Overdrive in trucks important or never mind

Whut'd he saaaay?

 

It depends on how it is spec'ed and what it is used for. I've driven many direct top gear trucks that just plain sucked and many trucks with od that equally sucked.

 

My best guess is that DT12 transmission is the overdrive model, if was the direct drive model the rear axle ratio would start with a 2, for example a 2.47.

 

If you are westbound on 70 at the Kansas Colorado line upgrade into headwinds, that overdrive will kill you. It's underdrive you want. Or even a better ratio back there.

 

Dt12 is probably same as Volvo 12 speed... 11th is likely direct and 12 is over drive and the ecm only uses 12 when conditions are favorable to do so. Simply asking if overdrive is necessary is a wide open question. Over drive just means the output shaft spins faster than input shaft of transmission. You have to match it up with a rear end gear and then you get your final reduction.

Take a look through cowpie1's posts - he has 2.64 rear end with double over transmission and he does just fine. The flip side for him he will have to use the really small gears to start moving with a heavy load but in the top gears he has tons of speed available, more than you'd ever legally need. The other side is a direct drive transmission with say 4.10 gears - this truck would pull a huge load over a mountain, but would top out at a relatively low speed. You will find heavy haul trucks similar to this. What you want is something in the middle.

 

There is a magic gear combination that will get you 10 mpg
If you send me $300 I'll tell you..

 

Overdrive or no overdrive depends on the rears. I think 3.42 is a little low for no overdrive. It won't feel weak. The opposite. Fuel mileage will suffer with 3.42's and trying to run 70 mph. That's a 58mph truck with no overdrive. I think it's a typo though.

 

It sounds like he is assuming the listing in Truckpaper or whatever is in fact correct. Just some lazy salesman who doesn't want to look up the exact specs on that truck so he clicks on the listing "no overdrive"