What is overdrive?

[Tarikleesimsek]

Hi guys.I kinda guess what it means but can anybody tell me the exact explanation and what it does?? Thanks guys.

 

[JeepinJarhead03]

it's a gear with a ratio over 1:1 such as 0.90:1

your rear diff has a ratio

say.. 3.73 turns of the driveshaft to 1 turn of the axle

at the transmission, your gears start out low and go up, as a very basic example let's use

1st gear 4:1 2nd gear 3:1 3rd gear 2:1 4th gear 1:1 5th gear 0.90:1

in 4th gear if your engine is turning 3000 RPM so is your drive shaft and your effective ratio of rpms to your axle would be 3.73:1

make sense?

with automotive gear ratios a lower number is a "higher" gear , works very much like a 10 speed bicycle, in gear 1 your feet may be cycling extremely fast and you're barely moving, in 10th while difficult to pedal, your wheels end up turning much faster than your feet

 

[hyde]

good explanation

in plain language:
a button to pass trucks manual override of 4th gear, kind of like immediate down grade to 3rd gear. or if you are towing or riding in slow traffic, keep O/D OFF you can speed up much faster, but mpg will suffer. Try it next time you are on highway doing 50, you will like the way it drives.

 

[iamweasel]

In addition to what the others said, the purpose of the overdrive is to drop revs while travelling on the highway - with the purpose of dropping MPG.
It's ON by default; the button on the gear stick is there to turn it OFF when you need the acceleration (torque) of a lower gear (higher revs - closer to peak torque at 4000rpm) e.g when towing or overtaking. As hyde said - it forces the gearbox to drop from 4th to 3rd

 

[tjkj2002]

Overdrive is exactly what the name applies.Simple terms is when in overdrive the input rpm's(engine rpm's) is less then the output rpm's(trans/t-case outputs).

Your overdrive in your 42RLE is 0.69:1,so if the rear output(t-case) is spinning 1000rpms the engine rpm's are 690.

 

[Tarikleesimsek]

:roflbow:God that was good! Thank you guys!