modifying a 1978 J10

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phatton
Posts: 11
Joined: Tue Dec 29, 2020 2:21 pm

modifying a 1978 J10

Post by phatton »

My, new to me, J10 has a tired engine (401) and a trashed 1399 transfer case. I'm torn between rebuilding the 401 and replacing the transfer case with a 1399 from a junked truck; or pursuing a ls1 engine, trans and transfer case swap. Leaving the truck stock is easier, but finding parts to keep it running is getting hard and the gas milage is not anything to write home about. A more modern drivetrain will give me adequate power, greater reliability, and better milage. My question is will a 80's j10 front axle bolt onto my 78 frame? It seems that the modern stuff has the front drive shaft on the drivers side. Thanks and I welcome your input.
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tgreese
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Joined: Fri Jun 08, 2012 6:31 am
Location: Medford MA USA

Re: modifying a 1978 J10

Post by tgreese »

Mileage will improve, but won't be up to the donor's standard. Poor aerodynamics will be insurmountable. Chassis design and components won't equal the donor. The new drive train will be more durable but I don't see any great improvement in reliability, once the issues are fixed.

If I did not want the 401 setup, I'd look for a replacement '80-up J-truck platform. It will have the driver-drop front axle and centered rear. The Corporate rear axle in these vehicles is comparable to the Dana 44 rear in the '78; no issues. Sell the '78 to someone that wants that combo. If it's not rusty, I'd repair the transfer case to make it a running/driving truck and flip it. The 401 will appeal to many. If it's rusty, part it out and get good money for the 401, esp. if it's a virgin block.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
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Yeller
Posts: 1521
Joined: Thu Apr 01, 2021 7:54 am
Location: Rogers County Oklahoma

Re: modifying a 1978 J10

Post by Yeller »

Parts can be mixed and matched from older model transfer cases to work with your current front axle. I have 6.0/4L80E combo about to go in my 70. I’m using a passenger drop NP241C from a 91 suburban, it bolts up with the help of a clocking ring to get the front output at the proper location. Functionally it’s the same as any of the newer driver side drop cases, at least as far as the computer is concerned. Also gives manual shifting, most everything newer than 2000 is electric shift.
The bus I ride is so short it is a yellow Smart Car full of squirrels, monkeys and clowns.

1970 J2500 Resto Mod
https://www.fsjnetwork.com/forum/viewt ... 12&t=21395

1974 Bronco “Broncno”
https://classicbroncos.com/forums/threa ... st-3411909
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