Need np203 advice

[zac]

I hate to rehash all this again, and I have done alot of reading here about this, just want to make sure I have it straight and know all the options. I grew up driving 203 equipped Chevs, that's just what 4wd was to me. Ever since then though I have had 465/205 trucks. So I bought a '79 K20 over a year ago with a th400/203 combo and full floater. I use it as a rarely-driven work truck, and my wife drives it some with the kids, so I wanted three people to be able to ride in relative comfort. So no 4spd. But needless to say, I am not enjoying full-time 4wd like I used to. I'm thinking about putting in a part time kit. So there are two kits available, correct? The cheap Mile Marker kit, and the more expensive one with the shaft, right? What's your preference? Also, what about the oiling issue? I've read that with both these kits you have to make sure to lock it up every couple hundred miles. But I've also seen people claim that's not necessary, depending on the year of your case and the kit you use. So what's the deal?

Also, I recently bought a set of new condition 31x10.50x16.5 tires to put on my 8.25 steelies. Don't know how long it's been since those were made. Problem: they are from two different manufacturers, they look to be the same height but I know better. So is running these tires going to kill the differential in my case, or just make my mileage even worse? Or both? Again, this truck doesn't get driven much, maybe 2000 miles max in the last year.

I'm tempted to scrounge up a 205, but I want to keep the th400 and I know the $$$ situation on those cases. It hardly seems worth the effort and money for this truck, especially since the average price for a 203 in my area is $50-$75.

Any input is appreciated.

[royo]

Put lock outs on the axle? You could also take the driveshaft out ? The only place I have seen part time kits is on evil bay .

[LONGHAIR]

A part-time kit is definately the way to go. Either one will do what you need. I have installed hundreds of them, both types. Functionally, you cannot tell the difference, it's more a matter of "perceived" strength. But in practice, I have never seen a failure of the gear in the cheaper kit. Thrust bearing? yes, gear no.
The weak link is actually one of the stock internal parts. The "stamped" ring gear that drives the chain is a known issue. They are cheap and easy to fix though.

I am always amazed to see that there are some of these things still running around in the "full-time" mode.

As far as "locking it in" every once in a while; It's no big deal, just pull the shifter into HI-LOC for a few miles. Don't lock in the hubs though, you just need to turn the internals. Locking the hubs and transfercase should not be done on pavement.

[Allensracing]

Longhair, I have a 78 3/4 ton th400 203 full time 4x4 combo also. I also want a hub kit. my hesitation in buying one is because of the full time transfer case. I tried removing the driveshaft for highway summertime driving. I assumed this was the same as unlocking hubs.
I quckly found out that the only way the truck would drive was in high lock. the full time transfer case has to be modified to run in 2 hi and no front driveshaft. regardless of which hub is purchased, the transfer case still needs an internal modification, correct?

[royo]

Originally Posted by zac

I hate to rehash all this again, and I have done alot of reading here about this, just want to make sure I have it straight and know all the options. I grew up driving 203 equipped Chevs, that's just what 4wd was to me. Ever since then though I have had 465/205 trucks. So I bought a '79 K20 over a year ago with a th400/203 combo and full floater. I use it as a rarely-driven work truck, and my wife drives it some with the kids, so I wanted three people to be able to ride in relative comfort. So no 4spd. But needless to say, I am not enjoying full-time 4wd like I used to. I'm thinking about putting in a part time kit. So there are two kits available, correct? The cheap Mile Marker kit, and the more expensive one with the shaft, right? What's your preference? Also, what about the oiling issue? I've read that with both these kits you have to make sure to lock it up every couple hundred miles. But I've also seen people claim that's not necessary, depending on the year of your case and the kit you use. So what's the deal?

Also, I recently bought a set of new condition 31x10.50x16.5 tires to put on my 8.25 steelies. Don't know how long it's been since those were made. Problem: they are from two different manufacturers, they look to be the same height but I know better. So is running these tires going to kill the differential in my case, or just make my mileage even worse? Or both? Again, this truck doesn't get driven much, maybe 2000 miles max in the last year.

I'm tempted to scrounge up a 205, but I want to keep the th400 and I know the $$$ situation on those cases. It hardly seems worth the effort and money for this truck, especially since the average price for a 203 in my area is $50-$75.

Any input is appreciated.

A good read
http://coloradok5.com/milemarkerpt.shtml

[Allensracing]

Originally Posted by royo

A good read
http://coloradok5.com/milemarkerpt.shtml

Thank you for that link, it is a very good explanation

[zac]

I would actually love the 203--if I never drove it on the highway. But after all these years with part time it's freaking torture to take it on the interstate. Plus after all the trouble I went through to swap 3.42 axles in, I would like to get more of the mileage benefits I was hoping for. Nothing special--maybe 10-12. I ain't gettin that now. I want this truck to take over as my parts chaser, so it will end up on the interstate quite a bit.

I had no idea you just had to lock the t-case and not the hubs to get the thing to lubricate. You learn something new everyday.

I guess I'll just go with the 501 kit. It's cheap and seems easy. I doubt I'll run into any of the issues I've read about with my relatively small tires and infrequent use.

[royo]

I have just finished a blazer. that I took out the t350/203 an put in a 700/208 it is like night an day. It is getting alot better gas mileage now. lol

[LONGHAIR]

Originally Posted by Allensracing

regardless of which hub is purchased, the transfer case still needs an internal modification, correct?

Yes. Think of the internals of a NP203 as an "open differential" like in a rear end. If you jack up either rear wheel....it spins and the truck doesn't move.
In stock form a NP203 works the same way with the front and rear driveshafts. If one end is "disconnected", the yoke just spins and the truck just sits there.
When you shift into one of the "LOC" positions the "differential" is eliminated, locking the front and rear output yokes together. The truck will move then, but it is not good to leave it that way for everyday driving....thus the point of the conversion kit. They eliminate the differential action with-out locking the front to the rear.

It's a simple operation that takes about an hour

[OrrieG]

In 85 I put a Doug Nash shaft kit in my 203. Drove it as DD and off road until 98 when I took it off the road for the current rebuild (74 drive train in a 59 Fleetside) putting about 60-70K miles on it. I took a look at it and everything is still in like new shape, a little chain stretch but not enough to warrant replacement. I believe some has picked up the rights to it and is making the same kit.

The Milemarker type kits use wedges and a thin wafer bearing. Over time the thin bearing fails letting the internals move. I have heard (never experienced) that this causes bad things to happen inside which destroys the aluminum output housing. But there are lots of them out there. I don't think time to convert is a big factor between the two, just the initial cost. Having said that, I see 205's around here all the time for the price of the shaft kit. I just did not want to do through the effort of redoing everything.

The shaft hit eliminates all the spider joint assembly and makes it a true in or out box. Still have the chain drive but I always ran out of nerve before I ran out of truck. I was limited by my still open axles. When I converted from full time I picked up about 3 mpg.