4-speed automatic w/OD = five speeds ???
Silly question, I'm sure.
But:
Is a 4-speed automatic w/OD act like a five speed?
Why are they designed like this, instead of a true five speed?
But:
Is a 4-speed automatic w/OD act like a five speed?
Why are they designed like this, instead of a true five speed?
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On most of them, the fourth speed is the overdrive.
4 speed, one of which is an overdrive is not a 5 speed.0 -
DeHeff
My Ford 500 has a 6 speed automatic. IIRC both of the top 2 gears are OD ratios.0 -
So OD describes a final gearing intended for highway driving?
My wife's car has three gears, and a high/low that comes on after the third gear.
I thought that was OD.
If a trans is described as having OD, can all the gearing be in the transmission, or is there always a second transmission?
BTW, I had a cycle with a five speed and a high/low, but that was for two types of driving, as opposed to trying to get a sixth gear out of it.0 -
quote:Originally posted by Tailgunner1954
DeHeff
My Ford 500 has a 6 speed automatic. IIRC both of the top 2 gears are OD ratios.
Hence my statement "On most of them" which was not meant to imply "all".
Overdrive simply means an input to output ratio of greater than 1 to 1 from the motor to the drive. His question was if a 4 speed overdrive was 4 speeds + 1 overdrive, equaling a 5 speed. My answer was no, it's 4 total gear speeds, one of which is the overdrive (greater than 1 to 1) and a total of only 4 speeds.
Same is true for 5 speeds or 6 speeds. The number includes the one (or in your case 2) overdrive gear ratios.
Sorry for the confusion.[;)]0 -
To answer your question, a four speed transmission with overdrive does give you five speeds. Watch your tachometer and speedometer as you go through all the speeds. You will see with each upshift, you get a decreased engine RPM for the same road speed.
Overdrive means only that when engaged, the output shaft or driveshaft is geared to turn slower than the input shaft which turns at crankshaft (engine) RPM.
Driveshaft RPM is further reduced by the differential to 1/3 to 1/4 of its' RPM at the drive axle.
There are devices as two speed axles that can give you double the amount of gears and electric overdrives that can do the same.0 -
quote:Originally posted by v35
To answer your question, a four speed transmission with overdrive does give you five speeds. Watch your tachometer and speedometer as you go through all the speeds. You will see with each upshift, you get a decreased engine RPM for the same road speed.
Overdrive means only that when engaged, the output shaft or driveshaft is geared to turn slower than the input shaft which turns at crankshaft (engine) RPM.
Driveshaft RPM is further reduced by the differential to 1/3 to 1/4 of its' RPM at the drive axle.
There are devices as two speed axles that can give you double the amount of gears and electric overdrives that can do the same.
My Ford is a 4 speed overdrive transmission. It has 4 forward gears. The 4th one is overdrive. It's not a 4+1 transmission, and most are the same.0 -
I may have misread the post and assumed the question was four speeds plus overdrive.
He has to count the number of shifts.0
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