78 k25
 

I just acquired a 78 gmc k25. It has the 44front, sf 14 bolt, 400 tranny, and I haven't crawled under it to check if 203, or 205. What's your thoughts on transfer. I plan on lifting and running 33-35 in tires. As far as motor, I am thinking 355 or 383, this depends on what components I can buy off my uncle, he builds dirt track racecars. My question is what is needed to be upgraded in my drivetrain to be able to be used but not break on me?

Re: 78 k25
 

Re: 78 k25
 

I will stop by my friends tomorrow and get some pics for you guys, in text, its green, rusty, has homemade grilled guard, and headache rack. And the best part, paid for and still didnt empty the wallet. Forgot to add, its ugly.

Re: 78 k25
 

Re: 78 k25
 

Awe yea !

Get it running an drive the shatt out of it !

Re: 78 k25
 

It runs and drives and is currently licensed, got about $400 in it as it sits.

Re: 78 k25
 

From what I can see from the picture it looks like your truck has no locking hubs on the front, so without seeing the t-case I'd say you have an NP203.

Re: 78 k25
 

It does have the 203, I would like to figure out the gears this weekend. Hoping 3.73.
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Re: 78 k25
 

Get rid of the 203 transfer case first of all. the rest of it don't sound to bad should be able to stand up to some abuse with the lift and tires you want to run. Not to bad a looking truck lift it and go out and beat on it. At least you wont have to worry about messing it up haha :D

Re: 78 k25
 

What's wrong with the 203? I probably won't have over 3-350 HP, and 35 inch tires. I doubt I break it, but i never had a truck with one, but I also never broke the 208's I've had.

Re: 78 k25
 

The 203 is an awd transfer case, if you can take it out of 4wd, then it's been modified. It's a very weak transfer case, hard on your steering components because it's always engaged and you don't even need 200hp to break it.

Re: 78 k25
 

I always heard the 203 were strong, but needed more care to be reliable. And I can't take it out of 4wd, so it hasn't been modified.

Re: 78 k25
 

The 208 is a good chain driven transfer case, but the 203, which is also chain driven, is a good boat anchor. I had a 203 behind a 4.3, in an s10 I build, and it didn't last the first time wheeling, the chain snapped. I swapped it for a 208, and never had a problem. My friend owns that truck now and he still wheels it hard 10 years later with no problems.
If you want a good transfer case look at a 208 or even better a 205. If you find a 205 keep the front hi-lo section of the 203 and build a doubler.

Re: 78 k25
 

I'm not gonna swap at this time, to much involved. Might find 205 for a doubler.

Re: 78 k25
 

The ft 4wd part doesn't bother me, but the chain strectch kind of does. Which trucks came with the 205 that will bolt up.

Re: 78 k25
 

You heard wrong.

Re: 78 k25
 

My 84 K25 had a 205, many other trucks had them, they were options for a lot of years. You just have to find a truck with part time 4x4 and had a th400. Just look online for a NP205 off of a th400. Which I think is the only trans the 205 came on, I could be wrong. Once you go to the 205 you'll want to put manual hubs on the front axle.

Re: 78 k25
 

The NP205 also came behind the SM465 and TH350 as far as GM is concerned. Ford, Dodge and International also used the NP205 behind various transmissions over a broad range of years.

Re: 78 k25
 

Dodge, Fords and Internationals were also mostly driverside driveshafts. And if the np205 is off of a th350 it won't fit his th400, the spline count is different, 27 vs. 32. I think the spline count on the SM465 is 10 and the th400 is 32, depending on the year.

Best to find one for a th400.

Re: 78 k25
 

This is all correct.

Re: 78 k25
 

Some later SM465 had fine spline for a 205, and in '91 only you could get a 4L80E with a 205 behind it.

Re: 78 k25
 

Also correct. And when/if switching to 205, it MUST be from a T-400, you cant use a 205 from either T-350 or M465 even with a 400 adapter. Or did someone already say that?