rear end question

[low82c10]

i tried looking on here for guys who have done a LS swap with the problem i think i have. im sure the 82 c10 i just did the swap on has a stock rear end. i got a 5.3/4l60e it seems like on the freeway i am at a really high RPM i know it shifts into every gear i dont have my tac hooked up yet but what kinda gears do i need to look into getting?

[gchemist]

I would opt for 3.42 gears. 3.73 if you do minor weight towing frequently.

[low82c10]

i dont really plan on towing anything i don't own anything to tow, doesn't mean i wont later down the road. im just worried more about getting on the highway and coasting like the motor/trans would in the stock truck it came from not have to worry am i going to blow something up

[Blackpony]

3.42 would be a good gear selection.
Posted via Mobile Device

[gchemist]

3.42 gears are ideal then. My 96 Jimmy tows well with a 4.3, 4L60E and 3.42 gears. Even with 29" tall tires. RPMs with 29" tall tires is ~2000-2100 RPMs. Perfect for cruising 70 MPH.

[low82c10]

thanks guys, what rear end will work for my truck as far as if i want to find a 12 bolt and maybe a posi? can those be found in a junk yard? from maybe a suburban ?

[gchemist]

I run a '77 12 bolt in my truck. Gears are 3.08's. High gears but tires are on the small side. Towing definatly sucks with any amount of good weight. I can't complain of 18.5 MPG at 70!!

You will not find 3.42 in a 12 bolt. You'll have to add them. Common gears are 3.08s or 3.73 gears.

[naphtali5725]

Originally Posted by gchemist

I run a '77 12 bolt in my truck. Gears are 3.08's. High gears but tires are on the small side. Towing definatly sucks with any amount of good weight. I can't complain of 18.5 MPG at 70!!

You will not find 3.42 in a 12 bolt. You'll have to add them. Common gears are 3.08s or 3.73 gears.

what transmission are you running? I have a 10 bolt with 3.08's and i'll be running a TH400... what are your rpm's at 70mph?

[gchemist]

I run a custom built 700R4. 255/60R15 tires. RPM at 70 = 1950

[Tucson38]

Always a tough call on differential ratios, economy vs performance. Too bad there wasn't a 2-speed differential. That would be handy.

[low82c10]

whats the deal with 10 bolt or 12 bolt? any difference? other then bolts?>

[wraprail]

Originally Posted by low82c10

i tried looking on here for guys who have done a LS swap with the problem i think i have. im sure the 82 c10 i just did the swap on has a stock rear end. i got a 5.3/4l60e it seems like on the freeway i am at a really high RPM i know it shifts into every gear i dont have my tac hooked up yet but what kinda gears do i need to look into getting?

You say you are at really high rpm? That makes no sence at all cuz you probley have 3.08 ratio right now which would give you really low rpms.
So you must not be shifting into OD

[donut]

Hook up the tach, then see what you have. You may already be in the "sweet spot".
I know my '86 is close enough that a gear change/OD is not in it's future.