Posted by Keith in Washington [108.162.246.92] on Monday, December 26, 2016 at 12:39:49 :
In Reply to: Swapping a NP420 to NP435 posted by John [172.68.34.61] on Monday, December 26, 2016 at 11:47:10 :
Your older crash box transmission is not a NP420. It is what most people call a "up to" or "after" transmission depending on its design.
I have not seen anybody put in a NP435 transmission into a ff PW.
You can put a NP420 transmission into a truck that gas a crash box transmission. There are two basic ways of doing it. I used the 2nd method in my truck and it works just fine.
Remember with a NP420 only 3rd and 4th gears will be synchronized. D.C. who is on this forum has a web site that will give you some information and Dave is a good source of parts. He is a great tranny guy. His web site is. http://www.jobrated.com/index.html
1) The first method is to replace the bell housing. Using one from a later PW is easiest. You will need to use a later version of tha NP420 from a ff PW or an M37. Do not get a NP420 from a civilian dodge as the input shaft is too long. You will need a PTO from a NP420 as the gears are different. You will need to replace the passenger side floor and the center floor hump. If you use a NP420 from an M37 you will need to swap out the shifter. The fly wheel and clutch assembly from the crash box trans can be used.
2) The second method requires you finding a specific NP420 transmission. You need to find a NP420 transmission from an early M37. That transmission will have the same mounting bolt hole pattern as your crash box bell housing. That means you can keep and use your crash box bell housing. To complete the conversion you will need a PTO from a NP420 and replace the center hump and passenger side floor board.
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