Hey guys, I'm a teen looking to buy my first car and I am trying to learn as much as I can before I buy. I've only ever driven my mom's 07 Odyssey and my dad's '98 Accord. So here are my stupid questions:

1. What's the difference between D and 2 or 1? I realize 1 and 2 are for steep hills or towing stuff, but shouldn't the Odyssey downshift to those gears automatically? If I put it in 1 or 2 is it then stuck in that gear?

2. What (part of the transmission?) allows the wheels to move freely of the engine's output. For example, I can put the Odyssey in drive and still fly backwards down a hill if I don't brake. Or as simple as braking while idling at a stop sign. Where is the connection between the crankshaft and wheels broken?

3. When a FWD car makes a turn, do the rear wheels slip since there's no differential and they rotate at different speeds? Or are the wheels not connected?

Thanks

 

Your car wants to use the most fuel efficient gear available. Sometimes you need to override that decision for power. D is drive, and puts the computer in control. 2 is 2nd gear, and 1 is 1st. Use them anytime you would select a lower gear. Some cars have an L option and that is simply a "low" gear, and how the car goes about that varies by manufacturer.

This happens at the torque converter. It is a circular housing, called a fluid coupling. The engine output shaft spins a plate inside that has fins, like a propeller. This will get the fluid inside rotating, and will eventually spin another propeller on the other side that is connected to the transmission. There is no physical connection between the engine and transmission, which is why the wheels and the engine can act independently.

This type of fluid coupling has some pluses and minuses. Manual transmissions do NOT have a torque converter, which is why they must have the clutch in, or be out of gear to stop. Torque converters are the reason why manual transmission cars get better mileage than automatics. There is energy wasted in moving that fluid in order to get the transmission moving. After a specified speed or RPM most cars "lock" the torque converter with a clutch. This means that now there is a physical link from the engine to the transmission. This is done to remove that parasitic loss of the torque converter moving fluid. It will unlock again when speed dips below a threshold so the engine doesn't stall.


In a FWD vehicle the rear wheels are generally not connected to each other.

 

Hey Phillip---welcome to FTE and the wonderful world of motor vehicles, those machines we love to hate but yet keep coming back time after time buying new ones!

Just wanted to share something I once read: "there are no dumb questions but sure are plenty of dumb mistakes............!" We all have learned by asking questions--even if you think they're dumb ask anyway, avoid the mistakes that come from NOT asking!

BTW excellent answer A/Ox4! How's that apprentice welder/culinary student these days?

 

She's doing well! We got her started riding the other day and now shes hooked!



Becky's Jump - YouTube

 

Thanks for your great answer, A/Ox4, and thanks for the welcome JWA. I'll post more questions here if I can think of any.

Thanks!

 

Better watch out---she'll be clearing those dunes with a lot more air in no time!

Some women take to horsepower just as much as us guys, sometimes they learn to ride a lot better too----don't teach her too much!

Phillip you're welcome and we look forward to helping if possible!

 

Let me answer #1 a little differently than A/Ox4. The transmission will not downshift automatically going downhill. It is important not to "ride the brakes" going downhill on steep grades. Manually select a gear that will slow you down just the right amount so you dont have to have your foot on the brakes most of the time. I live in the mountains and regularly smell burning brakes. Brakes that heat up may fade, that is, decrease effectiveness.

#2, minor point. A torque converter is different than a straight fluid coupling in that there is a third element between the two halves that redirects the oil flow to increase leverage, thus increases or "converts" torque.

 

A slight clarification: A torque converter converts RPM to torque. When the converter is slipping the fluid coming off the driven fan hits the stator and is redirected back to the driven fan, adding force to the fan. The more slip the more fluid redirected, so the more force hitting the driven fan. This creates more torque at the output of the torque converter, with a loss of RPM. This is what a torque converter converts, RPM to torque.