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Old 02-05-2019, 10:22 PM   #1
Shtudwn
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Convert Allison 2 wheel drive into 4x4

Hello,

I am planning on putting a Chevy 8.1L into my 76 K20. The Engine/trans combo that I have available has a Allison 2 wheel drive that I would like to convert to 4 wheel drive.

Has anyone else done this?

Thoughts on the conversion? Computer, difficulty?

What about the transfer case?

Thank you.
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Old 02-06-2019, 12:19 AM   #2
mongocanfly
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Re: Convert Allison 2 wheel drive into 4x4

its been done..just google (Allison transmission 2wd to 4wd) sounds like just change out the tailshaft housing...parts aint cheap and that's a big ol transmission...
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Old 02-06-2019, 11:07 AM   #3
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Re: Convert Allison 2 wheel drive into 4x4

Thank you Greg.

I had planned on building a 496 but that didn't work out. I can get a low mile 8.1 with allison 2wd for a reasonable price. Cheaper than building the 454 into a 496. I want to run a camper and sometimes pull my boat. Looking for a "draft horse" type setup.

Dan
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Old 02-06-2019, 11:59 AM   #4
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Re: Convert Allison 2 wheel drive into 4x4

make sure you research the electronics side of it and the t-case you want to use to see if the computer can even be setup for the low range ratio .

the few guys i have read up on said in the end they wished they had left it 2wd control and used the t-case as its self , or did a divorced case if you have the wheel base length for that .
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Old 02-07-2019, 01:23 AM   #5
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Re: Convert Allison 2 wheel drive into 4x4

I think it can be adapted to a 205 which is what I would do on any bigger motor,.

Got me wrong I like the 208 or 241 for a revvy small block where the lower gear works nicer.
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Old 02-07-2019, 02:14 AM   #6
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Re: Convert Allison 2 wheel drive into 4x4

Install a divorced t-case.
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Old 02-09-2019, 02:56 PM   #7
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Re: Convert Allison 2 wheel drive into 4x4

Thank you.

I should know this but I dont....I think I have a 203 T-case and would like to reuse it if possible.

This is a long bed truck...if that helps with discussion.

I see that there is a tail housing extension and an output shaft that are specific to 4x4. Are those the only 2 major components that I need?

BTW, I received the 8.1 and trans yesterday. Pretty cool stuff. I am anxious to get my shouse (shop-house) completed, get the 2 post car lift installed, and really get on this swap.

Thank you for the replies/information.

Dan
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Old 02-09-2019, 04:47 PM   #8
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Re: Convert Allison 2 wheel drive into 4x4

unless you find a rare divorced ford 203 input gear to make your 203 a divorced then good luck as there is not allision to 203 support i have ever seen . this is IF you have a 203 . what is your shifter pattern ? 4l-n-2-4high ? or do you have 2 spots that say lock ?

and long bed truck and divorced case is o.k. i have done a truck with a 4speed and divorced and had a 15" shaft between the 2 and equal length shafts front and rear .
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Old 02-09-2019, 05:13 PM   #9
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Re: Convert Allison 2 wheel drive into 4x4

Quote:
Originally Posted by sweetk30 View Post
unless you find a rare divorced ford 203 input gear to make your 203 a divorced then good luck as there is not allision to 203 support i have ever seen . this is IF you have a 203 . what is your shifter pattern ? 4l-n-2-4high ? or do you have 2 spots that say lock ?

and long bed truck and divorced case is o.k. i have done a truck with a 4speed and divorced and had a 15" shaft between the 2 and equal length shafts front and rear .
Yes, I have the Hloc and Lloc.
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Old 02-09-2019, 06:04 PM   #10
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Re: Convert Allison 2 wheel drive into 4x4

Since we are snowed in today i have been spending too much time on the computer....

I found this adapter:

http://offroaddesign.com/catalog/Tra...seAdapters.htm

Part No. FU4092

for a Ford 205 to Allison. I assume it is because the Ford 205 requires the 29 spline? They are saying its a married combo....
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Old 02-09-2019, 08:18 PM   #11
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Re: Convert Allison 2 wheel drive into 4x4

high loc and low loc = 203 full time case unless part time kit installed .

and the ford case is if your doing driver side axle drop . our gm trucks are pass side drop .

you can do married if you want but try and keep it setup as a 2wd trans or see if someone can change the low range ratio to 1.96:1 to match a np205 and run a 205 t-case setup . and then have ORD mod the tail housing for the VSS over the speedo cable .
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Old 02-10-2019, 11:22 PM   #12
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Re: Convert Allison 2 wheel drive into 4x4

email chuck at ORD, he can make it work with a stub shaft and spacer, that's what I'm looking at for my NP203/205 doubler to allison setup I'm planning.
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Old 02-10-2019, 11:50 PM   #13
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Re: Convert Allison 2 wheel drive into 4x4

Guy on ck5 did a ord magnum kit for Allison to 205 but running vss in 205 makes stock ECM not happy with doubler ratios .
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Old 02-10-2019, 11:56 PM   #14
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Re: Convert Allison 2 wheel drive into 4x4

Saw some of the ck5write up. Anxious to talk to ord as the stuff they offer is amazing! Not worked with them before. Thank you.
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Old 02-11-2019, 11:28 AM   #15
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Re: Convert Allison 2 wheel drive into 4x4

been ordering from them for years . 15+ now . . . .currently waiting for the 9am open to order more today .
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Old 02-11-2019, 12:21 PM   #16
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Re: Convert Allison 2 wheel drive into 4x4

Just emailed. Looks like they have some amazing parts. I am really interested i their lift kits. Very complete and a great deal of experience/knowledge there.

Thank you.
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Old 02-11-2019, 12:26 PM   #17
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Re: Convert Allison 2 wheel drive into 4x4

just placed my order .

and there lift kits can be super simple to crazy build specs . just ask them and they will build a kit to fit your budget needs .

some day i would love to a full front and rear 4 link kit .
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Old 02-11-2019, 01:00 PM   #18
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Re: Convert Allison 2 wheel drive into 4x4

I did find this out there.....

https://www.advanceadapters.com/prod...0-to-gm-np205/

50-9421 : 50-9421 - Allison 1000 to GM NP205 (#50-9421)
Retail Price: $578.55
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Old 02-11-2019, 01:57 PM   #19
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Re: Convert Allison 2 wheel drive into 4x4

ya no photo's . . . .

and ord sells there kit and shows photo and less money .
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Old 02-11-2019, 11:00 PM   #20
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Re: Convert Allison 2 wheel drive into 4x4

Chris from ORD got back to me with a lot of info. Great company that will take that kind of time to provide a great response! But to be honest.... I think I am even more lost....

OK, so what if I don't care about the NP 203 and switch to a NP 261? I believe the Allison is 29 spline and the 261 is 29 as well? Anyone know for sure? If that is the case...haha... then I can mary the two. Right?

All this and I still have a 2wd trans that I want to modify to 4wd..... but I am more confused because Chris said I have to gut the Allison to make the switch. Or at least I think that is what he said... Has anyone ever actually converted the Allison 1000 from 2wd to 4wd?

Thank you again for any and all help/ideas.

Dan
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Old 02-11-2019, 11:11 PM   #21
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Re: Convert Allison 2 wheel drive into 4x4

Make sure tócase matches your front axle pumpkin position you plan to use .
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Old 02-14-2019, 10:08 PM   #22
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Re: Convert Allison 2 wheel drive into 4x4

Youíre post isnít getting any traction because itís in the wrong area, post in the 4x4 section....


You will need an adapter for 29 spline to 23 or whatever the 203 transfer case is, itís done all the time when the 203 is used as s doubler in front of the 205.
I have read the Allison outpuit shaft just comes out the back....I donít believe it tho because most trans the output shaft is buried inside the trans and retained by a snap ring. Search on google for the conversion, there is a very comprehensive Allison thread on the cumminsforum.
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