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Old 11-02-2010, 12:01 PM
taildragger taildragger is offline
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Default Advice Needed on Tranny Change out

Can anybody tell me what is involved with switching out a 3 speed with O/D tranny from a 1984 Dodge Truck (shortbox) with a 225 slant 6 to a 904automatic tranny.
From what I've found out so far, probably a 904 tranny would be best suited for this, I have found 2 so far but need advice on which might be the better way to go (if there is any difference at all?) The first tranny is a 904 from a 67 valiant, the second is a 904 from an 84 Ram Van. Is there any difference in these 2 tranny's that would present any different difficulties when doing the change out?
Secondly- I've been told that I might have to change the cross member on the truck to accommodate the 904. Would just getting a cross member from an 84 truck with an automatic be suffice, or do I need to look and make sure that the cross member comes from an 84 with an automatic 904? As well, will this cross member bolt right up to the exsiting holes on the frame, or will new holes need to be drilled or any modification needed?
Third- Drive shaft lenght-- will it need to be shortened or lenghtened, or is there another option? (shaft from another vehicle of a certain make or year?)
Fourth- Because now if the standard stick shift(on floor) is taken away and replaced with an automatic shifter (on the floor), is there any shifter from a certain vehicle that would work better to connect to the 904 that might work best?
If there is anybody out there in Mopar Land that could clarify and sum up this whole process with any or all complications that would be greatly appreciated!! Thanks
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  #2  
Old 11-02-2010, 03:34 PM
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Ray Bell Ray Bell is offline
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You learn a hell of a lot just walking through junkyards looking at the bones of vehicles...

Take a tape measure with you, and preferably also a notepad. Write it down even if it seems insignificant at the time.
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Old 11-09-2010, 12:53 AM
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RoadRaceJosh RoadRaceJosh is offline
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The 904 will be shorter than the manual transmission you are removing. The slip yoke will almost certainly be different. You need a longer driveshaft. Find the same wheelbase truck in a wrecking yard with a 904 for the proper driveshaft. The '67 904 will have the small nose on the torque converter and won't be properly supported in the crankshaft pocket, but a bushing is available to remedy this. The '84 transmission may have electric lock-up. Check to see if there is a wire other than the neutral safety/reverse light switch. The existing cross-member should work fine. The correct holes may or may not be in the frame, but probably are. Get the proper steering column from a wrecking yard. Cable shifters are not as long lived or as reliable as the stock linkage.

Does your radiator have a transmission cooler? Do you have the oil cooler lines? Do you have the carburetor to transmission throttle pressure linkage? It's critical and you will burn up the trans if you don't have it.

BTW, there are many more slant six people over at slantsix.org
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Old 11-09-2010, 10:26 AM
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nhdriver nhdriver is offline
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The '84 trans would be the better choice. If it came from a van or pick-up it might have the low ratio gear set which is great in a truck to get the mass moving. Plus the lock up converter (which is [I]not[/I ]electric but hydraulically controlled) will help out on the highway by keeping your revs down a bit. throw in the difference in the hub diameter & there is no reason to go w/ the old '67 unit. Make sure you get the correct torque converter w/ it. (preferably the one that came in the trans you are buying)
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