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Catfish11 11-18-2012 07:47 AM

rebuilding 12 bolt truck rear end?
I have went over the tech articles here and also searched but have a few questions. 84 c-10, I found a 12 bolt that has 3:73 gearing non posi that I want to get rebuilt for my dieing 10 bolt that is in the truck right now.
I would like to add a posi unit as I use the truck for daily driving and weekend fishing trips thru mud and snow, So basically a stock rebuild. Currently I have 2:73 in the 10 bolt rear , could be wrong on the number but its very close. Looking on the web I will need to install different carrier for the use of different gearing, which should not be a issue since I am going to use a eaton posi. Any other issues I need to address? Its looking like it will run me about 1000-1200 dollars for new parts and labor? Thanks for any tips , or feedback.

gearheadslife 11-18-2012 08:32 AM

why not keep the 373's and just add a power tracs

big gear head 11-18-2012 08:57 AM

If you are going to use the 12 bolt with the 3.73 then why would the gears and the differential in the 10 bolt make any difference?

I agree with the post above. The Power Trax Lock Right will work great in the mud and snow. I've had one in my truck for about 15 years and I put over 140,000 miles on it and it still works great. A clutch type differential like the Eaton can slip when you are off road and leave you stuck in the mud. The Lock Right will not slip, even if you have one wheel off the ground. I love the Eaton Posi for street use in muscle cars, but a locker works better off road. The Lock Right pops and jerks a little sometimes, but it's not bad. If you have an automatic transmission then you will probably not even notice it. I have a 5 speed, so I notice mine a little more.

Catfish11 11-18-2012 10:40 AM

Thanks guys I will look into the power track.

the truck is a daily driver and now I am putting 1000 miles average a week on it on the highway. The stock 10 bolt is in need of a rebuild but I would rather rebuild the 12 bolt and put that in instead of rebuilding the 10 bolt. I dont think the 3:73 gearing will do me good on the highway.

big gear head 11-18-2012 11:10 AM

What gears are you wanting to use?

Catfish11 11-18-2012 11:20 AM

I would like to use 2:73 in the 12 bolt, basically keeping the same gearing that I have now in the 10 bolt so fuel mileage on highway will not suffer.

big gear head 11-18-2012 11:22 AM

What about a 3.07?

gearheadslife 11-18-2012 11:27 AM

the truck 12 bolt is no stronger than the 10 bolt under your truck
the truck pinion shaft is smaller than the car 12 bolt..(what was g.m. thinking) but you might be better off just fixing the 10 bolt 8.5" rear

Catfish11 11-18-2012 11:53 AM


Originally Posted by gearheadslife (Post 1612719)
the truck 12 bolt is no stronger than the 10 bolt under your truck
the truck pinion shaft is smaller than the car 12 bolt..(what was g.m. thinking) but you might be better off just fixing the 10 bolt 8.5" rear

I thought it was the other way around and the truck 12 bolt pinion was bigger than the car 12 , could be wrong though.
I know there is nothing wrong with the 10 bolt in my truck , but just my personal preference and I think it would add a little value to the truck in going with the 12 bolt.

big gear head 11-18-2012 01:34 PM

The car 12 bolt pinion is the same size as the 8.5 pinion. The truck 12 bolt pinion is smaller than both of them. The 8.5 ring gear is 3/8 inch smaller than the 12 bolt, the differential bearings are smaller and the 8.5 has 28 spline axles and the 12 bolt has 30 spline axles. The 8.5 can be upgraded to 30 spline axles easily.

Catfish11 11-19-2012 07:15 AM


Originally Posted by big gear head (Post 1612716)
What about a 3.07?

I guess that would be another great option. I was reading last night that there is not much difference in the 3:08 and 2:73. So I will have to look into this.
I understand that the 12 is not much stronger than the 10 but the 12 is more "preferred" and should have slightly bigger brakes. I dont want to put 500 dollars into the 10 bolt when I can put that into the 12.

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