Have a 1995 379 Pete with a detroit 60 500 horse with a 13 sp eaton fuller truck has 390 gears but tor the driveshaft out n it screwed up the rear differential I have two options at my disposal a set of 411's or 355's with my 390 I am good on flat ground at 70 I am taching bout 1600 when it starts pulling a hill it loosing alot like I said just need g opions from other owner ops
Need advice on rearends
Discussion in 'Peterbilt Forum' started by Bulldawg81, Apr 9, 2016.
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355 is ok, 411s will eat your fuel.
Eaton has a gear and road speed calculator on their site. -
Yeah if you're bumping 1600 with 3.90s, you'll be about 1700 with 4.11s
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Got to know your sweet spot of motor. Lugging will burn fuel-over revving with extra power uses fuel.
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I have the same truck but 3.70s lp 22.5 rubber and a 10 speed. With this current set up im running around 1600 at 70mph. My truck was speced for tall 24.5's so i actually have to drive 5mph faster to do the speed i want. With that being said if i had tall rubber on 24.5's and my 3.70 rears at 70 mph id be running around 1450-1500 rpm and for my truck thats right where she is happy at and where the motor really likes to start pulling.
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Bite the bullet and get an 18-speed and keep 355 gears
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Going from a 13spd to an 18spd will do nothing for him. I run that engine myself and from my experience I'd go with the 4.11's in your case. You'll only be 50rpm higher in your gears. It will be a total dog with the 3.55's unless you swap down to low pro tires. I run 295/75/22.5 with a 13spd and 3.58's and its around 1550rpm@70mph.
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