So I just got a 4x4 K5 blazer for no apparent reason and know NOTHING about chevy's. I am a big Ford guy but I figure I would give chevy a chance. I picked up this 81 K5 blazer with a brand new 350 and it purrs. Only problem is rear end locked up, broke U joints, and output shaft on transfer case is sticking out. I know I need a NP205 case but my question is about the rear end.

The guy I bought it from said the previous owner put a different rear end on and since the front and rear differential gears did not match 4x4 didn't work. The front differential is stock gearing and I know is a 10-bolt. The rear differential was a 12-bolt. (My guess is it should be a 10 bolt?)
So for a new rear end I need a chevy 10 bolt right? Does anybody know what the stock gearing is? I imagine I could swipe one off a similar chevy truck from the 80's. I've been doing research and have not gotten very far. Thanks in advance

 

only way you are going to know for sure is to take your front cover off and see what numbers are on the gears. just like how the rear axle is different whos to say someone didnt change out the front axle also at one time.

ive bought many k5 blazers over the years, they have came with 273 308 373 and 411 gears, though i dont think 411 was available from the factory, exactly why you should check.

but you can put a 10 bolt or 12 bolt back in there they basically are the same thing. the 10 bolt is way more common. should be able to find one in any junkyard

also double check that its a 205 transfercase i dont believe the k5s ever came with them but could be wrong i never owned one older then a 84. if you are replacing the np205 there are a few different mounting patterns on those things.

 

1981 K5's came with NP208 transfer cases... Very different beast than the gear driven iron case 205's. NP205's did come in the early 70's Blazers before the full time 203's of the mid 70's.

what are you planning on using the K5 for? How are your tires? I ask because a popular upgrade is a 14 bolt full floating axle from a 3/4 ton pickup. The design of the axle makes for a almost indestructible rear end. You will have to swap out the front axle and get yourself some 8-lug rims so there is some extra work to it. If you're going to give it some heavy abuse off road this is a good idea, however if you're just going to cruise and hit some light trails 10 bolts are easy enough to find on craigslist.

 

hell. if it is offroad ill second the idea of getting the 14 bolt. then you can just get some 8 lug hubs. as long as its not a dana 60 the 10 bolt and dana 44 are practically the same.

 

Yup y'all were right it was the NP208 transfer case. Just got my numbers screwed up from reading online forums all night. The case is actually ok. Just messed up the rear seal making it look funny and now it's all fixed up with a $6 seal and fresh fluid. This is my first chevy and first old project so I'm learning as I go.

Ya I think I will just have to count the gears in the front to see what I'm working with. The truck will be used mainly to travel gravel roads and light trails at the ranch to hunt down horses haha so no extreme abuse on this rig... At least for now which is why I'm probably going to settle with a 10 bolt. The local junk yard has them for $130. The truck has decent 35s on it that are practically new.

That 14 bolt conversion sounds tempting but at this point don't think ill have the funds to take it that far. Maybe in the future though! I'm thinking about making it a killer off road rig but for now if I could get it running I would be happy.

Another question I have on this rig is about the auto hubs on the front. I pulled the gears out of the old rear end (they were toast) so that the axles could move and I could move the truck into the barn. I figured what the heck ill throw it in 4L and let the front wheels drive the truck. It seemed that those auto hubs were catching, then releasing causing the truck to hop a little. Am I better off using manual hubs on this rig?

 

Sounds like you've got the right idea sticking with a 10 bolt. With 35's as long as you don't abuse it you'll be fine.

I'd chuck those auto hubs in the ditch and get a set of manual Warn or Mile Marker's.

 

i second that, those god awful things never work, i have seen them fail time and time again offroad, get the manual ones where you just click them on and be done with them

welcome to the wonderful world of chevys everything is usually simple as heck to work on

 

well the 14bolt isnt too expensive down the road for you. picked up my axle for 20 bucks. then new spring plates and ubolts were 100 total. now the only thing im waiting for is to have a beefy rear driveshaft made up. 1/4in wall so i dont bust it this time lol. 300 bucks.