A continuesly variable shift transmission is the best for effeciency and wear. Until they become mainstream, gears are where it is at.

Buses are nearly all automatics now because it is hard to find a bus driver that actually knows how to shift. Trucks are going the same way...which is good and bad. If a said person doesn't know how to shift a truck...what are the chances they can do everything else required?

I work at a trucking company and I see the kinds of people that apply (and are hired) every day. There isn't a single automatic truck in our fleet, most ranging from 9-13 speeds, so I can't really comment on this, but I can see it as an issue.

 

I guess the younger among us like manuals becuase they make it "feel" stronger. You can kick yourself in the pants by mishandling the clutch and slamming the shifter as though your life depended on it. 30 years ago, I would probably feel the same way. But modern automatics can provided just as efficient delivery and fuel economy as the manuals. Electronic instead of hydraulic control, locking converters, and better cooling & lube properties have made them the choice for heavy work. I just rebuilt my 1977 C6 in the garage. It is a fun and rewarding project for those with the tools and figure-it-out-ability to make it happen.

 

Although not as heavy as a loaded semi, you won't find many Fire Service Apparatus outfitted with standard transmissions. High-volume water pumps depend on the automatic transmission to drive them; I can't think of a recent model that makes use of manual trannys.

 

I have towed extensively with both. A modern 4 speed automatic with locking torque converter will closely mirror the manual's ratios. And with comperable ratios the automatic is a better transmission to tow with because the torque converter keeps the engine at or near peak torque more often than a manual can. Therefore, an automatic is a better transmission for towing as it delievers more power more of the time than a manual.

In practice, it does take more skill to properly use a manual under heavy loads. Note that 18 wheelers primarily use manual transmissions but as technology improves automatics will replace manuals in commercial trucks. This is because the automatic will improve fuel mileage and load capacity for a given engine.

Steve
'95 Clubwagon XLT

 

Geez. Reading this makes me wonder why we even have manual trannies at all anymore? Come on guys, be realistic here. Yes, while an auto's working right it will perform very well, possibly towing better than a manual, but will not get as good gas mileage cruising. Todays pickup size automatics will not last half the lifespan of a manual under heavy use and they can be 10 fold the price to rebuild. An old 3 speed auto is a very simple machine and not much of a challenge for anyone with a slight mechanical inclination to rebuild. On the other hand, a modern 4 or 5 speed electronic transmission is mind blowingly complicated and virtually impossible for the average mechanic to work on.

It comes down to personal preferrence, but my experience has been that those that prefer manuals are by far and away better and more skilled drivers than those that prefer autos.

Not intended as a put-down to those automatic lovers out there. I have friends that just aren't coordinated enough to drive a stick. They really make it look difficult and tear up the vehicle.

 

it is also a proven fact that an auto will use more power to turn than a standard.

 

Not true. At cruise an OD automatic with locking torque converter is just as efficient as a manual with the same gear ratio in overdrive. The locking torque converter clutch eliminates the converters slip and therefore the inefficiency.

What that means is that the modern OD automatic, in OD at criuse with the torque converter clutch applied has the crankshaft of the motor mechanically locked to the OD gear ratio just as it is in a manual. This isn't my opinion its fact.

I prefer using a manual in my sports cars and racing cars. They are more fun and allow a skilled driver more control over the vehicle. But that isn't towing. I prefer to tow with an automatic because it works better. I towed with manuals for a couple of decades when my family had a horse farm. I grew up driving an old F250 4 speed. I don't mind towing with a manual, I am good at it. I have had a modern F350 with a ZF 5 speed and comperable trucks with autos and now my little van with its auto. Autos tow better.

Nor can you claim that a manual is cheaper than an automatic to overhaul. I have done plenty of big manuals in 3/4 and 1 ton pickups. The ZF and NP4500s used in Fords/Dodges/GMs are expensive if you have to start replacing hard parts. And they don't always last _that_ much longer.

Steve
'95 Clubwagon XLT

 

Proven by who?

I don't see how that can be.

I have a lot of experience dyno'ing cars and know what kinds of powertrain losses you can expect from different driveline configurations and I never saw any data that would support that claim.

I also know that auto manufacturers are crazy about parasitic losses and wouldn't put up with an automatic transmission that had more loss than a manual.

Steve
'95 Clubwagon XLT

 

Why do you think AT has less parasitiic losses? Even in OD, the pump has to work and maintain pressure, and that's one major source of a loss.

 

All things being equal, including driver tendencies, and automatic will not get the gas mileage that a manual will. You can see that in just about any application, but it's especially apparent in trucks.

An auto will tend to keep the engine at a particular speed, but with the powerband in today's EFI engines, who cares? The powerband is typically at least 1000 rpms anyway.

I know that an automatic is not as efficient as a manual. If the mileage argument isn't strong enough, then look at the tachometer of an automatic while you're accelerating. You'll notice that the engine RPM is more closely connected to your foot than the speed of the truck. So it seems reasonable to me that automatics just aren't as efficient.

I would rather have a T-18 or an NP435 for towing, but that's just my opinion.

 

Guys, the pump turns at engine rpm, at cruise that's hardly a load. And planetary gears have less parasitic loss than a traditional in-line transmission transfer arrangement. The only way a manual will have less parasitic loss is in "direct" which is 4th gear in most all 5 speed overdrives. In 4th, the output shaft is locked directly to the input shaft. The transfer gear is out of the loop. But the transfer gear still has to be turned by the inputshaft as its is always in contact. Turning that transfer gear is nearly as much draw as the pump.

"Look at the tach" Really? At cruise, with the converter locked it doesn't slip. RPM isn't closely connected to your foot, it _is_ directly connected to the road speed, exactly as it is in a manual. Once the converter is unlocked, as in acceleration to cruise speed, it behaves as you described. However, that actually helps efficiency. The torque converter allows the engine to operate almost continuously at or near its torque peak. The engine is more efficient at that point in the rpm range. So if you want to compare fuel used to an amount of work done, the automatic wins every time.

If you don't want to believe me you might want to read what the SAE has to say about it. There are plenty of engineering papers published there on the subject of the efficiency of automatics vs manuals.

http://www.sae.org

Steve
'95 Clubwagon XLT

 

Ok - just one question then.

Why is every manual transmission equipped vehicle rated by the EPA to get better mileage than an identical vehicle with an automatic transmission?

 

And tell me again how accurate the EPA's ratings are?

If its work done vs fuel used, the automatic wins. I didn't say it, a powertrain engineer in GM's Allison division did. I just read his paper, along with others. This was a paper specifically on commercial trucks.

Don't shoot the messenger.

Do you guys have anything more than anicdotal evidence?

Steve
'95 Clubwagon XLT

 

This has turned into quite the debate. One thing to pint out is the simplicity and reliability of a manual. A gear shaft and a counter shaft. That's it! 200k from an auto is good. 200k from a manual and something went wrong.

Also, I have yet to see an auto dominate Indy.

Mike

 

I figured you were going to say that about the EPA ratings. No, they don't translate well into the real world, but for purposes of this discussion (comparing two vehicles side by side) I think they work quite well.

There are a number of factors in an EPA fuel mileage test that tend to inflate the numbers. The test is done on a dyno, the A/C isn't on, etc.

You're arguing that an automatic is more fuel efficient than a manual - so which one of the non-real-world factors in the EPA test negatively impacts automatic transmissions?

If you're going to make the claim that the tests don't reflect the real world, you should be able to explain why.

I quoted that fragment because I'm wondering if that statement applies only to Allison trannies, or to all automatic transmissions in general?