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Questions about manually downshifting automatic transmissions always increase at this time of year. It may be the warm weather, with drivers looking for a little fun and performance from their cars, or drivers towing utility trailers for spring yard work, or campers going on summer holiday trips. There can be many reasons for manually shifting your automatic transmission and some of them will increase your safety.
Most automatic transmissions use planetary gearsets to provide different gear ratios. A planetary gear set has a centre “sun” gear – planet pinions that rotate around the sun gear – and an internal tooth “ring” gear around the planet pinions. These gears are always in constant mesh, which differs from a manual transmission where the gears have to be physically engaged or disengaged during shifts. The gears of an automatic never grind or clash by design, so shifting manually doesn’t increase gear wear.
By holding or driving various combinations of the planetary gears, several gear ratios and reverse motion can be selected. Modern automatics use two or sometimes three planetary gearsets in combination to achieve the four, five, six, seven or even eight speeds found in today’s vehicles.
To shift the automatic, oil is directed from the control valve body to the clutches. Each clutch is made up of several discs. Half have internal splines and the other half have external splines. The splines are connected to the transmission case, shafts or planetary gearset components. When oil pressure is applied to a clutch, the plates are forced together and either hold or drive gearset components to give the different gears. During a shift, there is some wear on the clutch plates, as they slip slightly during application until the full oil pressure is applied but this wear is minimal unless done during very hard acceleration.
Manual downshifts are slightly different than automatic downshifts. During a manual downshift, additional clutches are applied to provide engine braking. Many transmissions drive in some gears through one-way roller or sprag clutches. These one-way clutches can freewheel during deceleration, but by applying an additional clutch, the one-way clutch is prevented from freewheeling so the engine can help slow the vehicle along with the brakes.
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at 12:50 pm
“… are easier to pull away from a stop on slippery roads or icy parking spots”
really? I’ve always manuals much better in the winter.
at 1:49 pm
“That’s why even in vehicles where manual transmissions are offered, automatic models still are the largest percentage of purchases by far.” This is only true in North America and apparently Japan… in most other countries manual transmissions are preferred.
at 2:03 pm
“Automatics are cheaper to repair than manual transmissions, provide quicker acceleration and better performance than many manual transmissions, and are easier to pull away from a stop on slippery roads or icy parking spots. That’s why even in vehicles where manual transmissions are offered, automatic models still are the largest percentage of purchases by far?”
Cheaper to repair? HOW? An automatic only has about ten times as many moving parts as a standard. Quicker acceleration? Nope. Have a look at 0-60 times for any vehicle. The standard is going to be a couple tenths faster, and will have improved fuel econcomy. As Michael said, over in Europe, nobody drives automatics, because they’re seen as “girly.”
at 3:55 pm
on the strip, automatics will generally be faster than manual. The shift times will proof it.
But when automatics are slower is due to the computer, TC, etc, bogs the car down if not launched at the right reps and the right mode.
at 4:46 pm
While some automatics have surpassed manuals in 0-100 km/h times and fuel economy, this is an exception and not the norm. Although it is true that in the hands of an average driver, they would be faster in an automatic than a manual.
However, I’m addicted to the connected feel of the standard transmission. Engine and wheels directly connected–it feels great, especially accelerating in a car with decent down low torque.
Also, while most modern automatics can get the right gear most of the time, there are times driving our automatic Civic that I really wish for a manual so that I can be in the right gear out of a corner, or accelerating uphill.
Also, winter driving–the automatics have “creep”, which is useful, but a manual can do the same (start in second or no-gas start). Plus there are times in slippery conditions where having “instant access” to neutral (a.k.a, the clutch) is invaluable in regaining traction to the wheels. And let’s see you try to rock out of a slippery spot with an automatic!
Sadly though, whether I like it or not the manual transmissions’s days are numbered (in terms of mainstream applications). Modern automatics, dual-clutch, and CVT transmissions make fuel economy and performance more accessible to the average driver.
at 1:53 pm
In a lot of newer vehicles, automatics get better fuel economy than manual. The technology is getting better every year. As for cheaper to repair? Doubt that.
at 10:08 pm
Besides, without a manual, when would you ever here those immortal words; grind a pound for me!