3 Types of Manual Transmissions

Car enthusiasts love manual gearboxes even though automatic transmissions have taken over the car industry. Today, one can’t even buy a supercar like Ferrari or Lamborghini with a manual gearbox. That said, there is a reason purist love manual cars. Previously, we talked about different types of automatic gearboxes. Now, let’s see what variety is there for manual gearboxes.

3 different types of manual transmission include Sequential manual transmission, Unsynchronized transmission, and constant mesh gearbox. 

Now let’s discuss different types of manual transmissions in more detail-

Sequential Manual Transmission

Most of us think of an “H” pattern shifter when we think of a manual transmission. However, there’s something called sequential transmission that’s unlike anything. If you are aware of a motorcycle gearbox, you know that just clicking the lever up or down changes the gears. That’s what sequential gearbox is.

If you have seen a superbike equipped with a quick-shifter, you know that it shifts quite fast. That’s the reason why sequential gearbox is often used in motorsport applications. Also, the sequential gearbox is a simple design and easy to repair. The unique thing about sequential gearbox is that it doesn’t allow you to skip gears. For example, you can go to 3rd gear straight from 1st gear. our review of Healtech quickshifter

Unsynchronized Transmission

Unsynchronized manual transmission is the first type of manual transmission invented in the late 19th century. This was the first time the gears were engaged by sliding them on the shaft. Mastering this type of gearbox required a certain skill of manipulating throttle, timing the shift correctly.

This was the case because the gears had to be spinning at roughly the same speed to mesh easily with each other. If the gears are spinning at different rpm when you change gears, it could grind gears and damage the gearbox. Those who have experienced this know that it’s not a great feeling hearing your gearbox scream in pain.

No wonder unsynchronized transmissions are also known as crash box because they would often refuse to mesh and make loud grinding noise. Learn more about double clutching an unsynchronized transmission below.

Why is double clutching required for older cars?

Double clutching is a technique that’s used with an unsynchronized gearbox. That’s why you don’t want to drive a vintage car without knowing how to double clutch. Here’s how you double clutch:

1) push down on the clutch pedal to free up the transmissions.
2) Move into the neutral gear position.
3) Release the clutch lever and rev the engine to the right rpm for the next gear. How much to rev comes from experience. But generally, if you are driving sedately then just a light tap on the throttle will be sufficient. If you are going fast and revving out the engine then you need to build up more rpm while in neutral.
4) Press clutch and shift into next gear.

As you can notice, shifting one gear requires you to press the clutch twice. And hence it’s called double clutching.

Synchronized / Constant Mesh Gearbox

Constant mesh gearbox is an improvement over unsynchronized manual transmission that needed complicated skills like double clutching. Constant mesh gearbox is what we have in all modern manual transmission cars.

The main goal of a constant mesh gearbox was that gears on both the shafts remain spinning in sync with each other. The gears on the layshaft are fixed but gears on output shaft can be moved as they sit on bearings.

Straight Cut Gears & Helical Cut Gears

Most of the cars today have helical cut (angled) gears inside the transmission case. Straight cut gears are mostly used in race cars. They are not used in road cars because it’s noisy and not smooth.

Straight cut gears
Helical gears (top). Straight cut gears (bottom).

For motorsport application, straight cut gears are good because they don’t produce side to side axial load. This lateral force is often generated in helical cut gears and applied through the input shaft. This requires a robust transmission components to handle this side to side force.

Helical Gear exerts unnecessary lateral force

Straight cut gear doesn’t produce this force, therefore, the rest of the components are less likely to fail even when a large amount of torque is applied through the gears.

With helical gears, the transmission casing and shafts need to be extra robust which adds weight. That’s another reason why race cars are better off without helical gears (weight saving reasons). And did I mention that they are easier to assemble?

Automated Manual Transmission

Automated manual transmission is an attempt to use the existing manual gearbox and make it close to automatic. For this, the gear selector and clutch are hydraulically controlled by the ECU of the car. The ECU software decides when to shift gear and signals the hydraulic actuators to do so.

Automated Manual Transmissions Use Simple Actuators
Automated Manual Transmissions Use Simple Actuators

That said, AMT transmission also has Tiptronic mode so that you can switch gears yourself and let the unit handle clutch work. Yes, they don’t work as well as a proper automatic transmission but it’s a low-cost solution for an automatic transmission.

Fun fact: AMT gearbox was also introduced in 2003 BMW M3 E46 in form of SMG transmission (sequential manual gearbox).

Also Read: Engine ECU Remapping FAQs; Should you do it?

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Siddharth Sharma

Siddharth has always been passionate about Cars and Bikes. He was the kind of kid that always had the latest Auto magazine in his school bag. He had this dream- to become a professional racecar driver. Finally, in 2012 he found himself racing as a rookie driver in the Polo R Cup national racing championship. Over time he had to readjust the sail and get into automotive journalism to continue enjoying machines on wheels.

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Siddharth Sharma

Siddharth has always been passionate about Cars and Bikes. He was the kind of kid that always had the latest Auto magazine in his school bag. He had this dream- to become a professional racecar driver. Finally, in 2012 he found himself racing as a rookie driver in the Polo R Cup national racing championship. Over time he had to readjust the sail and get into automotive journalism to continue enjoying machines on wheels.