Friday 23rd August 2019,

How Does a Synchromesh Work: Simply Explained

Bev Roberts 11. November 2014 Dirty hands, Magazine No Comments
Synchromesh by adogcalledstray

This chapter is the result of a very strange request;

Describe the purpose and operation of synchromesh WITHOUT getting technical or involving the gearbox in any way. It has been very difficult for me to complete this task within the parameters. This is my best effort.

The need for synchromesh;

Prior to the inception of synchromesh, gear-changing was a complicated business. As synchro boxes took over, the original type of gearbox became known as a `crash` box. The crash box was well named because any attempt to shift gears in the direct, modern way resulted in the gears crashing together because they were rotating at different speeds.

It was necessary to synchronize the speeds to make a clean shift. This was achieved by a process called `double de-clutching`. This system had to be learned by the new driver before he could drive effectively. Any mistake would be rewarded by damage to the gear`s teeth and much unpleasant `music`.

How a synchromesh gearbox works explained (very simply);

Imagine you want to push a wheelchair from the ground-floor of a house up to the first floor. The only solution will be a ramp, albeit a long one. Synchromesh works like a ramp between two gears. Different ratios are of different diameters. The synchro is a bundle of toothed discs, usually made of brass, in the shape of a cone. When the driver wants to shift gear, say from 1st to 2nd gear, the movement of the gear-stick moves the drive gear known as the pinion. The pinion is on the input-shaft which brings the torque from the motor via the clutch. As the shift goes through, the pinion runs up the synchro cone, slowing the pinion speed to match the speed of 2nd gear. This is called `a state of synchronous`.

The synchro discs are also a type of clutch and as they come under thrust from the pinion close up and become a solid unit. However, synchromesh is not bullet-proof, attempting very fast gear-changes will eventually burn out the cones. Compared to a well driven crash-box, the synchromesh box is quite slow but it achieves the object.

To see how it works in practice watch the video below to give you a better understanding what happens inside the gearbox.



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About Bev Roberts

Speed, the smell of hot oil, the roar of a straight-through exhaust and the scream of an engine at max revolutions. They have all been a large part of my life for almost 50 years. It is time to share my experiences with you, dear reader. Do you want to know more? Read on through my `Full Bio` and many articles.

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I was born in Hereford UK in 1948 and brought up in Gloucester UK. I played Rugby football internationally as a schoolboy. At the age of 17, a new and wet driving license in my paw, I entered motor racing. I was supported and financed by my parents and so my journey began.

In 1965 I bought a 1293cc Mini-Cooper `S` and campaigned it for a season. Having quickly made some good friends in the racing fraternity, several interesting opportunities came my way. I joined a sports-car team and raced in the Le Mans 24 hours in 1968 and 1969 in a Lola T70. Mechanical failure defeated both efforts. During that period I owned and raced a `D type` Jaguar and an AC Cobra. In those days cars like that were available and not too expensive, now they reside in museums and private collections. I had a chain of interesting cars through my youth including Jaguars, Minis, Mustangs and Lotus-Cortinas.

As a young driver I had my share of accidents too. Often the car would only be worth scrap-metal value by the time I got it home! I worked for an Aston-Martin/Jaguar dealership for a while, which enhanced my experience and gave me the opportunity to sample some very exotic machines, Ferrari, Facel-Vega, Iso and Maserati to recall a few of them.

At the end of 1969 I moved to South Africa to work on my uncle`s farm but the S.A. government had other ideas and drafted me into the army. After five years had passed I was thanked and released from the service. While I was there I bought a beige Cadillac Eldorado, previously the property of Marilyn Monroe. While I was away on a patrol my girlfriend had it re-sprayed pink! I was unimpressed by both the joke and the bill for the work!

When I returned to UK in 1974 I left it behind. On my return I found that the once-mighty British motor industry was in decline and was headed for oblivion. Motor racing was now very expensive so I turned to commercial transport. Driving large trucks gave me freedom and a chance to see some of the world. I don`t remember ever making a career choice but for the next thirty years a truck was my home. For about ten years in that period I owned two trucks of my own.

I also owned a famous MGB-GT, known as `Lucky`. If you`d like to read `The Story of Lucky` there is an article in Inopian`s archive. I finally retired, due to ill-health, in 2008. Since I had varied knowledge and many experiences on our subject I decided to share the stories of the cars I enjoyed (and hated) with the new generation.

Enjoy Inopian… it is constructed and written for you.

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