I have seen a lot of references on the boards to two types of cases that the f150 had available in the seventies, the np203 and np 205. I know that my 79 f150 has the np 203, a chain drive unit, with a granny geared 4 speed trans. Why was two different transfer cases made,when the 205 is the better case by far?

 

Don't know if one is better than the other, both have good points and bad. For the good-the 205 is all gear driven(just like the trans you have)and is considered bulletproof, these were used in all heavy duty applications. The bad-the only reduction ratio is 1.96 to 1, also lose about 10-12% of the power goin' into the case. The 203-good-it has a lower "low" range, around 2.63 to 1, both have cast iron cases, not alum., it is more efficient also, around 95% of the power going in comes out. But, both are heavy just the same. The gear drive unit(205)is considered to be the stronger of the two, this is mostly due to the fact that the chain will stretch(203) over time(sometimes to the point that it jumps)if the lube is not kept up to the full level or is contaminated. The 205 uses 90W-140 lube and the 203 uses auto trans fluid. The 203 is considered a hybrid design, it uses gear drive for the reduction and rear wheel drive just like the 205 but uses the "chain" to power the front driveline. I think if you have the choice the 205 is the way to go. The 203's are coming back into popularity, due to the fact that they are fairly tough, and easier to locate/less dollars to purchase, the 205's are starting to get pretty hard to find anymore and what you do find is usually only a bad core that someone else returned because it was not rebuildable. Once again it is not a matter of just which is best-they are both good, it's just a matter of which is best for budget, intent of use, and personnal preference. For extreme-205, for "light" duty-203. Hope this helps, Chuck P.

 

How can you tell the difference between a 203 & 205? Mine has nothing on it to identify it.

 

Thanks for the information, very helpful. My truck has the 203 because when the mechanic put new bearings in the gearbox, he put one in the t-case and showed me the chain. He also put 90 w gearoil in the trans and the t-case. You said the 203 gets transmission fluid, do I have a major screwup here? The original owners manual for this 79 f150 4wd, also states the transfer case gets standard transmission fluid. Do I need to dump the gearoil pronto? thanks again,

 

I have a F150 4x4 with a 203np, It should have Straight 30w or 50W motor oil depending on temp. I use straight 40w in mine.

 

The recommended fluid for the 203 is trans fluid, however, 90w or 30-40w will not hurt. Tranny fluid has a much lower rating, around 5-7w. This allows the fluid in the case to be "slung" around alot more. I think the main reasons for this are-#1, fuel mileage, with the lower(thinner)viscosity trans fluid, it takes a lot less to get everything to move through it as compared to straight gear lube, most noticable when cold-just try to pour gear lube when its below freezing! The second reason is the chain-it has very small areas in the links that must be kept lubed, even when its very cold outside, with straight gears, the fluid is used to "cushion" the gears as they mesh, the chain does not mesh as such. However, being a chain(like on a bike or cycle-sort of)the plates and links in the chain must have the lube penetrate in the little spaces between them to keep them moving with minimal wear. This is also why it is so important to keep the fluid clean. Dirt and junk gets "caught" in the plates/links and will destroy the chain. Gear lube also tends to hold the dirt in suspension, trans fluid will allow the junk to settle to the bottom, thus keepin' it out of the chain. At least until it gets stirred up again. As far as tellin' the difference between the two 'cases-the 203 will have a more rounded(ovaled)shape were it drops to the front drive output, I think they both have inspection plates/bearing keepers on the back side of the unit, the 205 has both and has a more "square" shape where the front output is. The biggest difference is the 203 is a full-time and the 205 is a part-time. But, a lot of 203's have been converted to part-time, this is an easy thing to do and saves most of the wear on the front end and chain. The 203 also carries a differential which allows slip between the front and rear drives. This eliminates the binding when on dry surfaces and turning by lettin' the front and rear turn at different speeds. Well, didn't mean to write a book here-hope this helps guys! Chuck P.