The 1929 Cadillac 341B (First Synchro-Mesh)

Some cars may not be remarkable in themselves but they introduce an innovation of huge importance. One such was the 1929 Cadillac 341B. We look at the old crash gearboxes of the past, and the smooth-shifting successor.

The 1929 Cadillac 341B was launched with a revolutionary new gearbox: the “‘clashless Synchro-Mesh Silent-Shift transmission”.

A red 1929 Cadillac 341B in a museum
The 1929 Cadillac 341B

Cars in the old days were difficult to drive largely because of their so-called “crash” gearboxes. The clutch pedal had to be pushed down, one gear was deselected and the lever moved to the next ratio.

A pair of spinning gears or cogs had to be slid together with horrible gnashing, crunching noises as their teeth met each other. Then the clutch was gingerly let back in.

The ability to drive almost everywhere in top gear was of great importance to Edwardian motorists, many of whom could not manage the “crash” gearboxes of the day and were unable to change gears on the move.

The internals of a car gearbox with big cogs
Synchromesh helped all these spinning gears to mesh quietly

The Cadillac 341B changed all that with synchromesh.

The interior of the Cadillac 341
The synchromesh gear lever

But then its sales prospects were ruined by another Crash- in Wall Street. Read on to find out how synchromesh worked, and how you perform the lost art of “double declutching.” Watch this youtube

Cadillac was founded out of the ashes of the Henry Ford Company in 1902. Ford had left the company after two years because of a dispute with his investors. The new marque derived its name from Antoine de la Mothe Cadillac, who founded the town of Detroit, Michigan.

The red Cadillac from the other side
The Cadillac 341 B brought silent gear changing

General Motors bought Cadillac in 1909 because of its high quality of build, and the marque became GM’s luxury brand. Not only that, Cadillac built a reputation as America’s most technically innovative car manufacturer.

They introduced the electric starter, electric lamps, an all-steel roof (before then cars had fabric roofs), safety glass, the first dual-plane crankshaft V8 engine, and, crucially for this story, the world’s first synchromesh transmission (source

The internal combustion engine isn’t ideal for transport. Unlike an electric motor or a steam engine, it cannot start from a standstill and so it needs an electric starting motor and a clutch, which smoothly engages the spinning engine flywheel with the stationary wheels.

Again, unlike an electric motor, the internal combustion engine has so little torque or twisting power that it needs to run at a high rate of revolutions. This in turn means it needs a gearbox to step down the revolutions and step up the torque, just as a lever helps to lift a heavy weight.

Even the Cadillac’s V16 engine needed gears:

A picture of a black and silver Cadillac Model 452 V16 engine
Cadillac Model 452 V16 engine

General Motors realised that many sales were lost due to newbie drivers struggling to change gears. So something had to be done, and the 1929 Cadillac 341B Roadster showed how to do it with the new synchromesh design.

Gears are monogamous and are much happier if they can run constantly in mesh together with their partner. So in a synchromesh box, all the pairs of gears run together in this way, but they are free to spin on the output shaft. Gear ratios are therefore selected by locking the desired gear pairs to the output shaft by using locking rings.

When the clutch pedal is depressed and the gearbox is disconnected from the engine these cone-shaped locking rings are slid up to the next pair of gears by moving the gear lever, and then they synchronise the speed of the gears to that of the output shaft. This they do by friction on the cones.

Another gentle pull on the lever locks the gear pair to the output shaft, and the clutch is re-engaged. You might feel the “click”, “click” through the lever as these two actions are completed.

And if you want to know what the old crash gearboxes sounded like, try selecting reverse gear before the engine revs have fallen. The nasty old sliding straight-cut gear pinions live on, lurking under the letter “R”. Lamborghini was the first (and nearly the last) to bother to put synchromesh on reverse gear.

Before synchromesh drivers used a technique to match the speeds of the spinning gears: this was called double declutching:

  • The accelerator or throttle is released, the clutch pedal pressed down and the gearstick moved to neutral.
  • The clutch pedal is released and the driver matches the revolutions of the engine to the next gear by doing this:
  • If changing into a higher gear, release the throttle and wait until the engine revs have fallen.
  • If changing into a lower gear, rev up the engine by “blipping” the throttle.
  • At the moment when the engine revs and the new gear are closely matched, the driver then presses the clutch pedal down again, shifts into the next gear, and releases the clutch.
  • Bingo! With practice, this results in a silent, smooth gear change.

Learning how to double-declutch is still a requirement for a commercial truck licence in some jurisdictions as many trucks still have crash gearboxes.

Actually, a sensitive driver could set off and change gears without using the clutch at all, starting the engine- and the car- in first gear and carefully matching the engine revs with road speed up and down the ratios.

If you are adjusting the speeds correctly you won’t need to touch the clutch pedal at all and the gears will engage with a quiet grunt.

In 1929 the previous Cadillac 341 had been upgraded to the 341-B with the yearly improvements GM customers expected: there was a slight increase in power, and an optional low-compression engine was offered.

A picture of the Cadillac radiator
The Cadillac 341B had slightly more power

There were slightly larger tires, double-acting Delco shock absorbers, new brakes, chrome-plated brightwork and electric windshield washers (source

But the big news was of course the new synchromesh transmission which at last brought easier gear changes. The 1929 Cadillac 341B had synchromesh only on the second and third gears, but the car was a revelation, and the new gearbox was swiftly copied around the world.

No less than five million dollars were put into upgrading the factory but then the hoped-for market growth was crushed by the Wall Street Crash.

How much is a Cadillac Series 341 worth?

A Cadillac Series 341 is worth an average of $63,000 today (source

The rear of the red Cadillac
No looking back: synchromesh meant no more grinding gears

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