auto tranny "torque doubling effect"? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 04-20-2008
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auto tranny "torque doubling effect"?

What is that? i was reading some comments on youtube and a guy said thats an advantage of an auto tranny. how does it happen? what is actually happening?
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Old 04-20-2008
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It's a hydraulic effect which happens in the torque converter (which is where it gets it's name).

You can find some nice animated tutorials online, and I'm probably not going to do a great job explaining it off the top of my head, but I'll give it a try.

Basically, the torque converter is a fluid filled metal "toroid" which consists of two sets of vanes. One set is attached to the toroid shell itself, the other is a "rotor" connected to the input shaft going into the transmission. The two sets of vanes don't touch but are very close to one another. The entire structure is filled with transmission fluid, about 3 to 5 quarts or so in a Ranger.

The shell bolts to the "flexplate" (basically the flywheel in a manual vehicle) and turns with the engine and the rotor goes to the transmission.

As the shell turns, it creates rotating forces in the fluid which push against the rotor. When the rotor is immobilzed (as it is in Park or when the vehicle is stopped) the energy imparted by the shell is dissapated as heat. At idle it's not so much energy, so it's not a big problem to get rid of the heat. This allows the automatic transmission to be constantly connected to the engine, and allow smooth takeoffs without a "bump" when you hit the gas.

As the shell speed increases, so do the forces on the rotor and if the vehicle can move this torque goes through the transmission to the wheels.

One of the interesting aspects of it's operation is the torque multiplying effect, which comes at the expense of speed. The force exhibited against the rotor can be up to 2 times torque being applied to the shell -- but the speed of the rotor in this case will be 1/2 that of the shell.

However, "perfect" multiplication doesn't happen because there are always frictional losses in the fluid coupling, dissapated as heat.

That's one of the advantages of an automatic that makes it better for towing for instance -- it can "break away" a large load much more smoothly and with less wear and drivetrain shock than a manual. If you look at your Ranger owners manual, you'll find this reflected in the towing capacity chart: automatics are rated higher.

But the frictional losses in the torque converters moving fluid are one of the main reasons an automatic gets worse mileage than a manual. Particularly at highway speeds where the rotational speed is well above idle for sustained periods.

That's why they made "lock up" torque converters which have an internal clutch which locks the shell to the rotor. This allows the highway mileage of an automatic in lock-up mode to come close to that of a manual.

Hope that helps, but check out some online explanations for a better and probably more accurate rendition.
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Old 04-20-2008
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yeah i understood how an automatic worked, like with the torque converter and smoother shifting and that stuff and the fluid and how it shifted, i just didnt quite understand the torque doubling effect. thanks for explaing it all though. it made a lot of sense that way. problably more than if you just tried to explain the doubling effect without how the whole thing works
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Old 04-20-2008
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No problem, Nick. I didn't know how much you did or didn't know and being who I am it's like: why use few words when a lot will do?
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Old 04-20-2008
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Originally Posted by n3elz View Post
...One of the interesting aspects of it's operation is the torque multiplying effect, which comes at the expense of speed. The force exhibited against the rotor can be up to 2 times torque being applied to the shell -- but the speed of the rotor in this case will be 1/2 that of the shell.
Good job. That's a fairly loose but reasonable explanation of a complicated system. Since it was the torque multiplication mode that was originally asked, I'd like to add that a well designed torque converter (including factory ones) are generally at or above 2:1 multiplication. This is also why most of the drag cars pulling wheelstands are auto equipped. You can rev a manual and dump the clutch to throw a lot of energy to the drivetrain momentarily, but with an auto, the greater energy continues due to this effect.

Second, the curved-bladed stator that rides between the two 'halves' is primarily responsible for the torque multiplication at stall. It redirects the fluid on the back of the vanes giving it more push (energy transfer) than just the spinning fluid would give. The stator is the invention that made the auto tranny truly practical. It's not a 'gear reduction' situation and the 1/2 speed difference is not typical, but rather it's the built-in 'slippage' that allows the engine to make more power (and the stator to multiply it) while the vehicle remains slow that permits the greater torque and load capability. It's also why auto tranny off-roaders don't need gears as deep as the manual tranny V's. Just that advantage alone can give you better mileage on the road between mudholes in-spite of the small percentage of cruise efficiency lost.

FWIW,
David
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Old 04-20-2008
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Thanks, David! I could not have offered that explanation because I don't understand it to that depth -- hence the "loose" explanation, lol. I understand the rest of the innards of the trans pretty well and I just rebuilt my first auto on my truck -- something I would not have tried just a few years ago. Works great, fortunately...

But I of course didn't have the TC open, and I still wouldn't have understood it at that level. Fluid dynamics is an interesting science for sure. Are you an engineer or just a well educated enthusiast?
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Old 04-20-2008
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That.. was actually a fantastic read, I was never to keen on why an automatic could haul so much more then a manual.. minus the clutch and such. But thanks for the read on that, its always good information to know!
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Old 04-21-2008
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Originally Posted by n3elz View Post

That's why they made "lock up" torque converters which have an internal clutch which locks the shell to the rotor. This allows the highway mileage of an automatic in lock-up mode to come close to that of a manual.
they make those for the ranger possibly? or you mean it already has it?
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Old 04-21-2008
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Wow that was interesting! Learn something new everyday!
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Old 04-21-2008
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they make those for the ranger possibly? or you mean it already has it?

Ranger's have them already. Count your shifts and watch your tach. Almost looks like 6th shift on most driving. Generally, you have to be more-or-less off the gas and "cruising" before it kicks in.

It has nothing to do with "overdrive" either. You can cancel overdrive and still get lockup in 4th gear instead in a 5 speed auto.
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Old 04-21-2008
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yeah I read about that in the manual something about tapping the throttle twice gets it to downshift... or something like that
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Old 04-25-2008
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The lockup came around awhile back if gets rid of the slippage in the converter. Every torque converter now days has it. Also most of the time the same truck with an automatic will have higher gear ratio than the truck with a manual because of the torque multiplication. All the torque converter consist of is a turbine and a impellor which slings fluid to the other with the stator directing it. The internals of a converter is quite amazing. The big allisons in the 5 ton military trucks have convertors that can be taken apart. I learned alot when not sleepingin automatic trans class
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Old 04-25-2008
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Originally Posted by WowMike2001 View Post
That.. was actually a fantastic read, I was never to keen on why an automatic could haul so much more then a manual.. minus the clutch and such. But thanks for the read on that, its always good information to know!
Yeah thats not intirely true on most big trucks the manual transmission is higher rated , Normally by around 2-3k pounds . And to argue my point have you ever seen anything over an 2ton chassis with an auto tranny very rare .
And when have you seen an 18wheeler with an auto so yeah .

Another thing on the driveline stress issues multiple friends of mine do hotshotting (Contract towing of loads , normally oil feild suplies and heavy equipment ) and most all have dodge and fords only one of them runs an auto and he has had the most problems from his truck . And these are guys pulling 15-35K pounds of stuff DAILY .

So I kinda have problem understanding this , In fact the Ranger and mazda B series trucks are the first ones Ive been around whose manual trannys are weaker than there autos .
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Old 04-25-2008
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So it could be more a factor of the crappy 5 speed manuals? lol -- figures.
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Old 04-25-2008
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Not sure I know in my 96 dodge 3/4 ton book the manual was rated almost 2200k pounds more and it was a five speed , but the newer Dodges have the awesome Asin 6 speed manual , I drove my buddys you cant even use 1st if your not under a load its such a low gear , especaily when you lock it in 4lo .

Im not sure about the fullsize fords but I know there manual is stout too , one friend has a 97 3/4 ton super crew 4x4 7.3l and the other runs a newer V-10 4x4 crew and both are manuals and they never have problems .
And 4 have dodges 1 3/4 4x4 and the other 3 are 1 ton 4x4s 98 , 2004 , 2006 , and all but 1 is manual and my buddy who has the 04 dually cumins auto has more problems than all of them combined .

So I'm not sure . I understand the theory above , just not when compared at looking at what most vehicles manuals towing capicity contradicts it ya know . It is something I would like to find out more about though .
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Old 04-25-2008
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Originally Posted by n3elz View Post
So it could be more a factor of the crappy 5 speed manuals? lol -- figures.
Well as someone before me stated .
Our transmissions are made in France , guess thats why they give up so easy lol .
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Old 04-26-2008
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It is not the Ranger's transmission that limits the tow rating, it is the nature of a clutch and the available gearing. If the Ranger manual had a low enough overall launch gear, it could match the auto's tow rating. Of course, a first gear that would provide that multiplication would be useless for daily driving without a trailer.

Transmission and axles ratios being what they are, a clutched Ranger will not pass Ford's acceptance criteria for launch on a test hill when loaded to the auto's GCWR.

In this country, the Ranger is most often a commuter vehicle or light duty hauler. Ford is not going to build or source a 5- or 6-speed manual with creeper low for the few Ranger manual owners who want to tow 5000+ pounds. For those who want to tow the most with a Ranger, the 4.0L auto is the powertrain of choice.

Rangers are not the only ones. Explorers, Broncos and F-series also typically have higher tow ratings for the autos than the manuals.
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Old 04-26-2008
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Some of the 5 ton military trucks run the auto allison but thats about all. manuals are cheaper an require less maintanance.

When it comes to the older dodge auto it should be laughed at. The same automatic behind the 1/2 ton is behind the 1 ton. Dodge's old auto couldn't stand the power the cummins put out so thats why alot of the cummins were turned down so much. Program that truck and it fries the trans. The new dodge 6 speed auto is a great transmssion. Has alot of good reviews and I have not heard many complaints out of them. Also the new ford auto is a good trans also. Are you sure when you say 1st gear on your buddy's dodge manual your talking about actual first of LOW. Low is needed for pulling but i don't see you starting off in 2nd gear "which is actually 3rd gear" much.

Manuals are higher rated for towing because they are cheaper to maintain and and straight forward easier to work on. An auto requires solenoids and clutches after clutches after clutches but when it comes down to it a good automatic will outdo a good manual anyday. Most people don't like automatics cause they don't understand how they work and people don't like what they don't understand.

Hotshot trucks stay on the road so much an automatic wouldn't be a good choice. You have to remember an auto has to stay cool and be maintained. A hot shot truck is far from being maintained.
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Old 04-27-2008
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I understand all of that , What I was pointing out is everone on here looks at OUR transmissions and thinks its across the board and Autos are better than manuals I agree A GOOD PURPOSE BUILT auto will out perform a manual but there arent many out there .

Yes it is a low gear and you can start off in it unloaded but even the Fleet salesman told him if your not loaded start in second you really dont need it unless your trying to get a load off the line or starting up a really steep incline .

As far as the old auto in my 96 3/4 ton Dodge I was rated at around 9100 #s and on a monthly bassis I had to pull a 24ft trailer and tractor weighing in excess of 13,200#s and it never flinched did this for the 3 years I owned it till I totaled it . But I had a gas engine . Not the cummins And my buddy will be the first person to tell you he uses his truck far beyond what its rated for and as you said its not made for that sort of service .

And I dont expect ford to bring out a decent manual for the ranger I wouldnt dreem of even towing 5K in one of these trucks , its not set up for it . Not saying you cant but I know I wouldnt .
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Old 04-28-2008
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I do think auto's are better than manuals and there are many great automatic transmissions. They have came along way from what they used to be. There are so many advantages automatics have over manuals it's just the manuals are so simpler people love them.

So your saying he starts off in second gear? Meaning 1st gear on the shifter and transmission. Low is it's own gear since it's lower than 1st. It's only needed for starting up steep inclines and pulling loads. Thats what it's made for.

You gas motor did not put out the power to burn up the automatic in your truck but i'm sure that automatic was taking a beating from pulling such a load. The same trans is in 1/2 dodge's and i personally just got done pulling one apart and they are made of nothing. They are smaller than the 4l60e chevy 1/2 ton transmission.

I don't see ford building a better transmissionf or the ranger as it's not made for pulling and never was ment for. Thats just the people pulling way more than they are supposed to and the law will solve that very soon. Weight requirments are about to be put on trucks because of people hauling skidders with 3/4 trucks.
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Old 04-28-2008
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I think the right AUTO is better , and by right A purpose built transmission for towing if thats what your doing . But only just recently have the big 3 offered decent AUTO trannys for such aplications , That is the point im trying to convey here , in addtion to the fact the just because one transmission in one truck is stronger than the other does not mean there all like that . Even though thats the way it will be in a few more years .

ME personally if I was back in the market for a TOWING TRUCK I would still get a manual just because the new 6 speed auto has not been out long enough , where as the Cummins and manual transmission is time Proven design , That being said im sure in another year or so ill eat those words .

I cant remeber because its been almost 6 months since I climbed in it but if I remember corect on the shifter it goes as fallows L-2-3-4-5-6 . But Its the same on a guys jeep at work he has a 2005 Wrangler X 4.0 with six speed that reads 1-2-3-4-5-6 and he also does not have to start in first although he does most of time .
Im not sure if it answers the question you asked .
The only cars Ive ever used all six gears in were a WS6 Trans-AM , 05 LEM GTO 6.0 , and a Celica GT-S and thats because they were racing style transmissions .

I dont expect FORD to build a better transmission for towing its not what the ranger is made for Like I said I wouldnt pull more than 3K in it . But I would have like ford to built a little bit more reliable manual .

And the law should , I personally and my freinds have experiance moving loads , what scares me are these guys that gat a big truck for no good reason other than compensating for other things . And want to do what they see in the comercails and pull something like a tractor for the first couple of times not knowing how it affects their handling . I think to haul anything more than 8k you should have to take a SAFE DRIVING TEST and get a license . But thats just me .
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Old 05-07-2008
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Manuals are used in high-load towing vehicles because of maintainance. Fixing an auto equipped for a tractor-trailer setup would be a huge undertaking. Tractor-Trailers usually have more than 15 gear ratios to choose from (5 speed plus a 3 speed) and the trannies arent even syncronized. It is just a box of gears, nothing too difficult.

Drag racers use automatics because they are a perfect shift every time and it is much easier (and less destrictive) to load the driveline for launch.

Top fuel drag racers skip the tranny and run a single gear ratio, wearing the clutch to keep the wheels right before where they would brake traction untill the clutch is completely engaged....then agian they have the funds to rebuild the engine before every big race day so they sure have the money to burn through clutches like underwear.

I've gone well over the reccomended towing capacity in my B3000 5-speed. But it has 4.10's. The key is balencing the semi-tall 1st gear (for towing) with the clutch and throttle. Too much throttle puts too much wear on the clutch. Too much clutch and the engine stalls. Problem is most people arent apt to learn it, will rev to 2,000 and slowly release the clutch. This does a big number on the clutch and if the vehicle if used for towing often it will need a new clutch before the vehicle is out of warranty. Our Bayliner is just outside the towing capacity of my truck but just within the capacity of my mom's old Nissan. The nissan huffs and puffs to pull the boat around on the road and likes to bite back when pulling the boat out of the water. Short of pulling the boat out of the water the Mazda pulls it like it is hardly back there.
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