What most people don't appreciate is that "grinding gears" isn't damaging the actual gears that transmit power, but the dog teeth on the synchro system.
Makes me appreciate that big truck transmissions generally do not have synchronized gearsets. I had to rebuild an entire transmission when someone had broken the main output shaft in one. No books, no drawings, nothing but brute competence. I will say, the way that they are made with dual or triple countershafts, the design is ingenious. The input and output shaft are only connected by a pilot bearing. The fact that the main output was snapped into two pieces, and the transmission didn’t fly apart is testament to the designer! The countershafts held the gears in their proper location, even though the shaft was toast! No synchronization there, just a good gear matching hand was required!
I have a Kawasaki motorcycle and the factory service manual chapter on repairing the transmission has one line about " paying attention to the mating dogs ". Made me chuckle.
@Franky997 grinding gears on old stuff like '47 chevy, farmall tractors, or cub cadet lawn mowers does damage the actual gear teeth. The whole gear slides to engage
This is terrific. Details like the back cut on the engagement teeth on both the synchronizer sleeve and the speed gear, are new to me. This is shown under magnification at 2:15, and is easily missed when you have the parts in your hand. This back cut is what holds the two parts together under load, and prevents the car from popping out of gear. When an older transmission pops out of gear people will tell you with authority and confidence: 'oh, the synchronizer rings are bad'. But the synchro rings have little to do with this function. However when this tiny back cut, on on the engagement teeth of the speed gear or the synchronizer sleeve is worn away, there is nothing left to hold speed gear and sleeve together. In this case a new set of synchro rings will do nothing to fix the problem. And that is very much worth knowing.
Thank you for your comments. Please note that the back cut is not present on all synchronizer sleeves and gears. I see it missing mostly on older transmission designs. There are several reasons why a transmission will jump out of gear and worn out back cut is one of them. Normally what happens is the oil is not changed when it should be and or the driver is rough on the transmission and the blocker rings start to wear causing grinding (gear clash) which in turn chews up the clutching teeth on the gear and on the sleeve which wears away the back cut. It's often a domino effect.
Would be good to explain that the synchro ring is made of brass hence it's gold color. Brass is softer and is sacrificial meaning it will eventually wear out and need replacement. Brass is the perfect companion metal to press against the hard steel gear and do no damage to it as it tries to either speed it up or slow it down so the the synchro hub can slide over and complete the lockup. It's important to remember that the synchronizer assembly must adjust the speed of the entire cluster gear and input shaft including clutch disc in order to perform the lockup into the selected gear. Quite a task and shows why you must have clean clutch release so that the disc is completely free to rotate. This is a very good video, especially with the gear train illuminated with the strobe light to show what happens.
Thank you for your good comments. You are correct. One note. although these blocker rings are brass there are other blocker rings made of other materials and sometimes either lined with a friction material similar to brake lining and others that use a bi-metal design with a sintered metal inner cone that is soft with a high coefficient friction. I will consider a followup video with this additional information.
@@Franky997Can confirm that because some years ago I worked for a company that made synchromesh rings for many of the major European car manufacturers. Selector forks were also made from phosphor bronze, but of a different grade.
I have overhauled countless gearboxes, measuring gaps and replacing parts, but this is the best explanation of how a gearbox works that I have ever seen.
Yes. He really has all the fine details down. Gear boxes for Spec Miata racing are rebuilt all the time. However the re-builds tend to have problems. If a rebuilder replaces the bearings, the brass synchro rings, and the seals then the gearbox will shift into gears easily and the box will hold oil, but will it stay in gear? Apparently if the back-cut (2:15 in the video) on the engagement teeth between speed gear and synchro sleeve are worn, these parts need to be replaced too. Someone who is simply installing a 'rebuild kit' will miss this.
You always think there must be an easier way. Loads of engineering and sleepless nights have gone into all these details to run smooth operations. Amazing and well explained. Great work.
As the sleeve moves towards the speed gear, the keys weakly push the blocking ring ahead until the conical friction surfaces make contact. The resulting frictional torque rotates the blocking ring so that it's teeth are 1/4 tooth pitch misaligned with the sleeve teeth which causes contact of the teethes' angled surfaces. This is called "energizing". As well as causing the blocking teeth to block the sleeve, the sleeve can now apply a strong force to the blocking ring via the tooth contact, increasing friction and synchronizing torque.
The best video for ASE, I watched this video 2 times before the test and still didn't pay enough attention. This video need to be watch 3 times for ASE manual transmission test
Thank you! The demonstration of the synchro in action at 7:00 helps it all make sense. (The first part of the video is the nitty gritty of what makes it work. The demo shows it in action.)
Drivemaster, you're the best Master. My language is Portuguese, but I didn't understand the Brazilian videos and I understood your video. I didn't understand how the synchronized ring works but thank for you, I understand now.
This is a very valid question and not an easy concept to understand so let me give this explanation a try. When the sleeve is forced in the direction of the gear to engage then next gear the keys will push on the blocker ring which pushes on the gear. Friction and heat is generated between the blocker ring and the gear. With the heat expansion forces occurs. This expansion from the heat creates a force that pushes the blocker ring and keys back against the sleeve. This force makes it difficult for the sleeve to continue in the direction of the gear until everything is in sync or very close to being in sync. When everything is in sync the friction, heat and resistive force is reduced to a point where the sleeve can now easily slide over and engage with the gear. I hope this makes sense.
@@DrivelineMaster thanks. I did more research today i found that the mass/inertia of the constant mesh gears trying to be slowed by the blocker ring will force the splines to be out of alignment (and unable to engage) until the gear speeds are in sync. Only then can the tapered splines be aligned by the driver pulling the shifter because there is no longer any force "binding" the splines
That is the reason the blocker ring can't immediately synchronize the rotational speed of the gear with the sleeve however it is the friction and the expansion forces that prevent the sleeve from moving over to attempt to lock onto the gear while they are rotating at different speeds.
Kids used to say they could drag race powershift as in brute force abuse without using the clutch, but the way the synchronizer is designed, this is impossible, because the harder you try to force a shift, the harder the synchro will ride up onto the cone and fight to prevent it
I wish teachers at school would teach the same way. Amazing video with lots of different presentations, I don't think this could be explained any better than this!!!
so, synchronization only works when the car is moving since we need the gears to be spinning correct? engaging first gear from a standstill therefore does not need to be synchronized just like reverse?
Pretty much correct, the synchronization only takes place when the gears are spinning. Even though the car is not moving if your engine is running and the trans is in neutral but vehicle is not moving some of the gears inside the transmission are spinning. If you push the clutch pedal to the floor and move the shifter quickly some synchronization might take place. If on the other hand after you push the clutch pedal to the floor you wait about 30 seconds before moving the shift lever then all the gears will most likely be stopped.
Question: Since the small clutching teeth is what mechanically locks the free spinning speed gear to the shaft and actually transfers the power why dont we see more of those stripped vs the actually gear teeth on high powered cars? It looks like it has much less material engagement would seem to be the weak link. I would also think the narrow sleeve that couples the two together would be prone to strip out before the actual speed gear teeth would strip under high power.
1) the small clutching teeth are already 95% in alignment with the teeth on the gear before the sleeve is allowed to slide onto the gear so there is no grinding. This is accomplished by the proper operation of the blocker ring. When the blocker ring becomes worn out and can no longer perform properly that is when the clutching teeth start the grind during the shift. This is the grinding noise that can be heard by the driver between shifts and is called gear clash. The reason these tiny teeth can handle the torque comes from the total surface area contact between the gear and the sleeve. The number of teeth and the length of the teeth determine the total contact surface area. I'm not an engineer but this is something that has to be engineered into the design. They must determine the maximum torque that the synchronizer and gear would have to be able to handle and how much contact is needed.
Between two gears, only one tooth on each gear is engaged with the other gear at any time. Between the parts of the synchronizer assembly, all of those small teeth are engaged at the same time, spreading the load out between them. Many small teeth are as strong as one large tooth.
One perhaps ignorant question on the final demonstration. What is the gear on the far left of the video? I assume it looks like the speed gear, and maybe I'm not adequately understanding the relationship between the speed gear and the speed gear clutching teeth.
I believe that was 1st gear speed gear. The speed gear and the speed gear clutching teeth are all part of one gear assemble. The speed gears area also the free spinning gears check out from time stamp 2:44 to view the speed gear AKA free spinning gear.
Who on Earth came up with this? I rebuilt two entirely different manual transmissions years ago. One on my '64 GTO and one on a '68 Ford Cortina. The inventors need a Nobel Prize in transmission design.
Not many explanations go into the importance of the key springs and tapers that let the pressure build against the friction ring and bring the gears to the same speed. Then suddenly snap and engage the teeth.... to me that is the most important function of the syncro.
Hay I have a 2008 dodge ram 1500 with a manuel 238 Getrag 6speed transmission in it. I'm have the same problem with second gear. Where can I find the parts for a 238 getrag and can I replace it with another manuel.
Unfortunately I don't have a source for that transmission. I once had a Getrag from a Toyota Supra and not even Toyota sold replacement parts short of an entire transmission. You can try West Coast Standard or midwest trans (www.midwesttrans.com/product-information/getrag-238-6-speed-rebuilt-manual-transmissions). try searching the internet using "getrag 238 rebuild kit" as your key words.
The best video to explain synchronizer. But I am a little confused, why did the sychronier blocker ring slow down the speed to snchronize with speed gear? It should be reversed, I mean, speed gear speeds up to sych with blocker ring.
When the transmissions is in 1st gear and you shift into 2nd gear (upshift) the speed of 2nd gear is rotating faster because the gear ratio for 2nd gear is a small ratio number such as 1st being 4:1 and 2nd being 3:1. Because the speed of 2nd gear is rotating faster than the output shaft and the synchro in 1st gear the 2nd gear must slow down to match the speed of the synchro and output shaft before it can engage and lock 2nd to the shaft. This happens with every gear change during upshifting. During downshifting this is reversed. The output shaft is going faster than the gear being downshifted into. Such as going from 4th at 1:1 down to 3rd at 2:1. Now when the blocker ring grabs the next lowest gear that gear will need to rotate faster or speed up to match the output shaft speed in order to synchronize. I hope this made sense. Also, those gear ratios are not actual but instead just used as examples to make a point.
There is a bit of magic involved in how well synchronization works. I doesn't seem reasonable that the blocker rings don't get chewed up after a few uses. It's magic.
Hi, so I have a problem with getting the car into 1st gear sometimes. It can be very hard to push it in but no grinding. This would suggest it's the blocker ring doing it's job and the synchroniser and main shaft gear aren't matching speeds. I've checked the slave and master clutch cylinder and I can't see anything that stands out. Do you have a clue what's going on. Shifting into all other gears seems fine. I also have to hold the clutch down for around 10 seconds before I can put the car into reverse without grinding gears. It just seems like a long time before the layby shaft slows down. Clutch actually feels solid and operating as it usually does. Any ideas.
A couple of questions when you have problems going into 1st. Is this when the vehicle is not moving or when downshifting while moving? or both? Have you tried replacing the lubricant with the recommend fluid? Because you said that you have to wait a good 10 seconds to shift into reverse makes me think you might have a spin down problem. This is where power from the engine continues to send power into the transmission input shaft even if the clutch pedal if fully pressed. What can happen is one of a few things. The clutch disk can stick to the flywheel, or the disk could bind on the input shaft and not slide away from the flywheel quickly enough, or the input shaft could be binding on the pilot bearing. All of these will delay clutch disengagement and cause hard shifting. I'm not sure what vehicle you have but I have had good luck using Redline Manual Transmission fluid solving shifting problems.
Im trying better to understand the basics of 90s Honda manual transaxles. Why is the imput shaft gears pressed on and not built into the shaft like rear wheel drive, drive gears? And when changing gears to a custom ratio sometimes only the driven gear gets changed. If your changing the ratio wouldn't both gears need to be changed? Thank you
Normally when a gear is pressed onto a shaft as compared to being part of the shaft it's because the gear needs to come off in order to remove or install something else. It's for assemble and disassemble purposes. Normally when there is a ratio change both gears are replaced. I don't see how it is possible to only change one gear. Let's say you want more low end torque and you want to change from a 3.5:1 1st gear to a 4:1 first gear. The input shaft gear must get smaller but in order for it to mesh properly with the output shaft that gear must be bigger. I have never done a ratio change on a Honda but it doesn't make logical let alone mechanical sense.
After several videos trying to figure this out, I finally get it. Excellent video. Now I wonder if there would be other ways to slow shaft/gear speed. Synchro's are spendy parts "labor wise" to replace. I also wonder what fluid would cause the least amount of wear & still give satisfactory shifting.
I don't want to give the wrong information. Most manual transmissions can not and should not use ATF. ATF can only safely be used in a manual transmission if and only if the service information or owners manual says so. Never use ATF in a manual transmission unless it has been specified by the manufacture as an acceptable winter oil option.
The internal teeth of the sleeve match up just right to the clutching teeth (dogs) on the speed gear as well as the blocker ring. Thus, the sleeve is free to slip over them - but once it does, they must spin together. So when the sleeve is pushed towards the speed gear, the sleeve pushes on the shift keys, which push on the blocker - all towards the speed gear. The internal cone of the blocker presses against the external cone on the speed gear, developing friction and either speeding up or slowing down the speed gear until it matches the speed of the hub/sleeve/blocker assembly. Once that happens, the sleeve can be pushed over the blocker and onto the the clutching teeth of the speed gear - thus coupling the speed gear to the sleeve, and therefore the hub, and therefore the output shaft.
The blocker ring rotates with the hub but the blocker ring is not fixed to a position but instead because the connection takes place because of the keys and the cut out on the ring. The ring can rotate separately about 2-4 degrees from the hub. The teeth on the sleeve, blocker ring and gear are space about 1-3 degrees apart. Because the teeth are cut at a pointed angle they don't have to align up perfectly. The video shows that sometimes but even being off slightly when the sleeve starts to move towards the gear the points on the teeth if not perfectly aligned will slide from one side of the tooth or the other forcing alignment. Kind of difficult to explain. I hope this made sense. Imagine two really sharp pencils and trying to hold them point to point. Unless you get it exactly perfect on each point as you move the points towards each other. If you miss hitting the point perfectly they will slide off the point to one side or the other. It's like that.
Could be several things. As the video shows the teeth with the cut back. if those are worn from years of grinding during gear shifting that can do it. Excessive free play in the shifter linkage or worn detent springs. Depending on how old the vehicle is old 1960 and 1970's vehicles could have misaligned bell housings. I even had a VW once that had the shifter boot installed backward that cause this. You could have worn shift forks or synchronizer sleeves. Anything that would prevent full engagement can cause it to slip out of gear. Holding the shifter ensured the synchronizer stays engaged with the gear.
They can be and are made out of other material. Some use a bimetal combination with a sintered bronze and brass material on the inside and steel on the outside. Others use steel and bond a friction material like a brake pad to the inside circumference. It's material that will work soaked in oil.
Here you go. The sleeve pushes on the keys which push on the blocker ring. The job of the blocker ring through friction between the ring and the gear is to grab the gear and make it go the same speed (synchronize) so the sleeve can slide over and lock the two together. If the blocker ring is unable to synchronize the gear to its speed a lot of friction is taking place. With more friction more heat is generated. With more heat there is expansion of components. The heat and expansion is a counter force pushing back on the blocker ring. That force on the blocker ring is transferred to the keys and then onto the sleeve. The counter force prevents the sleeve from moving close enough to the gear for the clutching teeth to touch. If the clutching teeth are allowed to touch before synchronization a grinding noise (gear clash) will be heard. Hope this helps.
I have 2 questions. 1) At the end 7:43 does the speed gear clutching teethes rotate? I see the angle cut teeth rotation, but not the clutching teethes. 2) And even with the clutch engaged, the counter shaft still rotates at a very high speed.lets say vehicle is stationary and starting to move. so there is no axle shaft or output shaft rotation. but the speed gears will have high speed rotation. So how does the synchronizer ring slow down the speed gear to make the connection in less than a second.
I have a few quesions, regaring an actual example in the topic. What can cause that I can barely get out of first gear in colder weather? The story a bit more explained: The MX-5 ND's manual recommends 75W90 GL-4 oil if the original oil is not available (which is often te case btw). One might thing that the original oil is also 75w90, but that seems not to be the truth, it's waaaay less viscous than a 75w90. I also put 75w90 in the trans and now even when I start at 15 deg C, it's hard to get out of first gear, I have to shift very eary into second. Also it's nearly impossible to shift into first while the car is moving. Putting the trans into reverse at 0 degress C is barely working. I don't experience any grinding btw. The syncro spec is as follows: 1: Triple Cone with Carbon coating 2: Triple Cone with Carbon coating 3: Triple cone 4: Triple cone 5: Double cone 6: Single cone with Carbon coating R: Single cone The original oil was very "dirty" looked like dark grey paint. Turned out it looked like this for everybody. Honestly it looked like someboday added molybdenium additive to the oil, but that's 100% not the case. So, can these symtoms caused by the more viscous oil? I mean, problems when putting it into gear is is one thing but I can barely get it out from first when above 10 km/h. After driving 4-5 minutes and the trans oil heats up everything feels way smoother again. What does one actually risk when a thicker or thinner oil is used thena what prescribed? Can a molybdenium additibe (LiquyMoly) cause any issues by times? (Synchro issues, and so on) Thanks and any info/explanation or suggestion would be appreciated. Absolutely great video btw.!
First of all 75W90 and 75w90 are supposed to be the same viscosity. the large or small W has nothing to do with it. These oils are tested in a lab at a specific temperature even if you feel they flow differently and one seems thicker than the other. What is critical is that you make sure your oil is GL4 grade. If you put in GL5 or GL4/GL5 this can cause issues. It's also possible that the old gunky lube was holding your trans together and the gunk between the blocker rings and the cones got flushed out with the new lube and the gunk was adding the necessary friction that is needed to shift. Normally the symptoms you describe have more to do with the clutch not disengaging. So let me ask. Can you shift OK with the engine off? If so your clutch might not be fully disengaging or your pilot bearing might be binding on the input shaft. I'm a big fan of Redline Manual Transmission Fluid (MTF). It's synthetic with superior friction qualities. if you can get this you might want to give it a try. Also check the owners manual. When I worked for Mazda some of those transmission would take Dexron Automatic Transmission fluid when the vehicle was being used in cold weather and 75w90 when it was used in hotter climates.
@@DrivelineMaster oh ok. Thanks. The w/W was just a typo. But if the clutch not disengaging then why does it work ok after a few minutes and why did the problem start immediately after the oil change? I think with engine off i chan shift but doesn’t it also depend on the wheel speeds (trans output shaft speed)? What i also can try maybe is to lift the rear put it in 1st and check if the wheels start spinning when i press the clutch pedal. Im not sure but if the clutch is completely disengaged then it should not move the wheels at all, right? Im planning to try something similar you mentioned if I can’t get the original oils. About the gunk. Yes, Im a but afraid that this is one of the issues. What do you think about the molybdenum additives? Is that a bad idea? Btw: the oil i put in was gl4/5. I didn’t think this could be a problem. Motul gre 300 75w90 btw.
Your right that if you had a clutch disengagement problem then the shifting problem should not have started right after the oil change. the W or w was the only difference I saw in your oil specs in your original message. Yes, if you raise both drive wheels, engine running and clutch pedal fully depressed that the drive wheels should not rotate. I once installed Redline 75w90 gear oil in a manual trans and it would not shift worth a darn and it would grind a lot. I took it out and put in Redline 75w90 Manual Trans fluid MTF and it shifted great. It was obvious that these were two different products both labeled 75w90. With the engine off and the vehicle not moving there is nothing to synchronize so shifting should be easy. Also clutch discs can stick to the flywheel or bind on the input shaft when the pedal is depressed. this can cause difficult shifting. Again this does not explain why the problem started just after an oil change. I would not put any additive in the trans unless it says right on the package that it's for manual transmissions. You don't want to make the oil slipperier there needs to be more friction between the oil and the blocker ring cones. If the oil was as bad as you say it's possible you flushed out what was holding the blocker rings to the gear and the clean oil is slipperier.
@@DrivelineMasterJust FYI: the original Mazda oil finally arrived and I put it in the car yesterday. It's WAY less viscous than the 75w90-s I tried before. Shifing is good now even in cold temps, no issuse at the moment.
