Author Topic: NP203 question (2 parts)  (Read 3894 times)

Offline KingNeptune

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NP203 question (2 parts)
« on: September 21, 2014, 10:26:57 AM »
1st question)    So my understanding is that if I have a truck with a 203, and there are lock out hubs. But no part time kit installed in the t-case, then in order to move the truck under its own power, the t-case shift lever has to be in either low or hi loc. When I bought my truck, it had the hubs. But didn't know if it had the kit. The PO had the lever in the lock position. So, I assumed that it didn't have the part time kit in the case. So, I tried driving with the lever in just hi, (not loc) and the truck drives with no issues. So I'm assuming it has the kit installed. Am I correct in this assumption?

2nd question) If it does in fact have the part time kit, then that essentially locks up the diff in the t-case. Correct? So in that case, I shouldn't lock the hubs, and put it into 4wd, on dry pavement, because it will blow out my front end, or t-case, or both. Am I correct?

Thanks for any answers you can provide.
1979 Chevy K10 and 1974 K5 GMC Jimmy     Eric

Offline zieg85

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Re: NP203 question (2 parts)
« Reply #1 on: September 21, 2014, 01:32:30 PM »
From what I understand, question 1 is yes.  2 is yes as well.  I don't think you are going to blow anything but it does bind it up on dry pavement.  Back in the day I converted one truck.  Found no difference in MPG and due to lack of use the front u-joints got stiff...  I actually liked the 4 wheel action unlocked as the traction was the left front first so it essentially was a front wheel drive which did excellent in snow
Carl 
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1986 C10 under construction
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Offline illinoisk30

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Re: NP203 question (2 parts)
« Reply #2 on: September 21, 2014, 02:02:41 PM »
I agree with zieg85. I never did one of those conversions and firmly believe it would not have changed the MPG much at all.
1977 Chevy K10 LWB Supercharged 406 TH350
1977 Chevy K30 DRW 400 TH400
1978 GMC K35 SRW 454 TH400
1979 GMC K35 SRW 400 TH400
1980 Chevy K30 SRW 350 SM465

Offline FlatBlack77

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Re: NP203 question (2 parts)
« Reply #3 on: September 21, 2014, 03:44:27 PM »
my 79 has a 203 without the kit but PO installed lockouts and insisted that it got better mpgs driving in hi loc.

i drove it for a very short time like that then locked the hubs and put it in Hi and noticed no difference whatsoever. and from what i have read, running in Hi loc with hubs unlocked is terrible for the case.

zieg85, you say your truck goes well in the snow? I got my truck in the spring so i havent had it in any snow yet so i have no idea how it will do. i like what you say though
"When you are a hammer, everything looks like a nail"
'77 C/10 - 350/350 mild street motor

Offline rich weyand

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Re: NP203 question (2 parts)
« Reply #4 on: September 21, 2014, 04:30:57 PM »
These things are monsters in the snow.  24" snowfall in Chicago the winter after I got it.  No problem whatsoever, even through plow ridges.  It was amazing.  I absolutely love it.

One thing on the NP203: there is no oil feed to the rear output shaft bearing when the xfer case is unlocked and the hubs are free.  The chain to the front throws oil around inside, which runs down ways on the inside of the case and fills a little pocket by the bearing.  But that only works when the chain is spinning, which it doesn't with both xfrr case and hubs unlocked.  Couple hundred miles and that reservoir runs dry.  After that, you are trashing that bearing.

The solution is to run it in HI LOC, hubs free for the first couple miles every day.  On a long trip, do it for the first couple miles after every gas stop.  This fills that little reservoir for another couple hundred miles.  You can shift it out of LOC while on the move.

If you are running around in LOC, or with the hubs in LOCK (like in the winter when you want to be able to engage 4WD without getting out to lock hubs), then you don't need to worry about it, because the chain is being spun from one end or the other, so oil is getting to the reservoir.
Rich

"Working Girl": 1978 K-10 RCSB 350/TH350/NP203 +2/+3 Tuff Country lift

Offline zieg85

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Re: NP203 question (2 parts)
« Reply #5 on: September 21, 2014, 04:34:43 PM »
Rich corrected me, sorry
« Last Edit: September 21, 2014, 04:36:44 PM by zieg85 »
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline FlatBlack77

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Re: NP203 question (2 parts)
« Reply #6 on: September 21, 2014, 06:49:31 PM »
monsters in snow huh sounds awesome 8)

i read that about the oil feed and its another reason ill just leave mine unconverted. not that its a huge deal or anything but mine is working just fine as a full time case and that is just fine with me
"When you are a hammer, everything looks like a nail"
'77 C/10 - 350/350 mild street motor

Offline rich weyand

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Re: NP203 question (2 parts)
« Reply #7 on: September 21, 2014, 08:05:30 PM »
I think the biggest reason to convert is chain wear, not mileage.  That being said, if mine had not been converted already when I bought it, I would have left it alone.
Rich

"Working Girl": 1978 K-10 RCSB 350/TH350/NP203 +2/+3 Tuff Country lift

Offline KingNeptune

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Re: NP203 question (2 parts)
« Reply #8 on: September 21, 2014, 10:39:30 PM »
I remember back in the day when these things were everywhere, people were putting the kits in not for mileage, or even because of the chain wear. It was because it wore the front tires bad really fast. I remember seeing tires with uneven wear, and severe cupping. That's why people were putting the kits in back then. People didn't like replacing tires twice as often as the guys with the 205's. 

And thanks guys for confirming my suspicions about running it in 4wd on dry pavement. And I'll remember that about running it in loc for the first few miles to let the chain lube everything. Good information.
1979 Chevy K10 and 1974 K5 GMC Jimmy     Eric

Offline Chadwick717

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Re: NP203 question (2 parts)
« Reply #9 on: September 22, 2014, 01:37:24 PM »
I have a 79 with the lockout hubs and the part time kit installed.  I haven't used 4 wheel drive much, but we went camping this weekend and I locked the hubs and threw it into hi loc.  It got up the mountain great.  However I was under the assumption that I could leave the hubs locked and put it back into hi and drive on dry pavement.  It ran fine doing this for a little bit, but then I would occasionally get a grinding noise under the truck, so I got out and unlocked the hubs, and it went away.  I later went back up the mountain and locked the hubs and put it back in hi loc and didn't have any problems, I just have no idea what the grinding could be.

Offline Dirka

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Re: NP203 question (2 parts)
« Reply #10 on: September 30, 2014, 10:25:54 PM »
Just adding a question that goes along with this,
Is there a way to tell if your truck as the part-time kit installed?
I take it from this post that you can have the lock-out hubs but not the part-time kit installed?

Offline rich weyand

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Re: NP203 question (2 parts)
« Reply #11 on: September 30, 2014, 11:03:43 PM »
Just adding a question that goes along with this,
Is there a way to tell if your truck as the part-time kit installed?

Put the hubs in free, and the xfer case in HI.  Put the transmission in drive.  If the vehicle moves, you have the part-time kit installed.  If the vehicle will not move, you do not have the part-time kit installed.

The reason is that the open differential in the unmodified NP203 will spin the front driveshaft with nothing going to the rear wheels when hubs are unlocked.  If the vehicle moves, it means the differential has been removed and the part-time kit installed.
Rich

"Working Girl": 1978 K-10 RCSB 350/TH350/NP203 +2/+3 Tuff Country lift

Offline Dirka

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Re: NP203 question (2 parts)
« Reply #12 on: October 01, 2014, 08:12:37 AM »
Got it thanks!