Questions about '74 All Time 4wd, HELP

[Thesiger]

Hey, I'm a new member and I don't know if this is the right section to post this, but hear me out.
I'm currently considering the purchase of a 1974 K20 Suburban, and I have questions. I don't know much about mechanics so I need some guidance in regards to know early 'All Time' systems work, and how to convert them to part time and what that actually does, how it works, and what it looks like. My biggest concern about buying this IS the All Time 4wd, since I don't understand it. Is it safe on pavement? How much does it wear? how much worse is the mileage? what are the benefits and risks of converting it?

As far as I can find almost no one talks about or explains this in video from, and few talk about it in chat groups like this. Thank you

 

[Strick]

Hello and welcome to the site. There has been quite a bit of discussion on the NP203 full-time case in some recent posts. Milemarker makes a kit to part-time the NP203 and there may be others out on the market as well. That K20 should net you a Dana44HD front and 14FF Corporate rear; both of these axles are great in my opinion. The NP203 is the least desirable drivetrain component BUT we share common traits like us both being 74 models and not working correctly all the time (getting older is WAY overrated). If you look in the section "similar threads" you may find more information on the conversion. I quit messing with NP203's years back and use NP205 part-time cases in all my trucks now. I found this to be the easiest and most productive conversion.

Strickland

 

[Memaloose]

I had my '75 K/20 converted several years ago but wouldn't have if I hadn't had the front driveshaft take out the tranny pan caused by a worn U joint. It's safe to drive on dry pavement. The front driveshaft always turns but is not engaged in 4x4 until you shift into 4x4. I didn't notice an increase in mileage in mine and I'm an economical driver meaning a light foot on the gas and following the speed limits.
90% of my driving in my '75 K/20 is off road in the desert. If I'm just off idle driving, I can get up to 14 mpg by my calculation. On the highway at a steady 55-60 mph, I get 10-11 mpg.
If you decide to leave it, I would strongly recommend replacing the U joints on the front driveshaft. Believe me, you don't want to have that shaft come apart! Thankfully, I was only going about 15 mph.

 

[Grit dog]

Hey, I'm a new member and I don't know if this is the right section to post this, but hear me out.
I'm currently considering the purchase of a 1974 K20 Suburban, and I have questions. I don't know much about mechanics so I need some guidance in regards to know early 'All Time' systems work, and how to convert them to part time and what that actually does, how it works, and what it looks like. My biggest concern about buying this IS the All Time 4wd, since I don't understand it. Is it safe on pavement? How much does it wear? how much worse is the mileage? what are the benefits and risks of converting it?

As far as I can find almost no one talks about or explains this in video from, and few talk about it in chat groups like this. Thank you

If the truck is worth getting, get it. Whether it is worth getting for all the reasons an antique gas pig truck is worth getting, ft 4wd should be very low or off the list of concerns or decision points. Other than of course whether it works, not unlike the rest of the truck.
Its fine. And/or can be converted to part time and parts are available.

 

[Thesiger]

This is awesome information! I guess I haven't looked deeply here, I don't really know how to use stuff yet. Strick, So the K20 pickups and suburban's are the same underneath? is there anything different to lookout for on the 'burbs? This one is a 350 automatic, don't know much else. fairly rust-free.

In looking to purchase something like this, is there anything extra I should watch for or give special attention to? To make sure its decent?

Memaloose, thanks too, this is all stuff I was wondering. Is yours a pickup? so I assume it would get better mileage than a 'burb? Sorry about your learned experience! ha ha

 

[Thesiger]

Grit, I guess since I didn't really understand older All Time stuff I was wondering about practicality, (If you can even say that talking about 50 year old trucks) wear, and mileage. for history on it, the thing seems bone stock, came from Minnesota, went to Nebraska, parked most of the 80s and maybe 90s. Apparently purrs like a kitten. has some steering wonder, small pwr steering leak. blinkers don't work, lights do. little body rust. 3,000 is the price, I'd like to offer 2,000. is this reasonable? I'd like to drive the wheels off this thing during the summer months.

 

[Thesiger]

You must be registered for see images attach

 

[Thesiger]

Another question, Does the K20 hop and jerk around corners on pavement in 4 HI like a regular 4wd? I would guess not since its safe to drive on pavement?

 

[Strick]

So the K20 pickups and suburban's are the same underneath?

You may need to ask some of these other guys on the K20 Burb frame. The crew frames are essentially the same on 20's & 30's with exception to the rear spring hangers and shock placement. I just traded an '81 K20 Burb (10K lb. Challenger lift) and don't recall it having the taller frame like my C20 and D30 CUCV. The drivetrain in the '81 is completely different than that in your '74. By the pic, you don't have locking hubs but only the flange that bolts to the bearing housing. Still, it looks like a very good truck to start out with and as some others have noted already, you can convert this into a part-timer with bolt in kit. An almost 50 year old truck over here in NC usually does not look as good as the one in the pic. Good luck with your build.

Strickland

 

[Big Ray]

The Np 203 has:
4 hi loc
4 hi
Neutral
4 lo
4 lo loc

Make sure you're in 4 hi. If you have locking hubs, make sure they're unlocked.
If it still hops you may have a locker in the rear end.

Edit: my order is from back to front. It matches the knob pic

 

[Big Ray]

You must be registered for see images attach

 

[Thesiger]

Awesome, thanks guys! the owner says that he'd be willing to drive it to me, (No small feat, I'm 560 miles away) So I believe the real test will be if it can make the trip. If it can, this thing has to be an absolute beast...

 

[75gmck25]

A stock NP203 truck will have fixed front hubs. There would be no reason to ever run unlocked hubs, since the front axle is alway driven.

My ‘75 K25 has the original unconverted NP203 and there are no issues with tight turns in the Hi position. I have the 8400 lb GVW option, so it’s a Dana 44 front and corporate 14 bolt FF rear with a Gov Lock.

The issue mentioned with the front driveshaft is that one end of the driveshaft has a double-cardan or CV joint, similar to what you find on the axle of FWD cars. It’s basically two u-joints directly coupled to each other so that the shaft can flex in multiple directions for the AWD on pavement. I have never had mine break, but it did start clicking very loudly and I found that one u-joint was completely dried out and shot. I replaced all the u-joints for that front shaft (3 total) with new ones that are supposed to be sealed, so I’ll see how it works.

 

[dvdswan]

NP203 Full-time t/cases are just as strong as the NP205 Part-time t/cases with one difference. The Chain. Whereas the 205 is all gear driven the 203 is has the chain instead of gears to run power to the front drive. The chains are very heavy but will stretch over time. The 203s are heavier than the 205 just because of the extra bulk for the chain and differential gear in the rear part of the t/case. There are kits to install the 205 behind the 203 low/high range gear (which is the front of the t/case) so you can essentially double your low range gear. So, you would have a HI/LOW/and super LOW (1:1, 2:1, and 4:1).

NP203

www.offroaddesign.com

The NP203 were originally a full time 4WD case, meaning all 4 tires receive power at all times. This was made possible through use of a differential in the back of the 203 that let the front and rear driveshafts turn at different speeds as just as a diff in an axle lets each axle shaft turn at a different speed.

Think how a LSD (limited slip differential) works, as soon as it senses the main power wheel slipping it engages the other wheel to regain traction. Don't know how long you've been rotating on the big blue ball but back in the 70s Jeep had the QuadraTrac system in the line. They had a commercial where they backed up a Ford, Chevy and Jeep on a log right at the differential so the rear tires would come off the ground then put it in drive and the Jeep drove off where Ford and Chevy stayed on the log. (only Ford and Chevy were part-time models)

For off road use, the 203 had a "lock" position in which the differential was locked making the front and rear outputs spin at the same speed (like a normal part time transfer case). Shift positions are: High, Lo, High Lock, Low Lock and Neutral.

 

[Thesiger]

I'm not following some of the technical aspects of what your saying, but I understand the concept, totally new to me.

I have not been on the big blue ball for very long, I only got my drivers' license last year!