NP203... no 4 wheel drive

[77 K20]

So a few weeks ago I was testing my new tires. Drove up and over a pass. 4wd worked fine. Put it in 2wd and drove down the 10 mile dirt road and then got on the highway. Probably 10 miles down the highway while cruising at 60 mph there was a sudden bang/clunk noise and I saw my transfer case level jump. Then all was quiet and "normal". I wiggled the transfer case lever to make sure it was in the 2wd position. It was.

So today I try to use 4wd and nothing. Tried repeatedly to get it into 4wd hi and even 4wd low. Nothing. Always 2wd.

And I do not have hubs anymore. Had problems with them last year and removed them and put the stock full time 4 slugs back in.

So- what happened? Truck still works and drives fine in 2wd.

Since I've owned the truck 4wd hi always worked fine. However it used to pop out of 4wd low when under load. Usually made a bad noise when popping out.

So is this just the stupid stock transfer case lever issue? Or did something break inside?

Transfer cases aren't my thing. I just know many don't like the chain in it, and that if they have the part time kit then the "shaft kit" should have been used. I have no idea what kit was installed on mine.

 

[dvdswan]

So if the lever goes into 4H and 4L positions with no issues just no 4WD. If you have full time hubs jack up the front end and try and spin the driveshaft. If it and the wheel/s spin then either the chain or front output shaft broke. If you can't spin it then your linkage is really out of adjustment.

 

[77 K20]

Of course when I have stuff to do, work calls me in all weekend. But finally got a chance to look at it. I watched underneath as my daughter shifted it around. Both of the levers that go into the transfer case are moving. I've keep the stock linkage lubricated.

I jacked up the front end while it was in 4wd and can turn the driveshaft freely with my hands.

So I guess cruising down the highway is the worst thing in the world for transfer cases.

So being in a small town there isn't much choices of transmission shops. I got laughed right out of one of them 12 years ago when I asked one to rebuild the transmission in my GMC Typhoon with some special parts I ordered from Art Carr. (this was after some other shop by the previous owner had it rebuilt with "HD parts and a shift kit". )

I did see one place online (Powertrain products inc) that has rebuit units in stock. $1040. Unsure if it is part time or full time. And then the idiots want a $350 core charge. And am unsure about what parts they use inside it.

Is the discontinued "Mile Marker Shaft Kit" still the strongest and best conversion out there? What is next best?

I've really really wanted an Atlas transfer case so I could actually have compression braking going down steep trails but when it was all said and done that option would be around $4,000.

 

[bucket]

Doubler?

 

[77 K20]

Doubler?

I thought about it- but when I priced out all the bits and pieces it came to the same price as a 4 speed Atlas transfer case. And the Atlas is smaller and lighter. (doesn't need a second crossmember added).

 

[Curt]

A 205 would be you’re best bet.I know that there is some after market support for a 203,but not like it’s gear driven brother.

My step dad had a f-250 with a 203 that did the exact same thing.More cost initially,but long term better results.IMO

 

[77 K20]

ORD has a rebuilt 205 for $1,000 but then I'd have to redo both of my new driveshafts and I'd have even less of a low range. If I'm going to re-do the driveshafts then it would be so I can get a nice very low range.

Starting to lean towards just fixing or slapping another 203 in there until I can buy either an Atlas or the ORD doubler... but with the Magnum underdrive. That would give me a 5.33:1 low range, along with 1.96:1 and 2.72:1. That is what I really would want.

There used to be a company called lowmax that did extra low range gears for the 205 but they are not in business anymore.

Have any idea of what caused your dad's 203 to break? (@Curt ) I'm still confused as to how it can break cruising down a highway.

Sucks I'm throwing away money, but seems like I'm always doing it on this truck.

I spent the whole summer working out of state and fixed up my truck so I can offroad all winter with my buddies. First real trip out and- disappointment. Atlas has a 9 week wait time. ORD has similar wait times. Don't really want to wait till summer to get it fixed when its hot and smoky here to use it again.

 

[75gmck25]

The GM pickups were popular in that timeframe, so there should be quite a few in your area in the junkyards. If you want to off-road I would find one that has not been converted and do a direct swap, since the original design is stronger than one converted with the cheaper Milemarker kit. The shaft conversion kit is stronger but no longer available.

Most folks converted the np203 in an attempt to get better gas mileage, and durability was a secondary concern. They were not converted to make them work better off-road. A stock case might have a stretched chain, but they are still extremely durable. I know there are also two different chain widths, so maybe the larger chain is also more durable.

Bruce

 

[77 K20]

I called a local transmission shop that was recommended by a friend. Been around for something like 37 years. Asked about rebuilding the 203... the guy chuckled and said he can't even remember when the last time they rebuilt one of those. Had no idea if he could get parts. Said most are boat anchors now.



Called another place I've had limited dealings with- a garage/off road shop and they also own a junkyard. They didn't laugh at least. Said they will do some checking around and call me back.

 

[75gmck25]

Rebuild kits for the 203 are mostly just seals and roller bearings. New chains are also available since a stretched chain is the main wear item. Even Jegs and Summit sell the chains, so they aren’t that hard to find. There is also a “chain saver kit” but I’m not sure how it works. Allstate gear.com seems to have a lot of parts available.

Np203s also continue to live in the off-road 4x4 world as part of doubler kits.

Bruce

 

[Turbo4whl]

Rebuild kits for the 203 are mostly just seals and roller bearings. New chains are also available since a stretched chain is the main wear item. Even Jegs and Summit sell the chains, so they aren’t that hard to find. There is also a “chain saver kit” but I’m not sure how it works. Allstate gear.com seems to have a lot of parts available.

Np203s also continue to live in the off-road 4x4 world as part of doubler kits.

Bruce

Where did you find the chain saver kit? I looked at Allstate Gear, did not see it there.

 

[77 K20]

I kept thinking about my problem... have a hard time thinking that I broke the front output shaft or the chain. My chain has never made the popping noise that is typical with a loose chain skipping teeth.

I've been looking at diagrams of the 203 and wondering if it was possible if the shift fork inside the transfer case broke? Disengaged? Rattled loose? Fell apart?

It is just so odd there was one clunk/bang, the shifter jumped a bit, then NO NOISE at all after that.

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Specifically I'm looking at #70 (shift fork retaining pin), #71 (lockout shift fork) #72 (lockout shift spring)

So if I was in 2wd at 60 mph and the lockout fork (that engages 4wd) drifted over and tried to engage the front side gear I can see it banging if both driveshaft speeds were not 100% equal. My tire pressures were not equal front vs rear. (I aired the tires down earlier in the day and my air compressor was having issues filling them up).

Is there any test to check out the shift fork with it in the truck? Or the only way to tell is removal of the transfer case and complete disassembly?

 

[75gmck25]

I have not seen the chain saver kit in quite a while, so maybe it’s no longer available. IIRC, it used to be sold as the Milemarker 509 Chain Saver.

bruce

 

[TubeTruck]

I had similar issues with mine when I put the slugs back in. Cruising about 50 the 203 was making some weird noises and sounded like the chain flopping around or gears trying to mesh that weren't supposed to. I swapped to manual hubs and all the racket went away. I do have the current part time kit in mine, not the old shaft version. If you can get your hands on a 205 it's about $1k to make a doubler, unless you get the right 205. The ORD kit is $700 I believe and a 205 should run you about $250. Get the ORD 32 short spline input kit (and a little machining) and you got yourself a doubler, and it's the same length as a 203 so no drive shaft mods necessary.

 

[77 K20]

Small update here- I've been busy traveling so I dropped off the truck last week at a shop I've never been to. My main mechanic friend retired and recommended the place. They also specialize in aftermarket offroad stuff- so they liked my truck instead of laughing at it.

The chain snapped. And I had the wide chain. The 2.5" instead of the 2.0". Calling around they so far have only found new 2" chains and they are around $300.

I told them at this point even throwing a used chain in there would be fine to get it rolling again. I'm now fully planning on ordering a 4 speed Atlas transfer case for it in the next year.

I still don't understand how without any warning a chain can snap when cruising at 60 mph down the highway. Oh well. I've had a NP203 in 3 different squares back to 1990 and never had an issue until now.