Not sure if it would be worthwhile cost wise, but there are vibration locating tools / kits for automotive applications and I understand there are also apps for phones. Not sure if anything more than a phone is required with the app? A couple of links below on them. They are referred to as NVH tests Keep us posted

ARTICLE ON PHONE APPS

One YOUTUBE LINK DEMO

That NVH app for either iPhone or Androids looks really interesting.

Even does more than the $2700 1990s “black box” some Chrysler dealerships had.

Does look interesting. Not sure I'm smart enough to figure out what the data is telling me if I were to invest in the app. I've narrowed down the rpm that produces the greatest vibration to 1250. A little less than what I thought it was. This is just by observing the vibration in the steering wheel and feel. Vibration is felt from front to rear of trans when the engine is running in park. The rear of the trans and even into the driveshaft the vibration feels greater. The exhaust system is vibrating also. The vibration is felt some in the engine, but does not seem to vary much from the rear of the engine to the front and is not as great as what is felt at the trans. Are there any components inside the transmission that could get out of balance enough to setup the vibration? Does not seem like there are a lot of moving parts inside the trans when it is running in park. Still plan to swap out the TC first to see if that fixes the problem. Just wondering if I should continue to disassemble the transmission while I have it disconnected from the engine to look for something internal.

Thanks for all the help,

John

I know it's going to sound "crazy"....but double check your firing order, make sure the plug wires are on the right cylinders and cap terminals....I bought a truck once that a shop sold cheap because all the ASE certified techs couldn't solve the drivetrain/body vibration it had at low speed.... took a few minutes to find it after ruling out the simple stuff...never know?

Worth a shot Cheap is good
A vacuum gauge may show something as well

the puzzling part is it was fine for the first 200 miles and then occurred after that in which time I assume the car was parked for a period ? It has to be engine/trans related based on the details.
Only other thing I can think of right now would be to check exhaust temps before and after the mufflers. might have dropped a baffle or have a nest but those are long shots. Cheap to check though
keep us posted

have you looked really close at the transmission mount ?
the new reproduction versions leave a lot to be desired, and many of the "new" originals are pretty hard by now.
just tossing this out there.
whatever you find out, let us know.

If it vibrates in gear standing still, only thing trans related is the converter - likely just the balance weight.
Possibly, a wild shot, the pump bushing is way over spec on clearance and not piloting the converter properly but that may be a stretch.

if the pump bushing is bad, out of spec, wouldn't that cause a leak, or at least some dampness in the bellhousing ?

I never checked for vibration in gear with out the car moving, so I just did that. In Drive and reverse holding the brake so the car cannot move and bringing the RPM's up against the converter, I get about the same vibration that maxes at 1250 RPM. Subjectively it is very similar to what I see and feel in neutral and park. So if during this test the only thing turning is the engine and the torque converter, it seems to rule out any internal transmission problem. I guess the pump is also running? Am I thinking this through correctly?

I rechecked the firing order and plug wire connections. All checked out fine. I have 15" of vacuum at 750 rpm idle and the vacuum is steady. Inspected the trans mount pretty carefully and did not see any issues with the rubber or metal. It is a new aftermarket one and is not ideal, but better than the old one that came with the car. IIRC, the metal bracket on the new mount was pretty flimsy, so I removed the rubber insert with the metal sleeve that surrounds it and put it in the original metal bracket.

Yes, the car set for probably a couple of weeks between the last time I drove it and did not notice any vibration and when I first noticed the vibration. The day I first noticed the vibration the beginning of the drive seemed fine and then after probably 10 minutes of driving I began to notice the vibration. I do not recall hearing anything like something that might have come loose, but I really was not paying real close attention since it was a nice day and I was just enjoying a drive.

When I rebuilt the trans, I replaced the pump bushing with a Babbitt bushing I sourced from A&A. I thought I had some measurements of the clearance, but cannot find them so maybe I did not take any measurements. It was the early narrow bushing. I don't see any trans fluid leaks anywhere.

Pump bushings are all the same width. I doubt that is your problem unless you spun it somehow. Even spun, I have seen some not generate a leak.
As for your stall test, nothing in the trans is likely your issue based on your test result.

Another silly thought,
What is your timing at the 1200 or so RPM vibration point?
Was the TDC mark verified to be in the right place?
What is your timing doing?
Initial is set at?
mechanical starts coming in at ?
Total mechanical is in by what RPM
And vacuum Advance, If hooked up
Is it to ported or manifold vacuum?

I don't have a timing number at 1250 where the vibration is most noticeable, but not too hard to get.
I used a piston stop to get on TDC before removing the old balancer and the timing mark was dead on. When I installed the new, refurbished original, balancer the timing mark on that one lined up also with the zero on the timing tab.

Timing is 13 at idle (around 750) with vacuum advance disconnected and plugged. I get 34 at about 2800 RPM. The timing is steady and consistent at idle and 2800. I did not pay a lot of attention to what it was doing as I was bringing the engine up to 2800, but don't recall seeing anything that might have indicated an issue.

VA is hooked up to ported vacuum. The carb is an original holley 4368 and the VA is hooked up to the port that the service manual shows as correct. I get about 47 degrees with the VA hooked up at 2800 RPM.

My intention has been to spend some more time trying to dial in the best timing and advance for this combo, but the vibration has put this on the back burner. The way it is setup, it runs pretty good. It starts easily, does not ping at least that I can hear, idles at a steady RPM, has good throttle response, and feels strong up to 5500 RPM or so. I had a wide band O2 sensor installed when I first put the engine back in the car and got the car on the road. I got the carb/ignition tune so it would idle at 14.2 -14.5 AFR and cruise at 14.7 - 15.1 AFR. Maybe a little on the lean side for ethanol fuel, but don't think it is pinging/detonating and don't feel any lean surge. I don't remember the WOT number, but it was ok as well.

I want to again thank everyone for the ideas and thoughts. I am trying my best to make sure the easy stuff to fix/adjust is done and nothing is overlooked before I resort to taking the drivetrain apart. I think I've got a replacement converter lined up that I should be able to get this week. So have a little more time to check and verify things before I dive into converter replacement.

Regards,
John

Using the piston stop I',m going to assume it was an adjusatble version that allowed you to keep backing ti out to find the exact TDC. Or was it the version that you rotate both directions, making a mark at each stop and splitting the difrrence ?

Another long shot but easy and cheap to try. Disconnect the vacuum advance and see if it has any effect. excessive advance
(doubtful) can cause misfiring. A cheap try

Yep I used an adjustable stop. It took me a long time to get to a point where I felt that I had the engine on TDC. The piston stop I used was a homemade one because I could not find the one I bought. The stop bolt was coarse thread, so it did not have as fine of an adjustment as I would have liked. So, repeated the setup probably half a dozen times or more until I got to where I had confidence that I had the engine at a TDC. I even did one setup using #6 just to see if it was different by much. I was not focusing much on the mark on the balancer since I thought perhaps the balancer had slipped and was the source of the vibration. When I did finally get to TDC, the balancer mark lined up with 0 on the tab. During the engine build before I put the heads on, I used a stop and a dial indicator to get on TDC pretty accurately. When the balancer was installed then, the mark lined up with 0. So, I think, even though I swapped the balancers the original one that was on the engine is probably fine.

I did run it without the VA and noticed no difference.

Thanks for your thoughts, very helpful.

R/ John

on a side note, I always file a shallow groove between the center and outside hub of the balance so if it should slip it's visible
had a customers car a few years back in which the outer ring would move every time you throttled it. That was a what the - is going on one

I didn't fully read all the posts so sorry if it was already mentioned but another source of engine vibration "all of a sudden" can be traced to the harmonic balancer. The inner and outer portions of the balancer are attached together by a thin piece of rubber. Its possible the outer piece (ring) slipped out of position causing an imbalance. The slippage would be impossible to see with the naked eye. The only way to check slippage is locate TDC on #1 piston using a stop or dial indicator through the spark plug hole and comparing the TDC mark on the balancer to the "0" on the timing chain cover. Good luck.

he's been down that road

I apologize for the length of this post, but wanted to update everyone on the search for a solution to the vibration problem I am having. To refresh everyone, the car is a 1970 Challenger R/T, 383/727 that is a stock restoration with about 350 miles on it. After checking all the easy stuff that I could think of and that you suggested, the conclusion was that the source of the vibration was likely in the torque converter.

I finally found the time to replace the converter and used a new flex plate. The vibration did not go away. I did not run the engine very long and drove it only a few miles, but it seems like maybe it is slightly less, but still noticeable at around 1250 RPM in neutral, park, stationary in gear, and going down the road. I used a rebuilt stock 10 3/4" converter that I got through Pat Blais. The converter that was in the car was also a rebuilt stock 10 3/4" that Pat supplied. Pat has them rebuilt at a converter shop near him. There were no obvious issues with the converter that I removed, small weight was intact, inside of converter looked clean. There was also no sign of any issues in the trans when I removed the pan to drain the fluid. The trans mount was carefully inspected when I removed it to pull the trans and found no issues or defects.

Before replacing the converter, I removed the engine oil pan to inspect the bottom end. When the engine was balanced, the replacement pistons were lighter than stock, so material was removed from the crank. There was no mallory metal that could have come loose to unbalance the rotating assembly. Everything there looked as it should. Checked torque on the mains and some of the rods and everything was fine. One thing I noticed earlier was that the vacuum at idle was 15". I pulled the carb and replaced the thick spacer gasket that was on the manifold. The spacer is a FELPRO 60123. It has brass grommets holding two thinner pieces of material together to make the approximately 1/4" thickness. The flanges on those grommets sit slightly proud of the gasket material and I think were preventing the carb from completely sealing to the manifold. I removed the grommets used some #2 permatex to glue the two pieces together and put it back together. The carb is the original R4368 Holley that I refurbished when doing the engine build a few years ago. It was clean and in good shape. After restart, the idle vacuum was now 17", but the vibration remained the same. The engine runs strong up to 5600 RPM or so, idles smoothly at 750 RPM, starts easily, does not overheat, does not make any unusual noises, and I cannot see or feel any vibration in the engine like I can in the steering wheel and through the seat.

My thinking is if the vibration is originating in the engine, but being felt in the steering wheel and seat it has to be transmitting through the motor mounts. There are not any other parts of the engine in contact with the body or chassis of the car. I checked the mounts for tightness and inspected the rubber as best as I could earlier and felt they were fine. Might be that I need to remove them from the car and do a better inspection. Anyway, I'm quickly running out ideas so any thoughts or suggestions are very much appreciated.

Regards,
John

I've been following and have to ask about this statement:
"There were no obvious issues with the converter that I removed, small weight was intact, inside of converter looked clean."

What exactly do you mean by this??? Isn't your 383 internally balanced with a steel crank??? No weights should be on the convertor IMHO.
Ron

I attached some pictures of the converter that I removed. The weight I am referring to is the small rectangular tab welded to the outer shell. I assumed that it was there to balance the converter, but perhaps it has some other purpose. Yes the engine is internally balanced and the converter is a 764 Mopar unit that is correct for an internally balanced engine.

Thanks,

John