I have a 2002 Camry 2.4l with the U241E 4sp auto trans. 4th gear has a ratio of 1.020:1. Toyota says this is the overdrive gear as is it locked out with the O/D off button. How can this be an overdrive gear since technically it isn’t even really a direct drive gear? Wouldn’t an over drive gear by definition have to have a less than1: 1 ratio?
The ratio could also have been stated as 0.98:1 so it is an overdrive. Lower gears such as 1.2:1 would be under drive. Direct drive is 1:1.
My apoligies I had the numbers reversed in the OP and have edited that.
Yawn. I’ll pull out my Toyota auto trans book later. Seriously.
You have to take into account the final drive ratio too I think. The total ratio probably ends up being “overdrive”
Its not an overdrive. 1.02:1 is an underdrive. The car probably has either a very small engine (third world edition) or a very low axle ratio. In the end, its all about the revolutions per mile, not just the ratio in the transmission. Tire size and final drive ratio have an effect as well as the transmission gears.
Fourth gear is direct drive on that transmission. The .02 ratio difference is a result of the counter drive/driven gears having a different tooth count to prevent a wear pattern in the gears.
The switch could be accurately labeled “4th gear off” but the “O/D off” use is understood by most and consistent with other vehicles.
Thanks for the info folks. I thought maybe it was just me thinking that 4th was not really an overdrive.
@Keith It is a US market Camry but the final drive is something like 2.74:1
Now this might be really off the wall but does anyone think there might be a way to get a real overdrive for this car or different final drive gears to try and get the RPM down a little at highway speed?
You should be seeing 2240 RPM @ 60 mph. If you are seeing something significantly higher, I’d suspect the lockup torque converter isn’t locking up. That is based on 215/60-15 tires. What size tires do you have?
That,s about what the tach says +/- a few RPM. I would just like it if I could get it down to under 2000. But as it looks it’s just a dream.
You could go to tirerack.com and upgrade to one of the 16 or 17" tire and wheel packages and that would get your RPMs down to about 2150. a lot to spend for about 100 RPM.
I figured I may be just dreaming, but it was worth asking, Thank You.
You have to remember when and where the term “overdrive” came into existence. When trucks and cars became powerfull enough to be able to slow down the engine from direct i.e. 1:1 overdrive units and transmissions began to come into vogue. Remember the Georga Overdrive for trucks. It allowed the engine to turn the drive shaft faster than the engine was turning. The ratio in the final drive (third member) still allowed the drive saft to turn many times for one turn of the rear wheels.
When autos became powerful enough to use overdrive, add on units were placed behind 3 and 4 speed transmissions mechanical transmissions that had a final drive of 1:1. Again the overdrive just spun the drive shaft faster than the engine. The rear end brought that speed down to a more useable speed for the wheels.
When 4 speed overdrive automatic and manual transmission came out the internals of the transmission provided the output ratio faster than the input ratio. With the automatic you could manually or electronically disengage overdrive.
When autos started using frontwheel drive transaxles, the term “overdrive” does become muddy as there is no drive shaft to be overdriven. But, there still is a pinion ahaft to the final drive that is overdriven when the transmission is in an overdrive gear. Sure the manufacturer could have gone to a lower reduction in the final drive but then the transmission would have to have 3-4 gears of reduction and one of 1:1. Why throw away a good technology in search of something new.
One problem with over drive manual transmissions is that the engine is driving the input gear, the counter shaft, and the overdrive gears in cruising mode. Unless the transmission is overdesigned the input shaft bearing, the counter shaft bearings,. and the output shaft bearings are under constant load. They do wear out and fail. It would be better to have a cruising 1:1 ratio and have a higher ration i.e. lower rumber, in the final drive, IMHO. After all the top gear in Nascar racers is direct i,e, 1:1
Overdrive, as a term has been around since the invention of gear sets. Overdrive and underdrive were terms used to describe gear sets the same way that step up and step down are used in in transformers.