Rear gears

[Ds2014]

So 3.42 it is! What carrier do I need? A 3 series?

[zieg85]

For that question I would consult whoever is going to supply it.  You should have a 10 bolt differential but you need to verify that for sure so when you chose what posi unit to go with.  Each carrier differs with gear ratios offered.

[gwcrim]

I just went from a 2.7 to a 3.73 posi.  Right now I'm running a TH350 and a 26" tire.  It's a bit gear bound now.  Future plans include taller tires and a 700R4 so I'll be fine.  Otherwise, I'd have stuck with a 3.42.  That's a pretty good all around ratio.

[Ds2014]

Thanks for all the info. What carrier,3series?

[Liltroy]

maybe neither. gm started using a weird carrier in either 81 or 82, I cant remember. neither 3 or 4 series gears will fit. if you have this carrier, you will need to switch carriers to use any aftermarket gears. I ended up sending back alot of gear sets before i figured this out. I finally went with a detroit true-trac differential that comes in a 4-series style carrier and all was well.Turns out the PO had installed an early 80's rear in my 74. wish I would have known this to begin with as it would have saved me, summit racing, and my mechanic alot of wasted time. Also, as a comparison, I went from 2.73 to 3.73. I run 31-10.5 tires on back as well and with a th400 trans I'm turning about 3200rpm at 65mph. it sucks on the interstate. I'm going to be going to a set of nitto 325/50 drag radials in the future(28") but I think all be switching to an overdrive transmission first. If this was my daily driver I would have went to a 3.08 at the most with no overdrive! Of course my engine only spins to about 4800 rpms so with that cam you got you can probably tolerate those kinds of rpms.

EDIT: its the 82-up that uses the carrier that doesnt fit anything so you should be good if yours is an 81. If your truck came with 2.73 gears then it should be a 3 series carrier. 3.40 down is 3 series, 3.42-up is a 4 series. If you're planning on a good posi unit though, go ahead and get them at the same time as most of the aftermarket differentials come with a new 4 series style carrier.

[Ds2014]

I'm looking for a POSI rear end for my 81 c10 2wd. Any ideas

[78BIG-TEN]

3 series case fits 3.42 down.Pretty sure they make a thick 3.73 set to fit 3 series.Higher gears will work with a spacer.Gm's posi was a goc lock,a good unit but not for a lot of abuse.Go with an eaton or auburn.I used a true track once on a truck with big tires and lasted about a year.It made a horrific sound in tight turns,but since then I believe they have made some improvements to them