Why Automatic Transmissions Fail

today we're going to be taking a look inside the failed transmission of this infiniti g35 and then when we try to hit fourth it's basically like it's a neutral [Music] oh it shifted really hard there now because this is a rear wheel drive vehicle the transmission is located underneath the vehicle itself and not near the front so we're going to need to drop it down now holding it on is this main bar over here which braces it against the body and the bell housing up at the front there but there's a bunch of other stuff we need to disconnect in the way now i'm going to start by disconnecting the exhaust i'm also going to start by draining out the trans fluid i'm going to go next to the drive shaft at the rear here next up i'm going to attack the front drop shaft i got the front pops off loose there so i kind of gave up on removing the transmission from underneath because those bell housing bolts are really hard to get to with that front diff in the way to the progress i got so far got the front end radiator radiator support off and all the headlights we're down to the bear engine everything's disconnected so the engine's out on the crane here you can see just how long this transmission is due to the four-wheel drive transfer case so here i finally got the automatic transmission removed from the vehicle i've already got a full teardown video on this transmission and how it works make sure you check the link above for that for the purposes of this we're going to skip through the teardown pretty quickly to see what the fault is now the transfer case is bolted to the output of the transmission is held in by a bunch of 14 millimeter bolts all the way around too bad i can't get my socket on here just pull that right off and i'm just going to remove the torque converter and then i'm going to remove all these 14 millimeter bolts and just pop off that bill housing the transmission is looking a lot more sizable with the belt housing and transfer case i'm just gonna pry out this front pump here so it appears that the front sun gear assembly and this drum came apart with this transmission pump next up i'm gonna remove the front carrier assembly here and you can see he's got a set of clutches those clutches already look pretty black and now i'll remove the band that goes around that drum next i'm going to remove the mid carrier assembly here holy this is burnt up now i'm going to remove the mid sun gear assembly here see there's some burn marks on the outside and now i'm going to remove the high load reverse clutch assembly and you can see these are pretty dark as well now it's time to turn this transmission over and makes a mess oh there goes all the transmission fluid quickly running here with my brother's old sweatpants and wipe that up this is going to be one dirty video while the transmission is draining on that side i've got another one of my brother's old t-shirts here i'm going to spread that under here and remove the transmission pan now i'm going to remove the transmission pad now i did clean the filter and change the fluid to give the transmission one last chance at life and i noticed that there was no particles built up in the transmission filter next up i'm gonna remove about twelve thousand five hundred and fifty two ten millimeter bolts here and i'll just pull off that filter it's going to gently remove the valve body here then once the plug is removed i can remove the valve body i'm going to start by unbolting the tail housing here and remove it from the output shaft and then of course we have this output shaft it runs the rest of the length of the transmission the next set of clutches inside of here is held in by this snap ring it's the reverse brake and with that snap ring out of there now the last set of clutches in there is for the reverse brake collection now i'm going to remove the back part of that reverse brake piston the last part we have is a one-way clutch see that this rotates freely in one direction and in the other direction it's nice and firm and then finally in here we have the forward brake set of clutches oh these look pretty bad and the last set of clutches inside of there is the reverse brake clutch and there we have the transmission casing fully gutted and here we have all the components removed from the transmission now we're going to take a look at the individual components to see what could cause these transmissions to fail now if you remember my videos on how automatic transmissions work they use a planetary gear set which has an input and an output and another part that's held stationary so for example if we're using this planet carrier as its input we're going to hold this drum outside here stationary the output is going to be this shaft here which is going to rotate at a different speed now you can get different gear ratios by adjusting which one is your input and which one stays stationary to get a different output speed and direction now in an automatic transmission all of the gears are always mesh with each other it's not like a manual transmission where they have to manually engage the actual physical gears the automatic transmission is going to use bands and clutches to hold that third part stationary in order to switch the gear ratio and that's where we come to the first major failure point on automatic transmissions and that is when the clutch packs wear out and they no longer can hold friction to hold this adjacent part stationary and it's just going to slip now taking a look inside of here you can see we have this clutch set and it's completely black inside of there and you can see the blackness has gone on to the adjacent planet carrier that plugs into it so this clutch pack is completely burnt out and was one of the main issues that was causing the slipping so after removing this snap ring here take apart this planetary gear set so you can have a closer look at that clutch now here we've got the clutch pack and piston that controls the movement of this ring gear on the first planetary gear set now when transmission fluid flows through these small passages inside of here it's going to fill up this piston with transmission fluid creating a pressure that's going to close these clutches together right now these clutches are open and they're free to rotate once they're locked together it's going to lock the thing that flies into here which in this case is actually the next planet carrier for the secondary planetary gear set and that will be locked to the ring gear on the first planetary gear so just remove the snap ring here and then these clutch plates can come out now you can see just how black these clutch plates are so i'm just going to give it a quick wipe with my brother's old shirt here now the way a clutch pack is supposed to work is you have these alternating clutches some of them have teeth on the outside and those correspond with the teeth on this carrier over here and then the next one has teeth on the inside and that's going to correspond to the teeth on the next planetary gear set after that and they form a sandwich they come together just like this and taking a look at this clutch band starting at the front here you can see we've got some pretty hard scoring on these externally splined ones and you can see a lot of wear marks on the internally splined ones as you go down further in the clutch pack the wear actually gets worse you can see the friction material on here is so thick i can actually scrape it off and then further down to the back the last one here looks pretty bad this one is completely completely burnt up it's just all black now as a comparison to this burnt up clutch pack here's a clutch pack in better condition you can see that the steel is all shiny and the friction material is nice and brown of course when these clutches wear out they can no longer hold the friction when the pressure is applied and that's just going to cause it to slip and in this case the transmission was slipping in fourth and fifth gear next up in the transmission we have the reverse high low clutch and this one's looking pretty clean and on top of that high low clutch we have this direct clutch if i take out these flex packs here you can see this one's pretty burnt up look how dark the friction material is there's even scoring marks on these plates over here next we have the reverse brake clutch and you can see that this one's in pretty good shape next up we have the low cost brake at the back of the transmission and this clutch is looking okay but the forward brake that sits around it it looks pretty dark and almost ready to burn up though it's not as bad as the other two we saw now the real reason why clutches do wear out is because a either your fluid is incorrect or you have the incorrect fluid level and that's going to cause some level of slippage which is going to wear these out a lot faster another thing is if your fluid is dirty the contaminants themselves could also grind and cause this thing to wear out if the transmission isn't designed correctly or it's under a lot of strain these are also going to heat up and they could literally burn out as you see here and finally the driving style has a lot to do with how long your transmission is going to last of course if you're shifting very abruptly these clutches have to engage and disengage fairly quickly which is going to accelerate where now out of the three clutches that were burnt up in this transmission between the input clutch high low reverse clutch and the forward brake the input clutch was the one that was the most burnt up and took the most damage now if we cross reference that with this repair manual you can see that fourth and fifth gear which is what we were missing on the vehicle actually relates to the input clutch so therefore we can conclude that the burnt up input clutch was the one that caused this transmission to fail especially in fourth and fifth gear now taking that a step further looking at the power flow diagram of this transmission from its input shaft to its output shaft for the fourth gear you could see that this input clutch here is responsible for taking power from the first ring gear to the second ring gear in the planetary gear set now because slippage is occurring between these two power cannot flow from this side of the transmission to this side of the transmission and then you just have a slipping training now if we compare that to the power flow diagram for third gear the power is going to flow past over here around this planetary gear set and not have anything to do with activating this input clutch which is burnt up so that's why third gear and the gears below it worked now another where point on transmissions is the front brake and that uses this drum here with this band to hold stationary instead of using a clutch pack and these bands of course could wear out and you can see this one's got a few dark spots on the inside here and a couple of marks on the drum itself now if your transmission is failing to engine brake or it's not engine braking properly that could be due to these one-way clutches they're basically like a bicycle wheel and allow you to freewheel in one direction but then when you pedal your wheel it's going to move it in this direction or in this case this is going to lock to the transmission casing and not allow any torque to be transferred to it in that one direction you can see on the inside here we have these little bearings now sometimes these bearings can lose their friction and completely wear out and make this a completely loose clutch now another big failure point on automatic transmissions is the valve body and the computer that controls it all now you'll see that this computer is completely submerged in transmission fluid and it is designed as such but they do fail at some points and might even need to be reflashed or to relearn your driving cycle and the valve body and the rest of the transmission uses transmission fluid as a lifeline if it doesn't have any proper fluid then it can't send the correct pressure to these clutches to lock them up properly now those clutches are controlled by these individual solenoids here and these solenoids are going to redirect fluid inside of this valve body according to the computer's demands through the transmission to lock up the appropriate clutches according to what gear is required from the ecu if the transmission computer itself hasn't failed it's very likely that one of these solenoids could fail and when one of these failed you could get a transmission code thrown or you could just get the symptoms of a slipping transmission now luckily if a solenoid is to fail they're pretty easy to replace you just have to drop down the valve body on the bottom of the transmission there's no need to take apart the whole entire transmission and they're pretty cheap to obtain now if your car fails to start it could be that the transmission is not recognizing that you're in either park or the neutral gear and that could be due to this switch over here that takes the position from the lever that's attached to it here and tells the computer what gear to be in in order to change the fluid pattern in order to optimize shift quality not only do we have solenoids but we have pressure sensors that sense the amount of fluid in the hydraulic circuit and temperature sensors that sense that it's at operating temperature to give you that nice smooth shift now if you remove the top half of this valve body you can take a closer look at what's inside i've removed the shift controller out of the way i've got this steel plate here that separates the top half from the bottom half and taking a look at this maze you can see that inside here there's a lot of small little channels where transmission fluid has to flow through to be directed to the appropriate clutch now further inside of here you have small things like these little filters here and they're responsible for filtering out any little contaminants in the transmission fluid that's why you got to keep your transmission fluid clean there's also small stuff like these little springs and check balls that keep one-way fluid flow here you can see just how critical transmission fluid is to your vehicle essentially everything here forms a hydraulic circuit in order to operate so if your fluid is not up to spec it's not going to do a good job at shifting now if your transmission has a lot of contaminants inside from warm clutch materials or if it's overheated well that transmission fluid could build up inside of here and cause a blockage and just like a blockage in your heart or your brain it's not really good for the life of your transmission just below the valve body inside of the transmission pan we have the transmission filter it's responsible for taking out any particles that are cycling through the transmission fluid so it doesn't clog up any of the arteries inside of the brain now this is a maintenance item you can definitely change this fairly easy by just dropping the transmission pan out and it's a good idea to clean it out once in a while now the bottom of the transmission we have this pad and it's got its own magnets here to pick up any magnetic particles floating around inside of here now of course this has to be filled properly with the correct level of transmission fluid otherwise if it's too low it's not going to be picked up by the transmission filter now looking inside a casing here there also equal amount of passages that allow fluid to flow from the valve body that sits inside of here into those clutch packs now when your transmission does fail this casing does allow you to connect various pressure adapters externally to each set of clutch packs or hydraulic circuits to measure the pressures so you can properly diagnose if it's just a simple solenoid issue a reprogramming issue or the actual clutches like in this case are burnt out now one of the reasons why a lot of people don't like to drive automatics is because of these torque converters kills a lot of slip between the input from the engine and the output shaft going to the transmission which kind of takes away some power and driving feel however the torque converter is also a big failure point on a lot of modern transmissions i've got a full cutaway video on how this torque converter works linked in the description above now in summary a torque converter can fail by first of all not supplying it with enough oil pressure the other thing is there is a lock up clutch inside here which is going to lock the input and the output together especially when you're cruising along it's got a similar clutch just like the regular clutches inside of here and that could definitely wear out causing a no lock up issue and finally there's also a one-way collection setting here that only allows the stator to rotate in one direction now you've seen all the components and how complicated it could be to repair an automatic transmission the next time your dealership asks you if you want to change your transmission fluid you should definitely consider doing a drain and fill at least once a year to keep things fresh otherwise you could end up with something like this now take it easy out there when driving one of these automatics especially if it's one of those failure prone honda or old chrysler cars that are known for eating transmissions now make sure you follow me on instagram for more behind the scenes footage and subscribe for more videos just like this one

Channel: speedkar99

Views: 197,489

Keywords: transmission, fail, slip, fluid, change, jerk, throttle, neutral, park, reverse, moving, speed, overdrive, gear, planetary, teeth, grind, backward, forward, driveshaft, CV axle, wheel, engine, car, infiniti, g35, AWD, 4WD, FWD, clutch, band, drum, burn, filter, pan, gasket, seal, computer, solenoid, diagnostic, repair, how to, teardown, engineering, analysis, torque, converter, valve, body, differential, housing, oil, lucas, stop slip, worn, honda, chrysler, dodge, acura, audi, ford, nissan, CVT, automatic, manual, DCT, DSG, RWD, drifting, cheap, abuse, race

Id: MQztW8uihWI

Length: 13min 57sec (837 seconds)

Published: Mon Aug 10 2020