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'78 K20 + NP203: Grab a beer and lemme know your thoughts

Minnesota

Minnesota

1/2 ton status
Joined
Dec 6, 2010
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Location
Greater Longtucky, CO Metro Area
Ok,

So I have a '90 K5 that is my offroad gentleman's adventure rig, but also drags my butt to NE Kansas to visit gramma. Blazer is stock 350/700R4, but then 3/4 ton axles with 4.10's, running 315/75R16's. ORD rear bits and Tuff Country fronts netting 4" front and 5" rear. I like it, and will continue to develop it as the wheeling vehicle.

More to the point, I just bought a 1978 K20 that I'd like to send in a similar direction, albeit more the county crusier/daily driver. That being said, both vehicles will stay on interchangeable wheels/tires, and I see the K20 losing the 3" body lift, and going to proper 6" Tuff Country fronts, rear ORD shackle flip + 2" blocks to start. It's a sweet truck (seemingly good 350, Vortec heads, full length headers, TH400) and will be investing in some sheet metal work on rockers and cab corners. It will not regularly tow anything heavy.

My question is as regards the np203 in the K20. I still have some recon to do, but have a funny feeling it might be on the outs. I'm relatively low budget, and definitely have to measure twice and cut once if I have to replace it. Thus, any thoughts appreciated on whether I stay 203 or do something else, and if so, what should I look for?

Muchas gracias in advance.

20141122_084355[1].jpg
 
The 203 is not a bad case, it's plenty strong, just has sort of a bad rap because it's full time 4x4. If you were thinking of swapping to a 205, you can get the same thing out of a 203 if you convert it to part time, unless you were thinking of going doubler or something... I have a converted and twin sticked 203 in my blazer and I love it, 4x4 is incredible, put that baby in 4 lo and on the trails it just crawls, it'll idle up, over and through anything, I barely hit the gas on the trail. And I would think it would be the same price of not cheaper, and definetly less work to convert your 203 to part time. Just my 2 cents.
 
I am assuming this K20 has a 14-Bolt Full Floater diff, and with a Turbo 400 in it, all you would need is a Dana-60 front diff with the 205 transfer case then you would have a 1-Ton truck. This is how small intentions turn into a money pit.
 
Cheapest option is to keep the 203 and possibly rebuild and maybe a part time kit. If you want a different tcase, look into the 241. 205 is geared the same.
 
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1-ton said:
I am assuming this K20 has a 14-Bolt Full Floater diff, and with a Turbo 400 in it, all you would need is a Dana-60 front diff with the 205 transfer case then you would have a 1-Ton truck. This is how small intentions turn into a money pit.
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ah - - - nope .

still not k30 frame .

and only th350 can swap the 203 for a 205 with NO tail shaft swap .

th400 has specific tail shaft for 203 AND 205 both fig 8 and round 6 style case.

me I would do 3-4" lift and maybe 35 max for dd/work truck . and keep eye out for 205 case and save a few bucks and get ready for the tranny tear down and tail shaft swap and any other parts needed when in there . . . . or just do a doubler kit with the 203 range box and the 205 case.
 
72blazerguy said:
Cheapest option is to keep the 203 and possibly rebuild and maybe a part time kit. If you want a different tcase, look into the 241. 205 is the worst geared tcase and if you go that direction, you will never again have compression braking.
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hello the 203 is no better in low gear ratio over a 205 case.

and there is nothing wrong with a 205 / 203 / what ever if it fits the bill needed.

heck I have been running 205 case in my trucks for years . no wish to swap out . best mod I did was twin stick the 205 :D

but yes if newer lighter yet beefy case skip the 208 and head directly for the 241 .
 
This sounds very similar to my build. Keep the 203 and rebuild it and install the part time kit while you are at it. I did just that and have been very happy with the end result. I picked up a solid 1 mpg doing the part time kit. I know, I know, a whole 1 mpg well, think about it this way. That was a full 10% increase. While 10% of nothing is still nothing I was happy with it. Also, if later on you wish to do a doubler you already have the 203 in place.

I would caution you about using the 4" shackle flip on the long bed truck. I have found it places the rear pinion angle too high in relation to the rear drive shaft. On the shorter Blazer wheel base it works out well but, the long bed truck just a touch too high, and you will end up placing shims to lower the rear pinion angle back down.

Besides, keeping the 203 requires less work which means more time enjoying the truck.

LT.
 
I'm gonna get bundled in the morning and take a look at the shifter linkage. Have a good download on how to do it proper. I don't think the truck has been abused, but time does take it's toll. Oh, and drained axles and t-case today. All reasonable, and definitely not under-filled. Fingers crossed.
 
sweetk30 said:
ah - - - nope .

still not k30 frame .

and only th350 can swap the 203 for a 205 with NO tail shaft swap .

th400 has specific tail shaft for 203 AND 205 both fig 8 and round 6 style case.

me I would do 3-4" lift and maybe 35 max for dd/work truck . and keep eye out for 205 case and save a few bucks and get ready for the tranny tear down and tail shaft swap and any other parts needed when in there . . . . or just do a doubler kit with the 203 range box and the 205 case.
Click to expand...

I am talking about 1-Ton running gear. I did not want to get into the minutia of every small difference between a 1 ton and a 3/4 ton. I guess you answered the question of how much of a hassle switching to an 205 would be. I own the ultimate trans/transfer combo of all time 4L80E/205. soon to be connected to a GEN VI 454 bottom end with a set of aftermarket Mark IV large oval port heads on top, which will be going into a 1991 chevy V3500 SRW. NOW THATS A 1-TON!
 
Also, on the shifter for the 203 they tend to give out after around 40 years of so. Off Road Design has a shifter they manufacture for just the 203 if you need. That shifter is on my list of things to do here soon.

LT.
 
Thanks guys. I'm finally getting around to taking a look at the linkage. I did get the oil in it changed, and what came out looked reasonable, and there was plenty of it, so that is encouraging. It did start going through the ranges with much less effort/more consistency, but still not ideal. The troubling development is that now I seem to have a very light whirring/tick that I did not have before. It's noticeable in 2-hi above 40 mph, and very pronounced off-throttle in 4-hi.

It's not one of those "OMG, shut it down, shut it down" kinda noises (maybe the 4-hi scenario), and also seemingly no related vibes, but something is not right. And it's definitely coming from the case. I have the boot off for enhanced audio.

Anyhow, gonna go clean up the linkage here in a sec and then adjust according to this link I came across.

Thanks for all the feedback so far.
 
Minnesota said:
Thanks guys. I'm finally getting around to taking a look at the linkage. I did get the oil in it changed, and what came out looked reasonable, and there was plenty of it, so that is encouraging. It did start going through the ranges with much less effort/more consistency, but still not ideal. The troubling development is that now I seem to have a very light whirring/tick that I did not have before. It's noticeable in 2-hi above 40 mph, and very pronounced off-throttle in 4-hi.

It's not one of those "OMG, shut it down, shut it down" kinda noises (maybe the 4-hi scenario), and also seemingly no related vibes, but something is not right. And it's definitely coming from the case. I have the boot off for enhanced audio.

Anyhow, gonna go clean up the linkage here in a sec and then adjust according to this link I came across.

Thanks for all the feedback so far.
Click to expand...

I've been working on my stuck 4WD shifter in my 78 as well. Had good success with unscrewing those 4 screws and lifting the thing up and just spraying PB blaster and WD40 down there. I can now get it from Lo loc all the way down to High
 
Well, despite getting the OEM linkage adjusted reasonably, then heading down the path of thinking my noise was hub related, looks like something's indeed cranky in the 'ol 203.

That being said, along the way, I sprung for ORD's twin stick shifter, and I haven't loaded my shorts like that for a long time, both when I pulled it outta the box, and when I got it installed. Pure parts sex. Not cheap, but boy is it cool.

Next week I'll drop off my CList 203 for a going-thru and part time kit, then plug and play when it's done.
 
Yeah I know the area pretty well. All I can say is "left hand milk stout on nitro for president!" Could you post or pm me the name of the shop or guy? I could use someone I can trust. I currently don't have someone I trust real well in the Denver metro area. I would drive up to Longmont for the right guy. What's he going to charge you for the part time conversion?
 
1-ton said:
I am assuming this K20 has a 14-Bolt Full Floater diff, and with a Turbo 400 in it, all you would need is a Dana-60 front diff with the 205 transfer case then you would have a 1-Ton truck. This is how small intentions turn into a money pit.
Click to expand...

A 1978 K30 with a TH400 would have had an NP203, not an NP205....

Martin
 
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