What rear diff do I have? '86 K20

[VTKidder]

I just bought a plow truck that has an open rear end, and would like to put a posi unit in instead. I have not checked to see what rear end I have, but was there one that was standard on 4x4 3/4 tons? The ratio is 4.10, and I believe it is an 8-lug truck. Are all 3/4 ton 8-lug? If a truck is equipped with a full floater rear end, A) would it show on the RPO tag in the glovebox? B) would a "dog dish" factory hubcap fit, or would it need to have the hole in the middle like a front differential hubcap has?

Just looking for some help on what I should keep my eyes peeled for. Thanks.

-adam

[edman87]

is it a full floater? If so, 14 bolt, if not 14 bolt semi float

[VTKidder]

I'm not sure if its a full floater or not. Since I got the thing last week, the only thing I've had a chance to do is put a new starter in and blow a brake line; haven't even peeked at the diff. It does have the OEM steel wheels with hubcaps all the way around. Since the full-floater has that protruding part with the 8-bolts, similar to a front diff, would the stock hubcaps fit over that part? If I were to guess, I'd say its not a full-floater.

[MylilBowTie]

I'm pretty sure it is a sf and not a ff but there is only one way to be sure. SF 9.5 ring and FF 10.5 ring

[Twisted78SS]

Take a look at the rear cover and go to one of the many sites that carry rear end goodies. Most of them have a diagram chart that shows the cover patern and identifies which rear you have. Might help you out.

This site may help
http://www.ringpinion.com/DiffList.a...peID=5&Type=GM

[Twisted78SS]

Here is a quick guide