posi or no posi

[84 400]

Hello,
I have a 1984 and 1985 c-10's. my 1985 has 305/700r4/posi rear end in it. My 1984 has a new 400ci with th350 and ? rear in it (looks stock). I am wondering if my 1984 has a posi in it. I know it had a 305 stock in it then a 307 then a 383 and now the current 400ci(i have only owned it with the 400). The reason i ask is because when i was moving it out of the garadge yesterday, to wash it, and i put it inreverse to back it in i gave it alittle to much pedle and it left two black strips. However if i give it the pedle on the street it only leaves one. I know to look on the glove box sheet but mine is long gone on the 84. And if it is not a locker is it worth swapping the one from the 85? Thanks alot guys and gals(sorry about the spelling)

john
the first pic is of the 85
the next is of the old dodge(don't know why i added that)

[C-10volvo]

my 84 has an open diff or no posi. it will SOMETIMES spin them both. if both tires have the same ammount of traction, they will both spin but that is very rare.

i would assume you have no posi

[Nolowrider]

I would put my money on no posi. If the truck was special ordered with a tow package, then I would save it has a posi. But, stock I say no. The only really way to tell is to pull the cover off and see.

[r0lf-]

No posi gets my vote.

[SanitysBane]

Low chance of posi on a stock truck.

[79BIG10]

I agree no posi is most likely. But one way to make sure is to pop the top off and look.

[Captkaos]

Rolling one backwards loads the gears differently and it will act like a posi in reverse. In fact, if you backup some with an open and then hammer it in drive it will spin both for a short amount.

[84 400]

well then is it strange my 85 has a posi
it is the 305 700r4 setup and def has one when i changed the fluid i noted it. it was sticking and that is why i changed the fluid. is it worth swapping to my 1984? Or am i better off going with n eaton or somthing. Money is very tight right now and with the honda rebuild (1985 honda xl 350r) it is killing my cash flow. i also maintain some of the trucks at my school one of which is a 1985/84 c10 with the 4.6 so i guess it is a 85. any way it has the open diff and snapped off a c clip so i have access to a spare rear end both for that truck the new and used are open diff .
thanks

[corn]

My 84 was open & I thought most were. Mine also never had a glove box decal but did have one on the driver side inner fenderwell...corn

[piecesparts]

Are you absolutely sure about the Posi in the 85? Is it a 10 bolt or 12 bolt and do yo onow the gear ratio? As for the other one, I am betting that it is an open rear end. there are times that you can load up the gears and get a two wheel burn with them, but only for a short period of time.

[84 400]

well the 85 can't spinnem they are new snow tires and the 305 just doesn't seem to have it. The 85 is a 10 bolt and when i opened it up it was not like any of the other 84 and 85 diffs i have opend. it has some sort of I shaped bar in there. this is a posi right. well iam just wondering if it is worth doing a swap before i sell the 85.

thanks