What Transfer Case For Turbo-400 K20 BBC Build?

[Ironangel]

Thanks in advance fellas, I'm helping a kid build his dream truck, a 1984 Chevy K20. Has a local shop build a 496 power plant with a Dart b lock, Brodix heads etc...I'm building his axles, a Dana 44 front, and a 14-bolt rear, My question is, what case to use? We're undecided at this point between a 400THM trans. or a 4L80e, but kinda leaning toward the 400 Turbo. So, what case? ~Ghostrider~

[hatzie]

What is he going to do with it?

The GM NP208C and the NP241 with RH Drop has 2.71:1 low range with a lightweight aluminum alloy case and silent-chain drive. Both of them bolt right up to the 4WD NV4500 and the adapters to fit them to the slushboxes are relatively easy to find. The 208 can usually be had for a reasonable price... the RH Drop 241 is a scarce critter.

The NP205 has 1.96:1 low range with gear drive and a cast iron case. It's a popular case because everyone thinks they "need" the "stronger" Cast iron case and gear drive... It's heavier than a dead horse and, IMHO, not enough better to make one worth the premium price. They come in two different bolt patterns so you need to find the correct adapter housing for your application.

Both cases can be had with slip yoke or fixed yoke output.
Low range on the 208 is much better than the 205 but it's not considered to be as tough a case. I've beat the crap out of several of them in Ford and Chevy 3/4 ton trucks snow plowing with no problems. Killed several engines GM 350 and 454 Ford 302, 351, and 460 along with multiple transmissions... 4L60, 4L80E, TH700R4, TH400, Ford C6, and Ford AOD. Killed several Dana 44IFS, Ford rears, and GM 14bolt Semi-floating axles but the NP208 & 241 cases held up just fine. Split open a Warner 1356 and a 1345 in an 86 F250, behind the 460 and C6 that eventually exploded, when the chains catastrophically failed but the NP cases held up to some fairly nasty abuse.

The output spline count on the TH400 is 32. Since the 4L80E is based on the TH400 the output spline count on the 4L80E is generally the same.

[sweetk30]

thats a BIG motor for dana 44 axle if you ask me unless its BUILT but at that point i would do a stock dana 60 and run it .

as to t-case with that kind of power i would od a np205 gear to gear case or if you want aluminum and better ratio find a np241 . skip over the np208 it has a few weak points they fixed in the 241 .

before you build the th400 trans tho make sure you know what t-case and the output shaft length is specific to each t-case . there all 32 spline for a th400 . and the np205 has 2 lengths dependent on early or late style.

if going 4L80 -e the adaptors are specific to them over a th400 . and look up these guys for a trans controler kit . www.usshift.com .

[hatzie]

The "weakness" of the 3/4 ton Dana 44 and the 10 bolt solid front axles is blown way out of proportion.
The IFS Dana 44 in the F150 & F250 Fords has some serious problems but the solid Dana 44 axles used in the 3/4 ton Dodge and GM trucks can take a fair amount of abuse. Even the 1/2 ton Dana 44 and GM 10 bolt isn't a wimpy little axle.

Ring gears on the 1/2 ton Dana 44 are 8.5", 3/4 ton Dana 44 are 8.8", the Dana 60 has 9.75".
To bring this into perspective. My 1969 Dodge Polara 500 has a built RB383 with 338bhp and 460 ft-lb of torque, with an A833 from a Fury, and the original 8.75" ring gear Chrysler rear. I have yet to blow that rear end up or even break axle shafts and I haven't been nice to it.

The half shafts are larger on the Dana 60 but they are also much more expensive. You can get huge half shafts for the Dana 60 but I'd rather break a 30 spline half shaft on a Dana 44 than tear the teeth off the ring gear or break the carrier on a Dana 60. It comes down to picking what piece you want this teenager to use as a fuse. 30 spline Dana 44 half shafts are relatively cheap, relatively easy to replace, and they don't take the rest of the axle with them when they break.

The axle tubes are not seriously larger. The Dana 60 has 3.125" tubes, the 3/4ton Dana 44 has 1/8" smaller tubes at 3", and the 1/2 ton Dana 44 has 2.5" tubes. This changes the load capacity, not the torque handling.

IMHO the King pins attaching the knuckles to the Dana 60 are a PITA. I'd much rather deal with ball joints.

[sweetk30]

my info above is from just my time with 4x4 trucks .

i went threw 2 dana 44 3/4 ton fronts with 36" tires and mild sbc . the 2nd blown axle assembly i said screw this and went dana 60 . unbolted it from the donor truck and have been running it now for close to 15 years . only serviced the wheel bearings 1 time and freshened up the king pin service parts no pins swapped .

i have tryed to blow it up even with a built 400 sbc and 38" tires . even now its under my plow truck with a 8ft or 9ft fisher plow depending on how much snow i need to move .

each to there own . its all in how you use it / build it / play with it and just luck !

[Ironangel]

Hey, thank you for taking the time to share your knowledge you guys! You can't buy this kind of knowledge anywhere and experience is something hard earned, not taught. My 4x4 experience is very limited and at almost 60, laying underneath these trucks makes me dizzy and sick to my stomach if I'm under there to long. I have a 91 Jeep Cherokee out there with 650+K on the clock. She still runs great, only replaced a flex plate and the front axle as a whole unit. Front (little bitty Dana 44) shelled out 150 miles from home in a blizzard, when I opened it up the pinion didn't have one tooth left on it! The ring gear was chewed up but all the teeth were there. Funny thing is, there wasn't enough metal in the bottom of the carrier housing to equal the amount of teeth gone off that pinion, it was a smooth shiny cone. I found an axle with the same 4:11 gear that still had the tie rods and rotors on it for $80 bucks! That was 5 years ago, I parked it when I got the rebuilt 350 done in Belle, my daily. Had to drive the Jeep today because my 72 C/10 shift linkage has apparently ruined the 350 turbo. Ya gotta love it! Anyway, thanks again you guys!

[hatzie]

Originally Posted by sweetk30

my info above is from just my time with 4x4 trucks .

i went threw 2 dana 44 3/4 ton fronts with 36" tires and mild sbc . the 2nd blown axle assembly i said screw this and went dana 60 . unbolted it from the donor truck and have been running it now for close to 15 years . only serviced the wheel bearings 1 time and freshened up the king pin service parts no pins swapped .

i have tryed to blow it up even with a built 400 sbc and 38" tires . even now its under my plow truck with a 8ft or 9ft fisher plow depending on how much snow i need to move .

each to there own . its all in how you use it / build it / play with it and just luck !

The tire size rather than the engine specs have more to do with what front axle you'll get away with.

When you start rolling more than 33" tires the slightly smaller parts in the Dana 44 become a liability... as you discovered. That amount of rubber is simply too heavy for the half shafts. The biggest tires I ran were 265/75R16 Michelin Ice and Snows... 31-1/2". Not going for looks just traction with a 7-1/2' Fisher plow and a bed full of sand.

I'm surprised you get away with a stock Dana 60 running 38" tires. Usually, the stock hubs and half shafts become fuses with big tires.