5.9 Magnum to TF904

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Old Geezzer

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Working on getting 5.9 Magnum hooked to my 904 trans. Picked up a new torque converter at Summit this weekend. I noticed that no matter how I spin the Magnum flex one of the bolts never line up. The 360LA plate lines up.
Also the Magnum tone/flex plate has counter weights already so do I add more to the converter? The converter is for a 318.

1.Do I just grind the one hole to match or do I need a different converter?
2.Do I added more weight to the converter?

Thanks OG

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Hey Geezz.
Mopar Action described some different flexplate bolt pattern and weights in their Savvy Savoy buildup. I used the flexplate that matched up with the TC bolt pattern and moved the weights over from the the other one that had the incorrect pattern but the correct weights.
The Mag said to file a slot over to make the pattern work. If you worried about balance a mig could be used to replace the metal lost.
Sometime in the past I slotted a flexplate on some project and never noticed any vibration.
 
The late model converter is a 90 degree version which has all mounting pads evenly spaced. The earlier converter has one offset pad for the counter weight (even if it's an internally balanced engine). Thankfully MoPar made them all 90 degree now, so for us who put these in regularly it's so much easier. I would get a converter made up that fits your trans and has the 90 degree pads, but you would probably be okay openning up the bolt hole on your flex plate so your converter will bolt up. But be careful that you use a converter that's not weighted. Also check your ring gear, it must be the same diameter (check the tooth count). In your pictures it looks like you have a wide ring gear on one and narrow ring gear on the other.
 
Thanks for info guys. The blue one is an old converter I had laying around,its out of a 360LA 727 combo. The red one is the new one that matches my TF904.
And since I'm keeping the EFI I need the tone ring flex. Just never noticed that it was already weighted. So now I have mopar P5249843 kit extra. Time to get the die grinder out. LOL
 
Old Geezzer said:
Working on getting 5.9 Magnum hooked to my 904 trans. Picked up a new torque converter at Summit this weekend. I noticed that no matter how I spin the Magnum flex one of the bolts never line up. The 360LA plate lines up.
Also the Magnum tone/flex plate has counter weights already so do I add more to the converter? The converter is for a 318.

1.Do I just grind the one hole to match or do I need a different converter?
2.Do I added more weight to the converter?

Thanks OG
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Hey Geeze,

I am doing this or at least trying to, now. I have this same issue and I am trying to do what apparently you did in this project. My question is, How do you keep the flexplate centered on the TQ when you elongate the one hole? I pulled my engine today and was doing what you are showing in your pics but when I matched the three holes it throw the center off quite a bit, enough to where I believe it will throw the balance off. I have a mopar crate magnum 360 and I took out a 318. I have a 904 with a 3000 stall converter that was behind the 318 that I want to use with the 360. I have a 2000 magnum flex plate. Also the bolts on the TQ seem to be a little sloppy fix in the flexplate holes. Can you give me some direction?

Thanks, cuda67

I know this post is a little old but I like the pics and I need help from somebody who knows what I need to do.
 
Cuda67 I lined up the three bolt holes and marked the one that was off. Clamped the flex plate to the bench and used a rat tail file to elongate. I did a trail fit as seen in the pics. Found larger headed bolts and put blue locktite on the threads.
No extra weight is needed since your using the Magnum flex plate. Hopes this helps you. OG
more info here: http://www.forabodiesonly.com/mopar/showthread.php?t=41302
shows what I did for oil pan and mounts
 
old geez,,, he is asking about the flex plate not being centered,, look at the pic of your red/orange TC,, the crank register button is off center on yours also,,he is asking if it will throw it out of balance,,not weighted balance,,,almost out of round
 
fstfish66 said:
old geez,,, he is asking about the flex plate not being centered,, look at the pic of your red/orange TC,, the crank register button is off center on yours also,,he is asking if it will throw it out of balance,,not weighted balance,,,almost out of round
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Thank you, fstfish, you put it in much better words. That is exactly what I am asking. I understand the process of lining up the three holes but that puts the flex plate off center. It would seem to me that the flex plate being off center, out of round. would cause the torque converter to be off balance. Is there something else I should do? Am I missing a step?
 
i dont know about this conversion either,,,i too would think if the flex plate is off center it would run like its out of round,,

wondering if an A 500 converter would fit a 904 trans,,that would solve the problem, im thinking,,,but some one by now im sure has done this swap,,maybe they will add there findings,,
 
OK now I follow(maybe LoL) The pic with the red convertor has no bolts in it. The flex is just sitting there upside down showing the weights.Your crankshaft is what centers the convertor to everything all you flex plate does is couple the power from engine to trans. Mine hooked right up once installed. I did marked the position of the flex plate to convertor as it was when I filed. IE:The offset pad to the hole I filed.
Hopes this clears thing up OG
 
have u run the car yet??? let us know if u have any vibrations,,,,if not then it is an easy swap,,, i have a 5.9 flex plate ,,in case i do the 5.9 /904 swap in to my street rod,,,,
 

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Sorry haven't fired it yet,slowly been working on parts for the EFI harness and found the deutsch panel connectors for the fire wall fed through.OG
 
Old Geezzer said:
OK now I follow(maybe LoL) The pic with the red convertor has no bolts in it. The flex is just sitting there upside down showing the weights.Your crankshaft is what centers the convertor to everything all you flex plate does is couple the power from engine to trans. Mine hooked right up once installed. I did marked the position of the flex plate to convertor as it was when I filed. IE:The offset pad to the hole I filed.
Hopes this clears thing up OG
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Geeze, when I dry fitted the flex plate to the TQ yesterday, bolted on, it was off center to the crank button thingy. If I elongate the one flexplate hole it will secure the flex plate in this off centered position. It seems to me that this would create an out of balance condition.
Maybe someone that has completed this morphing and actually has driven their car after this alteration will ring in with more information. Barring this I will take my TQ and the flexplate to a machine shop and have them center the flex plate on the TQ. The off center flex plate has to cause some sort of vibration as it will turn like an egg, IMO. Maybe the vibration is so slight that it is hard to detect, S#*t, I don't know.

Anyone that has done this and is driving the car since the marriage of parts, please, ring in.
 
Now I'm not sure why this is happening. You can this: bolt your flex plate to the crank and put the convertor in place and see if any of your bolt holes line up. Is it the same on both convertors? The other thing I heard done is to order a 904 convertor with the pads equal spaced for the Magnum flex plate. Maybe some one else will jump in on this. OG
 
I don't have much experience with the magnum motors and the flexplates but I did have to swap a trans in our old 98 ram 360 4x4, the new trans was from a 318 truck and I think I remember finding out that the flexplates on those have to stay with the converter, not with the motor to balance that. Also wouldn't putting a 518 converter into a 904 create an issue because the 518 uses a lock up converter?? Hope this helpes someone
 
the 318 is internally balanced,,not needing any weights on the convertor or flex plate,,,and a netural harmonic balancer,,,

the 360 is externally balanced,,,needing balancing on the front of the motor( harmonic balancer) and on the convertor,,either on the convertor or by using a after market flex plate designed to balance a motor using an un balanced convertor,,,

also the magnum motors have a timing mark on the flex plate,for using factory electronics, EFI & computer controlled distributor
 
fstfish66 said:
the 318 is internally balanced,,not needing any weights on the convertor or flex plate,,,and a netural harmonic balancer,,,

the 360 is externally balanced,,,needing balancing on the front of the motor( harmonic balancer) and on the convertor,,either on the convertor or by using a after market flex plate designed to balance a motor using an un balanced convertor,,,

also the magnum motors have a timing mark on the flex plate,for using factory electronics, EFI & computer controlled distributor
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Gotcha, couldn't remember what the deal was, lol we got a D-max with an Allison trans and haven't looked back since. I didn't realize that magnum 318s and magnum 360's were balanced differently I thought by then it was the same but like I said IDK much about magnums lol
 
wigsplitter74 said:
Gotcha, couldn't remember what the deal was, lol we got a D-max with an Allison trans and haven't looked back since. I didn't realize that magnum 318s and magnum 360's were balanced differently I thought by then it was the same but like I said IDK much about magnums lol
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good luck with you wanna be diesel D-MAX they are having problems with the electronic fuel injectors,,,5 grand repair bill,,2500 if you do it,,,,,ford same boat,,,
 

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fstfish66 said:
good luck with you wanna be diesel D-MAX they are having problems with the electronic fuel injectors,,,5 grand repair bill,,2500 if you do it,,,,,ford same boat,,,
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Yea I know, it's an 03 LB7 with Edge Juice with Attitude, loaded crew with everything but DVD, had 74k on it stole it for $14k. . . Can't get a comparable Cummins for that kinda money around here and the Cummins' trans wouldn't handle the almost 900lb ft I can put through the Allison with the programmer turned up. Nothing against Cummins tho, I still want a clean 91-93 cummins. I also work at a GM dealer so it wouldn't cost me that much lol and when they started having that issue GM put a 200k warranty on injectors. not worried man
 
Old Geezzer said:
Now I'm not sure why this is happening. You can this: bolt your flex plate to the crank and put the convertor in place and see if any of your bolt holes line up. Is it the same on both convertors? The other thing I heard done is to order a 904 convertor with the pads equal spaced for the Magnum flex plate. Maybe some one else will jump in on this. OG
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OG and Fast, I went back to it today and OG you are right. If you play with aligning the flex plate on the converter you can center it . The bolt holes are 3/8 and the bolts are 1/4 this allows alot of play when putting the two together. Now that is the easy part. I took some pictures which I will put on here that show this process. However, I found something today that doesn't add up. I have a 318 with a 904 and everything I have read or seen on this site and others confirms that 318's are internally balanced and have a neutrally balanced converter, right? I have an aftermarket on the 318 with 3000 stall and it has been in my car about 10 years. Today while checking the aligning of the flexplate I just happened to turn the converter over and low and behold there is one weight on this converter. What is up with this?
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The weight looks to be balancing just for the convertor and nothing to do with engine balance. Glad its coming together for ya. OG :happy7:
 
Just for those of you who are interested, I also elongated the hole in my stock magnum flexplate to run a standard 904 converter. Been driving it for a year now with no weird vibrations or any other issues. I was a little concerned about whether or not the bolts would back out, but I've checked them several times and they're still tight. I did use a little blue loctite on the bolts though.
 
UOP said:
Just for those of you who are interested, I also elongated the hole in my stock magnum flexplate to run a standard 904 converter. Been driving it for a year now with no weird vibrations or any other issues. I was a little concerned about whether or not the bolts would back out, but I've checked them several times and they're still tight. I did use a little blue loctite on the bolts though.
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Thanks for the information. It is great to hear from others with more experience. This site is great.
 
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