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Old 02-04-2011, 07:42 AM   #1
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6 Speed Transmissions

We all know 6 speeds transmissions are better for towing, and about everything else, including reliability. In thinking about them, it seems to me that rearend gear ratio is now much less of a concern because of all the gears. I would think 1st gear in a 6 speed is lower than 1st in a 4 speed. What you guys think?
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Old 02-04-2011, 08:31 AM   #2
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Carl

I love the six speed in my 08 Tundra 5.7L. Fifth and sixth gear are both overdrive gears. It has a 4.3 rear end. This gives it plenty of power in first gear, and in 6th gear, 60 mph is only 1,600 rpm. You really have the best of both worlds. Rear end ratio is indeed a non problem. Additionally, the 1,600 rpm at 60 mph allows for good fuel economy with the large potent 5.7L motor.

When I bought my Tundra in 08 the 4.7L motor only came with the 5 speed tranny. The 5.7L with the six speed provides the same or possibly better fuel economy when towing and essentially no transmission downshifting on small hills. I don't even use the tow haul mode when towing my TW except when I am in the mountains.

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Old 02-04-2011, 09:04 AM   #3
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I tow with a 2010 Silverado 1500 crew cab 5.3L gas with a six speed trani with the factory tow package. When I was shopping for it, I was very concerned that the 3.42 gear ratio was too high for towing my 25' Safari in the mountains. In the last three months I have been over the Appalachians a few times and from NC I am parked down in Florida now. With a full load I was really supprised how well it went over the mountains on I-40 going to Asheville. Going up it shifted two gears downward, but stayed at 55 mph without any problem. Going downhill the manual shift mode really saves the brakes, I hardly used the brakes on a 8% grade for several miles. In stop and go traffic in town I have no trouble starting off and keeping up with other traffic. Normal tow-driving in the country it gets 11 to 12 mpg at 55 to 60 mph. If I set the cruise control at 65 to 70+ on the interstate it drops down to around 10 mpg. It gets about 18 mpg not towing.

I am really happy with my truck-trailer combo!

I have found that I do not need the tow haul mode..
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Old 02-04-2011, 10:53 AM   #4
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We all know 6 speeds transmissions are better for towing, and about everything else, including reliability. In thinking about them, it seems to me that rearend gear ratio is now much less of a concern because of all the gears. I would think 1st gear in a 6 speed is lower than 1st in a 4 speed. What you guys think?
Yup, multi-speed transmissions -- computer-controlled with lockup converters -- have finally made calculations about rear end gearing/tire height/engine power band a moot subject.

The possible exception are those towing constantly at the upper limit in hot and mountainous terrain. Both conditions apply, not either/or. Always extra-heavy, and always in mountains. And it's only a possibility.

6,7,8 speed automatics keep the engine rpm at the "sweet spot" for power production. Computer-controlled engines and shift patterns make the learning curve of the old days moot as well. Empty or heavily loaded it's now pretty well past impossible to outguess the factory drivetrain (except for those with ghetto wheel/tire combinations and junior mountain man offroad lifts and tires; both of which are only about ego).

Used to be a purpose-built vehicle needed tire height nailed first, then rear gears and convertor stall speed. Then compression ratio and camshaft; and in that order. That was about the only way to get around the "all purpose" factory setups. What a guy in south Florida needed was different from another in central Colorado. With flattened torque curves (90% of TQ available across a vast rpm range) these new transmissions make possible nearly ideal power production.

It would be nearly beside the point -- beyond tire tread/casing design -- to try and circumvent what the factory can do now.

All of this is to the good. Means the driver can focus on bettering his skill behind the wheel. Some aftermarket dash gauges can now show real-time engine percentage use, THAT would be a useful addition to see how well I am using potential power at the lowest overall cost.

But if vehicle enthusiast forums are any judge there is still the desire to send money to strangers for a "kit", a "chip", a "tuner" to relieve the driver of responsibility. And shorten vehicle life, in general. (Despite those defeating emissions parameters to increase power or fuel mileage there is no guarantee of extended vehicle life adhering). There's a strong correlation here with the sheeple deathly afraid to ascend a mountain pass at 35-mph . . what they should worry over is coming down the other side. ("Ah got ma deezul, but I doan need no faincy hitch or disc brakes on a trailer".)

In short, the "end run" around factory parameters today is a dead end (with the possible exception of better fluids, filtration and shortened intervals on same).

.
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Old 02-04-2011, 12:14 PM   #5
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REDNAX, you mention 6,7, & 8 speed automatic transmissions. Out of curiosity, who's got an 8 speed.

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Old 02-04-2011, 12:32 PM   #6
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REDNAX, you mention 6,7, & 8 speed automatic transmissions. Out of curiosity, who's got an 8 speed.

Brian
I'l input here. I only know of a couple European mfrs and I think one Japnese mfr with 8 speeds right now. BUT,watch for them coming in a truck near you within the next couple years. Remember the 2016 CAFE regs?
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Old 02-04-2011, 01:16 PM   #7
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Auto manufacturers are thinking about this and Lexus may already have it.

Chrysler Announces Shift to ZF 8HP Eight-Speed Automatic Transmission - PickupTrucks.com News
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Old 02-04-2011, 01:17 PM   #8
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Just a Thought

A military Hummer 1 has tremendous torque at the wheels due to the axles having gear reduction AT each wheel hub. This reduces the torque stress on the transmission, transfer case, differentials and axles.

While pickup trucks donít have reduction gears at the wheel hubs, the next best thing would be to have low geared differentials and relatively small tires to approximate the Hummer 1 while the 6+ speed transmission with over drive will compensate for the low geared drive train. There would be less stress on the drive train, albeit with more revolutions.
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Old 02-04-2011, 04:10 PM   #9
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I was doing some comparisons recently. The numbers under the gear is the effective ratio for that gear * diff ratio. Since I can't get the format right in the post editor, I'll just use a screen shot.
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Old 02-04-2011, 04:15 PM   #10
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Drove tractor trailers for too many years. 10 speed was good. 13 was better. 18 was great.
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Old 02-05-2011, 06:23 AM   #11
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Drove tractor trailers for too many years. 10 speed was good. 13 was better. 18 was great.
Naw, 10 wasn't enough, 13 was fine, and 18 was work . . . .
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Old 02-05-2011, 06:44 AM   #12
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Naw, 10 wasn't enough, 13 was fine, and 18 was work . . . .
Yeah, but its only a memory now. Sal.
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Old 02-05-2011, 06:49 AM   #13
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Yeah, but its only a memory now. Sal.
Memory improves all sorts of things: I was never above 60k, had 500-HP in a long nose KW, and it was cruise-control Interstate all the way . . with a 15 mph tailwind. And no hills.
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Old 02-05-2011, 09:28 AM   #14
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Rednax- I agree with your overall assessment in post #4.

Moosetags- The new VW Touareg has an 8 speed trans and a tow rating of 7,700 lbs. The TD gets 28 mpg on the highway and provides a max torque of about 400 lb-ft as I recall. I would say this would make a great TV for any AS that weighs less than about 5,000 lbs. The TD is expensive though, 50K. I am going to put this on my wish list.

newroswell- Thanks for the table. I wondered how my Tundra ratios compared to other trucks.

Dan
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