Engine vibration

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Thanks for all the comments. I was 25 when I first put this engine in the car. I am now 62, and trying to remember exactly how it was is a bit fuzzy, but I still lean towards something with the 727, or possibly a bad balance job, though the latter seems odd since the components were balanced in 1979, and I don't remember a vibration when sitting still, and only after the 727 was installed. The last time the engine was disassembled was when I replaced the balancer with the Summit unit. I don't have any idea where that balancer went. My engine builder doesn't either. I wouldn't think the balancer is the culprit since I now have had three of them on the engine and the vibration began back in the 80's when the 727 was installed. The original converter I purchased for the 727 was a TCI. I replaced that with a Hughes neutral balanced converter when thinking it might be the converter, along with a Moroso heavy duty flexplate. As I mentioned before, nothing really changed. I keep leaning towards something behind the engine since the installation of the 727 (as I remember) seemed to be the start of the vibration issue. I am tempted to replace the transmission next as opposed to tearing the engine down to check the balancing job. I do think I will replace the engine and tranni mounts back to rubber. Though that is supposed to help with power transfer, I think it is only amplifying an issue that was there prior to this last build. The 410's don't help matters any, even with the GV. Maybe change to 355 or 323's. Like that off the line launch, but I want to cruise more than race. An ignition problem could be a possibility, though doubtful. I replaced the original electronic ignition with a DUI distributor and coil. Doubting the ignition because of the vibration being an issue of the past. Maybe a dowel pin misalignment. I have had the transmission in and out about three times in the past year, and every time things bolted up nicely. I will look into some of the other ideas some of you have had. Try driving in reverse and see if I can feel anything.
 
David Dickerson said:
Thanks for all the comments. I was 25 when I first put this engine in the car. I am now 62, and trying to remember exactly how it was is a bit fuzzy, but I still lean towards something with the 727, or possibly a bad balance job, though the latter seems odd since the components were balanced in 1979, and I don't remember a vibration when sitting still, and only after the 727 was installed. The last time the engine was disassembled was when I replaced the balancer with the Summit unit. I don't have any idea where that balancer went. My engine builder doesn't either. I wouldn't think the balancer is the culprit since I now have had three of them on the engine and the vibration began back in the 80's when the 727 was installed. The original converter I purchased for the 727 was a TCI. I replaced that with a Hughes neutral balanced converter when thinking it might be the converter, along with a Moroso heavy duty flexplate. As I mentioned before, nothing really changed. I keep leaning towards something behind the engine since the installation of the 727 (as I remember) seemed to be the start of the vibration issue. I am tempted to replace the transmission next as opposed to tearing the engine down to check the balancing job. I do think I will replace the engine and tranni mounts back to rubber. Though that is supposed to help with power transfer, I think it is only amplifying an issue that was there prior to this last build. The 410's don't help matters any, even with the GV. Maybe change to 355 or 323's. Like that off the line launch, but I want to cruise more than race. An ignition problem could be a possibility, though doubtful. I replaced the original electronic ignition with a DUI distributor and coil. Doubting the ignition because of the vibration being an issue of the past. Maybe a dowel pin misalignment. I have had the transmission in and out about three times in the past year, and every time things bolted up nicely. I will look into some of the other ideas some of you have had. Try driving in reverse and see if I can feel anything.
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The mounts won’t cause a shake unless they are worn out so why change them? They can’t be the issue.

Changing gears or anything else won’t fix the issue. You need to find the real problem and fix that, and I’m 100% sure it’s not gearing or mounts. I can’t stand sloppy rubber mounts. The OE’s use them because they are cheap and that’s about all that’s good about them.
 
If it's an actual out of balance vibration changing mounts will not help.
If it's a random vibration and the car is buzzing while up and down in the rpm band at different frequencies then change the mounts. Start with the trans mount and let us know what you find, You have several variables so start with one thing at a time.
 
yellow rose said:
The mounts won’t cause a shake unless they are worn out so why change them? They can’t be the issue.

Stiff mounts can telegraph all kinds of vibrations. Anyone who's ever driven a race car with solid mounts will agree with that. If there was no problem with vibrations, the manufacturers would mount everything solid and not have mounts of any kind.
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I drive my street car with solid mounts. The OE’s worry about every snowflake sissy whining about everything.

A solid mount won’t shake the car.
 
I once built a 360 about forty years ago and it ran rough but very fast. At my next pull down I took it to the engine balancer and he said it was in balance. I commented the it was not smooth and after looking over the pistons he said the piston heights were all over the place and an uneven power level and compression would cause more vibrations that an out of balance engine. I rectified the piston heights and put the engine back together and it became smooth a silk again!
 
So I have friend who had a similar issue. Bad vibration around 3K and up. Thing would rattle so bad it would shake your teeth. Put a new drive shaft on it checked all the angles did all kinds of stuff. About a year later I was helping him put a different torque converter in the car and I noticed that it only had one dowel pin in the block. Put the second one in and now the car is smooth as glass.
 
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