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1959 Buick Nailhead vibrations. HELP!

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Hello all, 

hope you are all doing well. 

I need help with my 59 LeSabre. Car was sitting for about 8 years until recently. 

Apparently it had some slight vibrations already before (previous owner told me so. He never cared since it wasn't to bad he said). We have a 59 Invicta as well and there are no vibrations at all, so I know there is something wrong. 

The symptoms are: 

Car starts right up and vibrates in idle a little bit (steering wheel shakes). As soon as you put it in gear (D, L or R) the vibrations stop. If you then start driving, the vibrations are really bad. Once the motor warms up, no vibrations in idle (still when driving). If you rev it up at the carb, you don`t notice any vibrations. Runs really good. If you sit in the car (in P or N) and rev it up, you feel bad vibrations (my buddy says he feels it coming from the transmission area). 

What we tried so far: 

> Engine mounts are good

> Replaced harmonic balancer (made sure its the correct one from the 364, not 401 / 425)

> had it running without belts (so can rule out: fan, water pump, alternator, steering pump) 

> Removed transmission (twin turbine, shifts fine btw) and had it running only with flex plate mounted and torque converter without internals (can rule out drive shaft and transmission and suspension)

> Flex plate is mounted in the proper position to torque converter 

> Torque converter front plate aligns with torque converter housing / bowl (hole aligns)

> Timing and ignition are fine

> Compression is good (115 - 125)

> Factory balancing weight is still on the torque converter housing (did not fall off)

> Flex plate is the correct one (not the one from the 401/425) and is not cracked


When motor is warm, it runs super smooth. No funny noises. So I don`t think there is any engine issue. 

Does anyone have an idea? 

I read that it is possible to mount the flex plate in a wrong position onto the crankshaft and that this could cause bad vibrations. I talked to Jim Hughes (Jim`s Dynaflow Service in Perrysburg, OH) and he says that it is not possible to mount the flex plate in the wrong position to the crankshaft. He says the bolt pattern is staggered and there is a guide pin. So it fits only in one position. I found attached picture that apparently shows a 364 crankshaft with this pin (not mine, found this pic on ebay). Can anyone confirm that? 

The service manual however says, that there are two holes (not a pin) that must align. Quote "position flywheel so 3/8" locating hole in flywheel bolt circle is matched with locating hole in crankshaft."

Is there a difference in automatic and manual transmission (flex plate / flywheel?). Is there a way to check the position without removing the transmission? 

I`m stuck here. Any help is highly appreciated 


Thanks a lot and Merry Christmas!!!







Edited by FabianC18 (see edit history)
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43 minutes ago, FabianC18 said:

Compression is good (115 - 125)

Not really.  That engine is pretty tired.  Last one that I chased a vibration issue on had part of a piston skirt in the bottom of the pan; another had loose parts in the torque converter..  Just drive it until you rebuild, then have it balanced.

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Hi Old-Tank. Thanks for your reply.

I should have worded that better. The compression is not like new. I now. 
but all 8 cylinders are pretty close. So there is not a dead one. That’s actually what I wanted to say. The engine was most likely never opened and runs good for its age. The overall reduced compression would not cause this vibrations. We had Torque converter and transmission apart. No loose parts. Unfortunately the transmission shop did mark the flywheel position and put it back together the same way as it was before. They did not pay any attention of any holes or pins. They didn’t know that the flex plate is used to balance the motor. So if it was wrong before (if that’s possible) it still is.


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Have you checked for spark plug wires leaking?  You can try isolating the wires with this:


plastic wire loam walmart


I have found this in the automotive audio section in my local Walmart and it is less expensive than what is shown in this link.  However it may be a tad too short to do the full length of all the spark plug wires.  Of course you can get the car in a dark place, run it at idle and look closely at the wires to see if any are arcing and maybe cross firing.  Then just isolate them at that location.  But I put this stuff on my 56 all the way from the plugs to the distributor and even put it on the new wires I got after I learned the old ones were arcing.  It was a clear improvement in smoothing the engine out. 

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Usually, if the bolt pattern on the end of the crankshaft is such that the bolt holes are unevenly spaced, then there is only one way to bolt it up.  The dowel wouid do the same thing, if it was there.  But you still have to make sure the "front" is aimed to the "front", rather than otherwise.


A vibration caused by mechanical issues (wrong damper, wrong flywheel, etc.) woud be constant regardless of the engine's temperature.  Getting worse with increasing rpm, rather than what you describe.  Which puts things back to "tuning issues" rather than mechanical issues, it seems.


What dwell is the ignition points set at?  Does the dwell change when the vibration is present from what it is when everything is smooth?  Condition of the spark plugs?  Consistent gaps?  Carb base plate to main body bolts tight?  Carb to manifold fasteners snugged down nicely?  Intake manifold bolts properly torqued?  When the engine is vibrating, with some body running the throttle, check to see if the flow out of the exhaust pipe is smooth or has "gaps"?


One reason I', focussing on the point dwell setting is that when the "window" Delco distributors came out, the "non-meter" method of adjusting the points was to insert the appropriate Allen wrench, then turn the adjustment screw, with the engine running, one direction until the engine missed, then turning it the other direction until it missed again.  Noting how many turns it took to go from one extreme to the other.  Then splitting-the-difference from the "missing" extreme to be "in the middle" between the two "missing" situations.


It is also very possible that the breaker cam in the distributor has wear on it, which can affect both the dwell and point gap setting.  If you can set the gap to spec, but the dwell is still not in spec, or near 30 degrees, then breaker cam wear is the reason.


Might check the coil performance/resistance hot and cold, too, for good measure.


Wondering if the "vibration" is really just "uneven running"?


Just some thoughts,


Edited by NTX5467 (see edit history)
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On 12/22/2020 at 9:04 PM, NTX5467 said:

Wondering if the "vibration" is really just "uneven running"?


That was my thought as well, particularly since engine temperature (warm vs. cold) is a factor.  Could it be a vacuum leak that 'heals' when the engine warms up?


If you have an infrared thermometer, try shooting each exhaust port as the engine warms up.  A colder cylinder may mean a local ignition or lean condition.

Edited by EmTee (see edit history)
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Hi guys, sorry for the late reply. Christmastime is always a busy time in our house. 

Spark plug wires are new as well as the spark plugs. Points and condenser are new as well. I`m pretty sure its not a tuning issue. Bit I will check everything you mentioned above. I have it at the transmission shop right now and we will check the flex plate again. The dowel at the crankshaft is only at the manual transmission cars, not the automatic ones. So it IS possible to mount it wrong. I`m gonna check this next and work from there. I keep you posted. 


Thanks and happy new year  



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  • 2 weeks later...

Hello guys, 

thanks for all your feedback. 

Times are crazy and I`m so busy with other stuff I still haven`t found the time to check everything you suggested and I don`t think this will change pretty soon. 

We need the room in the garage and probably just try to sell it as is to someone that has the time and room for the car. 

I would like to get 7800 Bucks for it and will post it here in the forum these days. 

Hope it finds a good home. 


Thanks a lot

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