360 & 401 Flywheel info needed - JeepForum.com
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Unread 03-29-2009, 02:35 PM   #1
monty97
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360 & 401 Flywheel info needed

I have a 78 J20 that has a 401 and I believe to be a torque-flight trans. The motor went out of it not to long ago, I bought a 360 that was in an 81 wagoneer and it had the TH400 trans. The flywheels are different, the 401 has a flywheel that uses 3 mounting bolts to attach to the torque converter. 360 flywheel has 4 mounting holes. Can I use the 401 flywheel on the 360 safely??
401 flywheel looks like this http://www.4wheelparts.com/prodDetai...eep-parts=true

360 flywheel looks like this http://www.4wheelparts.com/prodDetai...eep-parts=true

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Unread 03-29-2009, 05:41 PM   #2
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If your J20 has the stock tranny, it is a TH400 and the 81 would be a 727.

The flywheel needs to match whatever transmission you are going to use. If you are going to use the stock TH400, you need to use the earlier flexplate as the torque converter won't bolt up to the wrong flexplate.
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Unread 03-29-2009, 06:04 PM   #3
monty97
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Ok thank you, I was just wanted to make sure it was okay to interchange the flywheels. How do you go about ID'ing a TH400 or 727??
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Unread 03-29-2009, 09:56 PM   #4
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Also, forgot to mention, the 401 flywheel is balanced differently from a 360 as well.



#4 is a TH400 pan



That is a 727 pan (from the inside)
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Unread 03-29-2009, 10:11 PM   #5
monty97
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Is the 401 flywheel balanced by the extra material at the one end?? Just want to make sure I am not going to screw the 360 up by using the 401 flywheel.
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Unread 03-30-2009, 09:04 AM   #6
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Quote:
Originally Posted by monty97 View Post
Is the 401 flywheel balanced by the extra material at the one end?? Just want to make sure I am not going to screw the 360 up by using the 401 flywheel.
That's exactly what you will do. They are not balanced the same and you'll kill your main bearings. Some specific terminology is being interchanged and used incorrectly in this thread.


Flywheels are used with manual transmissions and clutches.

Flexplates are used with automatic transmissions and torque convertors.


Flexplates are inexpensive items. Don't use the 401 flexplate on the 360. Its too easy to do this right. Buy a new flexplate for a late 70's FSJ with a 360 and a TH400 (Quadtratrac) for $40 or less (usually).
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Last edited by PavementPounder; 03-30-2009 at 12:35 PM..
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Unread 03-30-2009, 10:55 AM   #7
monty97
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Okay thank you for the info. This is the reason I came to you guys for guidance, I do not want to hurt the engine in any way. Thanks again for the help.
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