12 bolt rebuild question

[Byoung330]

I am going to completely rebuild my rearend. Can someone point me in the right direction on best place to buy the parts. My truck is a 68 with a 6 lug 4.10 open diff. I want to convert it to 5 lug 3.73 Posi and I’m thinking about using Yukon parts. I saw online that they have a kit but includes drums and I’m converting to disc so I don’t want to pay for the drums. Seems like the duragrip is pretty good and affordable and I’m not trying to break the bank here just building a good solid driver. I don’t mind piecing parts together from different vendors if I need to. I’m open to suggestions and brands but like I said kinda economical since I still have to build the rest of the truck.

[mongocanfly]

Eaton trutrak and Yukon gears is hard to beat...can be bought thru about all vendors

[sweetk30]

just a fyi . with a th350 trans and 29.0 tire height you will only drop 300 rpm @70 mph from 4.10 to 3.73 . . . not knowing your combo i just used this as a test point .

so swapping gears might not be a most cost effective option . . . hope this helps .

and good luck with the build .

[mongocanfly]

Here's what k30 is saying...use this calc to help....http://www.csgnetwork.com/multirpmcalc.html

[Byoung330]

Originally Posted by sweetk30

just a fyi . with a th350 trans and 29.0 tire height you will only drop 300 rpm @70 mph from 4.10 to 3.73 . . . not knowing your combo i just used this as a test point .

so swapping gears might not be a most cost effective option . . . hope this helps .

and good luck with the build .

I’m actually planning on doing an ls and 4l80. So you guys think keeping the 4.10 is a good idea? My concern is getting some kind of traction.

[mongocanfly]

I've got 4.10s in mine and love it...had another with 3.73s and it was fine...my dd has 3.42s and I dont like it for the fact that its always downshifting...truck I'm building now is getting 4.56s....
I like to keep my ls at around 2000rpm at 65mph...performance is good and no big effect on mpgs...
What size tire are you running?...with the od trans you can run a lower gear just fine...the traction will be an issue no matter...but I'd go with a locker of some sort...

[sweetk30]

Originally Posted by mongocanfly

Here's what k30 is saying...use this calc to help....http://www.csgnetwork.com/multirpmcalc.html

this is the super easy one i use works for full man entry of #'s or use options already there . is 2wd leave 4x4 area blank . you can change about any value by clicking the white box . . . like 70mph click it and change it .

http://www.grimmjeeper.com/gears.html

2500 rpm @70 mph with 4.10 / 4l80-e / 29" tire
2270 rpm @70 mph with 3.73 / 4l80-e / 29" tire

[Byoung330]

Originally Posted by mongocanfly

I've got 4.10s in mine and love it...had another with 3.73s and it was fine...my dd has 3.42s and I dont like it for the fact that its always downshifting...truck I'm building now is getting 4.56s....
I like to keep my ls at around 2000rpm at 65mph...performance is good and no big effect on mpgs...
What size tire are you running?...with the od trans you can run a lower gear just fine...the traction will be an issue no matter...but I'd go with a locker of some sort...

Yeah I was thinking about Yukon Dura Grip and 29-30 inch tire

[mongocanfly]

30in tire...me personally I'd stay with the 4.10s...but that's me...theres just about every combination of ratio and tire size used in these LS swaps...anything in the 3s would work also...just go with what you feel is good..

[Mike C]

Another vote for the 4.10 gears. I think that’s a sweet combo with the 4L80 gear ratios. The only caveat is if you plan for coast to coast type travels unloaded I’d go the 3.73 for the lower highway rpm.

But 4.10 for all around performance usage.