Team Run Smart Home >  Trucking Forums > Welcome to the Truck Smart Forum > Direct drive transmission v/s overdrive transmission
Welcome to the Truck Smart Forum
View modes: 
Mike Anderson
150k
150k
Mike - 9/5/2012 3:28:37 PM
   
Direct drive transmission v/s overdrive transmission
I think it would be good to know the advantages of specing a truck with a direct drive transmission over an overdrive. I know this will save fuel as it is turning less gears. What are the other advantages?

Henry Albert
200k
200k
Henry.Albert - 9/15/2012 7:50:35 AM
   
RE:Direct drive transmission v/s overdrive transmission
Thats about it Mike... I wonder if the gear oil would last longer turning less gears.

Mike Anderson
150k
150k
Mike - 9/15/2012 4:38:50 PM
   
RE:Direct drive transmission v/s overdrive transmission
Good Chance.

Linda Caffee
200k
200k
Linda.caffee - 9/15/2012 8:03:32 PM
   
RE:Direct drive transmission v/s overdrive transmission
Why would that make a difference on the gear oil?

I agree on the fuel mileage advantage of direct drive.

Mike Anderson
150k
150k
Mike - 9/16/2012 2:58:00 PM
   
RE:Direct drive transmission v/s overdrive transmission
Just less gear gears to breakdown the oil or shed metal.

Bill McClusky
200k
200k
Bill McClusky - 9/16/2012 10:24:40 PM
   
RE:Direct drive transmission v/s overdrive transmission
Mike, load weights and terrain are two major factors to consider when deciding whether to spec direct drive or overdrive transmission. If I were specing a truck for line haul, light loads and relatively flat terrain I would certainly consider a Direct drive transmission. If I were specing for all load weights, 48 states, and all terrain types I would spec with an Overdrive transmission. I talk with many Owner Operators that have purchased a used truck with Direct drive tranmissions and run 48 states. Their biggest complaints are pulling hills, pulling away from docks with sloped ramps and they have to do everything right all of the time (including holding their mouth just right) to achieve good fuel mileage. Not knocking Direct drive transmissions at all. Just saying that they need to be used in the proper service duty to benefit from the minor improvement in fuel mileage which is the only benefit I know of.

Henry Albert
200k
200k
Henry.Albert - 9/17/2012 9:06:31 PM
   
RE:Direct drive transmission v/s overdrive transmission
Bill ,

I can't see any reason a direct drive would pull hills any different than a overdrive transmission due to the fact overall gearing stays the same. Could it be that these used trucks were also lower powered by the fleet they came from? I drove the Cascadia Evolution cross country from San Diego,CA to Gastonia ,NC at 76,000 pounds, cruise speed set 62 MPH and recorded 9.32 MPG for the whole trip. This same truck had a direct drive and pulling power was not a issue.

Bill McClusky
200k
200k
Bill McClusky - 9/17/2012 10:58:22 PM
   
RE:Direct drive transmission v/s overdrive transmission
Henry,
It's great to hear that the Cascadia Evolution performed so well. You had the luxory of driving the latest and greatest technology and most likely with a multi torque engine capable of 1750 ft lbs of torque. correct me if I'm wrong. I'm envious. Most of the O/O I have spoken with are in older model trucks that were purchased used, but some of them were in trucks as new as 2009/2010. I personally have not had the opportunity to drive a direct drive transmission over the road, so most of my conclusions are based on feedback I get from Owner Operators, and carriers. Those that are running light to middle weight loads in relatively tame terrain don't have any complaints. It's the drivers that are running heavier loads in all types of terrain that I hear the most complaints from. Some of these trucks came from a carrier that was using 9-13 convertible transmissions with 2.64 gear ratio.
It is possible that the engines are spec'd to 1550 ft lbs of torque which would certainly have an inpact on pulling power. I'll do some research and see what I can find as far as specs for some of these trucks.

Henry Albert
200k
200k
Henry.Albert - 9/18/2012 12:20:51 PM
   
RE:Direct drive transmission v/s overdrive transmission
Bill,

A direct drive has the same final gear ratio as a overdrive set up when set up correctly. The difference is when in top gear you are turning less parts than with a overdrive transmission.

As for the truck I drove on the cross country tour it had the engine set at 455 hp / 1550 foot pounds of torque.

Bill McClusky
200k
200k
Bill McClusky - 9/18/2012 1:24:26 PM
   
RE:Direct drive transmission v/s overdrive transmission
If you compare an Overdrive transmission with 3.55 axle ratio to a Direct drive with 2.64 axle ratio in 10th gear you are absolutely correct. The overall ratio is nearly identical. The difference CAN come in the other transmission gears overall ratios which will depend on the ratio set installed in the transmission. There are numerous configurations. I looked up the trans model and specs for some of the O/O that were complaining about the Direct drive. When i compared the overall ratios of all of the gears of their transmission model (direct drive ) to an overdrive version there were significant differences, especially in the lower gears The differences diminished as you worked up through the gears. Probably the reason they were complaining about pulling away from sloped dock ramps. This all points the the importance of properly spec'ing a truck right down to the proper ratio set for the type of service duty the truck will see. I have not had first hand experience driving a Direct drive transmission equipped truck over the road. To date, your are the first person I have spoken to that has been satisfied with driving a direct drive in a 48 state type of service duty. The drivers I have spoken to with direct drives that are running light to medium weight loads in relatively tame terrain seem to be satisfied. I would really like to hear from more drivers about their experiences with the direct drive transmission.

1 2

READY TO JOIN IN?

Please login or create a FREE account to join the conversation.

CREATE AN ACCOUNT

MEET THE PROS

Team Run Smart Pros are real drivers with real advice. Their expertise lies in years of experience on the road and continuous success in the business of trucking.

VIEW PRO BIOS

ABOUT TEAM RUN SMART FORUMS

Team Run Smart is an open community for all truckers who mean business. It’s where you turn to for expertise you can use right away. You’re in the trucking industry for the long haul in more ways than one. That’s why we’re here for you whether you drive a Freightliner or not. We’re all facing increasing industry pressures – from keeping operating costs low to staying healthier on the road. As a member of Team Run Smart, you’ll get advice from fellow truckers and dedicated Freightliner industry pros that you can use to overcome the pressures you’re facing. We’ll deliver the fresh content that can help you Run Smart.

START A NEW DISCUSSION

Please login or create a FREE account to join the conversation.