manual overdrive
04-13-04, 02:09 PM
#1
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manual overdrive
i was looking at the specs of the FD and it says that the transmissions for it are M/T and A/T. (well duhhh) But my question is... when i was reading the specs, it said that the MANUAL transmission was a 5 speed WITH an overdrive. Can you guys plase explain to me why and how a MANUAL transmission has an overdrive? any info will help. Feel free to flame on me too about being a newb and using the search. Cause i tried already for like 30 minutes with all these different ways. Still didnt find my answer. Thx
-jeremy
-jeremy
04-13-04, 02:52 PM
#3
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Maybe my answer doesn't apply to a rotary, (can't imagine why not), but in a 5spd, 5th gear IS overdrive. So for example, an old 4spd didn't have overdrive. That's what I've always known, so anyone feel free to correct me if I'm wrong.
I used to own a 95 AWD Stealth, which is 6spd for those who may not know, so in that case 6 was basically overdrive.
I used to own a 95 AWD Stealth, which is 6spd for those who may not know, so in that case 6 was basically overdrive.
04-13-04, 03:09 PM
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The term overdrive implies a state in which the wheels are spinning at a faster rate than the engine is spinning.
For most 5 speed cars, gears 1-4, the engine is spinning at a faster rate than the outputted wheels are. In 5th gear, the engine is spinning slower than the wheels.
If you look at gear ratios you will notice in most 5 speed cars fifth gear will almost always have a number smaller than one.
That is because for every rotation of the wheels the engine is spinning .7 or whatever the gear ratio is.
Overdrive is used on all cars and has nothing to do with automatic transmissions specifically. The only reason you notice it on automatic transmissions is there is usually a button that says O/D off which prevents the car going into the over drive gear (4th gear on most autos) so that the car can accelerate faster or cary a heavier load uphill.
A few 6 speed cars like the Corvette have two over drive gears, fifth and sixth. In which both gears have the engine spinning slower than the outputted wheels. In these cases the engine makes so much torque at low rpm, they designed a gear so that the engine can sit at really low rpm at high speed to increase gas mileage. At 80mph a 6 speed corvette will be probably no more than 1500 rpm.
Other 6 speed cars like Supras have only one over drive gear, and the reason for more gears is make more use of your power band. I.E. when upshifting yoru rpm's drop less on a 6 speed than on a 5 speed.
For most 5 speed cars, gears 1-4, the engine is spinning at a faster rate than the outputted wheels are. In 5th gear, the engine is spinning slower than the wheels.
If you look at gear ratios you will notice in most 5 speed cars fifth gear will almost always have a number smaller than one.
That is because for every rotation of the wheels the engine is spinning .7 or whatever the gear ratio is.
Overdrive is used on all cars and has nothing to do with automatic transmissions specifically. The only reason you notice it on automatic transmissions is there is usually a button that says O/D off which prevents the car going into the over drive gear (4th gear on most autos) so that the car can accelerate faster or cary a heavier load uphill.
A few 6 speed cars like the Corvette have two over drive gears, fifth and sixth. In which both gears have the engine spinning slower than the outputted wheels. In these cases the engine makes so much torque at low rpm, they designed a gear so that the engine can sit at really low rpm at high speed to increase gas mileage. At 80mph a 6 speed corvette will be probably no more than 1500 rpm.
Other 6 speed cars like Supras have only one over drive gear, and the reason for more gears is make more use of your power band. I.E. when upshifting yoru rpm's drop less on a 6 speed than on a 5 speed.
Last edited by twinturboteddy; 04-13-04 at 03:13 PM.
04-13-04, 03:10 PM
#6
I won't let go
Originally posted by RxSeven1
in fds 4th gear is a 1:1 ratio. 5th is overdrive. i believe its meant to lower your rpms for gas mileage.
in fds 4th gear is a 1:1 ratio. 5th is overdrive. i believe its meant to lower your rpms for gas mileage.
Overdrive is the transmission being overdriven by the motor.
o·ver·drive ( P ) Pronunciation Key (vr-drv)
n.
A gearing mechanism of a motor vehicle engine that reduces the power output required to maintain driving speed in a specific range by lowering the gear ratio.
04-13-04, 03:22 PM
#7
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Originally posted by twinturboteddy
The term overdrive implies a state in which the wheels are spinning at a faster rate than the engine is spinning.
The term overdrive implies a state in which the wheels are spinning at a faster rate than the engine is spinning.
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04-13-04, 03:30 PM
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Originally posted by novadan67
Not quite... Overdrive means that the output of the transmission is spinning at a faster rate than the input. You still have the rear end gear ratio to consider when talking about how fast the wheels are spinning.
Not quite... Overdrive means that the output of the transmission is spinning at a faster rate than the input. You still have the rear end gear ratio to consider when talking about how fast the wheels are spinning.
Bah same thing
Just trying to explain overall picture.
04-13-04, 03:38 PM
#9
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Originally posted by twinturboteddy
The term overdrive implies a state in which the wheels are spinning at a faster rate than the engine is spinning.....
The term overdrive implies a state in which the wheels are spinning at a faster rate than the engine is spinning.....
for rwd, OD implies the transmission output shaft is spinning faster than the engine speed. Due to 3.xx+ differential ratio, wheels always spin slower than engine in all gears.
old brit cars had a bolt on OD unit (planetary gears, like autox) that attached to the back of normal 4 speed with 1:1 fourth. used electric clutch to kick in on overdrive 5th.
for fwd, same thing but refers to pinion shaft speed, not output shaft.
04-13-04, 09:33 PM
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Also the Corvette is a special case (particularly in the minds of its' owners 
. Due to the high torque of the engine, they wanted to reduce the strength requirement of the the main driveshaft and "U" joints, so they used a very high gear ratio diff. This allowed raising the transmission gear ratios (lowering torque in each gear and torque on the driveshaft). Of course this doesn't help the half shafts.
It's a neat trick that has been used before.
. Due to the high torque of the engine, they wanted to reduce the strength requirement of the the main driveshaft and "U" joints, so they used a very high gear ratio diff. This allowed raising the transmission gear ratios (lowering torque in each gear and torque on the driveshaft). Of course this doesn't help the half shafts.It's a neat trick that has been used before.
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