10-Speed Peterbilt 379 - Save Fuel with 13-Speed Upgrade?

Ya on pavement 150k can be done with a 10 speed but off road the low low gears are the only way to get the weight movin. For the last 12 years Ive run 107k. Ive done it with 8LLs 10s 13s and 18s. They all did the job but the 18 definitely dose it with the most versatility. I know what you mean about drivers thinking that 72k total gross is heavy. I had a driver in a freight truck apologize for holding me up on a hill because he was heavy at 72k. He didn't believe me when I told him I had more than that in the box. I told him I don't have 22 tires and wheel to look cool their their to hold the extra weight. He just didn't get it.

 

I would like and 18 speed! I would put some higher gears in the rear, like say some 308 or maybe higher.

 

Well you need to remember high gear is still the same and thats where you spend most of your time. Depending on tire size and the RPM your engine runs at peak efficency should be the determining factor of your rear end ratio. 308s seem very high for an OD tranny but I guess with lo pro 22.5s it might work if you run a lot of flat land or lite loads.

 

I have an 18 speed in my truck and can honestly say I've split the lower range maybe 10 times. I very rarely need it, but when I do, it's sure nice to have.

If you listen to Kevin Rutherford, the hot setup is LP 22.5s up front, wide base singles on the drives, 2.64 rears, a 10 speed direct drive trans, and a 12.7 Detroit. Run it at 55mph. Oh, and don't forget the lift or tag axle instead of twin screws. Might work great in the flat, but I bet it would fall on its face in the mountains.

Heck, I can get 6.0mpg out of my 379 with an EGR ISX, 18 speed, 3.70 rears, and 11R 22.5s. Most of the time grossing between 74-80K. I have to run 58 mph to do it, though. If I wasn't already a rolling roadblock most of the time, I might try slowing down to 55. Come to think of it, I might do it anyway, just to hear the stream of expletives directed at me over the CB.

 

At Schneider they wanted drivers to "Skip shift" in the lower gears as they said it saved fuel. I drove many there with no problems. However, the truck, or as the mechanics called it "The Dinosaur", that I was assigned would not run correctly if you skip shifted even once.

Let me preface this part by saying sorry to those of you that were stuck behind me choking on my fumes as I rolled down I-71 going into Louisville KY back in April of this year. Even so, if you were one of the unlucky ones then, you can attest to what I write here.

A single gear skip shifted would send the truck's operation spiraling off into a whole new direction of F#@KED. It would be running perfect for days on end, but the first time you skip shifted even one gear in the lower side it would retaliate once you went to the high side.

It resulted in the thickest black smoke you ever saw. On one trip down I-71 / I-64 with traffic stop and go due to construction, I skip shifted 2-4 as I had been idling along when traffic started moving. Everything seemed fine for a few minutes... then all h@!! broke loose. That truck rolled the thickest blackest smoke you ever saw. Drivers on the CB asked if I had blown an engine. At one point it created such a visibility hazard that traffic actually stopped on the highway. There was no place to stop being in that one lane, no shoulder construction mess for what seemed to be forever before I finally found an exit ramp where I could get off and out of everyone's way. After pulling off, shutting truck down, restarting, turning cruise on, bumping idle up, you could drive again normally - as long as you did not skip shift. No problems and ran smooth, even with 44k in the box. It was powerful and passed every other Schneider truck I saw; hills and all.

After many attempts at many shops the cause was never found or corrected. If you are the Schneider driver that ended up with the truck after I left; I feel your pain; I put 58k on it myself.

Truck was 2004 Detroit 60, Eaton / Fuller 10 spd, in a 2005 chassis = 780,371 when I got out of it.

 

What was the Trk number?

 

Truck number 42677