whats the diff between full throttle and over drive off? (1 Viewer)

lx450landcruiser

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SO when i full throttle my cruiser and the RPMs jump up is that the same as when i hit the overdrive off button? or is the full throttle just drop down a gear as aposed to over drive just being shut off?

thanks mike
 
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same thing...far as I know.

An automatic is a "4-speed". The overdrive gives it the 5th gear.

Turning it off just down shifts it to 4th gear.

At least that's how I understand it.

Flame away!
 
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*non technical ramble ahead*

Here are the prompts I use for their associated actions :


Big hills = overdrive off
Non-hilly = overdrive on
Passing = PWR button on
Aggresive intercity driving = PWR button on
Senior driving mode = Overdrive on / PWR off


*guesses*


If overdrive is indeed a fifth gear , then overdrive-off is holding fourth gear ; allowing an easier time on hills .
PWR button on is like asking the tranny to hold each gear a little longer before shifting up . This allows your momentum to be conserved easier . Similar to holding a bicycle gear a little longer before shifting ... you avoid that 'uggh' altogether


I run 35" boots ... I also installed a Truspeed recallibrator . My off the line oomph is a little less than exciting , but if I start to hammer down on the gas moderately beyond 2nd I can really take off . I also drive forever with the PWR button on .

Oh how I look forward to getting my 4:88's someday though ..
 
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you will love your 4.88s. i have the same "boots" as you and i find myself messing with the "pwr" and "overdive" less. as simple as these questions are there prolly on a few peoples minds. how about the "2nd start".....this should be good.........
 
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Okay, this discussion is really pathetic and the facts are so wrong it is scary.

First, All 80 series LC's in the US were sold with 4 speed automatic transmissions.

Second, overdrive is 4th gear, there is no fifth gear.

Third, the answer to the first question is it depends. On what? Well if you are going over 50, the torque converter should be locked up. Pushing down on the throttle will first unlock the torque converter (about 300 rpm jump), and if pushed further, the truck will downshift to third gear (about 1000-1200 rpm jump). Now comes the interesting part (at least for those of us with the 95-97). The torque converter will not lock up in third gear unless you turn the overdrive off (or as it should really be called, block fourth gear out). So if you are going up a long hill that has you in third gear, you should consider turning the overdrive off to lock up the tranny and lower the temp and raise efficiency.

Now if you are going between 50-60mph, it is possible with a full throttle application to go directly from 4th gear locked, to second if you apply full throttle. The truck will also shift down from 4th to second below 50, the only difference is the torque converter will not have been locked out.


Cary
 
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Cary,

that is correct.

Overdrive

By definition, an overdrive has a faster output speed than input speed. It's a speed increase -- the opposite of a reduction. In this transmission, engaging the overdrive accomplishes two things at once. In order to improve efficiency, some cars have a mechanism that locks up the torque converter so that the output of the engine goes straight to the transmission.

In this transmission, when overdrive is engaged, a shaft that is attached to the housing of the torque converter (which is bolted to the flywheel of the engine) is connected by clutch to the planet carrier. The small sun gear freewheels, and the larger sun gear is held by the overdrive band. Nothing is connected to the turbine; the only input comes from the converter housing. Let's go back to our chart again, this time with the planet carrier for input, the sun gear fixed and the ring gear for output.


Ratio = 1 / (1 + S/R) = 1 / ( 1 + 36/72) = 0.67:1

So the output spins once for every two-thirds of a rotation of the engine. If the engine is turning at 2000 rotations per minute (RPM), the output speed is 3000 RPM. This allows cars to drive at freeway speed while the engine speed stays nice and slow.

This isn't from me but from How stuff works-Website.

Have fun :cheers:

Mike
 
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Somehow I knew Cary would come along...so I was off by one gear. :flipoff2: The explination was basically the same. :D Thanks again Cary.
 

lx450landcruiser

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thanks guys thats been a question of mine for quite some time now i just finaly was able to remeber to post it. :D
 

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