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Tips & Tricks

Sequential Transmissions

Clutchless Shifting

by
Bartek Bartoszewicz Tuning Professional

#Getriebe

#Motor-Tuning

Sequential Transmissions

If you love being able to control your car in your own way but you don’t want to go without the convenience of an automatic, why not find a happy medium?

A sequential transmission gives you exactly that. In this article, we demystify the technology and tell you the pros and cons of this type of gearbox.

CONTENT

1. What is a sequential transmission?
2. Which makes of car have a sequential transmission?
3. Sequential transmissions in motorsport engineering
4. Tuning: retrofitting sequential transmissions and dog boxes
5. How to handle a sequential transmission
6. Transmission questions?

What is a sequential transmission?

First of all, the term ‘sequential gearbox’ tends to be used inconsistently. Fundamentally, it only refers to the actual process of shifting: you have to shift each gear up or down in sequence – you can’t jump from second to fourth for example. But the term is also used to mean a transmission that’s a cross between manual and automatic.

Unlike manual shifting, you change gear in a linear sequence. So you can only ever go up or down one gear. However, the process is largely automated: all you have to do is touch the lever. That’s why the sequential shifting system is often referred to as semi-automatic. But ... in today’s sports cars, that’s not entirely accurate. For example, at the red light they go straight from fifth to first, which contradicts the usual definition of a sequential transmission.

Since you can’t skip a gear, your freedom is somewhat limited. But you do get more of a feel for the car and for driving. One big advantage of a semi-automatic is that there’s no torque converter, which means your fuel consumption is lower. When it comes to gears, a fully automatic shifting system is obviously far more convenient because there’s no clutch. But no clutch also means no influence. So a sequential transmission gives you the best of both worlds.

Which makes of car have a sequential transmission?

Major manufacturers have different names for a sequential transmission (in both the original and colloquial sense), including:

SMG (BMW)
R Tronic (as in the Audi R8)
Smart

Porsche GT3 CUP (six-speed claw transmission)

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Sequential transmissions in motorsport engineering

The technology behind sequential transmissions originates in motorsport. No doubt you’re familiar with the unmistakeable earsplitting sound a sequential transmission makes – like a wheezing crackle. The reason it’s so loud is because of the straight cut (spur) gears. But the types used in Formula 1 and the like are the deluxe version, because the priorities are very different to those for road driving. Race cars usually have a rocker switch on the steering wheel, whereas normal cars have a gear lever. Either way, shift command transmission is exclusively electrical.

Semi-automatics change gear incredibly fast on account of the special clutch design (and dual clutch transmissions are faster still). Race cars sometimes even have triple clutches. Cars for road use have helical (bevel) gears and draw-key gears, where a cone/wedge presses balls between the main shaft and the gears in order to change gear.

On a sequential transmission as opposed to a manual one, traction interruption is minimal, which is a big advantage. But the gears are under much more stress, which means they wear faster. This is irrelevant in motorsport where the transmission only has to deliver top performance once, and can then be replaced. As a sequential transmission has no torque converter, it also saves you fuel.

Sequential transmissions in sports cars usually have their own oil circuit with an electric oil pump. This ensures that a consistent pressure of 40 to 50 bar is maintained for shifting. The clutch is hydraulic instead of manual, and a second valve block controls the gear change.

Tuning: retrofitting sequential transmissions and dog boxes

If you want to retrofit your car with a sequential transmission, you can do it yourself if you have the experience, or of course you can have it fitted by a tuning workshop you trust. Transmission installation is another of our specialities. If you’d like to book an appointment to talk about it, just send us a chat message or fill out our contact form.

Retrofitted sequential transmissions are usually installed in combination with a dog box – an H-pattern gearbox that uses ‘dog rings’ instead of syncro rings. So there’s no speed adjustment involved. Instead, the idea is to establish a tight positive fit and traction. When you have a dog box you don’t need a clutch, which means you can change gear faster, but the shift also requires more force. Most sequential racing transmissions are mounted on a dog box with a selector drum.

If you want to retrofit your transmission for extreme performance, you’ll need a dog box gear set along with other parts like an upgraded oil cooler. And obviously you’ll also need a corresponding shifter to make those rapid-fire changes possible. All the parts are available from our store in the transmission parts section.

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How to handle a sequential transmission

Quick but calm – in this video, our colleague JP explains how to avoid snapping your gear lever and what double-clutching is all about:

Transmission questions?

We’re happy to answer them. Send us a chat message or check out our FAQs.

Bartek Bartoszewicz

Tuning Professional

His first car was a Polo Mk1 with a 40 Weber twin carburetor and 129 PS (95 kW). His second was an Audi 50. Today Bartek tunes Lamborghinis to 1000 PS (735 kW). Even as a young boy, Bartek disassembled vehicles and put everything back together better. He wrote his high school diploma with oil on his fingers. The trained automotive mechanic with a focus on engines and gearboxes was determined to go into motorsports. In his 10 years in Formal 1, he supervised 73 races, including as engine mechanic for Ralf Schumacher at Toyota. Since 2010, he has dedicated himself fully to his company BAR-TEK® and helps his customers to bring VW and Audi engines to peak performance.

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