# What Is an SMG Transmission? | Otto Explains | AutoTronix **Section:** Otto Explains **Canonical:** https://autotronix.om/otto/smg-transmission-explained **Language:** English **Arabic version:** https://autotronix.om/ar/otto/smg-transmission-explained --- ## Short Answer SMG, short for Sequential M Gearbox, is BMW M’s automated manual gearbox. It is a manual gearbox with a conventional clutch, but a control unit and a hydraulic system operate the clutch and change gear, so there is no clutch pedal. BMW put it on sale in the M3 in 1996 and later replaced it with a dual-clutch gearbox. It can shift quickly or drive itself in an automated mode, but each change briefly interrupts drive, so it feels different from a conventional automatic. --- ## What is an automated manual gearbox? It is a manual gearbox in which a machine does the driver’s clutch and lever work. In the SMG, BMW used a gearbox technically identical to the car’s regular manual and added a control unit and hydraulics that open and close the clutch and select the gears. The car has only two pedals. Unlike a conventional automatic, there is no torque converter. BMW is not the only maker to use the idea: Suzuki’s AGS, launched in 2014 on the Celerio, also uses an actuator to carry out the clutch and gear changes automatically. --- ## How does an SMG change gear? When a change is requested, a solenoid valve lets pressurised hydraulic fluid into the clutch master cylinder, which disengages a clutch of the same type as a manual gearbox uses. Hydraulic cylinders in the shift actuator then move the selector shaft to engage the next gear, and the clutch closes again. While this happens, drive to the wheels is briefly interrupted, much as it is when a driver changes gear in a manual car. On downshifts the system matches engine speed automatically, which BMW calls double-declutching, and it refuses a downshift that would over-rev the engine. --- ## How do you drive a car with an SMG? There are two ways. In the sequential mode the driver chooses every change, with the centre lever or with paddles behind the steering wheel. In the automated mode the gearbox changes gear itself, according to the selected program, the speed and the accelerator position. BMW’s Drivelogic offers eleven programs, six sequential and five automated, from gentle to very sporty. When the car stops, the second-generation SMG selects first gear by itself, and pressing the accelerator moves the car off. In the automated mode, easing off the accelerator slightly can prompt an upshift, much as a driver lifts off when changing gear in a manual car. --- ## How did the SMG develop? BMW M put the SMG on sale in 1996, exclusively in the M3, and described itself as the world’s first supplier of a fully automated manual gearbox. The second-generation SMG II followed in the M3 in 2001, based on the M3’s six-speed manual gearbox and shifted by lever or paddles; BMW quoted its fastest shifts at 80 milliseconds. The third-generation SMG III, announced in 2004 for the M5, had seven speeds, with the hydraulic unit and actuators built into the gearbox casing, and BMW said it shifted about 20 percent faster than the second generation. BMW M then replaced the SMG with M DCT, a seven-speed dual-clutch gearbox developed by Getrag, first in the M3 in 2008. --- ## How is an SMG different from a dual-clutch gearbox? An SMG has one clutch, so each gear change has to open the clutch, move to the next gear and close it again, with a short break in drive. A dual-clutch gearbox such as BMW’s M DCT has two clutches, each serving its own set of gears, so the next gear can be prepared on one side while the other is still driving. Both have no clutch pedal and both can be shifted manually, but a dual-clutch can change gear without interrupting the drive. The two are easy to confuse because both look the same from the driver’s seat. --- ## What should SMG owners and buyers know? An SMG combines a manual-type clutch, a hydraulic system, solenoid valves, sensors and a control unit. A fault in how it shifts can therefore be mechanical, hydraulic or electronic, and the symptoms can look alike. [Reading the gearbox control unit’s fault codes and live data](https://autotronix.om/otto/diagnostic-scan-explained) gives a direction, and testing confirms the cause before parts are replaced. For an older BMW M car with an SMG, a [pre-purchase inspection](https://autotronix.om/otto/pre-purchase-inspection) that includes how the gearbox shifts is worthwhile, and a gearbox that jerks or slips deserves diagnosis rather than guesswork. AutoTronix Garage handles gearbox diagnosis and repair, AutoTronix Lab handles electronic diagnostics, and AutoTronix PERFORMANCE offers pre-purchase inspections for performance vehicles. --- ## Common Questions **Does a car with an SMG have a clutch pedal?** No. It has a clutch of the same type as a manual car, but hydraulics open and close it for the driver, so there are only two pedals. **Can an SMG be driven like an automatic?** Yes, in its automated mode it changes gear by itself. Each change still briefly interrupts drive, so it does not feel like a conventional automatic. Easing off the accelerator slightly can prompt an upshift. **Is BMW’s M DCT the same as SMG?** No. M DCT replaced the SMG. It is a seven-speed dual-clutch gearbox with two wet clutches, while the SMG is a manual gearbox with a single clutch operated by hydraulics. **Do other car makers use automated manual gearboxes?** Yes. Suzuki’s AGS is one example: it uses an actuator to carry out the clutch and gear changes automatically, gives two-pedal driving and also offers a manual mode. --- ## Related Otto Explanations - Why Is My Gearbox Jerking or Slipping?: https://autotronix.om/otto/gearbox-jerking-slipping --- ## Related Services - Gearbox Repairs: https://autotronix.om/garage/gearbox-repairs - Advanced Car Diagnostics: https://autotronix.om/lab/advanced-diagnostics - Performance Car Pre-Purchase Inspection: https://autotronix.om/performance/performance-pre-purchase --- ## Book a Service WhatsApp: +968 9966 8600 https://api.whatsapp.com/send/?phone=96899668600&type=phone_number&app_absent=0 Location: Mabellah Industrial, Street 7, Muscat — Saturday to Thursday, 9 AM to 9 PM