Automatic VS Manual Transmission

[JDgreen227]

I would like to have a technical conversation about modern automatic transmissions and why more and more heavy duty trucks are only available with automatics.

I know, there are lots of people who do not know how to drive a manual, or just dont feel like shifting gears becasue it interferes with their cell phone use, smoking, eating, or whatever else they do while driving. Manufactures offer what people want.

My question is: What technical advantage do automatic transmissions offer for heavy towing?

I would say torque multiplication and less shock load on the driveline. I drove medium duty trucks for a living for close to 30 years, and about 1982 our fleet began ordering new trucks with automatics. I talked with the mechanics who worked on the trucks, and they told me one of the main reasons for the switch was because novice drivers were less apt to overspeed or lug the engines when having an automatic transmission. Our heaviest straight trucks used a 5+2 manual combination and many of the drivers simply didn't want to learn how to shift them properly.

 

[Dmace]

Automatics allow more "off-the-line" pull due to the torque converter allowing the engine to raise rpms and make more power before moving due to slippage in the torque converter. This also creates heat which is an automatics worst enemy. Once it's locked, thats another story but that is only at higher speeds in most trucks. Also with the torque convertor, autos can run taller gearing that may stall a manual from the start.

Manuals give simplicity, longevity and more power to the ground once moving. They also give you the option to hold gears for hills both in accelerating and braking but new autos with tow/haul and Electronic Range Selection now offer that as well.

I love rowing through the gears, especially in a diesel truck but if towing was my main use, an auto it would be...

 

[Raspy]

From a fleet owners point of view, the auto can be driven by less qualified drivers, all you have to do to go is step on the loud pedal. As mentioned, there is less lugging and less driveline stress. Autos can be better at starting out on hills and for backing, if the gearing is right.

But a manual is golden once rolling and especially in the mountains. They are more efficient and never hunt for gears. So you can back off the throttle and not have it upshift, then downshift when you step on it a bit. You can hold back and pull, and hold back and pull, without the trans over thinking and over responding.

In my Dodge Cummins with an auto, I installed a mystery switch that manually locks the torque converter. I can hold it in 2nd, 3rd or 4th where it cannot shift. This "simulates" (somewhat) a stick in the mountains and works reasonably well. The tranny becomes more efficient and the engine is directly connected to the ground.

 

[RoyJackson]

But a manual is golden once rolling and especially in the mountains. They are more efficient and never hunt for gears. So you can back off the throttle and not have it upshift, then downshift when you step on it a bit. You can hold back and pull, and hold back and pull, without the trans over thinking and over responding.

Bolded text puts me in mind of a relatively recent incident...

The truck was a 2005 Nissan Frontier with the newer (and much more powerful) V-6 and a 6 speed manual.
A co-worker I I were driving west on the PA Turnpike to a supplier in Buffalo, NY.
We're cruising at 70, cruise control on.
The PA Turnpike goes over the Appalachian Mountains and we're merrily speeding along...and dropping a bit of speed...and dropping a bit of speed...until the truck was shuddering a bit.
Yep...you know I forgot to downshift going up those slopes!

So, a manual tranny truck and cruise control aren't necessarily a good combination when the operator loses awareness!

 

[Reg]

I would like to have a technical conversation about modern automatic transmissions and why more and more heavy duty trucks are only available with automatics.

I know, there are lots of people who do not know how to drive a manual, or just dont feel like shifting gears becasue it interferes with their cell phone use, smoking, eating, or whatever else they do while driving. Manufactures offer what people want.

My question is: What technical advantage do automatic transmissions offer for heavy towing?

Well, one "TECHNICAL" advantage is that less skill is required in the operator.
Don't discount this TOO much, for the individual it can be an individual choice, for a fleet manager the RANGE of skills has to be considered, particularly the low end of that range.
Once locked up a modern torque converter loses very little in efficiency to slip.
I can back up a 40 ft trailer at 15 MPH, as long as I get a good starting shot at it - around curves, not so well - and not so fast (-:

I tow horses, I really CAN drive a manual trans very, very smoothly without having to concentrate a great deal.
I don't smoke, yak on a cell, suck coffee cups, text, eat, or do any of the other distracting practices, I take driving very seriously, but if/when I miss a gear it is still a miss and can be a jolt to the four legged "pets" back there.
{Yeah, they're "Pets" any way you cut it}

Then there is the "What if I am at a show and have an emergency need to attend to a horse ?" Ya just KNOW my rig will be the ONE rig that needs to be moved, like NOW !
90+% chance that the one person who can handle a 40 ft trailer can't also handle a manual trans (-:
Hard enough to find anyone who can handle horses AND trucks/trailers (-:

 

[BXRICK]

Mostly stuff already stated one way or another here...
I was raised on manuals.
When I started driving pickups, however, I always heard - "Don't buy a used truck with a manual that has plowed driveways." It's just too hard on the clutches.
I've driven one ever since - it's just easier, I guess.

 

[strum456]

To summarize:

Manual Transmissions:
1. Are more efficient at transferring torque to the ground, which produces more power at the wheels and increases fuel efficiency.
2. Provide better engine braking, due to a direct connection between the engine and transmission
3. Are more reliable and are cheaper to maintain.
4. Do not search for gears on hills.
5. Can be used to start the engine in the case of starting system failure.
6. Keep drivers more in tune to what is going on.


Automatic Transmissions:
1. Multiply torque for starting out
2. Prevent lugging
3. Reduce driveline shock
4. Require less skill to operate


Did I miss anything?

 

[JDgreen227]

To summarize:

Manual Transmissions:
1. Are more efficient at transferring torque to the ground, which produces more power at the wheels and increases fuel efficiency.
2. Provide better engine braking, due to a direct connection between the engine and transmission
3. Are more reliable and are cheaper to maintain.
4. Do not search for gears on hills.
5. Can be used to start the engine in the case of starting system failure.
6. Keep drivers more in tune to what is going on.


Automatic Transmissions:
1. Multiply torque for starting out
2. Prevent lugging
3. Reduce driveline shock
4. Require less skill to operate


Did I miss anything?

Sticks may be more reliable and cheaper to maintain, with one exception: You didn't mention anything about clutches. It would be interesting to compare the overall costs of the two types if you factored in clutch replacement. Witness my '53 Jubilee tractor, still has OEM transmission but is now on it's third or fourth clutch.

 

[frischtr]

Sticks may be more reliable and cheaper to maintain, with one exception: You didn't mention anything about clutches. It would be interesting to compare the overall costs of the two types if you factored in clutch replacement. Witness my '53 Jubilee tractor, still has OEM transmission but is now on it's third or fourth clutch.

Clutches aren't that expensive... The stock replacement clutch for my NV5600 is under $275. And that's for a diesel... Labor is the kicker if you aren't doing it yourself, but then slush-box repair isn't cheap either. Clutches last a looooong time if you aren't doing boosted launches and ridiculous amounts of towing and not treating it properly. If you are doing those things, get an upgraded clutch once and be done with it...

 

[tcartwri]

Sticks may be more reliable and cheaper to maintain, with one exception: You didn't mention anything about clutches. It would be interesting to compare the overall costs of the two types if you factored in clutch replacement. Witness my '53 Jubilee tractor, still has OEM transmission but is now on it's third or fourth clutch.

You almost never use the clutch in a heavy truck, so they last a lot longer than you would think. A good driver would never need a clutch replaced over the lifetime of the truck.