Automatic Transmissions and Torque Converters Explained

[slowcivic2k]

Please add comments or suggestions. If there is anything you would like to see added/reworded, post or PM me, and I will get right on it. EDITED: August 9, 2008 One area that a lot of people seem to fear and mostly misunderstand, is the automatic transmission. I'm going to attempt an explanation of these mystery boxes to the general base of Honda-Tech. This is a lot to swallow at first, so beware. You may have to read it a few times. Inside a basic automatic transmission are many standard parts, and some depending on the layout. (planetary, helical clutch pack type, CVT) A planetary gear set, or a set of standard helical gears can be used. I will focus on the basic mechanical methods, the electronic transmissions are much easier to understand, as solenoids control just about everything, making design excessively simple. The first area of the automatic to be discussed, is of course where power enters the transmission: the torque converter. This piece of equipment is what makes an automatic transmission work without stalling, and also provides additional torque to the transmission. In most cases it is around 1.5 to 2.0 times the engines torque output. We are going to discuss how below. As you can see from the picture above, there are five major parts in a modern torque converter, they are from top to bottom, the impeller/cover assembly (1) (also called a pump), stator (2), turbine (3), torque converter clutch (4), and the TCC apply housing/cover (5). The stator will be explained a bit later, but for now we will focus on a very basic 2 element (impeller/turbine only) converter. If you can imagine two fans side by side, and one of the fans blowing into the other, this is how a torque converter works, except it does this with an actual fluid. The air pushed off the blades of one fan, will strike the blades of the fan next to it and spin it. The impeller (first piece) is attached to the donut shape on the inside of the converter, and is driven by the engine as it is welded to the inside of the converter, which is bolted to a drive plate or flex plate. This part is not shown in the picture above, but is identical to the turbine. The job this part has is to propel ATF by using centrifugal force from the engines rotation to strike the opposing side, the turbine blades. The faster it spins, the more force it applies, which will also be discussed later. The turbine is the other set of blades opposite of the impeller, and is driven by the displaced oil from it. This piece is splined to the transmission input shaft and is driven by the impeller, this operates similar to a manual transmission clutch disc. The torque converter clutch is also affixed/splined to the turbine. Its function is to input power to the transmission. The stator is the third and is the middle piece. This component is the wonder of it all, and will be explained in great detail later. It's basic job is to redirect fluid from the turbine back to the impeller. The stator is normally splined to a support shaft (I in the picture below.) to keep it stationary and allow its one way clutch to work. The flex plate (or drive plate) flexes during torque multiplication, and is the result of the impeller pushing oil on the turbine and the stator pushing the same oil back into the impeller, causing the two to repel sightly, and the flex plate to flex in turn. It helps dampen the ride by allowing this movement to occur. Now how does this all work? The transmission oil pump is always driven by the engine, either through the torque converter snout tangs, (Red 6 in the torque converter picture.) or through an auxiliary shaft. (which would be III in the picture if it was shaft driven.) The shaft is not present on this one, but this is where it would be. It would have splines like the others. Pump oil will fill the torque converter up, and the fluid will be forced through the blades of the impeller due to centrifugal rotation of the converter via engine rotation. This fluid force is curved by the impeller blades to strike the blades of the turbine at a specific angle to provide sufficient power to turn the transmission. (When you order a performance converter, these angles will change to better suit power transfer.) Now its not done there, once the oil forces the turbine to turn, it has to go somewhere, and since the turbine is basically the opposite in design, it flows back downward towards the center. (just opposite of the impeller, which brings oil in from the center and throws it outward. If the turbine were allowed to exhaust its oil into the center uncontrolled, it would create a huge turbulence inside, and create vibrations and lots of heat. This is where the stator comes in. Its job is to redirect the fluid from the turbine, back into the impeller, which creates a pressure. This piece is only functional when the impeller and turbine are not turning the same speed, as the speed difference is what causes the turbulence. When the shafts are turning close to the same as one another, the stator freewheels, as both blades are turning similar enough for the turbine fluid to enter the impeller again, without the need to redirect it. The tags in this picture are WRONG, the turbine in this picture is the impeller, and the impeller in this picture is the turbine. This picture happens to illustrates fluid flow well. This video should help some of you out. Now lets make more sense out of all of this. There are two types of flow in a torque converter, vortex flow, and rotary flow. Vortex Flow is the flow of fluid through the blades when the two blade speeds are different, like the engine is turning 4500rpm (which is the speed of the impeller as well) and the transmission input shaft (turbine) is only turning 3000rpm. This causes turbulence and is where the stator does its job by redirecting the fluid back to the source, to multiply engine torque by creating pressure, which is just like a gear reduction, only it happens before power gets to the transmission. Rotary Flow is achieved when the two blades are turning at a similar speed to one another. At this point the stator's job is done, and is simply pushed along a one way clutch until a speed difference occurs again. Rotary flow produces almost no torque multiplication because the engine and transmission are turning at near the same speed, which would indicate cruising speeds or light throttle. The overall goal of the torque converter is to achieve rotary flow, by using vortex flow to get there. Usually in each gear, there is about 500rpm difference from when you let of the pedal, to full throttle. The RPM changes but the gear does not. This is the torque converter attempting to make extra torque to get the turbine up to engine speed faster. What is achieved: Vortex flow achieves additional torque by reapplying the turbine exhaust oil back into the impeller, placing pressure on it, and multiplying the apply force. Rotary flow achieves a near 1:1 ratio, where speed is needed, and torque is not. Once the blades are of similar speed, they can no longer produce torque since an object cannot turn faster with the same power applied to it than the source that supplied it without physical gearing, and even if it could, it would be counter productive since the impeller would lose its apply force, similar to starving an engine bearing of oil at high rpm. This concept does have a function, to slow the car down after letting off the gas. You can also think of the two flows in a gear type manner, Vortex being a reduction gear, like 2:1, and rotary being a direct drive gear, 1:1 or close to it. It is a change off, if rotary flow is high, vortex is low, if vortex flow is high, rotary is low. One of the common misconceptions with automatics is that the gearing is significantly taller. But when the torque converter also acts as a gear reduction, this makes complete sense. A typical manual transmission has a 3.25-3.75 first gear. A typical automatic has a 2.25-3.00 first gear plus the 1.5-2.0 reduction in the converter. The ratios vary, but don't be fooled, because the converter is never figured into the gearing on a spec sheet. Common questions: Why does my car creep forward while its in gear? It's because this is the converter at work, and in some cases, there is enough flow at idle to propel the car forward, sometimes there isn't. If you have a heavy load, it may not creep at all. Why do automatics get worse gas mileage? They will use more fuel because the impeller and turbine will never turn the same speed, since they are not mechanically connected, this results in wasted power, due to blade speed differences and an increase in torque as an end result. The lack of a mechanical connection creates the problem, and that is where the torque converter clutch comes in. What does a torque converter clutch do? This is the mechanical link used when rotary flow is high, to provide a direct 1:1 ratio for the best possible fuel mileage, without sacrificing acceleration and torque multiplication. Many people think their automatic is a 5 speed, but in fact it is a 4 speed, with a converter clutch, which will feel like a 5th gear shift when it locks. Simply pressing the gas or the brake will disengage it, and the rpm will jump up/down around 200-400rpm depending on the engine. Looking at the picture above, the TCC solenoid will apply oil pressure between the turbine and the TCC face, pressing the clutch onto the machine surface in the apply housing. This locks the turbine to the converter housing making it turn at engine speed. Most vehicles today have converter clutches that engage as early as second gear to minimize any loss. What is stall speed or stall RPM? Stall speed is a basic test that stresses the converter and clutches in a transmission to determine if there is a problem with either. The stall speed is the point of maximum torque multiplication, and there is a specification for almost every converter in each gear position. If stall RPM is low, an engine output problem could be indicated. If it is too high, a clutch may be slipping, (only if the RPM continues to rise and the car doesn't move) or there may be too much engine power, find a better converter. Just like a clutch disc for a performance car, converters need to be changed to suit the engines output. Some common problems can be caused by the torque converter, and can be hard to diagnose without the proper knowledge. If a car has a hard time accelerating from a stop, but will cruise normally, most likely the stator's one way clutch has failed. This means that the stator can rotate in both directions, instead of just one. If the clutch seizes, meaning it cannot turn either direction, the vehicle will take off normally, but the top speed of the vehicle will be severely impaired, usually it will not allow even the biggest vehicles to go any faster than 45mph. This can quickly destroy the transmission oil due to overheating, and possibly ruin the transmission. Comments and questions welcome. Modified by slowcivic2k at 9:14 PM 8/21/2008

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[slowcivic2k]

4T60E Transmission, a staple GM Transmission.


Now on to the actual transmission. The case of the transmission serves to house all the internals. But on both inside and outside, there are numerous devices that may not look so friendly, and allow the transmission to do its job without your help. The oil pan, side pan, servo covers (2 pictured) shaft speed sensors, the PRNDL (Gear Position) switch, cooler lines, and a lot more.



4T65E oil pump and housing.


Oil Pump: This provides lubrication and hydraulic pressure for the circuits in the valve body, apply force for the clutches and bands in the transmission, and oil for the torque converter. This pump is a variable displacement vane type pump. It has the ability to change its output based on load, by using a pivoting housing that can be controlled by the TV valve, or a solenoid if its electronically shifted. It is always driven by the engine. Some use a gerotor type design, similar to a Honda oil pump.


Reluctance type (VRS) magnetic speed sensor.


Shaft Speed Sensors: Very similar to the speedometer sensor in design and function, these sensors are used to determine if the incoming RPM and outgoing RPM are within a reasonable frame, to determine if the transmission is operating normally. If a clutch slips, the sensors will detect this, and throw a code. Most of the time these codes are OEM dependent, but of course there is a standard code set for automatic transmissions.



Servo piston and actuating rod.


Servos: These are almost only found on planetary type gearboxes, (Honda uses a servo to engage the reverse gear fork) which use bands to create the held member for a given gear. They are normally round in shape, and usually 3-4 inches in diameter. Many are serviceable from the engine bay, but they can be found anywhere inside the transmission. The job of this device is to convert hydraulic force into a mechanical action, by using a large round piston and apply rod to push a band onto a planetary member, much like a brake drum. (Dual-Servo drum brakes) Fluid is placed on the backside of the piston, forcing the rod to engage the band at a hydraulic advantage depending on the size and pressure.



Friction bands for various vehicles.


Bands: Bands are used to hold something stationary, by affixing a band that is physically attached to the case, to the object to be held. They can be various sizes and styles, but their operation is the same. They are usually made out of friction paper. Common uses for bands is a forward gear band, and reverse band. These are found predominantly in planetary gear sets.



Clutch disc (1), steel friction surface (2), Belleville return spring (3), clutch piston (4), and the drum (5).

Clutch Packs/Drums: These are used to drive members of a planetary gear set, and can be used in conjunction with one way clutches (or sprags) to do this. The assembly consist of a drum, which is affixed to the one end of the object to be driven, steel plates and clutches, and a piston in the back to force the clutches into the steel plates, this engages a gear, or a planetary member, depending on design. The steel plates spline to the drum, and the clutches spline to a shaft, or planetary member. If the outside of the drum is precision machined, a band may also hold this member stationary for certain gears to make the assembly much smaller.



Accumulator piston, cushion spring, and an after market rod to eliminate any cushion.


Accumulators: This is a cushion device, and is round in shape and usually 1-2 inches in size. It's job is to cushion the apply of a gearshift by allowing hydraulic pressure to push downward on it, so the clutch applies smoothly. It resists the oil apply pressure with spring pressure on the opposing side of the piston. The picture above shows the stock spring, and the replacement metal rod to make the clutch apply faster, and harder. The TV valve or MAP sensor can feed oil to the backside of the piston, to help engage the gear faster during high load acceleration.



Valve body from 200R GM Transmission... I think...


Valve Body: This is the complex PCM of the transmission. A series of hydraulic circuits that allow hydraulic oil to apply many different devices. In many cases they are not serviceable, but after market kits that replace the spool valves and springs to enhance performance are available. These can turn the traditional economy transmission into a performance machine.



Generic shift/pressure solenoid valve.


Solenoids: These can be on/off or duty cycle solenoids that can both be either normally open, or normally closed, depending on if the pressure is normally exhausted, or normally applied. They can apply clutches for gears, along with other comfort pressures. The PCM or TCM, if equipped, uses engine sensors to determine the drivers demand, by using throttle angle, manifold pressure, and rpm.



Direct clutch piston from a Chrysler Transmission, perhaps 41TE?


Check Balls: A simple metal ball. There can be many of these in a transmission, and their purpose is to momentarily delay fluid flow to a certain part (shift circuits normally have check balls for accumulator fill-up) or to prevent pressure from being lost on apply, and allow pressure to escape once a clutch is released.



Not sure where this one came from, probably older GM.


TV Valve: This valve is controlled by gas pedal movement, and is used to determine shift timing, and shift apply pressure in some cases. It is normally operated with a separate cable, or in some cases, a vacuum diaphram, (called a modulator) which looks much like a large fuel pressure regulator can be used in place of a TV valve. These are found on hydraulic shift transmissions that do not use engine sensors to shift them.



Either a 200R or 700R4 governor valve.


Governor Valve: Normally used in hydraulically shifted transmissions, they are responsible for shifting the car once the correct governor apply pressure is reached. It does this by pumping ATF based on engine speed, and once the correct speed is reached, its pressure will shift the car. Modern electronic transmissions will use the speed sensor and other sensors to shift the car at the desired time.


Now on to the meat and potatoes of the transmission, the gearing.


Planetary gear sets are rather ingenious, and are used more than most might think. There are 3 members to a planetary gear set, and 4 parts.

Sun Gear: This is the center gear of the set, and provides the smallest gear in the gear set.

Carrier: The carrier provides the largest gear in the gear set, and we will discuss how in a bit. The job of the carrier is to provide a mount point for the pinions to rotate on. It is the second member of the gear set.

Planets/Pinion Gears: The planet gears simply interface the last member, the ring gear, and the sun gear. These gears will rotate along the two gears, rotate stationary, or hold the sun and ring gear as one.

Ring Gear: Sometimes called a annulus/internal gear, this is the last member, and it's numerical ratio puts it between the sun gear, and the carrier.





How is numerical ratio figured?

This can be a bit tricky first off, but its not too hard to do, and with some practice and help from here, it will make it easy as pie. The carrier is the only gear ratio that we cannot figure by counting its teeth, but we can determine the ratio based on the other two, which have a solid number of teeth. in this case, we will use this for example:

Sun: 25
Ring: 74
Carrier: S+R

From here, we can calculate the ratios for the gear set. First, we must understand how the planetary gear sets transmits power at reduction, direct, and overdrive. The three members must occupy one state each, the three states being Drive, Driven, and Held.

If we did not hold a member, the power would simply rotate on the pinions in the opposite direction, resulting in no output (because planetary gear sets must have a input gear set, and reaction gear set). Therefor the pinions are a critical component. Figuring ratio is the same as a manual transmission: Driven / Drive = Ratio.


1st gear: Sun is Drive gear, carrier is Driven, ring is Held.

74+25/25= 3.96:1

2nd gear: Ring is Drive, carrier is Driven, sun is Held.

74+25/74= 1.32:1

3rd gear: Sun and ring are Drive, carrier is forced Drive, no Held member.

1:1

4th gear: Ring is Drive, sun is Driven, carrier is Held. (Reaction Carrier)

25/74= 0.33:1

Reverse: Sun is Drive, ring is Driven, carrier is Held. (Input Carrier)

74/25= -2.96

As you can see, there are many gears you can use out of this gear set, but there are some tricks to calculating the gears in this case. As you look at 4th and reverse, there are some problems, because the equation is the same, but in overdrive, how can that be? Automatics use compound (two planetary gear sets) or Ravigneux gear sets. (two sun gears, two sets of pinions on a common carrier and one ring gear) To get 4th gear in most automatics, the input sun gear is held stationary with a band/clutch and a one way clutch, and the input carrier is the drive member, and the reaction carrier is the driven member. Reverse is always achieved by holding the input carrier stationary, this allows the sun and ring gears to rotate opposite of each other, and produce reverse.

3rd gear is attained by driving any two members of the gear set, since when this happens the sun spins slower because of its smaller tooth count, while the ring spins faster because of the higher tooth count. When the two engage at the same time, they bind up because a transmission cannot occupy two gears at the same time. But the reason is all works is because there is no held member, so it has nothing to bind against, except the carrier, which is the member that prohibits the two from turning a different speed. The pinions force the gear set to rotate at a 1:1 ratio.

The basic planetary gear set is easy to understand, but gets harder because to get all the desirable functionality out of an automatic transmission, (including a park position, compression braking, and fast shifting performance) two gear sets (compound) must be used. This makes things a bit more complicated, and will make understanding a bit harder, because it changes with every transmission.







Many import transmissions do not use a planetary gear set, but instead use a set of helical gears, just like a manual transmission. In place of the synchronizer hub, slider, ring/spring, and gear teeth, is a clutch drum that contains friction clutches and steels that spline to the shaft and gear respectfully. These are very simple to rebuild, and will normally take about just as long as a manual.

Now that the gear portion is done, it will be time to explain how it actually shifts gears automatically. An automatic comes in two types, Hydraulic-shift, or Solenoid-shift. In either case, they shift gears in the same manner, but use a different device to shift the transmission. Refer to the picture below:





This is the most basic hydraulic transmission, and it has 5 forward speeds, one reverse, and a TCC (torque converter clutch) in 4th and 5th gears. The 4 valves inline with each other from top to bottom are the 1-2, 2-3, 3-4, 4-5 shift valves. The shifter moves the manual valve, and uncovers oil passages to the desired position. (what you see on the console) It does this by moving the manual spool valve when the gearshift is moved, and allows oil pressure through the specified point. The manual spool valve is staggered so that it cannot be in two positions at once. For example, in reverse, the shifter moves one spot to the left, and uncovers the passage from the oil pump, and to the reverse bands/clutches. But when OD is selected, the spool valve moves two more clicks, past neutral and into overdrive, and as it moves, it covers up the reverse passages, and uncovers the OD passages.

For the transmission to shift 1-5 automatically, we need devices to tell it when to shift, since it is not electronic. In this case I chose to use a TV Valve, and Governor Valve.

The Governor valve in this case is centrifugal valve that is driven like a speedometer gear, and has weights attached to it that fly out as it goes faster, and allows more oil pump pressure to pass through it. As speed increases, so does this pressure. Some valves operate like small pumps, and achieve the same result.

The TV valve is a throttle position valve, plain and simple. As you step on the gas, this valve moves and helps delay the shift. (as acceleration is desired, so higher RPM is needed) By stepping on the pedal, the valve moves, and increases TV pressure. This pressure is fed to the back side of each shift valve, and assists the pink springs in keeping the valve closed, until governor (speed) pressure is too great, and the valve moves to the open position, allowing the oil pump to apply the next clutch.

Each of the shift valves have a pink spring that is calibrated to a certain pressure. In this case, we will say that the governor valve makes 1psi of pressure for every mph of car speed, and the 1-2 shift valve spring is calibrated to 12psi. In first gear, with little throttle pressure, the shift comes sooner, at around 12mph because the TV valve is not helping the spring, so the minute the governor valve gets up to 13psi, it can overcome the 12psi spring, and move the shift valve to shift to the next gear. If you mash the pedal in 1st gear, it will rev out to its max, and around 40 or so mph, it will shift the car. It shifts late because the TV valve is providing its maximum 28psi of pressure to help the 12psi spring, resulting in 40psi of closing force. So the minute the governor valve reaches 41psi (40mph) it will shift.

Each shift valve stays open to apply oil pump (mainline) pressure to the next shift valve when it opens. When the car shifts to 4th and 5th gears, oil pressure is also routed to the TCC (or PWM) solenoid, allowing the TCC to apply when the solenoid opens. (or closes) This allows a direct connection to the engine, and will feel like a 6th gear shift in some cases, dropping engine speed by up to 500rpm. This helps improve fuel economy on the highway comparable to a manual, but the minute the brakes are pressed, or the gas pedal is moved significantly, it will disengage, as it cannot handle the full load of the engine.

In an electronic shift transmission, TV pressure and governor pressure are eliminated, and a shift solenoid is used to control the shift. These transmissions will have a TCM that determines shift timing, based on vehicle speed, and engine load. (MAP or MAF input) This makes valve body design much easier, and diagnostics very simple as well, as spool valves can wear down and cause internal leaks that may not be readily detectable during service, whereas a solenoid can be both tested for holding power, and if the coil itself is any good at all.


Parking tangs shown on the differential, a rod would push the corresponding pawl into the space in the teeth, preventing the differential and therefor the wheels, from turning.

Parking is achieved by using a reluctor style wheel and a parking pawl that is engaged by the manual valve rod. When park is selected, the rod pushes down into the angle on the pawl, which locks it into wheel, and prevents the reaction/differential side of the transmission from turning. This is standard equipment on most transmissions, as the clutches are all disengaged, and the vehicle would roll, if the parking brake failed to engage/hold the vehicle.

Most people with automatics refuse to use the parking brake. (Yes, it IS a parking brake, on an emergency brake!) This places great load on the pawl, rod, and differential engagement teeth. Parking up/downhill only increases the effect, which is why the parking brake should be applied to keep the vehicle stationary.

After years of neglect, the cables will seize, the piston or caliper may seize, and the shoes may completely fall off the car. (Larger SUV's with internal drum parking brakes and a standard disc brake in the rear) This usually provides another 60-100 dollars to a brake job.

Now there are a number of things you can do to improve your automatic transmissions performance. High friction clutches, high stall converters, modified valve bodies/accumulators, wider bands and bigger servos. Even a totally different gear set can be found for some cars. These parts many times are less expensive than a manual transmission.

Choosing the right fluid is not really negotiable in an automatic. Import ATF is different from most domestic fluids because of the type of gears, and friction surfaces used. Thicker oils or the wrong viscosity ATF can cause a clutch to drag on release or slip when applied, destroying them in short order. ATF used by transmissions with planetary gear sets will usually foam up when it hits rotating parts, but this lubrication is needed for a Honda transmission, as it uses individual gears, so the oil needed in that transmission will need to be thicker, and have additives to prevent foaming.

The condition of the fluid is also vital to its operation. ATF will not change in color with normal use, therefor a service interval must be specified. This fluid must be able to lubricate and allow sufficient friction so that the clutches work normally. A change in color indicates contamination, from many different sources. A failing clutch assembly, busted radiator cooler, (allows ATF and engine coolant to mix) or over oxidized (old) fluid are commonplace. The scent of an oil can indicate neglected oil, or burned clutches. Sometimes many consider flushing their neglected transmissions, while others shy away as flushing it could cause failure. If that be the argument, flush it, and have it fail on the spot when you expect it, not when your trying to tow a boat home with a cooked transmission. It will fail at some point, its just now that much more predictable.

Automatics (and some manuals) normally have a cooler specifically for the transmission. Even with the stator eliminating most of the turbulence in the converter, it still gets very HOT. This loss is caused by the lack of mechanical connection and produces a lot of heat. The effects are increased with towing and stalling. (pressing the gas while in gear and not moving, or heavy loads.) Sometimes the converter can get so hot, that the outside of it turns blue, indicating severe overheating. Normal temperature ranges can be from 200F to 450F, depending on the cooling and construction of the transmission.

Questions and Comments welcome.


Modified by slowcivic2k at 7:53 PM 8/9/2008

[cabofixe]

Wow, that is a great post. Thank you for this great explanation of Automatic Transmissions. I currently drive a '97 Civic with an Automatic transmission. In my Factory Service Manual it says that my "automatic transmission is a 3-element torque converter and a dual-shaft electronically controlled unit which provides 4 speeds forward and 1 reverse." Now what I would really like is to make a PCM that I can control. A switch would control whether it uses the OEM programming or my own programming. And then I would like to electronically control when it switchs with two switches on my steering wheel.... But I guess, now I'm just day dreaming.

[slowcivic2k]

Yep, has the turbine stator and inpeller like it should, and 4 forward speeds, attained by toggling the A/B shift solenoids on and off.

This company makes one for diagnostic purposes. It's basic job allows you to hook it up to the transmission, and shift the car manually with a button without PCM control, just like your day dream. Wake up, its already here. The Schaffer Shifter.

http://www.schaffertest.com/whyuse.htm

[cabofixe]

Thanks for the link! I have tried asking people if anyone could do it and they treat me like I'm an idiot. Thanks!

[Throwdown]

nice post this should be in the Transmission Topic Index/GOOD LINKS/ETC. sticky

[Blown90hatcH]

Nice post man. Pretty good information, but for the most part, Honda automatic transmissions do not have planetary gears.

[91DA9]

Yeah, great post, lots of good info. A good way I read to describe autos is a desk fan blowing into another one.

I am not really scared of autos because I don't know how they work, it is just because they are less efficient, and more complexity pretty much always guarantees more failures. Semi trucks use meshed gears for a reason.

[slowcivic2k]

Originally Posted by Blown90hatcH

Nice post man. Pretty good information, but for the most part, Honda automatic transmissions do not have planetary gears.

That was part of the second post, that Honda's (and most imports for that matter) use a set of standard helical gears, instead of a planetary gearset, and the clutches in such a transmission can be thought of as an automatic synchronizer. (As the drum (or hub) in most cases affixes to the gear, which contains the steels and clutches)

[Syndacate]

It's a lot to take in at once..I'm not gonna lie :-D.

I'll add it to the FAQ too.

[dude_123]

Excellent...Thanks for the great write up, it's a good review for me.

[vteczone]

good info!

[blinx9900]

wow great info!

[slowcivic2k]

Glad to see people still read it. Thanks.

[sanimalp]

thanks for this post.. the torque converter in particular has always been a box of mysteries to me.. I figured it was something like a centrifugal clutch on a go cart, but turns out thats not really the case. good info.

[slowcivic2k]

Glad to be of help, I've modified the posts and added more info and clarity.

[PRCIVIC]

WOW! Thats a lot more info than when i study, I will read it to see if i can find why my 92 auto civic shifts by itself at 5k rpms from 2 to 3 even when i have the stick in second.

[slowcivic2k]

Thats an odd problem. Was it ever apart before?

[BlazinSlowHonda]

Thats great man, only thing I feel it could use is a list of Honda Trannys and USDM models with shift functions ie. Electronic, Hydraulic. And Converter types for ease of diagnosics! Thanks Bro for the hard work!

[PRCIVIC]

Are asking about my tranny problem? 2 to 3 at 5k rpm's? Sorry but, what did you mean with your question; "Was it ever apart before?". I don't have a perfect english!!!

[Evs-One]

Good thread.

Automatic transmissions are an enemy of mine!!! I've had to rebuild a couple out of 05+ Odysseys due to insurance policies(wouldn't pay for replacement, only rebuilding)...not tooo bad, but Hondas are definitely not as easy as a GM TH350


It's always fun testing clutch packs though

A lot of Honda auto issues can be fixed by cleaning out the valve bodies and screens.

Oh yeah, Honda autos suck badly for the most part and cannot handle much power- someone needs to design hi-po clutch packs

[theoneysr]

What fluid do you use to fill the torque converter??

[ken9]

Very nice write up. I never thought someone would do a whole research on auto transmission. Auto car have no fun driving. = (