Practical Transmission Tuning: Everything Else

Back to course

Watch This Course

$199 USD $99.50 USD

-OR-

Or 8 easy payments of only $12.44 Instant access. Easy checkout. No fees. Learn more

Enroll Now
8 easy payments of only $12.44

Course Access for Life

60 day money back guarantee

Everything Else

13.16

00:00	Now, that we've covered what are arguably the most important internal components of an automatic transmission, it's time to look at the remainder of the internals so we have a more complete understanding of how the system comes together.
00:11	In order to maintain focus on what's most important to your learning, there are some transmission components that I'll be quickly breezing through or not covering.
00:19	Getting deep into the weeds on every little bit and every piece inside a transmission is not necessary to become a better tuner, and at HPA we want to provide an efficient learning process.
00:30	Here are a few remaining components worth mentioning.
00:33	Let's start with the other shafts besides the one that transmits power from the torque converter turbine to the transmission input, which we already discussed earlier.
00:42	There's a shaft from the transmission case to the stator, which holds it in place and feeds fluid into the torque converter that's used to actuate the torque converter clutch.
00:52	Then there are the shafts and housings within the transmission to connect various components and transfer torque towards the transmission output.
00:59	Their number and arrangement will vary between transmissions, but the basic principles of transmission control remain the same.
01:06	Similarly, items like the transmission pan, pickup, filter, and pump shouldn't be completely ignored since they do serve key functions and must be in proper working order.
01:16	Regarding the pan and pickup, much like a high g-force situation can starve an engine of oil, causing a loss of pressure, don't forget that the can happen to a transmission.
01:26	Baffling and other measures to control transmission fluid motion or an aftermarket pan and pickup may be required in some situations.
01:34	For example, a front sump transmission pan picks fluid up from the front of the pan.
01:39	This location can more easily starve during an aggressive launch as oil shifts rearward due to forward acceleration.
01:46	Loss of fluid pickup can cause loss of line and clutch pressure, slipping clutches, slowing acceleration, and potentially causing damage.
01:55	The aftermarket offers rear sump conversions for some applications, so when fluid travels backward on a launch, the pickup is ideally placed to receive it.
02:04	In road racing, rally, and off-road racing, fluid motion in all directions is a concern, not just rearward motion from acceleration, so more thought may be required to keep the transmission pump fed a reliable source of fluid.
02:18	While the transmission pump is a very critical component, for many applications it isn't something you need to upgrade because the factory item is more than sufficient.
02:27	Of course, like anything, if a project is wild enough, you might have to upgrade the pump, shafts, housing, clutches, and more.
02:36	Speaking of clutches, they perform a key role in torque transfer and gear changes in an automatic transmission.
02:42	When we get into shift tuning, a large portion of what we'll cover relates to engaging and disengaging clutches in order to execute gear changes with the speed and feel desired for the application.
02:54	There are a few common types of clutching devices in automatics.
02:58	Multi-plate drive clutches and multi-plate brake clutches are both made up of stacks of alternating friction discs and steel plates.
03:06	The key difference is how they're used based on what they connect to.
03:10	A drive clutch engages one component to another component that is rotating, causing them to rotate together.
03:17	A brake clutch engages a moving component to a stationary item, such as the transmission case, and slows the motion of the item to a stop, then holds it until the clutch is released.
03:28	That's why this is referred to as a holding device or a brake.
03:31	Another type of holding device or brake is a brake band, which slows a rotating housing to a stop, just like a drum brake.
03:39	Often there's one drive clutch for forward motion and a second drive clutch for reverse.
03:44	Beyond that, depending on the transmission design and gear count, there may be additional clutches or bands of a driver -braking nature to achieve various gear ratios.
03:53	If at this point the notion of changing gear ratios by engaging a clutch doesn't make sense, not to worry.
03:59	It'll all come together as we review the next pieces of the puzzle, planetary gear sets and housings.
04:05	Unlike a traditional manual transmission gear stack with one physical gear per ratio we want to use, automatic transmissions use one or more sets of gears which vary in design, but generally include a central interior gear called the sun gear, multiple planet pinion gears which ride on a planet carrier orbiting the sun gear, and the planet gears also engage a ring gear which surrounds the planet gears.
04:30	Hopefully the names sun and planet help visualize the orbiting motion of the planet gears around the sun gear.
04:36	In a standard planetary gear set, the sun gear, planetary gears, and ring gear are easy to identify and make up the whole system like in this GM4L60E.
04:46	The first planetary gear and carrier assembly includes the ring gear for the second planetary gear set.
04:52	The second planetary gear and carrier assembly includes the ring gear for the third planetary gear set, and the first gear ring gear is a separate piece.
05:02	This added complexity does provide additional flexibility though, since each planetary gear set can result in multiple drive ratios depending on which portions of the planetary gear set are allowed to move.
05:15	Let's go through the modes of operation of a single standard planetary gear set.
05:20	First, if all components in the planetary gear set are allowed to move freely, the planetary motion uses all the applied torque.
05:28	None is transmitted to the transmission output.
05:31	This is a neutral or no drive condition.
05:35	To apply torque from transmission input to output and vary the gear ratio, one or more components of a planetary gear set, which are the sun gear, planetary carrier, or ring gear, are held by a clutch or brake component I mentioned earlier.
05:49	For a larger gear reduction, the ring gear is held stationary, so the sun gear is the input member and the planet carrier is the output member.
05:58	In this state, the force from the sun gear to the planetary gear drives the carrier, since the ring gear won't move.
06:06	This provides a gearing reduction, so the carrier will rotate more slowly than the input shaft and sun gear.
06:13	For example, if the sun gear has 20 teeth and the ring gear has 60 teeth, the planet gears will have 20 plus 60 teeth equaling 80 teeth altogether.
06:25	This is simply how the math works out to keep the planetary gear system moving happily.
06:30	The gear reduction is calculated output to input, so we take the planetary gear tooth count of 80 and the sun gear tooth count of 20, and you have an 80-20 ratio.
06:41	If we divide both sides of that ratio by 20 to reduce it, we can simplify it to a 4-1 ratio.
06:48	That means for every four rotations of the sun gear, the planetary gears and their carrier will rotate one time.
06:55	The mechanical advantage provided by the large gear reduction can be used to help get a heavy load moving or improve acceleration at low speeds.
07:03	For a smaller reduction necessary for the vehicle to achieve higher speeds, the sun gear is held stationary, the ring gear is the input member, and the planet carrier is the output member.
07:14	Using the same tooth counts, we have 80 teeth on the planet gears and 60 on the ring gear, so an 80-60 ratio, which simplifies by dividing both sides by 20 in this case, to a four-to-three ratio.
07:26	If you get out a calculator and divide four by three, you'll get 1.333 to one, where the three is repeating.
07:33	So, the input rotates about 1.3 times for every one rotation of the output.
07:39	For an overdrive function, meaning beyond a one-to-one ratio, the sun gear is held stationary, the planet gear is the input member, and the ring gear is the output member.
07:50	Overdrive ratios are useful in maintaining high vehicle speeds with relatively low engine speed for improved fuel economy.
07:57	This is the inverse of the above equation, since input and output have simply been reversed.
08:01	So, 60-80 simplifies the three-to-four ratio, or three divided by four gets you a 0.75-to-one ratio.
08:10	So, the input speed will be slower than the output speed.
08:13	When it comes to reverse, the planet carrier is held stationary, the sun gear is the input member, and the ring gear is the output member.
08:20	Because the planet carrier is locked in place, the planetary gear can't orbit the sun gear.
08:25	So, instead of driving the ring gear in the direction of rotation as the planet gears, the ring gear rotates in the opposite direction, causing the output of the transmission to rotate in reverse.
08:36	The output in this case is 60 teeth, shown as minus 60 since it's spinning in reverse, and the input is the 20 teeth on the sun gear, for a minus 60-to-20 ratio, reducing to minus 3-to-1.
08:49	Lastly, any two lockable members of a planetary gear set, which could be sun gear, planetary gear, or ring gear, can be held to achieve a 1-to-1 direct drive ratio.
08:59	The ratio is 1-to-1 in this scenario, because input and output speeds are identical, as the whole planetary gear set moves as a unit.
09:07	So, now I've described four forward gear ratios plus reverse, all from one simple planetary gear set.
09:13	By using multiple planetary gear sets, and more complex and modern designs, including LaPelletier gear mechanisms, modern automatics can achieve much higher gear ratio counts without a lengthy gear stack, or becoming much heavier than older models having half the ratios.
09:30	One transmission taking advantage of a more modern design is the Lexus AA80E transmission.
09:36	It only uses two compound planetary gear sets, but with six braking and holding mechanisms, it creates eight forward gear ratios.
09:44	The popular ZF 8-speed uses three compound planetary gear sets, and the 10er80 gets 10 speeds from four planetary gear sets, all in a package that's shorter than a T56 6 -speed manual transmission.
09:57	Now, that we have a background in automatic transmission construction, we can apply this knowledge to understanding how gear ratios are achieved, how the power flows through common automatic transmissions of today and years past, and how to use that knowledge not only during our tuning process, but also during diagnosis of faults.
10:15	Once we know which components are involved in achieving each gear ratio, or gear, we can use that understanding to narrow down which components may have failed if a vehicle stops shifting into one or more gears.
10:26	For example, if gears one and four stop working, we can review the power flow of the transmission to see which component has to be held or braked to achieve those two ratios.
10:37	If we find a held component is needed for gears one and four, and other gears don't hold that component, we've likely found our issue without even taking the transmission out of the vehicle.
10:47	In terms of tuning, understanding which components are involved in each gear and shift process is key to working around known weak points in a transmission system.
10:56	While there's too much variety across the range of automatic transmissions to cover every single one's intricacies in detail, always remember they follow the same principles.
11:06	While 8-10 speed transmissions do look complex, if we slow down, take our time, and walk our way through each, we can break the big picture down into each component system from engine crankshaft to transmission output and understand.
11:21	Also remember that pragmatically, if you have time to put an old 2-4 speed on a bench, take it apart, and see your way through it with what you've learned here, that's great.
11:31	But in order to tune that, or a more complex transmission like a 6R80, 10R80, or ZF8, we don't have to go through that process first.
11:40	One big shortcut is levering the wealth of information in factory service manuals.
11:45	This Lexus AA80E 8-speed transmission diagram clearly illustrates the friction elements and solenoid applications to achieve each gear, saving us time and removing guesswork.
11:57	Here Lexus shows us the gear ratios achieved, and we can see they also mention 4 disc clutches, 2 disc brakes, for a total of 6 holding and braking systems, so we have a better idea of what we're working with.
12:10	With knowledge of all the core transmission components in hand, we're nearly ready to discuss gear ratios and more depth.
12:16	But before we do that, let's quickly run through what we covered in this module.
12:20	The transmission pan pickup location can be critical to avoiding starvation, just like an engine oil pickup.
12:27	The fundamental components of a planetary gear set include the sun gear, planet gears, planet carrier, and ring gear.
12:35	The drive and holding components cause different portions of the planetary gear set to move or remain stationary.
12:44	Holding or rotating these items causes gear reduction, which can be calculated based on the tooth counts of the gears.
12:52	Modern automatics use advanced compound planetary gear sets to achieve even more total ratios than older designs without significantly increasing transmission size or weight.
13:04	With this knowledge of transmission internals and a factory service manual, you can diagnose many faults without even removing the transmission.