Back in 2006, original equipment manufacturers (OEMs) offered buyers the choice between an automatic and a manual transmission in 47% of new cars. By 2018, only 2% of vehicles sold had a manual transmission, according to edmunds.com. Today, good luck finding a manual transmission in anything but an enthusiast car.
Video transcript: How Does a Manual Transmission Work?
Featuring John Gardner, ASE Master Certified technician, automotive technology instructor and host of Motorhead Garage, with AMSOIL Director of Product Marketing Len Groom.
John Gardner: Sitting at a stoplight, revving it up, pop the clutch, and you’re off. Wow. Shifting through the gears and flying. Gotta love it.
Nothing better than a manual transmission. But with it, well, comes a lot of movement. You can see everything down there from the flywheel going through all the gears to the output shaft. Welcome to this AMSOIL Tech Tip.
It’s all about the manual transmission. Where do we start? Well, right here at the input shaft. Now the input shaft comes in, and then there’s all your gears.
The power is gonna go through the counter and then the synchronizer is gonna lock and then what happens it goes to the output shaft. I can show you all the different gears. Here’s first gear right here. Now first gear, you’re coming in through the input shaft, You’re coming down to the counter shaft.
That’s always moving. And then depending on the synchronizer, you can see it’s over here locking this gear to the shaft. That’s first gear. Small gear driving a big gear.
Torque multiplication, first gear.
Now second gear, once again, the input’s coming through, and then I go through almost two gears the same size. Maybe that one’s a little bit bigger, so I’m starting to lose torque and get some speed, but notice the synchronizer’s locking that gear to the shaft. Second gear. Third gear, once again, coming in through the actual input shaft.
It’s locked directly to the output shaft. There’s direct drive, one to one. You’re coming in and going out. And reverse, we just throw another gear in the mix and the output shaft goes backwards.
That’s cool, but I have it for you right here on the table in action. Check this out. I just said it comes in through the input shaft. So the synchronizer’s in the middle.
Nothing’s going on. So what happens if I lock that gear in, now I’m coming in, down, up, and you can see the output shaft is now turning with the input shaft because it’s locked with the synchronizer. Now there’s a lot going inside these manual transmissions, and there’s a lot of problems like leaks, gear problem, noisy teeth, and shift forks. Len,
There’s a lot going on inside of there.
Len Groom: Yeah. And it all needs lubrication.
John Gardner: Especially these synchronizers.
A lot of people don’t know they have to bring these gears up to speed. So when I’m moving over, man, they’re actually causing some friction in there.
Len Groom: Right. It acts kind of like a clutch and there’s some frictional characteristics. So when you’re building a gear lube, you’ve got to really watch what you’re doing because there’s so many things going on. Just the chopping action of those gears meshing together will tend to chop the oil at a molecular level and it tends to thin out, which can compromise protection.
The synchronizers you mentioned, that acts like a clutch. We need to deal with the frictional characteristics. It can’t be too slippery. It can’t be too grippy, so you have a nice smooth shift.
All of that can be affected by the oil. Heat is also a key factor here as well. So the oil needs to be extremely robust, additized properly to be able to protect that transmission and give you, you know, flawless performance.
John Gardner: Now the synchronizers themselves, now they’re brass and there’s some problems with the fluid as well if you don’t have a good fluid.
Len Groom: At certain temperatures, gear lube can develop an appetite for yellow metal. Right? Unless you formulate for that, which we do. So heat doesn’t necessarily become a problem with our transmission fluids.
John Gardner: And that’s awesome. Just go to AMSOIL.com if you have a vehicle with a manual transmission or an automatic transmission. It doesn’t matter what you drive. They have a product for you.
Even with manual transmissions on the endangered species list, questions about automatic vs. manual transmission fluid still arise. Whether you opt for a stick or a slush box, you want to use the correct transmission fluid to maximize its performance and life.
Three responsibilities of a good manual transmission fluid
Just because they’re less complex than automatics doesn’t mean manual transmissions have simple lubrication requirements. A good manual transmission fluid must serve several roles, including…
1) Enable smooth shifts
Nothing connects vehicle and driver like a smooth-shifting manual gearbox. Enthusiasts won’t tolerate a transmission fluid that interferes with that link.
Here, we have some cross-over between automatic and manual transmission fluid. But they go about enabling smooth shifts differently based on different component architecture.
Most manual transmissions are equipped with synchronizers. As the name suggests, the synchro equalizes its speed with that of the gear being engaged, allowing a smooth shift. Without it, the gears spinning at different speeds would clash as they try to mate.
The synchronizer unit is comprised of two main components: the sleeve and the blocker, or synchronizer ring. When the driver selects, for example, first gear, the sleeve moves to the first gear and locks onto the gear engagement teeth, also known as dogs. Depressing the clutch pedal and selecting second gear results in the sleeve moving the other way and selecting second gear in the same fashion.
Before the sleeve can lock onto the gear, the rotational speed of each must first be synchronized. The friction between the blocker ring and a cone on the face of the gear equalizes their speed, allowing gears to mate without clashing. The entire process happens quickly and goes unnoticed in correctly operating transmissions.
Lubricant viscosity plays a vital role in shift feel.
Viscosity that is too high could prevent shifting until the transmission warms up or result in abnormally high temperatures during operation. Viscosity that is too low could cause the synchronizer and dog gear to engage too quickly, resulting in grinding or hard shifts and abnormal transmission wear.
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Brad Nelson is an AMSOIL Technical Writer II who develops content about lubricant technology, product performance and vehicle maintenance. He works with engineers and product specialists to translate testing, application requirements and approved performance claims into clear customer guidance. Nelson’s work includes AMSOIL Blog articles, AMSOIL Magazine features and technical explanations concerning motor oils, gear lubricants, vehicle systems and maintenance practices.
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