Transfer Case Identification
I've got a 1977 Chevy Pickup 4WD, originally equipped with a 400 CID motor but without an RPO sticker so I don't know much else about the truck.
I'm basically trying to find out the info on the transfer case. I see that from 73-87 that three different types of transfer cases were available. According to the site I checked, only two of those were available in 77.
The RP 203 and the RP 205. Now if I knew anything about transfer cases or 4WD, I'm sure I could tell the difference without trying to dig for numbers.
From what I read the 203 is a full-time chain driven unit. Does this mean the chain is visible from the undercarriage of the vehicle? or is this contained behind a cover of some sort?
The 205 is Gear driven...doesn't say full time.
So I guess what I'm asking is---What exactly is "Full Time"? DOes that mean there is no option to turn it off? So if I had locking hubs on my wheels than I probably don't have a 203? If I look under the truck and I don't see a chain then I don't have a 203?
Any insight here would be appreciated.
Quite a bit of insight here.
The easiest way to identify your transfer case, looking at the back of the case where the rear driveshaft yoke is located, focus your attention slightly to the right of that and if you see a 3-bolt cover about 2 inches in diameter it is a NP-205 (NP= New Process, as in the company that manufactured these transfer cases- New Process Gear.)
If there is no 3-bolt cover it is the NP-203 full time.
There are kits sold to eliminate the full-time functioning of the 203.
The chain in the 203 is contained within the larger of the two housings which make up the 203 the other (the front) is the range box with the gearing to allow low range.
The NP-203 utilizes a differential to allow slippage between the front and rear drive shafts and eliminate binding and subsequent parts breakage. Removing the front driveshaft, or unlocking the hubs on a vehicle with an unmodified NP-203 can be temporarily overcome by simply locking the shift lever into the "hi-loc" position
The general rule of thumb (not exactly accurate though) automatic transmissions were equipped with the NP-203, and the four speeds were equipped with the NP-205.
The TH-350 transmission was equipped with the NP-205 before the 203 was put into production for the 1973 model year.
If there is anything specific you would like to know about your truck just PM me and ask away, I have owned nearly 30 of these truck over the years.
Most likely your trucks' VIN# goes like this CKR147F followed by 6 numbers.
C= Chevy, K=4 wheel drive, R= 400 engine, 1= 1/2-ton, 4= regular cab,
7= 1977 model year, F= Flint, Michigan. assembly plant (this COULD be one of 7 plants, but most likely because you have the 400 engine it came from Flint, I could still be wrong here though.
The 6 numbers following the above information is the sequential serial number given while on the assembly line, some years and some plants started their production runs at 100001 instead of 000000.
Thanks for the info :thumbup:
There is some weird crap happening with that truck, I'm really not sure what to figure as "Original Equipment" and "Previous Owner Modified".
It had "Z" listed as the plant, which I didn't see on the list of plants...so that was a little weird. VIN does say it was a 400 CID w/ 4BBL & 3/4 Ton.
Here's where it gets a little weird. I read on a VIN decoder site that 77 and later trucks with either 400's or 454's came equipped with TH-400 transmissions...well, this thing has a TH-350 in it, I'm pretty confident it's a TH-350.
Anyhow, I'll take a look at the transfer case tonight.
I'm going to PM/email you because it's very important I get this thing identified as soon as possible. I'm giving the truck to my pops and he's going to order a new drivetrain for the thing and we're going to install it next week.
I looked to the right of the main driveshaft and I see an 8-bolt cover. It appears that if you were to take off the 8 bolts this would give you access to the gearing that drives the front wheels...hope I'm looking in the right place.
I can snap a picture..but from what you said, I don't see 3 bolt cover so it has to be a...NP 203
I'm going to go snap a picture or two.
here's a picture from the rear of the transfer case...can you confirm if this is NP203?
That is definitely a New Process-203 transfer case.
There is (I forgot this earlier) an identification tag riveted on the front of the same housing between the range box and the front driveshaft that would have identified it also.
In the pic where the screw in plug is between the rear drive yoke housing and the front drive cover plate is, this is used for filling the transfer case with 80 weight gear lube, the 205 would have an intermediate shaft cover plate with three bolts there.
Does this truck have locking hubs? If so- then sometime in the past someone has installed a part time conversion kit. I won't get into that right now, but it's not really a bad thing to do to this transfer case.
Whick axles does this truck have? The front can either be a Dana 44, or a GM corporate 8.5 inch 10-bolt, and the rear SHOULD be the 8.875 inch 12-bolt.
As far as gears go you could have 3.08, 3.55, or 3.73's, and possibly some other ratio. Those are just the most common.
There are some odd hubs on this truck that you can spin a little switch on...not sure if those are locking or not.
If you only had the full time, it would just have a dust cap where the lockout hub would be.
One way to check this would be to leave the shift lever in "hi", jack up the rear axle, put the transmission in neutral, and reach under after locking the hubs and spin the rear driveshaft.
If the rear stops turning after only a few degrees (and taking up all the driveline play in all components) it still has the full time parts inside the transfer case.
If it continues to turn, the part time kit was installed properly and functions just as if the truck had the NP-205 transfer case.
Question of the day is...
Assuming someone did indeed install the kit into the NP203 that is currently installed in the truck...and I put a new NP203 in (without the kit)---will I encounter any problems?
The best mileage I got out of it was when I swapped in a 305 I had rebuilt, it gave me 18 mpg highway with 3.55 gears and 31/10.5/15 tires and a full load.
The NP-203 full time transfer case has an internal differential that allows front and rear drivelines to operate at all times without the typical binding and subsequent bucking while turning the truck on pavement, UNTIL you shift the lever into the HI-LOCK position which only locks the transfer cases' internal differential.
I certainly wouldn't hesitate to run the full time case as you will probably never realistically get much more mileage out of it, looking at one of these trucks with ANY of the NP-203/205/208 transfer cases in it from behind while travelling on the road you will notice the front driveline rotating even if equipped with locking hubs disengaged.
The only thing about the full time 203 is if the front axle is equipped with locking hubs, and you disengage them the 203's internal differential will send all power to the front axle and you won't go anywhere, simply locking the cases differential by shifting into HI-LOCK will remedy this situation.
Thanks for all of the great information. My pops ordered a new motor, tranny and transfer-case to drop into the 77. I stole the 454 out of it and the thing had transmission problems...Neither of us has the experience or time to invest in rebuilding the TH-350 or NP-203 (if there was a problem with it).
So now pops is going to have basically a new truck. Truck lived in California most of its' life so it's pretty clean and rust free.
The only stuff he has to worry about is brakes and electrical, otherwise he's going to have basically a new truck. :thumbup:
Is this a NP 203??
After looking at the picture on this post for the NP203, I am unsure if this is what is in my truck. I have a 1978 F150 Short Bed 4x4 that I just recently purchased. The motor had been changed but it still had the original C6 tranny and what I thought was a NP203 transfer case. It does have the locking hubs on it and I can tell someone has done some work to this truck here and there. Looking at the back of my transfer case, the front driveline cover is on the left and the rear is on the right side. Both of my exhaust lines run down the inside of the right frame rail. I am assuming that the previous pic is different because it is a chevy?
Is this an NP203?
For you fellas looking for more info about the NP transfer cases, here's an old article that's still out on the web:
It has some interesting discussion and data on the cases.
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