Member

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    Headers aren’t touching the body and it does vibrate while the car is not moving but not as severe. I don’t have a noticeable vibration at idle.
     
  11. jay27

    jay27 Well-Known Member

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    If you have the old trans mount try that first , you mentioned it was fine before but the driver side mount probably didnt look like it currently does. See what if anything that changes for you.
     
  12. JD Erisman

    JD Erisman FABO Gold Member FABO Gold Member

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    Correct, other than the internals of the engine build, the only differences between the 360 I pulled and this 408 are the Fluidamper, B&M flexplate, and the Mancini Mag engine mounts, one of which is squished on one side and I’ll give your suggestion a try and see what that does.
     
  13. jay27

    jay27 Well-Known Member

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    Let us know what you find.
     
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    • JD Erisman

      JD Erisman FABO Gold Member FABO Gold Member

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      I will, thanks for all your input. Winter is coming quick and the build took a lot longer than I thought, soon my drive time will be over for 6 or 7 months. I don’t know how far north in Saskatchewan you are but your winter must be knocking at the door soon too.
       
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      • Oldmanmopar

        Oldmanmopar Going left turning right FABO Gold Member

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        We had a motor come here from a car that had the same issue. It was making a loud knock when installed then it went away. It also vibrated. The knock was the heavy metal that was welded in the counterweight of the crank for balancing hitting the back rail on the block. The slug of nickel fell out and that was the vibration. That was the second one that I saw this happen to. Something to check.

        Or could it be a dead cylinder your feeling?
         
      • jay27

        jay27 Well-Known Member

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      • Montclaire

        Montclaire Well-Known Member

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        Oldman, your inbox is full
         
      • JD Erisman

        JD Erisman FABO Gold Member FABO Gold Member

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        Oldman, did you pull the motor, drop the pan and found the chunk of nickel? Probably the only way to find out.
         
      • furrystump

        furrystump Well-Known Member

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        I wouldn’t pull the pan yet. Do you have a IR thermometer? If so start it and let it idle. Take the temp on each header tube. See if you have a dead cylinder. You could pull the plugs and look for a dead/fouled plug. That mount looks like the motor is really sitting in there at an extreme angle. I would post pictures of the trans mount and other engine mount
         
      • furrystump

        furrystump Well-Known Member

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        If you pull the shims, where do the headers hit?
         
      • furrystump

        furrystump Well-Known Member

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        Dump the poly mount, all they do is break tail shafts.
         
      • skep419

        skep419 I'm the guy that likes SPAM

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        5 and 7 wires swapped?
        rear wheel studs hitting brake shoe equalizer bar?
        flexplate bolts backed out?
         
        Last edited: Oct 28, 2020
      • JD Erisman

        JD Erisman FABO Gold Member FABO Gold Member

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        • Thanks for all of the replies, they are appreciated. If I pull a motor mount shim one of the head tubes is so close to the steering box it will bang it when the engine rocks side to side with acceleration. It wasn’t like that before I dropped the engine in; I only needed one shim with my other 360. I don’t have a tranny mount picture but I’ll include a picture of my passenger side mount, it’s not very good but it’s the best I could do with the headers in the way. I checked all of the spark plug wires for proper location and checked the headers for contact with the car and I checked the the timing. I emailed Mancini Racing a picture of the drivers side, squished engine Mag mount they sell. 60B5AEA9-2E5F-40F1-A5F4-A387160DFDD8.jpeg Shockingly, they never wrote me back. Here is a picture of the passenger side engine mount. I don’t have a picture yet of the tranny mount.
         
      • 512Stroker

        512Stroker We are all here because we are not all there.

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        Your passenger mount looks normal
        The driver mount looks like it is out of alignment due to to mounting bracket not the fault of the engine mount itself. I would source a new bracket for the drivers side. A new bracket may help you with your header clearance issue.
        IMHO I dont believe that drivers mount is causing your vibration issues.
         
      • Thomas Dennis

        Thomas Dennis Well-Known Member

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        Torque converter not balanced properly Have you put it on jack stands and run it? Have someone slowly bring up the rpms and see if you can see or hear where the noise/ vibration is coming from
         
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