Ongoing vibration issue

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David Dickerson

David Dickerson

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Haven't chimed in in awhile, but looking for more opinions on an ongoing vibration issue I have been dealing with in my Duster that nothing I have done has alleviated the problem. I have a noticeable vibration that starts around 2200 rpm and gets very noticeable at 3000 while the car is at rest. It becomes less noticeable above 3200. Makes the car unenjoyable to drive since that rpm is right at cruising speed between 55 and 65, and begins to pulsate at sustained speeds. Again, this occurs while the car is standing still. I started by changing everything external like torque converter, flexplate, harmonic balancer, unhooking accessories, with no improvement. Finally decided to build a new motor thinking it had to be an internal issue in the engine. Built a 408 stroker and still have the same results. Though previously everyone said it couldn't be the transmission, I have to wonder since it is the only thing left. I did convert my engine and tranni mounts to urethane, but would be surprised if that could be the problem. The tranni is a 727. Wish I could run the engine with the tranni unhooked, but not on a MOPAR. Anyone ever had an issue with the input shaft or pump causing vibration issues? Thinking of trying to find another 727 that I can just throw in there for testing purposes. I am out of possible causes, and the solutions so far have added up to quite an expense. I must say though that the 408 is very welcome under the hood over the 340.
 
Sounds to me like you're fighting a balance issue.
You don't say what balance your 408 was built for (internal/external), or what your previous 340 was, either (they were built both ways, depending upon year- so you could still be fighting the identical issue).
Replacing the torque convertor/flexplate will not accomplish anything unless they are replaced with the proper units, ie throwing a brand new neutral balance TC on it when the engine requires an external balance... An incorrect harmonic balancer could also be contributing to the issue for the same reasons.
Please elaborate on your build and what parts you used, in addition to how you had your rotating assembly balanced.
 
That's a lot of money for motor / trans mounts.


I had a 92 Chevy lumina, it had rubber isolated struts the hold the engine inplace.

One was bad so I decided to replace it with a piece of bar stock.

You would have thought I put a 500 ciu V8 in the thing, the entire car shook!

Since you are throwing parts at it I would change out the mounts to stock and see how it feels.


Still could be the trans rotating assy!
 
I had the same issue with a 360 /727 and it turned out the motor had dowel pins from a 4 speed car.
 
Unlikely that TWO engines would have vibration problems. I would be looking at the tq c'ter.
 
The 408 is an internally balanced engine. I made sure of that. The torque converter was replaced, so I doubt two converters would vibrate at the same rpm. Both were for internal (neutral) balance. I purchased the 408 from ATK completely assembled and balanced with forged crank and pistons. Used Trick Flow powerport 190 heads. All roller valvetrain.
 
There is a difference. I didn't know it. My tranny bolted in fine. The four speed pins I believe may be slightly offset as to use a dial indicator to get standard bellhousing centered. Similar to this. Hopefully someone will chime in.
Quick Time RM-146 Quick Time OFFSET DOWEL PIN - 10MM, .014 Offset

I changed u joints rebuilt my rearend and all kinds of crazy stuff trying to figure it out.
 
Kendog 170 said:
There is a difference. I didn't know it. My tranny bolted in fine. The four speed pins I believe may be slightly offset as to use a dial indicator to get standard bellhousing centered. Similar to this. Hopefully someone will chime in.
Quick Time RM-146 Quick Time OFFSET DOWEL PIN - 10MM, .014 Offset

I changed u joints rebuilt my rearend and all kinds of crazy stuff trying to figure it out.
Click to expand...
And the torque converter also lined up with the wrong dowel pins? If I were to take the dowel pins out of the current transmission, would I see an offset in them if they are the wrong ones?
 
David Dickerson said:
And the torque converter also lined up with the wrong dowel pins? If I were to take the dowel pins out of the current transmission, would I see an offset in them if they are the wrong ones?
Click to expand...
I would think so yes. This was back in the 80's and my buddy helped me with it. He was surprised I didn't mess up the front pump of the tranny. I put up with it for about a year.:BangHead: But if you used a different motor did it already have dowels in that motor? Probably not your problem but just wanted to make a point of it.
 
Kendog 170 said:
I would think so yes. This was back in the 80's and my buddy helped me with it. He was surprised I didn't mess up the front pump of the tranny. I put up with it for about a year.:BangHead: But if you used a different motor did it already have dowels in that motor? Probably not your problem but just wanted to make a point of it.
Click to expand...
Yes, there were already pins in the new block.
 
512Stroker said:
OP stated that the issue is when the car is at rest.
Brings up another question , what happens when its going down the road?
Click to expand...
Did not know if he meant at rest on the wheels or up on jackstands. Just trying to rule out another possibility.
 
I'm for changing out the aftermarket mounts. I've heard before that a poly trans mount will cause vibration. It is about the only thing left besides the trans, and I doubt that is it. I was having a vibration in my truck, and I talked to my transmission builder, and he said that there's nothing in the transmission to vibrate. It turned out to be a bent flexplate.
 
furyus2 said:
I'm for changing out the aftermarket mounts. I've heard before that a poly trans mount will cause vibration. It is about the only thing left besides the trans, and I doubt that is it. I was having a vibration in my truck, and I talked to my transmission builder, and he said that there's nothing in the transmission to vibrate. It turned out to be a bent flexplate.
Click to expand...
Not to hijack the thread but it is all relevant.
Which auto trans do you have?
Have you tried using a factory tail housing counter weight?
 
Never seen a bent flexplate that wasn't SO obvious as to not even being able to be bolted on ( dropped engine, etc) never seen one "slightly warped"
Cracked flexplate is much more common
 
Converter could have weights welded on incorrectly. Or maybe none at all. have to take it apart and look.
 
Vibration shows up at the same rpm while going down the road. No, the car isn't up on jack stands when tested. It vibrates at rest on all four wheels. If you are going up a hill and can keep the engine at a constant 3000 rpm, it will begin to pulsate. Increase the rpm to 4000 and it diminishes. Same at rest. I tried loosening the motor mount bolts to see if that might make a difference, but no change. Haven't tried anything with the tranni mount. I do have a Gear Vendors (OD). It does seem like the poly mounts are almost like solid mounts. Any vibration at idle (slightly rough due to the cam) is transferred to movement of the body. They were extremely tight in the K-frame. I used the original motor mounts, burned out the rubber, and inserted the poly inserts. I still would like to throw in another 727 just to rule it out. I say that because back in the 80's, when I first put the 727 in with the 340 and 410 gears, I had some vibration issues going down the road at about the same speed. I thought it was a drivetrain issue because it wasn't really noticeable at rest (rubber mounts), and my driveshaft was shortened without balancing. I even tried a counterweight on the tail housing. I finally put 323's back in and it was better at cruising speeds. This brings me back to the transmission since it is the only original thing left. That was a long time ago, so my memory of how it was is a little vague, but it did start after I installed that transmission.
 
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