Transmission Question

Anything past 1.00 to 1 is overdrive, meaning 13's and 18's are double overdrive..... .86 and .73.
The old 13's they used to call double overs were actually triple. .86, .73, and .62.
I thought Bruce was preaching running a direct 9 or 10 and 2.64 gears. What he doesn't explain is how low and reverse ratio jumps out of sight....making it hard to take off or back up an incline.

 

All those "experts" are flying so high they don't have to really drive trucks and get so disconnected from reality its not even funny - kind of like politicians who like listening to their own voices so much they just keep on talking. Only non-driver can recommend 9 speed over 18 speed and only rookie can buy this kind "advice". I won't even touch 2.64 gears

 

They will allow you to gear to drive in direct and still keep the drivability of the extra gear. An 18 single over can be geared to run in direct and still offer 17 completely usable gears. A 13 gives you 12.

Or you could always put it in the top hole and make good time.

 

How does it make that much difference you still end up with same gearing at the wheels. Wouldn't trying to drive a 2.64 diff take as much fuel as a overdrive transmission. At full weight try to take off on a steep hill bet your clutch wishes you had got a slow diff ratio. The faster you drive the more wind you have to push more fuel you burn.

 

In the OD trans it has more gears turning or its just a bigger gear turning and they say that is a loss in fuel mileage. Sad part is these guys give advise but it mostly pertaining to Swift or some other mega carrier.

Although if you could get away with running a higher gear and a direct drive trans instead of a 13/18 you are more likely to not have as many trans related issues. I only say that cause there is less parts in a direct trans.

 

An overdrive makes more heat when loaded, so it is less efficient. Even though the ratio is the same, fuel mileage will suffer.

If you are running all flat miles, probably not a big issue. But as soon as it has to climb at all the losses are larger on an order of magnitude.
So as soon as you throw a bump at it you are going to be downshifting in places where you might not with a direct.

As an example years ago I put a .80 over 6 speed in my Harley. With the stock rear gearing it would hold speed on flat ground but it was difficult to build speed.
Dropping the rear gear helped some but you can still feel it pull down on a hill it is noisy and makes heat.
Now days the 6 speeds are not overdriven, a deeper 1st gear with a direct high gear is the answer, then the primary reduction is decreased to bring the ratio back.
Now there is no power loss through an OD it will build speed and climb small bumps without downshifting, it is quieter and makes less heat all with the same RPM in high gear as the OD trans.

I'm pretty sure there are measurable gains long term from not spinning the driveshaft as fast on a higher gearset.

Granted you are going to need deeper low gears to get it rolliing with that setup.

 

I think it would depend on the rearend ratio. If your running 3.55's or higher it would be pretty much useless to run a double over. I'm running 3.73's behind a 13 double-over and I love it, but I seldom put it in the top hole, I can split it from 10th to 11th and run good in the 55 - 65 mph zones, and then put it up against the dash and the button in direct (12th) and run from 70 -75 on up to triple digits which any more is plenty for me. Oh bye the way I'm running a mechanical engine turning 2450 but seldom wind it that high.

 

thats really a question of what you want the truck to do, if you dont mind TOTALLY slugging it up a mountain side then yes, stick to a 9 speed, im in a loner 9 right now same truck as mine, same isx engine, this truck is just a year younger with 200k less miles, but my 13 would DESTROY this 9 speed up ANY grade, which leads to less time on hill, which leads to better fuel economy