Rear End Gear Ratio

I have a DD series 60 14.0 in a
Columbia with 3.70s and a straight 10 speed . I used to be able drop one gear pulling 45k of water in a dry van and smoke a Gordon 8 axle heavy haul rig coming out of culver OR. I was getting 8.0-10.0 mpg pulling dryvan then running a flatbed. Until I blew 1st turbo since then mpg is like 6.0-7.0 mpg on some trips can get as low as 4.0 mpg when hauling heavy loads of scrap out of MT to ID.

 

Volvo VNL 780

• ModelD13
• HP455
• Engine RetarderY

Transmission

• Type10 SPEED
• MakeEATON/FULLER with 342 gears???need to know if this is a good set up

 

That's a pretty typical setup for OTR/Linehaul work.

 

I have driven a few trucks with 3.42 and never was fond of it. Some with 10's, some with 13's. 2 Cummins and 1 Detroit. I even had to dump a 2013 Chevy pickup because it had 3.42 diffs, and I grew to hate that setup. I am sure it works ok for some, but I could never grow to like 3.42 in anything. Not sure why OEM's have such a love affair with that ratio.

 

I'd rather have something a little more aggressive like 3.55 or 3.73's and just drive the truck a little slower.

 

3:58
2:... anything is too high. Small Detroit won't rev. If you are not speed governed you can probably get away with a higher ratio, but if you are hauling consistently above 30k pounds, it will fall on its face

 

I have 3:42 in my Volvo 780.
625 hp D-16, 2250 ftlbtq.
75 mph @1600 rpm
4k or 40k, goes up the hill the same way

 

Sure, some don't mind 3.42. I don't run those kind of speeds, never felt a need to, not even in my personal vehicles. And the many two lane rural highways I have to deal with weekly with up to 46K in the box, not a good fit with 3.42. Each has to look at their situation.

 

What gearbox? RTLO-22918?

 

I have those 3.42's in my Sierra. In hindsight, I should have swapped in 4.10's after I bought it. It can't hurt the MPG much. I mean I'm lucky to even see 17 MPG on the highway out of the 4.8 on a good day.