NP203 Questions....Help Me!!

[iliveintn]

For starters I bought the thing abandoned so I got no explanation of how the 4wd works or what they had even done to it, hence the newbie-ness, and the shift pattern for the 203 is nowhere to be found in the thing.

Okay so I have a 72 blazer with a NP203. It has front lockout hubs so I'm guessing it has the part time 4wd kit installed in the 203. If it does what is the process to unlock the front? Earlier this week I was messing around with it and put it in 4wd for the first time since i've had it. The hubs were really really hard to turn but I finally got them locked. I put it into the different 4wd gears but noticed something kinda weird.

I pushed the stick as far forward as I could and I put it in gear and regardless of how much gas I gave it it just would slowly lurch at the same speed (very slow....less than 2MPH).


After I was done messing around I put the xfer case in neutral, unlocked the hubs, and reversed it a good 30 or 40 feet. It seems like it is riding the same speed/RPMs as usual but the front driveshaft is still spinning.

What do i need to do to unlock the front? Also what is the best way to tell if the case is full time or part time 4wd? I realize the lockout hubs point me in the direction but who knows, people do some strange stuff.

[Hoods69BadBowTie]

The NP203 has no drain plug I believe just a fill plug. The NP205 has a fill and drain plug on it. Sounds like the 4wheel drive aint been used in forever hence sticky hubs. Also seems like somethings wrong with your transfer case as well. Does it only do the slow lurch thing when its in 4x4 or in 2wheel drive as well?

[OrrieG]

The bottom bolts that hold the round plate on the chain case is also the drain plug. It sounds like you need to take your hubs apart and give them a good cleaning. If they are old enough there is a good possibility that they are not disengaging, it was common with the older Warn hubs. That is what would cause the drive line to keep turning. If the truck has been converted and the hubs are not disengaging it is the same as running any part time 4wd with the front axle engaged on pavement. The shift pattern from all the way forward is low-front axle engaged, low rear axle only, neutral high rear axle only, hing - front axle engaged. With out a conversion kit the extreme forward and back were loc. In the next ones were low or high full time with the spiders in the transfer case acting to keep the front and rear from binding.

If it has the conversion kit when you have it in the low or high position next to neutral you should be able to turn the front drive line with your hand with the hubs disengaged. If you engage the hubs and push the lever to the extreme front or back position you will not be able to turn the drive line.

Something else that might be happening is the 203 shift levers are notorious for not disengaging from 4wd when they get old and worn. I have had two that when going from low-loc or high-loc back to low or high open the shift lever would move but the lever to the transfer case would get stuck between loc and open. The fix was to crawl under and pry it back into place with a big screw driver. It was frustrating enough that I converted my stick to a twin stick.

Hopefully everything is just gunked up. Disassemble and clean the hubs (a good idea at least once a year), clean up the shift lever, and change the fluid in the transfer case.

Another possiblity is that the chain is stretched enough that the lurching was the chain actually jumping the gear. Its pretty obvious under load. You can also check it by disengaging the hubs, putting it in high loc and slowing turning the front drive shaft. If the chain is tight you will have the same tension turn each way. If it is stretched when you reverse the direction it will feel easier until the chain slack is taken up and pulls the gear. A little slop is ok but if there is a lot you can hand grenade the chain and gears. If it feels loose you can pull the round aluminum cover (watch out for the needle bearings) to access the chain and gear. It will be obvious if the chain is stretched and you can move the gear, or in extreme cases slip the chain over to the next tooth. Chiltons or Haynes manuals have pretty good exploded diagrams and rebuild information.

There are two types of conversion kits. One uses a wafer bearing and some wedges to modify the spider gears. Over time the bearing wears out which causes extreme end play in the gear assembly which causes caustrophic failure problems in the output housing. The second is a complete shaft that replaces the spider gears with a sliding in/out function. It was originally designed and marketed by Doug Nash as DNE2, I think someone else has now picked up the right to the design and is marketing it. Only way to really tell is to pull the rear housing and see if the spiders are still there or its the shaft type.

If the 203 is hosed think about a 205 conversion. When mine pukes again that is the route I am going. The 205 is gears, no chain and much simpler. A lot of guys use the 203 reduction assembly in conjunction with a 205 to get a 4:1 low ratio in addition to the standard 2:1.

[Dooley]

1972 GM's did not come with full time 203 transfercases. If you have a 203, it was installed by someone, not GM.

Here's some info on the 203 and how it's supposed to work.

[Davetopay]

A 72 should be a 205 T case.

Shift pattern is from the dash pulling backwards:

4 low
N
2 Hi
4 Hi

The 205 is a gear drive case and SUPER strong.