Re: does the heat of an engine effect the shifting of a transmission?

Hello Jeff,

To begin, when you are referring to your project as "transmissions", you'll need to be a bit more specific. What you are referring to is an automatic hydraulic transmission (Auto for short), opposed to a manual transmission (commonly called a "stick"). There is another modern transmission that is gaining popularity called a continuously variable transmission or CVT. This link is a good place for some basic transmission info: http://www.answers.com/topic/automatic-transmission

"does the heat of an engine effect the shifting of a transmission?"
Nope, heat has absolutely nothing to due with shifting. Shifting occurs in one of three ways, throttle body (gas pedal), a vacuum modulator (small engine component) or by computer. Though these are very different methods, they all have one thing in common; they determine the amount of torque being placed on the engine as part of determining when to shift. You can find more in-depth information here: http://www.familycar.com/transmission.htm#Throttle%20Cable

#1 "is the shifting effected if the car is front or rear wheel drive?"
No, both front a rear vehicles use the same methods mentioned above to shift.

#2 "does the gear ratio effect the shifting?"
Yes, but one thing that I don't want to do here Jeff, is over-simplify the process. An automatic transmission is still considered one of the most complicated machines on the planet. A transmission uses a series of "planetary gears" to achieve the various speeds very quickly and smoothly. Planetary gears are nearly impossible to explain on paper, though this site has an excellent interactive diagram on planetary gears, along with a lot of other good transmission info: http://auto.howstuffworks.com/automatic-transmission.htm

If you need some basic information on how gearing works, gearing ratios etc, this link is another excellent source:
http://auto.howstuffworks.com/gear-ratio.htm

Let me give you a couple of key points that you must keep in mind with automatic transmissions:
Torque is the primary determination of when a transmission shifts. Taking off very fast, pulling a trailer or climbing a hill means high torque. In these situations, the transmission will take longer to shift, making the engine rev higher before shifting to the next gear.

All transmissions are not created equal. Different vehicles have different transmissions based on weight, engine size, and expected type of use. All of these transmissions have different gearing ratios, maximum speeds and shift at different times. A truck would never have the same transmission as a compact car; however a truck and a cargo van very well may have the same engine and transmission. Considering the type of engine with a transmission is so important, they even have their own word together. "Powertrain", means both the engine and transmission.

I hope this helps.

Sincerely,
Norman Parker