Truck setup/axle/ratio questions

Stewedpickles

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Joined
Jan 12, 2009
Location
Middle GA
K10 Truck setup/axle/ratio questions

I have a '75 K10, 400CI, TH350, NP203 with a 12 bolt in the rear and a 10 bolt up front (don't know axle types eg D44 etc...), 3.07 open diff front and rear. I plan to place 33s, a 4" lift, and lockers front and rear. The truck seems a bit sluggish with the 3.07 gears. For the lift I'm considering a rear shackle flip and new front springs. I plan to use the truck for light to meduim trails, but it will still be registered so I can drive to and from. If I understand 4wd then the front and rear ratios need to be the same.
1. What gear ratio range would be reasonable for on/off road use?
2. What diffs do I have, front and rear?
3. Are these strong enough or should I consider an upgrade?
4. Anyone see red flags with my setup?
Jeff
 
Well your axles are, 10 bolt Front, and 12 bolt rear. Properly named would corporate 10 bolt and 12 bolt
The 10 bolt will show weakness with a locker, (breakage)
The 12 bolt may hold OK, but if you do break, you also loose a tire and wheel. The 12 bolt is a c-clip axle. If it breaks there is nothing to hold in the axle tube, so it just kinda rolls out.
With 33's you would be a lot happier with 3.73's and even happier with 4.10's
The SB 400 will want to run hot in the woods. It's one of the more difficult engines to cool.
You may also want to get one of the weld on kits to sure up your frame at the PS box, before it rips the frame.
 
Thanks Upnover, that helps me up a lot. I think I'll stick with the lift and 33's for now and keep an eye open for diffs when I have the funds. I figure someone will be selling theirs at some point during their upgrade.
 
I think my description above may be inaccurate. I was just looking through the Feb 2009 issue of 4 wheeler and saw a write up about differentials. Evidently counting the cover bolts does not ID the diff as I thought it would so I took pictures.
Are these still 10 and 12 bolt GM diffs?

ai558.photobucket.com_albums_ss21_stewedpickles_f3275558.jpg

ai558.photobucket.com_albums_ss21_stewedpickles_f485c5e3.jpg

ai558.photobucket.com_albums_ss21_stewedpickles_8acaba6e.jpg

ai558.photobucket.com_albums_ss21_stewedpickles_29c039a0.jpg
 
axel ID

That is a D44 front and a 12 Bolt rear. The D44 and the 10 Bolt fronts look very similar. GM used D44's up front thru 1976. They changed to the 10 bolt in 1977. The 12 bolt was used up until 1979 and on early 1980 models. Then they changed to 10 bolt rear. Hope this helps.
 
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