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4l80e swap

Ricky Bobby

Ricky Bobby

1/2 ton status
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Nov 19, 2015
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Location
Texas
Sooooo a friend of mine gave me a 91 dually with a good 454. He said the th400 lost reverse. So I pull motor and trans out planning on putting motor in my wife's k20. Well I start looking at the transmission and HOLY SHIT happy dance it' a 4l80e. I'e gone threw 5 built th350's in my k5 and have always prayed for a 4l80e. So it's a 2wd... find out I cut threads off and 4-1/2 still sticks out. Perfect for my th400 205 tcase I have.
 
So far I bought a boss hog night stalker torque converter, trans-go's full manual valve body kit "No computer needed", nice 13" trans cooler with 500cfm fan, -6an fittings and a winter' cable shifter for it. Anything else anyone can think of that I'd need? I have a flywheel but I can reuse my old starter right?
 
Last edited:
sweetk30 said:
4l80-e requires its own adapter for the t-case to trans .

if round pattern 205 you have then you just need this http://www.northwestfab.com/4l80E-to-TH400-NP205-AdapterSpacer-Kit_p_98.html

if you have a older 205 with fig 8 it can be done but might require a special thickness spacer made like i had done years ago for a project .

lots of info here . https://ck5.com/forums/threads/has-...-to-mate-with-a-4l80-and-d60-question.166233/
Click to expand...
What about if you have a 4l80e/241 would that adapter work on a 205?
 
I used a 4l80/241 adapter to mount my 203 for my doubler. It will work with a 205 if you have everything else.

You can also use a 400/205 adapter and turn a portion of it down to fit the 80.
 
454Sub said:
I used a 4l80/241 adapter to mount my 203 for my doubler. It will work with a 205 if you have everything else.

You can also use a 400/205 adapter and turn a portion of it down to fit the 80.
Click to expand...
the problem with the th400 adapter is 3 fold .

1st = o-ring grove register is a tad different size . yes can be machined to fit .
2nd = thickness of the adapter from th400/205 to 4l80-e/205 is off a hair on the short side .
3rd = the trans mount ear's on th400 round adapters are cast forward as the pan on a th400 is shorter than a 4l80-e . 4l80-e adapters are cast center or rearward to clear the trans pan and flange for the pan since the pan is much bigger .

now some have ground he adapter to clear the pan / machined the ring down / nipped the tail shaft to make clearance for the tail shaft to input shaft end play so its not bottomed out . but as i linked before above northwest fab has a bolt in spacer to take care of all 3 problems at 1 time.

now as to the round 6 pattern on a np203 t-case/range box . yes it can be done and is super easy to do . the round adapter centers perfectly on the 203 seal holder . then clock it were you would like it and mark the holes and drill/tap . be careful the length of bolt used in the face as the gears are just on the other side and can bottom out and cause all sorts of problems. and also swap out the allen socket head screws for the seal retainer for button head allen screws to clear the inside of the round adapter . i have pics of all this little stuff in my thread here https://ck5.com/forums/threads/4l80...05-ord-doubler-3-sticked-its-all-done.253000/

and pics of some of these adapters in here https://ck5.com/forums/threads/t-case-adaptors-list-inside.322407/#post-3560173
 
I had an adapter made for when it was still mated to the th400. Should I just use my old th400 shaft?

20180421_163156.jpg
 
Not right now. It' at the trans shop but it' the 2wd fixed yoke. Figured I'd just cut off the threads. I'l get some tho. Adapter is from 3/4 drill stim.
 
i would figure out the tail shaft length required now before the trans is all built out . or get a good used or new full spline shaft like i did in my first doubler build . the gm part # should be in there . then once installed you have full spline and then just cut to fit as needed .

edit : second post in this thread has the pic of said shaft and part # https://ck5.com/forums/threads/4l80...05-ord-doubler-3-sticked-its-all-done.253000/
 
Dead gum.... Awesome rite up and build! I'm torn between a doubler or a magnum/titan black box. Would love a box but the doubler is more reasonable on price. Couldn' imagine trying to fight a doubler to get in without a lift.
 
by the time you find a 203 box that you need + adaptor and redrill pattern to fit + rebuild box + doubler kit + 205 that you need and hope no input swap needed or machine the case to fit bigger bearing + rebuild of 205 and possible new shift rails = a lot of cash and time and work .

magnum box open and install direct no mods needed to a round pattern adapter + rebuild and swap input gear in 205 and twin stick rail kit = DONE

about the same price if you add up all the details in the end . PLUS true 1:1/2:1/2.72:1/5.44:1 ranges to play with over 2:1 or 4:1 . plus its a tad bit shorter also .

me both times i had all the parts minus the kit . so i was in them for less than a lot of guys have to pay out . if i had it to do again i would pick the magnum for range options . but i have yet to drive a doubler kit truck so i am bias to the #'s
 
See I already have both tcases but that selection sounds so nice! Hey sweetk30 did you use the stock torque converter?
 
my stuff is mostly stock engines so i dont play that far in to the internals . all gm spec stuff here or mabye a noyoyo shift improver kit at the most .
 
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