Happy New Year everyone,

My 1970 Challenger has developed a vibration that can be felt and seen (I have a video, but it is too large to upload) in the steering wheel and also felt in the seat. The vibration occurs when the car is in park and continues while driving. It is there at all engine speeds, but more pronounced at 1200 to 2000 RPM. I said developed because I got the car on the road about a year ago and for the first 200 miles or so, I did not notice any vibration. The vibration seemed to start all of a sudden a few months ago and nothing that I've checked seems to be the source of the problem. The car currently has less than 400 miles on it since a total restoration. My suspension, wheel balance, and alignment guy drove the car and inspected it thoroughly for any loose or otherwise obvious problems. He said that the source of the vibration is not in the wheels/tires, driveshaft, wheel bearings, rear, etc., which makes sense since it is very noticeable when the car is sitting still running in park. The engine is an essentially stock rebuild of the original N code 383 mated to the original 727 trans. The trans was rebuilt by me and the torque converter is a refurbished stock 10 3/4 unit I got from Tflite Patty. I've run the engine with the PS and Alt/Fan/WP belts removed and the vibration remains the same. I replaced the harmonic balancer with a refurbished original one. It runs true without any wobble and did not make any change in the vibration. The engine has a stock flat tappet hydraulic cam from Mr. Sixpak with his lifters. There is one lifter that rattles a lot if the engine is not run for several weeks and takes a while to pump back up. The engine runs good, starts easy, runs cool, and has good power. I can see some shake in the engine at idle, but seems like what one would expect for that engine. I cannot feel the vibration in the engine like I can in the steering wheel. I pulled each plug wire while the engine was running about 1500 RPM and got about a 100 RPM drop on each cylinder. The drop varied some with 80 RPM being the least drop on #1 and on #5. I'm about out of ideas before I start diving into either the engine or transmission and then not sure where to begin. Thanks for any help or suggestions you can provide.

Regards,

John Brough

. Layer it back. What has changed from the first time this started? Have you added or changed anything?

Engine/trans mounts tight? k-frame bolts tight?

Could the torque converter have thrown a balance weight?

[spoiler][/spoiler]

These issues can be maddening, but that's what I'd check first - loose bolts.

Has it gotten worse or has it always been about the same?

As mentioned check the converter bolts.
Once the Converter bolts are tight one may also be able to see / check if the flex plate bolts are loose at the crank by trying to move the converter CW /CCW.
Rotate the motor around and check the flex plate for cracks preferably watching it while bumping it around with a remote starter switch.
Verify the engine mounts have not collapsed
Check the entire exhaust system for any place it may be touching anything.
Check for anything on the engine or trans that may be touching the body anywhere.
A real longshot would be a rotating heat riser butterfly
Would be very helpful if you could do the above on a 4 post lift
keep us posted

Make sure the trans to engine mating bolts are all tight. Otherwise I would suspect the converter.

First thanks everyone for your thoughts and suggestions.

I too have been trying to figure out what I might have changed to cause the vibration. There have been no mechanical changes or additions to the car from the pre-vibration state. After first noticing the vibration, the vibration has remained the same, although there are not a lot of miles or run time since then. Shortly before noticing the vibration I did reset the points and adjust the timing. I don't remember if it was immediately before or not. I checked the dwell and timing again yesterday and they were spot on. I did not pull the distributor cap to see if something might be going on inside the cap. I don't hear any strange noises. Hard for me to believe that this is a possible source, but will check.

When my alignment/suspension mechanic inspected the car, he looked closely for loose bolts and anything that could be touching any part of the body of the car. He has more than 50 years experience with brake, suspension, alignment and has worked on many Mopars back when they were regularly on the road. Before looking under the car, he drove it and after the drive he told me that he would find something under the car that was causing the problem. The vibration in the steering wheel, made him think it was something loose or hitting something under the car. He found nothing and said that it was either an engine or transmission problem in his opinion. I do need to checkout the motor mounts a bit more closely. They are new, but Chinese mfg. They look OK, but may actually remove them to inspect.

I did spend some time looking at the TC. The bolts to the flexplate are tight. The flexplate appears to be tight to the crank. The bolts to the crank appear OK but really can't see a lot. I did not see any cracks in the flexplate. I did not watch the flexplate/TC while bumping the engine over to look for any looseness. Will put that on the to do list. I also did not watch the converter with the engine running to see if there was anything obviously not running true. I have a 2 post lift, so can do that. The engine is externally balanced and the TC is a stock 10 3/4" neutral balance unit. I looked to see if there may have been a balance weight on the TC that came loose, but did not see anything. I have the stock shields on the bottom side of the bell that would keep any part that came loose from getting out. I did not find any loose parts in there when I removed the shields. I have not checked the engine to trans bolts, so that will be on my to do list.

I have stock manifolds on the car, but the heat riser butterfly in the right side manifold was removed.

I too was beginning to suspect the converter. Assuming I don't find anything else, probably will pull the trans back, inspect the flex plate thoroughly and swap out the converter.

It was suggested to me that perhaps a chunk of mallory metal put in the crank during balancing might have dislodged. I don't know if there is any mallory in the crank or not, my receipt for the engine work just says balance crank assembly. The new pistons I put in during the rebuild are about 60 grams lighter that the old ones, so I suspect when it was balanced they had to remove metal from the crank. Intend to get back in touch with the shop that did the balancing and see if they have any recollection, but it has been 3 years.

I edited the video I made with my iPhone that shows the steering wheel vibration to a few MB with the intent of posting it. However, the file format is not one of the allowed formats, so don't know how to show you what I'm dealing with. So, I added a couple of pics to give you an idea of what I'm working on.

Thanks again for the ideas and suggestions. If you have additional thoughts I'd love to hear them. I'll try to keep this post up to date.

R/ John

Why did pictures get rotated?

Neutral balance?

A bit of a long shot but you mentioned that the steering column vibrates: check that the bolts that attach the steering box to the K-member are tight. Is there any way that you can put your car on the lift with the engine running and have someone else look/feel different spots that can cause vibrations?

Something isn't right here. A stock '70 383 should be internally balanced. If it is truly externally balanced and you have a neutral TC on it, then you need an aftermarket flexplate w/ the scallop cutout.

If a piece of mallory got dislodged from the crank, you'd probably have a hole in the oil pan or block.

With all that stuff checked, I’m kinda thinking vacuum leak. Maybe some trash in the carb? After that I’d think torque convertor.

I hate vibrations!!!! I fought two of them. One was wrong converter or flex plate. The other all I could do to make it tolerable was remove urethane engine and trans mounts to mitigate.

Everytime I post pics from my phone it turns them

Good question but we can click on them to rotate.

My bad. It is internal balance. Not external

I bought a '73 Charger with a 400-2bbl in Phoenix back in the 80's that had a problem just like you describe. I brought the car back & sold it before I ever corrected the problem. Most people I described this to simply said it was the flex plate. I would check this & the torque converter first.

I had the wierdest vibration issue, that was only felt in the steering wheel . . . it would appear once over 55/60mph . . . and, the engine sounded like it was pinging....I checked so many things.. . then FINALLY found the problem . . . When I had restored the car, I used the old pwr steering pump that was with the car . . . HOWEVER, there was part of the bracketry MISSING !!! . . . this is a small block car, so I thought I had everything, BUT - the triangle shaped bracket that goes between the pump & block, was missing. This in turn, allowed the rear bracket to crack, then break. . . in such a fashion, that it was"keyed together", until enough rpm caused it to start to vibrate - AND making it sound like the engine was pinging . . . not sure if that helps you out, as big block uses different pwr steering brackets . . . but maybe something to "steer" you in right direction ?? , , , ,

Good luck

great suggestion but from the OP

Quote

I've run the engine with the PS and Alt/Fan/WP belts removed and the vibration remains the same.

Bummer i had one in a66 Dodge wagon many years back, even did bearings in the engine, never did find it but put 50K on it

I ruled out an issue with the PS pump by running the engine with the PS pump belt removed. I verified tightness of motor mount bolts, trans to engine, steering box to K frame, and flex plate to TC. I did not remove the motor mounts, the rubber looks good, no sign of any cracks. Cranked over engine while watching flex plate and TC, did not see anything unusual. Reinspected what I could see of flexplate looking for cracks or looseness at crankshaft. Used a small prybar to see if I could move the TC in any direction other than in the normal rotation and everything was tight. Pulled the dizzy cap, all good there. Ran the engine with car on lift and looked at TC. Did not see any obvious imbalance or vibration. I could feel some vibration when I laid my hand on the trans bell and on the trans pan. The engine seemed much smoother, although there might be a very slight vibration. So thinking I'm at the point where things have to come apart. I'll likely pull the trans from the engine to more thoroughly inspect the flexplate and most likely replace the TC as many of you have suggested.

I've not checked into a vacuum leak being the source of the vibration. As I said starts easy, runs cool, has good power, and no ping that I can detect/hear. I cannot feel or detect a miss in the engine. The RPM drop test seems to indicate that each cylinder is firing. The vacuum gauge is steady at 15" at idle. I would have expected a bit more, maybe 17 or so. Will spend some more time on this while I'm trying to lineup a replacement converter.

Thanks for your thoughts and suggestions.

R/ John

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

You are correct. If it were externally balanced then, in addition to that side weight you have, there would be a larger imbalance weight on the face of the converter.

My thoughts are something wrong in the balancing. It was most likely always there from the start up. You have done just about everything else possible. Was this the original engine and crankshaft to the car?

Maybe it has developed a misfire. Have the plugs been looked at.

Not sure if you've already gone down this road, but maybe the trans mount? Its been a long time but I had a vibration, though I think only when driving, that went away when I replaced the Energy Suspension red poly mount with a stock trans mount.

I also am starting to think that the problem has been there since the start and I just did not notice it. It is the matching numbers 383 block. It is the crankshaft that was in the engine and I believe it is original, although when we tore it down for the rebuild a few years ago, it was obvious that it had been gone through before, so anything is possible. It is a forged crankshaft stock stroke for a 383. The shop that did the machine work for me balanced the rotating assembly. They had to take material out of the counterweights to get it to balance with the lighter pistons that I used. I did not get any data with the balance job, just a note on the bill that it was balanced. The shop is very respected and reliable, so it is hard to believe that the balance is off, but mistakes do happen.

At the beginning of the search for the source of my problem I did a RPM drop test for each cylinder by pulling each plug wire one by one. Cylinders #3 and #5 did not drop as much as the others. They were not dead, just a bit less. IIRC they were about 80 RPM and the others were around 100 RPM. I'm going to repeat this test and verify the previous results. Also going to try again to verify that the vibration is not the result of a misfire. I did pull and inspect all the plugs and did not notice anything that would suggest a misfire, but will do that again. The vibration does not feel like a misfire at least based on my experience. I don't feel or see the vibration in the engine like I do in the steering wheel and through the seats.

Yesterday I found an issue with the left motor mount insulator that I thought might be the problem. The stud on the aftermarket insulator was too long and the end of it was gouging slightly into the block. The right side had clearance. I found an original insulator in my parts stash that was in OK shape and also the rubber seemed much softer, so I put that in place to see if it made any difference. There was no noticeable change in the vibration.

Thanks again to everyone that has provided their thoughts and experience to help me figure out this problem.

Regards,

John

I was referring to this type of weight that is used for cast crank external balance engines.

Are all 3 of your mounts rubber? Poly has been known to transfer some harmonics.

Have you brought the car to the shop?
A quick demonstration of the vibration might get some address by them.
I'd expect a properly balanced rotating assembly should not be the source.
Do you have a magnet oil drain plug, or have cut open an oil filter to see if there is any obvious bearing or other metal showing up?

I have not yet been in touch with the machine shop. They are about 3 hours from me, so taking the car to them while not out of the question is not real easy. I will be in the area where the shop is located next week and plan to go talk with them. Agree a properly balanced rotating assembly should not be a source. I don't have a magnetic drain plug and have not taken the oil filter apart. However, I did remove the oil pan and it was very clean. I did not find any obvious metal or other debris.

The insulators and trans mount are rubber aftermarket items that are less than OEM quality IMO. I think I got them from NAPA. The driver side insulator is now an old rubber insulator that was on the engine when I got the car. It has some numbers on it, but don't think it is an original MOPAR part. I installed it yesterday to see if it would solve the problem. It did not. I am going to install an old right side insulator that has a MOPAR part number on it just to see if anything changes. I don't have an old trans mount to try.

John

have you looked really, REALLY, close at your transmission mount ?
sometimes they can contact the crossmember and be hard to see where, making one think all is good.

Have you done a compression check?

Wow - amazed this has not been figgered-out yet!

For entertainment sake, here's an old true Mopar story my old business partner told me about many years ago - I was in business with him from 1984-1992. A buddy of his bought a NEW 1967 Charger with a 440 in it back in the day. From day 1, the car had a strange vibration coming from somewhere. The car was back to the dealer numerous times - they replaced: the wheels, the tires, the driveshaft & U-joints, the fan, etc. They COULD NOT get the vibration figured-out. Last resort before buying the car back, was to schedule a meeting with the factory rep from Chrysler. So the day comes & my old partner & his buddy - the car owner show-up to the dealer. The factory guy is there & he says "let's take it out for a ride." The Chrysler dude is driving & they finally jump on the highway - he mats the gas pedal until the motor blows. He says: "looks like we found the problem!" The car gets a new 440 & problem was solved. True story............

That solution has crossed my mind.

I replaced both motor mounts with old used ones. One has a MOPAR number the other is an old aftermarket I believe. The rubber in them seemed much more pliable than the rubber in the new mounts. Anyway, no change in vibration. I removed the transmission mount to take another very close look at it. It looks like what it is, a brand new rubber mount. When I bought the mount, the metal U-shaped bracket that holds the insert was made from much thinner metal and looked flimsy. I removed the rubber insert with its steel shell and installed it in my original bracket. The original mount rubber was junk. So, I don't have an original trans mount to try.

I ran the engine with the trans mount removed, and the vibration was pretty much gone. Possibly completely gone. I had the car in the air on my lift with the trans supported on an under lift stand, so I had to use a ladder to get in the car and start it. I did not run it very long since my garage door was closed. I also did not get under the car while it was running to see if I could see/feel any vibration in the transmission. I may repeat this test with some additional help, but not sure what more I could learn from that. I think I've learned that the vibration is being transmitted from the engine/trans through the trans mount into the body. I suspected that was the case, since I could feel the vibration in the seat and steering wheel ( and see it in the steering wheel) but could not feel it anywhere under the hood.

I'm thinking I'll pull the valve covers first and do some inspecting of the valve train to make sure all is well there. Then maybe the intake and valley pan to get a good look at the cam and lifters. Could a bad lifter, bent push rod, bad rocker, or even a cam that is going south on a cylinder cause an imbalance in the engine firing that transmits through the mounts to the body? It is a stock flat tappet hydraulic cam with the original pushrods and rockers.

R/ John

Years back my buddy had a similar situation and i noticed he didn't have those rectangle washers under the two trans. bolts. The bolts were bottoming out and mount was ever so loose because of it.
Just another thought.
Ron

A vacuum gauge will quickly answer if you have an issue in the last bolded paragraph. A cheap often overlloked diagnostic ? tuning tool that everyone should have

Myself I would repeat the test on the lift with additional help. Might be able to buy rent or borrow exhaust hose or find something else that will take the heat HOSE LINKY That will help tremendously with the exhaust fumes.
I started out with with a kit $$, a door port and a cheap exhaust fan (for green houses?) Worked well until the fan gave it up. So I bought a Dayton Commercial unit that i set outside, hook the hoses up and I can run a car for quite some time. Great for heating the shop up if it's cold LOL 🥶☃🥶

I think pursuing your path MAY expose the issue. Do make sure the trans is at the same height as with the CM in place. one can then raise or lower it a bit, Keep us posted

glad to hear about the transmission mount investigation.
do you suppose the mount you had there was a tick too short, causing the transmission to hit the crossmember, or was it just the bad rubber it was made of ?
have you tried to space the mount away from the transmission ?
i forget. is this mount a spool type or the earlier block type ?

Unless you do this exact same test with only the trans mount installed being different, it really means nothing. You can't compare results of a test between a car on a lift with the transmission mount removed to a car on the ground with the transmission mount bolted in place. The very concept of putting the car on the lift compared to it not being on a lift just doesn't work, lots of stuff is different between those two comparisons.
Unless some serious measuring was done between the position of the tail shaft of trans on a lift stand, and careful measurements of the trans mounted on the mount, your results could be inaccurate. If the differences between the tail shaft height with out the mount and with the mount are only 1/8" different, the entire problem could be as simple as a driveshaft u joint angle bind, or a bind between the two motor mounts and the trans mount. With the trans supported on a stand, its free to move side to side and up and down as much, or as little as it pleases, and only eliminates the fact that securing the trans stops the vibration, it doesn't put the blame anywhere.
You could put the mount back in, with the bolts slightly loose and retest to see if the vibration is gone or still present. If its gone, then I would tighten the bolts to the trans and test, then tighten the bolts to the mount and test, then maybe change the order in which the bolts are tightened, and see if one or the other solves (or at least helps) the vibration. If the vibration is still present with the bolts loose, you may want to add shims (washers) to lift the trans above the mount.to see what that might do.

PB,
I agree but he didn't say whether it was a 2 or 4 post lift, If it were a 4 post with jack trays or a trans jack would be a big plus IMO

I agree that removing the trans mount does nothing to help figure out what is causing the vibration in the first place. My objective of the test was to try and figure out how the vibration that was produced in the engine/transmission was being transmitted through the seats and steering column/wheel. Since replacing the motor mounts did not help at all and I did not have another trans mount I thought that removing it would isolate the rear of the transmission from the body. I don't believe that there is anything wrong with the transmission mount that I have. There is no contact anywhere between the mount and the crossmember or body. Since the vibration occurs while running the engine in Park, driveline geometry does not come into play. I removed the mount on a 2 post lift, left the crossmember in place and removed the through bolt and two bolts into the transmission without lowering or raising the end of the transmission appreciably. I then started and ran the engine only in Park. I don't think any transmission mount will be able to dampen the vibration that is coming from the engine/trans so I am going to focus on finding the source of the vibration.

I have used a vacuum gauge a lot during this search. Yesterday I went back through the ignition system. The distributor is an original points unit that I refurbished. It does not have the electronic vacuum advance on it, it has a conventional vacuum advance can. Timing at 750 RPM idle with VA disconnected is 15 BTDC, vacuum is 16" and steady. Vacuum was measured off port on rear of carb. VA is hooked to a ported signal from the front of the carb. Carb is an original Holley 4368. Timing all in at 2850 RPM is 35 w/o vacuum advance.

With the engine idling I took a RPM reading from my timing light and then removed the wire for a cylinder at the distributor cap and recorded a second RPM reading. I repeated this for each cylinder and at an initial ( all wires in place idling normally) RPM of around 1040 and a second test at a RPM of around 740. For the 1040 RPM test the RPM drop varied from a high of 115 RPM to a low of 55 RPM. For the 740 RPM test the high was 50 RPM and the low was 30 RPM. With a plug wire disconnected the RPM's jumped around a lot, so I had to try to make an estimate of the average RPM from watching the numbers on my timing light. This obviously introduces some errors in the data. Other than confirming that each cylinder is firing I'm still trying to figure out what the data is telling me.

I also used a IR temperature gun to measure the exhaust temperatures as near to the outlet of each cylinder as possible. They varied from 640F to 540F on all cylinders but #1. It measured 470F to 490F on multiple tests. Again, not sure what the low temperature on one cylinder is telling me. Temperature variation could be just leaner or richer mixture at each cylinder since I'm relying on a carb.

I've been working on cars and engines as a hobby and made my living as an engineer working in and around lots of industrial machinery for more than 50 years. I've never run into a problem like this that seems to have no answer. I'm sure the answer is there and I will find it eventually, but it is at this point trying my patience. Thanks again to everyone that has helped me try to figure this out.

Regards,

John

Couple other things to try to isolate.
Take a half empty bottle of water with the cap tight and hold it here and there in a manner the you can observe the "rings" formed on the water surface. My mechanic mentor (in the early 70's) showed me this and it surprisingly helped isolate location of various vibrations (end to end, side to side)..
Ratchet straps over transmission and cinched tight to cross member can help eliminate mounts as source. put one over the bell housing to uni frame, and they can also be used to pull the front of engine down (up or side to side). Try different configurations.
With all that my gut feeling is it is internal, or t.c. Also not mentioned is fif there was any major structural replacement of the uni frame assy that may need inspected.

I would get the hoses or suitable substitute and repeat your test to confirm your previous results.

Compression checked today.
Engine cold, all plugs removed, throttle and choke propped open

#1 - 165 psi #2 - 170 psi
#3 - 160 psi #4 - 170 psi
#5 - 170 psi #6 - 165 psi
#7 - 170 psi #8 - 165 psi

#3 is a bit lower than the others. Rechecked it and got the same number.

Cranked engine over with all plugs removed to look and listen for any signs of something that could be causing the vibration. I was under the car on the lift. Nothing noticed.

Plugs look OK to me. I don't see any sign of fouling, misfire, damage, or detonation. Not the best pictures I know.

Removed valve covers to take a look. Clean inside, no obvious damage to anything. All valves move as expected when cranking the engine over. I did not try to measure lift.

I'm about ready to rule out a misfire as the source of the vibration. I've ruled out the torque converter or flex plate since those have been replaced. I am pretty sure that vibration is so great that the motor and transmission mounts cannot dampen it out. I do plan to investigate the transmission mount a little further before I rule the mounts out. Nothing from the engine or trans is hitting anything on the body of the car. The front frame rails and inner fenders are original and were in good shape. I did replace the cowl, firewall, and all the floors. The torsion bar mount is original and was in good shape.

I'm narrowing down the possibilities to something internal in the engine. I did not check the transmission to engine alignment when I put the car together. Both dowel pins in the block are in place and the engine and trans are matching numbers, so I assumed it must be right. To measure the alignment, I think I would need to disassemble the trans so I could bolt up the empty case and use a dial indicator to measure the alignment. This is quickly becoming a major job.

John

Washers are there.

Agreed, just that engines don't develop a balance issue. Unless a weight flys off and you would have noticed that. Balancer/ tourque conveter issues wold be my next look.

He has already swapped the converter and flex plate. I am not trying to be offensive to him in any way but rather he is beginning to chase ghosts as my old German boss would say. (IE: chasing his tail.)

He did one thing that MAY have alleviated the problem. I would go back and repeat that test to confirm or deny its affect. Then go from there

I will say I had one years ago that I did everything short of pulling the motor and tearing it down. Even did new bearings. NADA, never did find it, but I put 40K + miles on the car before selling it to a friend. 5 years later he said it had been the best car he ever owned except for that 67-72MPH vibration

Yep . I see that now.

How far is the DS yoke into the trans?
Got a pic?

So you have a video according to your first post. Set up a YouTube account and post it so we can see it. It might reveal something.

No offense taken. I absolutely feel like I am chasing my tail. It should not be this hard to figure out. I intend to repeat the no trans mount test. I will have some help so I can not only evaluate vibration inside the car but can also evaluate from underneath. I will be able to raise and lower the end of the transmission some to see if that changes anything. Although with the trans bolted firmly to the engine, how raising or lowering the end of the transmission could change the vibration when the transmission is in Park is not clear to me. I ordered another transmission mount. It is also a rubber mount and aftermarket. Made by Anchor. Don't expect it to fix the problem, but would be great if it did.

I am beginning to second guess my observation that the vibration suddenly appeared. Perhaps it was there all along and I wrote it off as a wheel/tire issue. I am running aftermarket Magnum 500's with bias ply Polyglas tires that were hard to get to balance. Certainly if it turns out to be a balance issue with the rotating assembly, that did not just all of a sudden happen. There are no weights that flew off.

R/ John

I do not have a pic. I'll get some. I am using the stock driveshaft that was in the car originally and rear springs/ride height are stock. Although on the lift it probably will be further out than it would normally run. I don't think it is anywhere near bottoming out on the output shaft. Plus the vibration occurs when the car is stationary in Park, neutral, and in gear when holding the brake. Seems like if the yoke was the problem it would occur only when moving.

R/ John