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08-14-2009, 07:07 PM
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#1 |
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Registered User
Join Date: Feb 2007
Location: maryland
Posts: 218
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Np203 help
I have a 66 4x4 with 78 running gear. It has a NP203 transfer case that is giving me a hard time. As far as I know you are supposed to have it in HI for daily driving but it wont stay in that gear. I just had it shipped in from CA and the truck driver had it between gears so it was grinding when he started it and I think it screwed up the gear, fork, or both. Who knows how long he let it run like that before he got here.
The way it is now if you run it in 2HI Lock the RPM'S are HIGH (3500) but i'm only going about 40/45 MPH Are the gear ratios the same for 2HI and 2HI lock?? Can I just pull the front drive shaft and run in 2HI lock until I have time to pull it and rebuild it? Thanks for the help (front) Low Loc Low N HI Hi Loc |
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08-14-2009, 09:08 PM
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#2 |
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Another Day, Another Dollar
Join Date: Nov 2008
Location: North Vancouver, BC
Posts: 1,316
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Re: Np203 help
i do believe that all the loc function on that puppy does is locks the front and rear diff to to the same rpm.
think of it as a third differential. it isn't going to change your ratios at all, but if you don't have locking hubs it is going to make some funny noises cornering at low speeds on the pavement...... you should be good to go if you yank the front shaft.
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-78 K20 Cheyenne 454 long box, 4" lift, 35" MT's, '84 cab, '80 box "its hip to be square" 
Last edited by willett; 08-14-2009 at 09:09 PM. |
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08-15-2009, 11:04 AM
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#3 |
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Registered User
 
Join Date: May 2007
Location: Deale Md
Posts: 4,663
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Re: Np203 help
any pics of your truck?
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James 63 GMC V6 4speed carryall 65 chevy swb bbw V8 auto 68 K20 327/4 speed, buddy buckets 2002 GMC CC Dually Duramax 64 GMC lwb 3/4 V6 4speed SOLD 66 GMC swb bbw buddy buckets SOLD IG duallyjams The only thing that stays the same is constant change! |
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08-15-2009, 12:18 PM
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#4 |
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Registered User
Join Date: Feb 2007
Location: maryland
Posts: 218
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Re: Np203 help
This is the only one I can get to load. I'm terrible with computers.
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08-16-2009, 08:27 AM
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#5 | |
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just can't cover up my redneck
Join Date: May 2004
Location: Columbus OH
Posts: 11,414
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Re: Np203 help
First of all, what gear ratio is do you have in your axles? A 3/4 ton truck that old could be pretty low, which would give you high RPM issues.
Second, you need to varify that you are indeed in high range. This would be easyest to do by actually getting it into low range. The RPM change will be drastic. Lastly, NP203 shifters are well known to be troublesome. They are very complex inside. They have to split movement of 2 different out-put levers with only one in-put lever. Simply taking it apart, cleaning, and re-greasing everything inside, will do wonders for it.
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Bad planning on your part does not necessarily constitute an instant emergency on my part.... The great thing about being a pessimist is that you are either pleasantly surprised or right. 
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08-16-2009, 11:10 AM
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#6 |
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Registered User
Join Date: Feb 2007
Location: maryland
Posts: 218
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Re: Np203 help
Its all 78 running gear and I am not sure of the gear ratio. The rpm's are about 3000 when doing 45mph. I have 33 inch tires. What is a safe RPM limit for a basically stock 350?
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08-16-2009, 06:31 PM
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#7 |
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Registered User
Join Date: May 2008
Location: Alta Loma, Ca.
Posts: 930
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Re: Np203 help
Something is wrong. Hi and Hi loc are the same ratio and Lo and Lo loc are the same ratio. Lock just locks the interaxle differential (in the back of the t-case) and keeps the front and rear drivelines going the same speed with no slippage. Check the adjustment of the shifter. It is under the truck and you will see a hole to line the linkage up. Stick a nail or bolt or whatever fits in it and adjust the linkage. What transmission do you have in the truck?
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08-16-2009, 08:16 PM
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#8 |
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Registered User
Join Date: Feb 2007
Location: maryland
Posts: 218
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Re: Np203 help
I have a turbo 350
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08-16-2009, 09:50 PM
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#9 |
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Registered User
Join Date: May 2008
Location: Alta Loma, Ca.
Posts: 930
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Re: Np203 help
The 203 is a 200lb t-case. If it is messed up inside I would recommend finding a 241 t-case out of a passenger drop leaf sprung Blazer or Suburban.
If you have the round adaptor you can bolt one in out of a Blazer or Subrban that has a 350 or 700R4. Both transmissions share the 27 spine output shafts. Plus the 241 t-case is only around 80 lbs. You will be able to sell the 203 for the range box if someone wants a doubler behind a 350 or 700R4. |
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08-17-2009, 03:49 AM
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#10 |
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Registered User
Join Date: Feb 2007
Location: maryland
Posts: 218
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Re: Np203 help
I know where a NP208 is out of a 89 blazer that had a bad 700r4. Will the splines match my 350?
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08-17-2009, 11:27 AM
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#11 |
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Registered User
Join Date: May 2008
Location: Alta Loma, Ca.
Posts: 930
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Re: Np203 help
Yes, 700R4 and turbo 350's had 27 splines. Get the adaptor and crossmember too if you can. Your driveshafts may have to change also. The front one from the Blazer may work, but the back one depends on the output yoke of the 208. You can get 350 tailshafts to adapt to the round 6 bolt pattern if you dont have it already. I am not sure but you may have to measure the tailshaft stick out of the output shaft to make sure they are the same. Measure this at the trans and adaptor. If the adaptors are the same length and you have the same round pattern it should just bolt right up.
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