Vibration (worse) after 904 rebuild

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JoePole1

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Hey Guys. I have been battling a vibration issue for a while now but had it almost beat and was only slightly noticeable around 70 MPH.
This was done by driveline angle changes, u joint replacement and finally swapped out my driveshaft.
I just recently had my 904 rebuilt and after I installed it, including the same torque converter, I am getting pretty nasty vibrations at around 55 MPH.
The vibration also happens while revving in neutral/park.
I have a 5.9 Magnum with the factory flex plate. Converter is a Factory 340 2400 stall with the weights removed for zero balance. Balance is done with the flex plate.
The only thing I can think of is that although I removed the large converter weights when I first built the engine (2 years ago), my build pictures show that I may have left the smaller thin weights around the circumference of the converter. When I installed the converter this time the orientation was different and located those weights in a different spot causing the balance to change. The Magnum does have an offset mounting hole that needed to be enlarged slightly for the converter to mount. Maybe all of my previous actions only minimized the vibrations. Dunno.
At this point the only thing I can think of is to remove the converter outer weights and try again. Do you think the small weights are possibly the cause of the imbalance?

My converter with heavy face weights removed.
IMG_20220418_090006_hdr.jpg


Example of small outer weights
20200531_124014.jpg
 
Last edited:
Hey Guys. I have been battling a vibration issue for a while now but had it almost beat and was only slightly noticeable around 70 MPH.
This was done by driveline angle changes, u joint replacement and finally swapped out my driveshaft.
I just recently had my 904 rebuilt and after I installed it, including the same torque converter, I am getting pretty nasty vibrations at around 55 MPH.
The vibration also happens while revving in neutral/park.
I have a 5.9 Magnum with the factory flex plate. Converter is a Factory 340 2400 stall with the weights removed for zero balance. Balance is done with the flex plate.
The only thing I can think of is that although I removed the large converter weights when I first built the engine (2 years ago), my build pictures show that I may have left the smaller thin weights around the circumference of the converter. When I installed the converter this time the orientation was different and located those weights in a different spot causing the balance to change. The Magnum does have an offset mounting hole that needed to be enlarged slightly for the converter to mount. Maybe all of my previous actions only minimized the vibrations. Dunno.
At this point the only thing I can think of is to remove the converter outer weights and try again. Do you think the small weights are possibly the cause of the imbalance?

My converter with heavy face weights removed.
View attachment 1716258091

Example of small outer weights
content://com.amazon.cloud9.FileProvider/images/screenshot/1717464679532830051623.jpg

If it’s calling for 0 balance on the converter then any weights still on the converter would cause an imbalance. So I would take off the small weight like you are talking about and hopefully that will fix the problem.
 

If it’s calling for 0 balance on the converter then any weights still on the converter would cause an imbalance. So I would take off the small weight like you are talking about and hopefully that will fix the problem.
Thanks for the response. Any thoughts as to why the vibration changed in intensity and RPM.....by a lot?
 
Thanks for the response. Any thoughts as to why the vibration changed in intensity and RPM.....by a lot?

Truth be told it’s hard to explain. I just know process of elimination would be get rid of any weights on the converter and see if it makes a difference. The gear set swap, well I wouldn’t expect that to cause a vibration unless something was bound up and not put back together properly. But usually when that happens the transmission won’t even be able to be fully assembled.
 
What damper do you have on the crank? And I dont know about a Magnum 360 but an LA360 is externally balanced. I've used an offset balance B&M felxplate and a neutral converter with good results on an LA but there are different dampers. Just throwing that out there. Good luck.
 
I am running the Blueprint engines damper with the correct Magnum weight installed. After thinking about it I will verify the weight didn't somehow come off.
 
Dampener is good. Only had the converter out during rebuild. Was "OK" prior. I am looking at possibly replacing. Checking Edge, Precision and Turbo Action.
 
The 5.9 flexplate could be your issue. Pre-'96, balance weights were on the converter, and there was an offset bolt hole. '96 and on, the flexplates had the balance weights, bolt holes were squared up, and the converters were neutral balanced. Which one do you have?

20240604_084305.jpg
 
The 5.9 flexplate could be your issue. Pre-'96, balance weights were on the converter, and there was an offset bolt hole. '96 and on, the flexplates had the balance weights, bolt holes were squared up, and the converters were neutral balanced. Which one do you have?

View attachment 1716258302
Weights on the flex plate.
 
Okay. When you said the flexplate had an offset hole that had to be enlarged slightly, made me wonder.
 
The small outer circumference weights are normally there to neutral balance the converter. External balance are then added for particular engine balance.
 
Dampener is good. Only had the converter out during rebuild. Was "OK" prior. I am looking at possibly replacing. Checking Edge, Precision and Turbo Action.
Reached out to Precision of New Hampton and Turbo action on June 4th. Gave their tech all of my vehicle information. Said they would call me back for with recommendation. Never got a call back. I contacted Edge Racing Transmission and spoke with Andre on June 6th. Super nice guy. Owns many Mopars and we discussed building a Converter for my 904 application. Should have it any day. Good price too. I also wound up buying a B&M balanced flex plate from a FABO member here. Will follow up.
 
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