SM420 is shot

[odog]

Ok a couple of weeks ago, I went to leave work and the truck went bang. Has an SM420 tranny and a t221 tcase. Today I finally got a day off and pulled the tcase out. The output shaft on the tranny has splines that are worn to a knifes edge. The input side of the tcase has NO spline, they are worn off, I assume the final striping was when I heard the bang. So here is my dilema, do I do the NV4500 swap I have been talking about on my NV4500 will it fit thread, or do I find an output shaft for the tranny and an input collar for the tcase. I think the less expensive route may be to rebuild the sm420, but not sure. Any thoughts??? This was my daily driver, firewood hauler, but now its lawn art. Truck is a 1/2 ton 4x4 69 chev with 327'

[Redcap]

Easiest and cheapest route is probably just finding another SM420/T221 or SM465/NP205. I bought my 465/205 combo for a hundred bucks last year.

[vectorit]

I agree, SM465/NP205 would be the most fast and economical way to go from the sounds of things.

[67mater]

there should be a coupler between tranny abnd acse. i have the same setup and replaced the coupler before it sheared. So, you may just need the tranny shaft. i can get a pic of the coupler.

[odog]

67 mater you are right there is a coupler between tranny and tcase, however the splines in the coupler are gone on the tranny side. The output shafts splines on the tranny are sharp, almost nonexistent, and the couplers splines are nonexistent. However on the tcase side of the coupler they are fine. So I need the coupler and the output shaft on the tranny.

Redcap I think I may have found a SM465 bolted to a 396, but not sure what tcase it has. What year were the 465s found in? The truck I found is a late 70's early 80's. The guy said I could have the motor and tranny if I come get it. Everything is supposed to run well. so we shall see

[snj8198]

Hi odog,

The '70's to early 80's sm465's had the np205. The 465 granny gear is not quite as low as your 420 (7.0 v.s. 6.55) but regardless it's tough to beat. If you could get your hands on the assembly for a couple hundred bucks ish it would very take little maintenance before slapping it in. I forget the length difference between your 420/221 and the 465/205 combo. You may want to figure that incase you need to address driveshaft length differences.

-steve

[odog]

Thanks Steve,

I looked at the truck last night and it didnt look like a 205 tcase, but Im sure its a 465 tranny, its got the granny low then 1st 2nd 3rd on the shifter. But I am not sure, I need to do more research. I have a fresh 205 sitting in the shop if the one on it now isnt any good (the one on it looks tiny). I am kinda excited about the 396 that comes with the tranny. I probably will take it regardless, its kinda nice having extra stuff laying around. The guy I got my frame from when I built this truck had a 454 with an auto trans and the 205, with the drive lines. When I got the frame, he gave me the tcase and drive lines too, so maybe I will get lucky and have the right drive line.

[snj8198]

the only other tcase behind the 465 was the np208 later in the 80's. I dont remember if the 203's ever got slung behind the 465's in the early '70's but it's possible. You don't want that. I think I heard of the Rockwell 221 behind them too but don't remember. I have a complete 221, keep that in mind. I sold my 465's and used my last good 205.

[odog]

I know its not a t221, thats what I had behind the 420. Its a good tcase, strong, but after 44 years of hard use, its finally said uncle. I will look into the tcase on this one, is the 203 chain driven? I dont want that. how about the 208?

[snj8198]

ya that 203 is chain driven and it's a full time unit. You don't want that. The 208 is chain driven and aluminum cased but tends to hold up well unless you are pushing it hard in the back country. really you want the 465/205 as you know they are stout and plentiful.

[odog]

Ok when I looked at it, the truck is not full time, it has locking hubs, the tcase is aluminum, but not as big as a 205, so most likely a 208?? Also will a 205 bolt up without an adapter if it is a 465? I am leaning more and more towards this.

[snj8198]

If it's an aluminum case then it's an np208. They started that combo somewhere about 1985ish. You will need an adapter for the 205. It's about 6 inches long, has the boss for your shifter, and has a a figure 8 bolt pattern.

[bmchevy1979]

Didn't they switch to a 32spline output shaft on the sm465 when they started putting the np208 behind it

[snj8198]

Originally Posted by bmchevy1979

Didn't they switch to a 32spline output shaft on the sm465 when they started putting the np208 behind it

I don't remember if they did or not. They definitely used the 32 spline shaft with the 205 starting in late '88, as they also switched to the round bolt pattern. But I don't remember what shaft they used for the 208 when they started that combo a couple years earlier.

[odog]

Red cap thank you for the links, that provided some good info. I think I am looking at a 465 with a 208 in which case I will go that route. Now I just need to get another day off to take it out and swap it in.

[Redcap]

Originally Posted by odog

Red cap thank you for the links, that provided some good info. I think I am looking at a 465 with a 208 in which case I will go that route. Now I just need to get another day off to take it out and swap it in.

I would bet you money you are looking at a 465/NP208 combo. It will get you going, but keep your eyes out for a 465/205 combo to replace it. I don't think very much of the 208 case as I've destroyed a few of them.

[Redcap]

http://www.novak-adapt.com/knowledge/sm465.htm

http://www.advanceadapters.com/tech-...l-information/

[snj8198]

sounds like you have a coupler for the 32 spline 205 that came later but you are needing the 10 spline for the earlier years 205. I gota have another one somewhere here, I'll start looking tomorrow.

oh, went back a reread further back, maybe im wrong. lemmie know what I can do to help.

[odog]

Steve, Maybe you are on the right track. Is there an adapter for the 32 spline 205 and 32 spline tranny, and one for the 10 spline tranny and 205. If so maybe I have the 10 spline version. I'm gonna do some research and see what I can find.

[snj8198]

Well the difference between the two versions was the early year adapter was the 8 bolt "racetrack" shape and used the 10 spline female coupler. The later combo had a round pattern 6 bolt pattern and used a 32 spline female coupler. The input shaft on the 32 spline was larger iirc as the case opening was larger making room for the larger input bearing and again the larger diameter shaft. So just as long as you have the right bolt pattern adapter to case and the proper splined coupler you should be in good shape. Snaps some pics if you get a chance. Again I can snoop around as I bet I can find what you need if you indeed need different parts. I know I have an 8 bolt adapter but not sure about any more couplers.

[odog]

I will try to get some pics after work tonight.

[67gmcstepside]

If you decide to rebuild the 221 I have 2 spares I can pull parts from. I only have 1 TC outout shaft as I just sent 1 to another member for his rebuild. Just cover shipping and you can have what ever parts you need.

[odog]

ok here are some pics of the tranny, tcase and adapter.









The ist pic is of the tranny side of the adapter. The second pic is of the tcase side of the adapter. the 3rd pic is of the tcase with the "short shaft" wih 32 internal splines. The 4th pic is of the output shaft on the tranny, 32 splines. the last pic is of the 465 to 205 adapter with the seal and the adapter that was on the tcase with its seal. Both adapters showing tcase side. Notice how the 465 to 205 adapter is smaller on the tcase side than the other adapter.

[snj8198]

That looks like the short 32 spline input gear. I thought those were only used behind the TH400 when that case still had the 8 bolt pattern. Stout set up but looks like we are searching for the right adapter now. I thought the adapter on the right in your pic was the correct one. Now you got me scratchin my head. Sorry odog but I'm stumped too. Im searching the internet.

[odog]

This tcase came off an auto tranny, so probably was a TH400. I took the adapter on the right off the tcase, it has the round bolt pattern. Am I trying to mate an apple to an orange here? I though about machining a new recess in the adapter to fit the bearing and the seal on the tcase, but by the time I mill it out to accept both seal and bearing, there will be nothing left. My boss and I poured over this after work and there just isnt enough metal in the adapter to do it. I searched and found a few adapters on ebay, but they all are the same as what I have. I looked on advanced adapters and the search I did there just took me to a 465 to 208 adapter. Is it possible to even mate a 32 spline 465 to a 205? or were the combos both 10 spline originally?