News, GM pickups to get 8-speed transmissions.

[oldtrader]

It is easy to understand why they are making this change. Federal Fuel Mileage Regulations demanding more mileage. The easiest way to increase it, is a new more gear transmission, to keep the engine operating in a way to acquire a few more miles per gallon.

[armory]

Originally Posted by d4g4m

And just think, when chevy got it's first auto trans it was only 2 speed. And they called it powerglide no less!!! Had it in my first car, 58 Impala convert 283 2 bl carb, 2 speed auto

YAY, I had a powerslide in my 66 Belair w/283 and one in my 69 Camaro w/327. Great transmissions.

[RayinAK]

Originally Posted by Drover

At what point are the efficiency gains of more speeds outweighed by the losses of constant gear hunting?



Since highway cruising is done almost entirely in the tallest gear, it's almost immaterial if there's 3 or 27 additional gears. There may be very minor efficiency gains if the transmission has a closer gear ratio to step down to when going up an incline, but not enough to trouble with having 8 or 9 or 10 gears or whatever. The point of adding more gear ratios is to provide more closely spaced gear ratios and thus lower shift points on acceleration. That's the major source of efficiency gains from more gear ratios.

While all that is true, having more gears help keep the RPM down, specially at cruising speeds on flat roads. The lower the RPM, the lower fuel consumption. The same reason for using CVT's. But the later don't seem to be as popular with most drivers as regular automatic transmissions.
http://www.popularmechanics.com/cars...ds-is-too-many

According to Ford Motor Company’s chief engineer of transmissions, Craig Renneker, more gears give powertrain engineers more gear spread to work with. This means first gear can be shorter for better off-the-line acceleration while the top gears can be taller for better fuel economy. Having more gears allows smaller, more economical engines to power larger vehicles or improves the efficiency of existing engines.

But you can always go higher. Fiat/Chrysler CEO Sergio Marchionne says ZF’s new nine-speed automatic could go into new front-wheel-drive offerings beginning in 2013. Mercedes-Benz is known to be developing a nine-speed version of its G-Tronic gearbox to back its AMG performance models.

It’s not just automatics that are seeing the gear count creep ever upward. Manual transmissions have been relegated to either performance or low-price fuel-miser cars in recent years, but even they are seeing the trend. Porsche unveiled its all-new 911 at the Frankfurt auto show, showing off a new seven-speed manual option.

[ipaper]

Also, you have to keep up with the competition. Dodge already went to an 8 speed transmission and ford is talking it for the F150. GM don't want to be left behind.

[Chadro77]

Originally Posted by AlfredB1979

GM transmissions are usually junk. Or did you just gloss over the 700r4 and its descendants and pretty much every GM FWD trans out there?

Good God man, the 700r4 came out over thirty years ago. Are you gonna bring up the Vega next?

As far as descendants, Sorry but the 4L60, 4L80, and 6L80 for instance are solid trannies. What FWD trannies are you referring to?

[RayinAK]

Originally Posted by Chadro77

Good God man, the 700r4 came out over thirty years ago. Are you gonna bring up the Vega next?

As far as descendants, Sorry but the 4L60, 4L80, and 6L80 for instance are solid trannies. What FWD trannies are you referring to?

GM manual transmissions are quite good, too. I really enjoy shifting the 5-speed one on my 1988 Sierra. Since the 5.0 liter 350 motor has plenty of power, on a 20-25 MPH school zone with a flat road I can up-shift to 4th gear and remove my foot from the gas pedal. It will cruise a little over 20 MPH with the motor idling.

By the way, the 5-speed automatic on the 2010 Toyota Rav4 V6 with a 270 HP motor works quite well keeping RPM down, which makes for an economical fuel consumption. If it had a 6-speed automatic transmission, it would do much better on the highway.

[Drover]

Originally Posted by RayinAK

While all that is true, having more gears help keep the RPM down, specially at cruising speeds on flat roads. The lower the RPM, the lower fuel consumption. The same reason for using CVT's. But the later don't seem to be as popular with most drivers as regular automatic transmissions.
How Many Speeds Is Too Many? - New Car Transmission Technology - Popular Mechanics

Cruising speeds on flat roads is the scenario in which the number of gears is least relevant. As long as the car has enough gears between the first and last gear to make it drivable, you can make the final gear ratio as tall as you want. If you want a .72 cruising gear for instance, it makes no difference cruising at highway speed on a flat road if you have 3 or 8 other gears below it. Having a .72 top gear on, say, a 4-speed transmission wouldn't be optimal for drivability because you would have either wide ratios from gear to gear with high-rpm shift points or a huge gap between 3rd and 4th. But in your flat highway cruising scenario, you'd get the same fuel economy with a .72 top gear on a 4-speed transmission or an 10-speed transmission.

Once you get to about five speeds, you can pretty much have as tall a cruising gear as you want as you can still make the spacing between the gears sufficiently close to make the car reasonably drivable. Once you get to six speeds, you've reached the point where you can have a tall cruising gear and have close-ratio shifts all up and down the gearbox without compromising one or the other. Beyond that, the major reason for adding still more gears is to keep shift points low and RPMs low under acceleration or load (such as caused by inclines), which again is not an issue when cruising along on flat roads.

[uscgto]

hopefully the entire SUV line-up gets the 8 speed auto.