Hypothetical question about transmission overdrive

[SZR48207]

Let's say tomorrow I buy a brand new vehicle with an automatic transmission.

This transmission in particular lets you turn off Overdrive.

For the next 100,000 miles I do all my driving with OD turned off.

Trans fluid is serviced per manual specs (let's say a fluid drain and fill every 30,000 miles).

Would the transmission be in any better shape than if OD was left on? Would the engine be any worse off?

 

[actionstan]

I imagine the transmission would be fine, the engine may wear slightly faster due to higher rpms at highway speeds. But any extra wear may be extremely low. You would have spent more money on gas, that would be the biggest difference.

 

[Brybo86]

I would think with OD on ... the engine is spinning slower ...so better for engine yes

I doubt it would matter for the trans. less shifting ...longer trans life

 

[Kuato]

Originally Posted By: Brybo86
...
I doubt it would matter for the trans. less shifting ...longer trans life



+1. I frequently lock out the upper gears when driving in lower speed areas.

 

[Now]

More rpms means more oil pressure and more fuel.

No damage to oil lubed parts, just your billfold.

On the tranny, if you lug a high torque engine the tranny clutches could slip. Dodge had a problem with the 47RH and 47RE due to towing in OD below 60 mph.

Keep things revved up and you can't go wrong.

 

[getnpsi]

New overdrives on some vehicles are different from older transmissions, thick of a bicycle with cogs front and back... My 2006 ranger...2nd gear uses the overdrive with a different gear then flipped back to get a real "3rd"...or maybe the other way around. Anyway in that case the 5r55 or whatever its called was using everything inside no matter the land speed or engine rpm.

 

[SwampSurvivor]

On the 5r55 it's

1st (1, no OD) 2nd (2, no OD0) 3rd (2, OD) 4th (3rd) , 5th (3rd OD)

 

[Bamaro]

Isn't the term "overdrive" somewhat antiquated today? It meant something years ago with 2 and 3 speed trannies but today all that is really important is the final drive ratios. I have heard that there is some slight efficiency with the 1 to 1 gear but other than that it's all about the ratio at the drive wheels and not whether it is "overdrive" or not.

 

[spackard]

Also, it's nice to have a mechanical switch to lock out OD, so when you're in the city and stop for errands you aren't forced to press the electronic "opt-out" OD switch again. And again.

 

[zzyzzx]

Originally Posted By: Kuato
Originally Posted By: Brybo86
...
I doubt it would matter for the trans. less shifting ...longer trans life



+1. I frequently lock out the upper gears when driving in lower speed areas.


I do that too. I have almost 222K miles on my 1995 Escort original automatic transmission.

 

[jrustles]

Originally Posted By: Bamaro
Isn't the term "overdrive" somewhat antiquated today? It meant something years ago with 2 and 3 speed trannies but today all that is really important is the final drive ratios. I have heard that there is some slight efficiency with the 1 to 1 gear but other than that it's all about the ratio at the drive wheels and not whether it is "overdrive" or not.


Technically and irrespective of the final drive ratio, any gear input-output ratio below 1:1 is overdrive. Some cars today have two or more ODs.

BMW does things differently, most of their manual transmissions have a 1:1 ratio as the "tallest" ratio, but the final drive 'rear end' ratio is quite tall, ie 2.93, where most other cars have overdrive transmission gear ratios and final drive ratios around 3.8 - 4.6. Don't know why BMW chose their way, but I kind of like it. Maybe it's slightly more efficient than overdriving then really underdriving (via final drive ratio)


Oh yeah, to answer the original questions hehe I'd agree with brybo. Staying out of OD is just one less shift to make and a lower degree of input-output torque differential.

 

[OVERKILL]

Originally Posted By: jrustles
Originally Posted By: Bamaro
Isn't the term "overdrive" somewhat antiquated today? It meant something years ago with 2 and 3 speed trannies but today all that is really important is the final drive ratios. I have heard that there is some slight efficiency with the 1 to 1 gear but other than that it's all about the ratio at the drive wheels and not whether it is "overdrive" or not.


Technically and irrespective of the final drive ratio, any gear input-output ratio below 1:1 is overdrive. Some cars today have two or more ODs.

BMW does things differently, most of their manual transmissions have a 1:1 ratio as the "tallest" ratio, but the final drive 'rear end' ratio is quite tall, ie 2.93, where most other cars have overdrive transmission gear ratios and final drive ratios around 3.8 - 4.6. Don't know why BMW chose their way, but I kind of like it. Maybe it's slightly more efficient than overdriving then really underdriving (via final drive ratio)


Oh yeah, to answer the original questions hehe I'd agree with brybo. Staying out of OD is just one less shift to make and a lower degree of input-output torque differential.


The O/D (6th) on the M5 is 0.83 with a deep first gear (4.23) and a final drive ratio of 3.15.

It is an interesting comparison to the American 6-speeds like the T-56 with a 2.66 1st gear and double O/D, 5th being .74 (Viper) or .80 (F-body/Mustang), and 6th being .5 (Viper) or .62 (F-body/Mustang). There are other version too but those were the common ones around the same era.

 

[widman]

I have often, mostly in mountains in underpowered cars, turned off the OD in switchbacks so it isn;t doing excess shifting.

In the 60's I rigged my overdrive on my 50 Studebaker so I could use it in each gear, giving me something between 1st and 2nd, and between 2nd and 3rd, as well as the 3rd + OD.

 

[Hokiefyd]

Originally Posted By: jrustles
Originally Posted By: Bamaro
Isn't the term "overdrive" somewhat antiquated today?


Technically and irrespective of the final drive ratio, any gear input-output ratio below 1:1 is overdrive. Some cars today have two or more ODs.


Yes, and Honda sticks to this model to the letter still (at least in our CR-V). It's a 5-speed automatic, and both 4th gear and 5th gear are overdrive gears, because their ratios are less than 1:1. There's an OD-off button on the side of the shifter, and it literally locks out both overdriven gears. It's kind of annoying...the shifter has P-R-N-D-2-1, with the OD-off button. So you can mechanically select 1st, which locks in 1st gear. You can mechanically select 2nd, which locks in 2nd gear. You can put it in D with the OD-off engaged and allow only the first three gears. If you can have it in D with the OD-off not engaged and allow all gears. You can't keep the transmission in 4th gear if you wanted.

Ironically, if I wanted more control over this transmission, I'd prefer to allow 1st-4th gears rather than 1st-3rd gears, but oh well...