engine/trans vibration

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Cuda1965

Cuda1965

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I have a bad cyclical vibration coming from my 65 barracuda engine/trans that I cannot identify. the vibration is felt through the whole chassis. The vibration starts only after the engine/trans is warm/driven for a few miles, no vibration when cold.
Some background, I have a 92 360 magum crate engine with a 65 904 trans. i just had the 904 professionally rebuilt for street strip, after reinstalling the trans I noticed the vibration at around 45-50 MPH. Immediately I thought something wrong with the trans, most likely the rebuilt converter (this was the same converter that was in the car before vibration, just rebuilt). I pulled trans, sent just the converter back to the trans guy, he said there was nothing wrong, but I insisted he install mopar performance weights as recommended for the magum eng.
I reinstalled converter and trans...still same vibration. I thought maybe other drivetrain issue: drives shaft/tire/rear end etc. so I put car up on jack stands, disconnected drive shaft, so just the engine and trans was isolated and take the rest of the drive train out of the equation. I still have the vibration, the engine has a slight constant vibration through the whole rpm range but the real annoying cyclical vibration (it rises and falls) is at 15-1800 RPM. You feel it in the seat/steering wheel/gas pedal.
Any one have any thoughts what to look for??
 
Is the TC centered properly in the crank? You know about the 65 and older TC to the 67 and later crank-pilot mismatch right?

Is it there in every gear?

Did you change the trans mount during the other changes?
 
Take off the belts for the water pump, ps, alt etc and see if the vibration is still there, I discovered a bad alternator vibration and it sounds like exactly mine was b4 I found the problem
 
I ended up with a bad vibration after a trans rebuild w/torque convertor. Disconnected the torque convertor slightly and fired the engine- vibration was gone. Retured converter for balancing and re-install. Then the converter threw the weight that was welded on. I no longer trade with that shop.
 
Murray said:
I ended up with a bad vibration after a trans rebuild w/torque convertor. Disconnected the torque convertor slightly and fired the engine- vibration was gone. Retured converter for balancing and re-install. Then the converter threw the weight that was welded on. I no longer trade with that shop.
Click to expand...
I thought about disconnecting the convertor but the engine cannot be cranked to start unless the converter is bolted to engine.....how would i do that?
 
AJ/FormS said:
Is the TC centered properly in the crank? You know about the 65 and older TC to the 67 and later crank-pilot mismatch right?

Is it there in every gear?

Did you change the trans mount during the other changes?
Click to expand...
I am not sure what you mean by "centered properly", but this converter was built about 7 years ago to match the magnum eng to the 65 904 because I found the original owner who installed the eng/trans had the wrong convertor, I purchased the car unfinished...., when i go it on the road i noticed an issue and had the trans rebuilt and new converter made back then 7 years ago, no issue with that new converter since, during this recent rebuild the trans shop said the convertor was a "a real nice unit" and only did a "inspection" and "freshing up" of the converter.
The cyclical vibration is mostly prevalent when the trans is in drive: 3rd gear
 
The 65 converter (stock) had a smaller diameter nose then the hole in the crank of the later engine. It is possible your converter was built with a large pilot nose. years ago those converters (hybrid) could be obtained, but now are very pricey. If your converter has the small pilot nose, you need an adapter bushing in the end of the crank. You will need to measure the pilot nose of the converter. If it measures 1.81 inches, that's fine. If it measures 1.55 then you need the bushing.
PS: I sell those bushings. If you do need one PM me.
 
Flexplate/converter balance issue, offset in crank. Driveshaft.

Does it vibrate in park at higher RPM?

Have to test to elimate what isn't causing the issue.
 
If the vibration is mostly in third gear; that seems to indicate it is related to a certain speed; yet you indicated in an earlier post that it was not,IIRC.
Mopar unibodys have a natural tendency to vibrate at about 55 mph. Almost anything can set it off. And it is a very slow, dreadfully annoying, oscillation; I'm gonna guess at less than 60 cps. It's kindof a rolling woo-woo-woo-woo. By 60/62 it is fading and by 65 it is gone. And it does not change with swapping the rear gear, or the trans or the driveshaft; like I said dreadfully annoying.
I found my tires seemed to set it off, big tires in that day; N50-15s. I have later experienced the exhaust system setting it off as well, and open windows too.
In my cases nothing in the car or chassis was actually seen to vibrate, yet there it was; woo-woo-woo. There was no cure except to not drive 55.
When my current ride (68 Barracuda) started doing it, I finally found a partial cure in changing the pinion angle to a lessor amount.
One time I found an out-of-round tire was exciting it. The tire/wheel was balanced, but the slight "hop" at speed got the body going. New tires solved that one
 
Last edited:
crackedback said:
Flexplate/converter balance issue, offset in crank. Driveshaft.

Does it vibrate in park at higher RPM?

Have to test to elimate what isn't causing the issue.
Click to expand...
It has a slight vibration in park at all RPM, the annoying cyclical vibration is most prevalent in 3rd gear at 1500-1800 rpm, even sitting on jack stands with drive shaft disconnected.
 
That sounds like the same problem I had before, same RPM as yours. After days of looking and testing I found the exhaust pipe would touch the frame and that was causing the vibration. Moved the pipe and the vibration went away
 
AJ/FormS said:
If the vibration is mostly in third gear; that seems to indicate it is related to a certain speed; yet you indicated in an earlier post that it was not,IIRC.
Mopar unibodys have a natural tendency to vibrate at about 55 mph. Almost anything can set it off. And it is a very slow, dreadfully annoying, oscillation; I'm gonna guess at less than 60 cps. It's kindof a rolling woo-woo-woo-woo. By 60/62 it is fading and by 65 it is gone. And it does not change with swapping the rear gear, or the trans or the driveshaft; like I said dreadfully annoying.
I found my tires seemed to set it off, big tires in that day; N50-15s. I have later experienced the exhaust system setting it off as well, and open windows too.
In my cases nothing in the car or chassis was actually seen to vibrate, yet there it was; woo-woo-woo. There was no cure except to not drive 55.
When my current ride (68 Barracuda) started doing it, I finally found a partial cure in changing the pinion angle to a lessor amount.
One time I found an out-of-round tire was exciting it. The tire/wheel was balanced, but the slight "hop" at speed got the body going. New tires solved that one
Click to expand...
Cuda1965 said:
It has a slight vibration in park at all RPM, the annoying cyclical vibration is most prevalent in 3rd gear at 1500-1800 rpm, even sitting on jack stands with drive shaft disconnected.
Click to expand...
Jax340Dart said:
That sounds like the same problem I had before, same RPM as yours. After days of looking and testing I found the exhaust pipe would touch the frame and that was causing the vibration. Moved the pipe and the vibration went away
Click to expand...
Jax340Dart said:
That sounds like the same problem I had before, same RPM as yours. After days of looking and testing I found the exhaust pipe would touch the frame and that was causing the vibration. Moved the pipe and the vibration went away
Click to expand...
That may be something for me to look at, I have TTI headers on the car, the headers are extremely close to the frame in one spot and also several places where the torsion bars slide right through them on both sides.......
 
I had to shim my engine up for TTI clearance on the 1970 K-frame; 1/4" per side minimum. I made some flat-iron plates and torched a slot into them, and slid them in there,not pretty but functional.
 
AJ/FormS said:
I had to shim my engine up for TTI clearance on the 1970 K-frame; 1/4" per side minimum. I made some flat-iron plates and torched a slot into them, and slid them in there,not pretty but functional.
Click to expand...
I had all sorts of issues when I installed 2 years ago, Had to shim one side, had to ding in the pipes to fit (made me cry to dent such nice units) in several places: PS steering shaft coupling, drivers side frame, passenger side torsion bar, I had the header in and out numerous times....... may be I shifted the engine slightly when removing/installing the rebuilt trans.....I know I have several very close areas where the header pipes may hit....
 
If the headers are close to the frame, once the RPMs increase and the motor twists it might be making contact with the frame. I thought it was the driveshaft at first because it was new after I put in a Gear Vendors. The shaft had .040 runout. The drive train shop made a new, new drive shaft and it had .007 runout but the vibration was still there. I saw where the pipe just after the collector was close so I smacked it with a hammer, problem solved. I did cut the pipe and welded on a new collector on it.
 
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