15 speed direct drive with 2.85 rears slow up hills and poor mileage
Discussion in 'Trucks [ Eighteen Wheelers ]' started by javelinjeff, Jun 21, 2015.
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truck went into shop that is known for making Cats run,,ECM was re-flashed to 550hp,,trim codes were way off,gained 1.8 MPG bobtail returning from shop back to house,boost is now over 32 under hard acceleration,was at about 22 before(bobtail),,if you have a pre-emissions cat with retrofit DPF or you need a DPF,,I strongly advise you to check this place out--Fletchers Diesel Repair in Lancaster California,,I've been to MANY shops trying to get this thing to run strong,this is the first place that actually made it happen,,I will post my fuel MPG's after my next load
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great, glad you got it and please keep us posted.
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I've never seen a direct 15 with an electronic Cat in front of it from the factory. Direct 15's died out in like 1985 electronic Cats came out around 1993. 2.85 gears are about a half a gear taller than a 3.36 (13 or 18 speed) and a whole gear above a 3.90. I'm assuming your trans is an overdrive @ either .86 to 1 or .74 to 1. In 14th gear you should be like having 3.90 rears should pull hills great!
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I pull a frameless dump and had a deep reduction 15 until I snapped the shaft that holds the low gears (according to weller) pulling an 8% grade in 5th gear. Swapped in a deep reduction 18 speed and am running 3.55s in the rear with the 3406e motor in my w9. Currently if I run from Missouri loaded and back to New York empty in getting an average of 6.22 mpg. With the 15 I was getting 5.75 if I remember right. I would lose 10+ mph. Now I might lose 5 when I go up the hills
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