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?

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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