Hello,

I was looking at a 79 ford Body on a 75 Highboy FRAME... He said it had all time four wheel drive??? Is this a real thing or is he BSing me??? And if it is real, is it a good thing?

 

It could be possible. This means that it has an Np203 transfer case. This is a full time transfer case and is always in 4wd.
Is it a good thing? Well it is if you always want 4wd.
Most folks convert these so they are not always in 4wd. The 203 transfer case is not exactly the most desirable.

 

Is it just gas milage??? Or does it not hold up because when you are driving it does damage... I always thought 4x4 on dry pavement is bad.... And if it is ok, is it as good of a 4x4 as normal one?? Why is it not desirable?

 

The NP205 part time t-case is more desirable not to mention much more stout, it's gear driven as opposed to chain driven.

 

Hmm,,, Is there much in changing out the NP203 to the NP 205.... Must be hard because you need linkage to shift it on the 205 and not on the 203 correct?

 

Actually there are two linkages on the 203, and only one for the stock 205. (exception is a twin stick 205). The 203 can shift from hi range to low range as well as lock the center diff in either low or high range. It is always in 4wd but it can be shifted from high and low range.

Swapping out a 203 for a 205 is not difficult, it requires brackets for the 205, as well as the shifter and linkage. Driveshafts are different too.

 

What is the draw back of a 203??? Does it kill hte diff to be on pavement in 4wheel all the time??? And does it work as well as the 205 4x4???

 

Drwabacks of the 203, is its size, weight and weaker chain driven design. While strong, not as strong as the 205.
Full time operation means that more parts are moving and this contributes to parasitic losses. This chain driven chain is less efficient than part time cases.
203's can be convterted to part time, but kits cost almost as much as the 205 itself.

Understanding the operation of the 203.

full time 4wd means exactly that, it is in 4wd all of the time. Since high traction driving requires that the front wheels move at a different rate than the rear, someting must compensate or be able to differentiate. A differential is built into the 203 and can compensate for a difference in front to rear axle speeds during o road driving.
Unfortunately this works well on the road, but not unlike any other differential, it sends power to the axle with the least amount of resistance. This is bad for off road. The fix: lock the center differential so that the output is equal from front to rear. This is known as the LOC position on the shifter. Note that there is no 2wd selection. This is good for off road, but not for on road driving so the center diff must be unlocked to drive on the road again.

The 205 is simple. Engage 4wd in either high or low range, and lock the front hubs when 4wd is needed. Dis-engage 4wd when it is not. Simple.

 

On the 203 technically the front wheels are not driving all the time you are just turning the internals of the axle and turning the driveshaft when in HI which would be the same as driving with your hubs locked on a 205 transfer case. The front wheels only have power to them when in Lo LOC and in HI Loc that is when you have four wheel drive. So rather than swapping out t-cases save some money and put in a part time kit into the 203 and it will be fine. Shift patterns are as follows:

NP203
LO LOC= 4wd Low range
LO= 2wd low range no power to front wheels just internals turning
N= Neutral
HI= 2 wd Hi range no power to front wheels just turning the internals
HI LOC= 4wd High range

The 203 gives you the advantage of low range gearing in 2wd. And also a better low range than the 205.

NP205
4LO
N
2HI
4HI

The 205 will turn axles and front drive shaft in 2hi with front hubs locked but will not once they are unlocked.

So with the part time kit installed on the 203 you will save on wear and tear on the front bearings and axle u joints and get better gas mileage be cause the front driveline will not be turning all the time. But the NP205 is a superior transfercase due to it geardriven internals and lighter.

 

Good explanation

 

Thanks I hope that clears everything up for him.

 

This statement is "not true". There is output to both front and rear diriveshafts always. Regardless of whether the case is in LOC or not.
The LOC selection only locks the center differential and creates equal output to both front and rear shafts.
The center differential is designed to provide output to the axle with the least resistance.
The differential cant stop output like a part time case can, and the front is not just riding along like it would if the front hubs were engaged. The front output is always engaged since the chain is always turning. It will always turn unless the case has been converted. By comverting the differential is always locked and cant be disengaged, but the output for the front can be de-selected. By eliminating the center differential, this is possible, but only with a conversion.
The problem here is that the chain slings oil to the a reservior which is responsible for the lubrication of the rear output shaft. Once the conversion is complete the chain cant fill the reservior and the bearings go dry. It would require 4wd engagement or locking the hubs to turn the chain and fill the reservior again.

A stock 203 cant de-select the front output at all. Mechanically impossible. Proof? remove the front driveshaft and try to make any progress at all. If the case is left in its normal mode, the truck will not go anywhere. Remember the least resistance thing? Well the lack of front driveshaft is the least resistance, and 100% of the output will go to the front. Rear will get zero and the truck is stuck. Engage any "LOC" and the rear will get output but the front yoke still turns.
The same is true if one removes the rear driveshaft. Front output always turns with a stock 203.

 

Well I stand corrected sir I guess my understanding was that it could disengage the front output in stock form so essentially you were just turning bearings and such in the tcase much like the 205 when running your hubs locked and in 2hi. Well I'm glad I didnt miss lead too many people. I learn something new everyday.

 

I dont think it was mentioned in a misleading way at all. Often times our internet provides us with many interpretations with regards to theory of operations. Some have conecepts of certain operations, and actually for the most part correct. Often times small items are left out or simply overlooked.
Rep to you for your explaination and use of shift patterns. You did a fine job of explaining the converted 203 and provided shift patterns. Nice job with that.

 

Well together I hope we answered his question and made his decision easier.