transfer case questions

I have a few noobie questions about my transfer case(first time 4x4 builder) first question is how do identify what kind it is, its a 70 Jimmy by the way.    My second question might be a dumb one but here it goes, the easiest way to run my exhaust around my transfer case is to more or less have it resting on it.  I was told that I may have a magnesium casing(thats why I want to find out what it is), I know it has a really low ignition point, could exhaust get hot enough to ignite it or... am I just being paranoid. My second question is if the case is fine will it get hot enough to cause any sort  cooling trouble.

Thanks for any help  

if its all stock then its a np 203 full time case, very stong, heavy, not very low low range gear, and often misundestood buts its a good t case.....um about the exhsast, i have duals and the side that closest to the t case just slighty bends around it, not resting on it or anything like that, and magnesium case!! where did you hear that??? the old np 203 and 205 and good ole cast iron don't worry about overheating the case as long as you got correct amount and type of oil youll be fine ...but given its age you probaley need a new chain.........  
Solid axle chevys can't be beat!
My dream truck: 73-91 chevy 3500 crew cab srw with dana 60/14bolt, 6 inc long travel lift with KING shocks, 37 inc tires and a 24v cummins diesel, nv5600 and np205

It is not a NP 203, that Tcase was not used until 73 and only with automatics too. It is a NP 205 with a cast iron case. There is plenty of room to get a pipe past Tcase without touching it. You do not need 2.5 inch dual on a SB but some seem to think you do. 2 or 2.25 inch max will work fine and is easier to route and bend. One more thing, on the Tcase metal. The last year that the 205 was used "across the board" was 1980 (they went to 208 in 81 in most apps) and in 1980 some of the 205 cases were aluminum in 1/2 models as they were trying to trim weight for MPG before 208 was swapped in.  

Thanks for the advice on the exhaust guys.  But I still would like to figure out exactly what transfer case it is.  Chances are its a 205 but is there any serial number I can find or something that you would be able to tell me exactly.  I know this truck has been fooled around with so it may or may not be stock.  It also as an automatic in it with the shifter on the column and all so I am assuming thats stock but is there a number on that as well? I'll post back if I can find anything myself.

Thanks  

GM used only a 205 from 67 thru 72 in 4x4's. Nothing else. A 205 also has the classic small round plate with 3 bolts holding it on in center of case in rear that retains idler shaft.  

yeah i need to read more closley and notice it said 70 not 73..... ......... so it is a np 205 for sure, its a great case, strong but really heavey as well, and the low range isn't really as low as newer model cases but it works if your not a rockcrawler or slow trail creeper, ive found this t case works good for dune trucks who need decent speed, but more gear reduction than 1:1 that 4hi gives....n 205 looks similar to a 203 but you can tell them apart...  
Solid axle chevys can't be beat!
My dream truck: 73-91 chevy 3500 crew cab srw with dana 60/14bolt, 6 inc long travel lift with KING shocks, 37 inc tires and a 24v cummins diesel, nv5600 and np205

I have an NP205 from an 80' 1/2 tonchevy mounted to a TH350. Is it possible to mount the NP205 on my 700-R4 on my 89' 1/2 ton or is thet a bad idea?  

Your 89 has a NP241 which is kinda a improve 208 and is not a bad Tcase. 205 weighs more and has a much taller low range than 241. Plus input spline on 205 will not match and you will need to change input shaft or get a adapter for it. Also if this is a P/U the front output is in the wrong place unless you swap in a solid axle with pig on passenger side.  You want that truck to run, slap in some deeper axle gear for the effort and money spent for Tcase swap and you will be pleased. The real beauty of a 700R4 is that it tall OD gear lets you run some serious axle gear and still be civil cruising. Many do not take advantage of this though and worry about stronger Tcases and drive shafts when if they just regeared they would not have to worry about that. Such a shame.  

Yeah i just got done swapping a 14 bolt rear into the 89 with 4:10 gears and a true trac. the truck runs great i was just wondering what i should do next. Any ideas  

dsmartin2s:
Yeah i just got done swapping a 14 bolt rear into the 89 with 4:10 gears and a true trac. the truck runs great i was just wondering what i should do next. Any ideas

Make no mistake, a 4.10 is not great gear for lifts and big tires though some seem to think it is. The "idea" gear ratio depends on tire size. A 4.10 is not bad with 31's but with each increase in tires size that 4.10 effectively becomes a taller gear. So many spend money on exhausts, "magic" air intakes/air cleaners try to find more power will lifts. Some even figure engine swap is the answer when real answer is if they would just take the time to PROPERLY regear truck for tire size, the power issue will go away. And with them so will tranny, drive shaft, Ujoint and Tcase problems too. If there is a magic bolt on/in fix for a lifted 4x4's, it is a new set of proper axle gears.  

Im planning on adding a torsion key lift about 2.5 in with add a leaf and some meaty 33s will 4:10 still be ok? the truck will probably never go any higher than that  

If it has a OD tranny it is not best combo. Without OD you could get by okay. OD would make that 4.10 look like a 2.73 axle with 33's on it in OD. (not a good combo for performance or tranny life)  

what should i do in the future cause i just put that true trac in that 14 bolt and it was a little pricey. i just want a really solid truck. Should i go with lower gears in the future and a new limited slip?  

By True Trak are you talking about the gear based LSD?  As far as gears if you plan to play real hard and/or might remotely increase tire size I would regear it deeper. Once you have lived with a truck with deep axle gear you will not want to be without them. When properly geared you do not even need low range most of the time. If you find yourself reaching for low range a lot it is time to think about deeper gears.  

to the tranfer case question every one tryed telling you what it is not how to id it so hear you go the basics for older trucks  the all aluminum case is the 208 =weak
chain drive not good for torc.  castiron case with aluminum end caps  is the 203 strong enough for most people and a very good transfer case
and the solid castiron is the 205 the best t-case out thier its a gear drive and wont go out unless you run it out of oil.
the exshast q. run dual 2-2.25 one on each side of the t-case and as long as it is not touching the t-case it will not overheat it.