Automatic Transmission Function - A

[DieselDood]

Ok guys.....there is always someone looking for advise on an automatic tranmission. Now I'm not going to say go with anyone. All I'm gonna do is give you a breif run down of operation. Hopefully this clears up some things.

Torque Converter: The torque converter has a fluid coupling. To get an idea of how this operates it is like taking 2 fans and facing them towards eachother. Now turn one fan on. The other fan will turn due to the air movement. A converter works in a smilar fashion. The Different companies out there have found a way to make the second, non powered fan spin at a higher rate. They do this with the Stator. The stator changes the direction of the air flow. The stator dictates Stall Speed and converter effency.

Stall Speed: Remember when you were a kid...maybe you still are....And you put your left foot on the brake, and your right on the gas to do a big old smokey burn out? Well now do the same thing, but don't let the tires break loose. The point where the engine revs to but does nothing. That is the Stall Speed. The stall speed is done within the converter with the Stator.

Planetary Gearset: A planetary gearset is a very strong gearset. It has 3 main parts. The annulus gear, the the planetary carrier and the sun gear. To explain this, think of hellical cut gear in the center, around it you have 3 smaller hellical cut gears and outside of that you have the Annulus gear. This looks more like a drum, inside it is where the small planetary gears run.

Clutches and Bands: The various clutches in our transmission are slightly different than most other transmissions. In the Overdrive(rear section) of our transmission there is a VERY large spring that holds the Direct clutch. The Direct clutch is applied even when the truck is sitting still. The Direct Clutch is used for 1st, 2nd, 3rd, and reverse. The only time the Direct Clutch is not applied is in 4th gear.

Overrun clutch and Overrun sprag is a simple one way clutch. They are 2 different assemblies that do the same job, but in different areas of the transmission The Overrun Clutch is in the rear of the main case of the transmission, it is used for 1st, manual 1 and manual 2. The Overrun Sprag is used in all forward gears in our transmission. It is located in the overdrive section.

The Bands: The Front band is applied in 2nd gear and 2nd gear Manual selection only. The Rear band is applied in Reverse and Manual 1st only. It is used in Manual first for engine braking.

Reverse: The Front Clutch, Rear Band and the Direct Clutch are applied
First: The Rear Clutch, the Overrun clutch, the Direct Clutch, and the Overrun Sprag
Second: Front Band, Rear Clutch, Direct Clutch and the Overrun Sprag
Third: Front Clutch, Rear Clutch, Direct Clutch and the Overrun Sprag
Fourth: Front Clutch, Rear Clutch, and Unapplies the Direct clutch and applies the Overdrive Clutch.

Manual First: Same as above, but applies the rear band for engine braking.
Manual Second: Same as above.


I hope this helps you guys understand the function of the transmission a little better.

DD

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Excellent info .........thanks fer the tune up, my understanding of auto knowledge needed this

So can you add to this as far as what auto tranny upgrades do and how they effect the overall package in bullet proofing?

Cheers, Kevin

[Tom05]

Great information DD!!

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[DieselDood]

Upgrades:

As we all know, the CTD's can produce WAY more power than they were sold as. At some point something has to give.

Most of the time it's the Converter Clutch in our trucks. How does that work?

Well the guys with a handshaker have instant "lock-up." Our trucks with the automatic have the best of both worlds. The fluid multiplication and the Locking abilty of a manual.

Like I said above, the converter works with the 2 fan principal. Obviously there is some "slippage" there. The fans will never turn at at 1:1 ratio. So, to make the transmission more efficient they add a clutch to the system. This now gives us the 1:1 ratio, just like a manual.

No big deal....right? Sorry....just like the guys with a manual transmission, when they start Bombing, the clutch starts to slip. We have the same issue. So what do they do? Add more clutch material for one. Another way is to use multiple clutches.

Manual clutches they can add more pressure plate, pressure. A stock automatic has....for simplicity sake, 100psi on that clutch. Now if you add more clutches, lets say a tripple disc converter, you've now more than doubled your holding power within the converter clutch.

Now no more slippage!

DD

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[TurboTweaker]

now if your going to tripple your holding power of the convertor were does the power go next? good qestion i ask. the convertor is linked to the trans with the Input shaft and hub. they are know to break under power, i would know i have broke 2 (Thanks to diesel dood we got the truck back on the road in a day). so DD what else are you holding back from the conversation?

The Fat Kid
Andy

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2007 DHRA Quick Diesel Indy Champ Triple D Performance made it happen

[DieselDood]

Ahh yes the input shaft and hub.

Weak pieces at best. In my opinion (myself included) over 350hp on these trucks is taking a chance without billet parts. A heavy foot and a bump in the road can end up with a tow bill.

What happens? There are 2 ways these brake.

The first is the obvious. It twists off. Usually they brake off inside the converter. The converter has to be cut open and the shaft removed. :fist:

The second....we'll have to use our immagination. Remember the push pops that you got as a kid (or still do)? The little stick with the wheel on the end. That's basically how the input shaft and hub are. The shaft is splined into the hub and held in with a snap ring. The Hub is splined on the outside to accept the front clutch. I've seen 3 of these brake and they have all shown the same signs. There are lubricating and bleed off holes in that hub. It appears to me as the splines walk up onto eachother causing a hairline fracture to those lubricating and bleed off holes. The hairline crack spreads and now allows the hub to seperate. The splines slip and before you know it, it's broken. Now the stick spins inside the wheel and you don't go anywhere.

In any case, the transmission has to be removed, and the front half has to be basically gone through and cleaned up. So far out of the shafts I've seen, the seals have been ok. But that doesn't mean they all will be. There are metal shavings EVERYWHERE in there. A good cleaning is DEFINATLY needed. If one of those shavings gets past the filter, you may have catastrophic transmission damage.

DD

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Last edited by DieselDood : 01-29-2006 at 06:10 PM.

[ndurbin]

Is the hub billet or just the shaft or both when ya upgrade to billet parts?

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1994 2500 Reg. Cab 4x4 SLT Laramie CTD/DTT 330hp/765trq - Work Truck
2002 Ford F150 Super Cab - Daily Driver

[DieselDood]

Originally Posted by ndurbin

Is the hub billet or just the shaft or both when ya upgrade to billet parts?

When you buy the Billet parts, the Shaft and the hub are both Billet. Although the snap ring isn't.

DD

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[DieselDood]

Let me know what you guys would like me to expand on. I can go more indepth on the function of the transmission if you'd like.

DD

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[ndurbin]

Can ya expand on some of the the changes made to the valve bodies?

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1994 2500 Reg. Cab 4x4 SLT Laramie CTD/DTT 330hp/765trq - Work Truck
2002 Ford F150 Super Cab - Daily Driver

[BigD]

Yes! Keep going. The transmission is my next bomb. So I'd like as much info as possible!

Thanks,

D

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2007 Ram2500 Laramie Mega Cab 6.7 auto 4X4. N-Fab nerf bars, pre-runner, rear runner 2" level kit, 20's XD795 Hoss - Black. BFG's 305/55/20 Hella 4000 lights. Smoked cab lenses. I'm done with the outside!

[DieselDood]

Originally Posted by ndurbin

Can ya expand on some of the the changes made to the valve bodies?

While I can't give away any secrets, especially ones I don't know. (IE DTT, Suncoast, or Goerends VB setups) I can talk in some broad generalizations.

The mystery in how an automatic transmission shifts is in the valve body. How does it work?



The Basics:

Remember this is also basic hydraulics. If there is fluid in, lets say a coke bottle with the bottom cut out and put it nose down. Then you put it in a bucket filled with fluid. Now put the bottle 3/4 to the bottom of the bucket. Due to the neck of the bottle, only so much fluid can get in at a given time. Open up that hole and more can fill the coke bottle. Even when pressure is applied only so much can fit through that opening.

There are 2 sides to a valve body. In the middle is the seperator plate. In each side of the valve body there is a maze of passages, some with shuttle valves, some with control valves, some with solonoids. Each of the passages in the maze has a different purpose.

The seperator plate has holes for some passages. Some are the size of the "maze" others are restricted. In some places there are check balls that will block a larger hole once the clutch is applied, and use a smaller hole to keep the clutch applied. To change how the transmission shifts compaines will change springs for some of the shuttle valves making them easier or harder to move. Depending on the shuttle valve, this can change shift timing and on some transmissions the firmness of the shift. Some will also open up the seperator plate in certian areas to allow more fluid flow. Now the fluid may more easily pass through the seperator plate, causing a more firm shift.

Another thing that his always discussed. Line pressure. Lets say you have 100psi. Now you bump the pressure to 130psi. Which will have more holding power? 130psi of course. Like I said before the passages may not become much larger, BUT with a hydraulic system if you apply pressure at one end of a garden hose, you will have the same pressure anywhere within that hose. So the line pressure is pretty simple. Up the line pressure, you have more holding power.

Utoh! We added pressure, now the fluid is moving faster through out the valve body!?! This is where the mystery of springs, and the various oriface sizes comes into play.

All the companies out there use similar pressures. Each has their own idea of how a transmission should shift. Each of these magicians has found the "right" combination for what they, and their customers are looking for. I like smooth shifts. Stephan Kondolay likes firm shifts. Neither are right or wrong. They accomplish the same thing.

DD

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Last edited by DieselDood : 02-01-2006 at 03:17 PM.