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Busting the "shortshifters cause excess synchro wear" myth

There is a trend we are seeing more and more on a number of forums of people claiming that "short shifters cause excess synchro wear".

It's simply untrue, and here's why ...

All a properly engineered short shifter does is reduce the throw at the top end of the gear lever.

With a properly engineered short shifter, the bottom end of the gearlever is moving exactly the same distance as with a standard shifter. In other words, your gearbox doesn't "know" if you are using a standard shifter or a short shifter.

All that changes is the distance moved at the TOP of the gearlever.

Here is a photo of a Porsche factory short shifter ...

Given that Porsche invented the synchromesh system, if short shifters caused excess synchro wear, then Porsche wouldn't make factory short shifters.

Here is a photo comparing a Porsche Factory standard throw shifter (A) to a Porsche M241 Factory Shortshifter (B) and an aftermarket shortshifter (C) ...

Image credit: Photo courtesy of SeineSystems.com http://www.seinesystems.com

The most important change in lever design between the Porsche factory standard shifter and the Porsche factory short shifter in the photo above is the distance from the pivot hole to the bottom of the shift lever. Look at the differences in the distance "x" in the photos above.

Note that the distance from the pivot hole to the top of the shiftlever on shifter A and the distance from the pivot hole to the top of the shiftlever on shifter B are the same.

A shiftlever is exactly that - a lever. By moving the pivot point relative to the bottom of the lever, you reduce the required throw at the top of the shift lever.

Many short shifters also use a pivot that adds a second pivot for the side to side movement of the lever, so that you don't "crowd" the gates. ie such systems give you a short back and forth throw (like 1st to 2nd in a standard h-pattern gearbox), but maintain wider spacing between the 1st to 2nd plane and the 3rd to 4th plane etc. This helps ensure you select the correct gear.

Synchro wear simply comes down to how the car is driven. If you crunch through gears, don't match revs, and don't give the synchros the time they need to do their job, then it doesn't matter if you use a short shifter or not - crunching gears and not matching revs will always cause gearbox synchro wear.

There is a simple to understand article about how synchros work here ...

http://en.wikipedia.org/wiki/Manual_transmission#Synchronized_transmission

It reads ...

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"In a synchromesh gearbox, to correctly match the speed of the gear to that of the shaft as the gear is engaged, the collar initially applies a force to a cone-shaped brass clutch attached to the gear, which brings the speeds to match prior to the collar locking into place.

The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings (also called blocker rings or balk rings, the latter being spelled "baulk" in the UK).

The gearshift lever manipulates the collars using a set of linkages, so arranged so that one collar may be permitted to lock only one gear at any one time - when "shifting gears," the locking collar from one gear is disengaged and that of another engaged. In a modern gearbox, the action of all of these components is so smooth and fast it is hardly noticed.

The modern cone system was developed by Porsche and introduced in the 1952 Porsche 356 - cone synchronizers were called "Porsche-type" for many years after this. In the early 1950s only the second-third shift was synchromesh in most cars, requiring only a single synchro and a simple linkage - drivers' manuals in cars suggested that if the driver needed to shift from second to first, it was best to come to a complete stop then shift into first and start up again."

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Anyone who says that a short shifter has caused excess wear on their gearbox needs to learn how to shift gears properly.

As it says above "The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings". So clearly the simple solution is to avoid mismatches in engine revs vs the speed the wheels are turning.

You do that by learning to blip the throttle properly on downchanges so that your engine revs match the gearbox shaft speed, and not flat shifting on upchanges. Simple.

Learn how to "heel and toe" if you want your synchros and transmission to last.

Excess synchro wear is caused by one thing only - shifting with mismatched engine speeds vs wheel / gearbox shaft speeds with no mechanical sympathy for the job the synchros do. Period.

When you understand that undisputable fact, it becomes obvious how the "shortshifters cause excess synchro wear" myth got started. Someone clearly wore out a gearbox's synchros by not matching revs, not having any mechanical sympathy for the job synchros do, and then instead of looking at how they drive, decided to blame the short shifter instead.

Synchros are supposed to wear, just like clutches and brakes. The point is that if you don't match revs, then your synchros will wear out faster than someone else's synchros who understands how they work and drives accordingly.

It's exactly the same kind of wear issue you find in clutches if you constantly do hard standing start launches. If you drive your car like that, your clutch will wear out faster than someone who doesn't launch like that. The cause is not the clutch itself - it's how the clutch is used.

Conversely, the more you match revs and have mechanical sympathy for the job that synchros do, the longer your synchros will last.

Learn to "heel and toe"

In the past, people were often taught how to double de-clutch and how to "heel and toe".

Nowadays it seems like this skill is rarely taught.

There are two articles here about the heel and toe technique ...

http://www.edmunds.com/ownership/howto/articles/45792/article.html

http://www.edmunds.com/advice/youngdrivers/articles/119593/article.html

... and a video here ...

http://videos.streetfire.net/video/Heel-Toe-Double-Clutching_57431.htm

created on 2009-02-11 11:02:23 by adamr

updated on 2009-02-12 11:38:58