hello,
so i tried searching out some answers, and did find some help, but just couldnt find an article here that followed all my symptoms? so i felt the need to ask for help.
its 79 f150, 351m. by deduction i think i have the np203 tcase, cause the shifter in truck is loc, 4hi,,n,4lo, loc. now i am really not familiar with this type of tcase (nor any tcase). so hadnt really shifted it much to this point, always been in 4hi non loc position, but before this forward and reverse always drove fine. this truck stays on property, so not an on road driver truck. anyway, yesterday decided to shift it into 4lo for helll of it, shifted fine, little blue locked light on, started driving, little incline and some snow, felt like i was spinning tires? rpms and throttle all fine, it reved up, but no go? so let it roll backwards to flat ground, put back into drive, and the truck barely will go forward, its like it has just enough power to move truck, but not much else. tried shifting it, 4hi,lo,loc shifter shifts fine, blue lock light will come on, but all gears the same, just can barely move truck. reverse works fine, no issue. when trying to go forward i can hear a slight little whining noise under the truck? so since theres some forward movement, its like its barely engaging the gear in tcase? or is that not possible? so im hoping to get some ideas for testing to find what the issue can be? what steps to take to narrow problem down?

ohh and it doesnt have manual locking hubs

thank you

 

May be coincidental, but it sound more like an auto trany problem. Working in reserve but not forward.

When you say it's slipping, do you mean neither the front or rear tires turn? Because if neither turn/spin. I'm thinking transmission.

When it's slipping, do you hear clicking sound when the rear tires spin, but the front tires do not. If so then it is the chain in the transfer case is loose/ bad. My very first vehicle ever was a 76 high boy with a bad NP203. Same problem.

 

Drac beat me to it...

 

thanks for reply..
firstly, im just learning this is a all the time 4wd system on truck? odd. so thats why i am confused on how to distinguish problem from the transmission or the tcase? since tcase is always working? again, confuses me some.
back to your question, my tires didnt, and are not spinning when going, i said i seemed like i was spinning out when i wasnt going up the snow, but tires weren't spinning, i just didnt have enough GO to move truck forward? and now when i put drive selector in drive, 2, 1, all the same, firstly no, i dont feel the truck "shift in gear" as you normally do when putting into a forward drive gear (D,2,1). but reverse is fine. and the tcase shifter on the floor, feels ok, shifts into all gears (by feel)? but when i try to drive forward, the truck will go forward but hardly, and i can floor it, and still barely be moving. hence the feel of slipping. and there is a slight whine i can hear when trying to go forward.
but as stated im confused how to tell if its a transmission problem or tcase problem? this all the time 4wd system is confusing to a newbie to the truck world! haha.
thanks

 

Since it happened on an incline my first instinct is that your tranny fluid is low. Ther is a dipstick back by the firewall in the engine compartment to check this.

 

yes, first thing i thought of also! haha.. i checked it while it was warm and idling on level ground. it was a tick low, at the bottom line , but that bottom of the normal range of the 2 lines.. so while a tick low, isnt that with in range, where this may not, or shouldnt be happening? i plan on getting some atf today, on the to do list to top that off. but i guess i thought " a little low" wouldnt create what is essentially non driveable condition? why have a "range"on the dipstick to be in then? since i am technically in the range, i wouldnt think this is the issue? but yes yes yes i am crossing fingers and hoping its that simple! but i just wanted to try and find out some tests i could do to help narrow where the issue was. its a long ride to town, so i wanted to know what else i may need to buy before i left! haha.. I.E. tcase oil, or tool to check something else, etc...
thank you for the help.

 

It sounds like you have enough tranny fluid to make things go but I wouldn't rule out it being low enough to make it slip until it has been topped off.
The next thing I would check is the vacuum line that runs down to the transmission. First, with the engine not running, disconnect it at the upper end. This could be connected to a vacuum source on the intake manifold or at the base of the carburetor.
Hook a vacuum pump and gauge to the line and pump it up to see if the vacuum bleeds off. It should hold steady. I have even sucked on clean lines by mouth to do this check. If it leaks, replace the rubber sections of the line and check again. If it still leaks then the vacuum modulator has gone bad. That is the small canister looking thing that the bottom end of the vacuum line attaches to. It is easy to replace but there is a small rod inside that you will need to keep track of and return to it's place. I doubt this is your issue but this is a simple check to eliminate this.
Since you were on an incline is it possible for something to have moved slightly and throw your shift linkage out of adjustment?
Last but not least, it is entirely possible that driving it up the hill shifted enough crud around inside the tranny to plug up your screens or possibly the cooling lines.. You'll have to drop the transmission pan to service it.
That's all I can think of.

 

Im thinking it's far and few in between when a transfere case fails to a point that the rear wheels done turn. With typical Transfer case problems the rear wheel turn but not the front. And the 203 is prone to that problem as it has a chain instead of the gear drive like the 205.

Also if it is moving good in reverse, then the transfer case is not going to be the problem. ( well typically). Auto trans, the C6, often went bad with 80,000 miles on them. you say it trys to move, but with not a lot force, revving it up moves a bit more but really sluggish. Sounds like the trans.
If there is any oil on the stick at all. it should drive forward. Yes, the oil is fine with in the range on the stick.
These transmissions, require more oil pressure going on direction than the other,( i cant remember which way), but they go one way and not the other. I've been told that is a problem twith the pump. Which could also be a plugged trany filter.

Drop the trans Oil pan and change the filter.
So when you go to town, get a trans filter kit (includes a pan gasket) and enough oil I think like 9-10 quarts.

if that don't work, you need a trans rebuild.

Curious, never heard of a 79 150 with a 203?? anything is possible

 

Sounds like your NP203 transfercase isn't fully locked.
There is a differential in the t-case. When in 4 high power goes to which ever axle is easiest to turn. Even though light is on you may not have it fully in the locked position to lock front and rear axle together making them turn at same speed.

Edit: After reading your other replys I'm leaning more towards tranny now.

 

thanks for the help...
so i topped off the atf fluid, and still no change. no go. bummer. reading more and more, and i guess with your insights, i spose it may be a tranny problem not the tcase. just got done messing with it, shifting back and forth reverse to drive, and reverse engages normal, and goes, and forward gears it just doesn't fee like it engages, that solid forward bump when it goes into gear, it doesn't do that anymore, feels no different when i shift from N to D to 2 to 1. also was shifting tcase into all the gears, 4loc,hi,lo,loc, no change in how it feels. shifts smooth. and again, in any forward gear, i can hit the gas, truck revs up and then it will barely start to move, i could probably hold it from moving forward myself, thats how weak it feels even at high rpms. if its tranny, is this a torque converter issue? or best off buy rebuilt trany and converter, and be sure? really sucks!

 

thanks 79fordblake,,, im still trying to figure where the problem lies, i was leabig towards tcase casue it was fine, then i shifted the tcase shifter to different gear, from 4hi to lo loc, and then this problem started. so i just assumed tcase issue.... so if you read all the chain of replies, it soounded maybe more a tranny issue now.. but i do not know. one thing i did change atf fluid and filter about 2 months ago, was clean when i changed, and no metal, and still is clean, dipstick u can see its still nice and red. so thats not an issue.
but back to your post, if tcase isnt engaging, is there a way i can force it to engage at least band aid fix? or any thoughts? im no pro mechanic, but can do and will try some stuff.
thanks!

 

Sometimes the t-case is shifted easiest with engine off and trans in neutral to get the load off of it.
I left my comment before I read the whole thing. It does kinda sound like tranny now. Weird though if fluid looks good and had been fine. Maybe a seal blew all a sudden?