Do short shifters increase synchro wear and tear? This is a heavily debated topic on every tuner forum. It may not even be a concern for our gear boxes. But this IS Ford here. I'll do my best to explain it all. I'm leaving out a bunch of details and nuances for simplicity sake (or cuz idk lol). Maybe as a group we can decide if a short shifter can indeed expedite synchro wear and tear. Take this ALL with a large grain of salt lol This is written to spark debate, not state a fact in stone! This is just my understanding of a modern manual transmission.
The synchros move at road speed (or lack there of) because they are directly connected to the OUTPUT shaft. The gears (1-6) themselves are also on the output shaft but spinning independently from it on needle bearings. In other words, the forward gears are NOT directly connected to the output shaft, at all.
The gears are spun via engine power brought into the transmission on the INPUT shaft. It has its own set of directly connected gears that are meshed (in contact) with the gears on the output shaft. So the moment you turn on your car, the gears are freely spinning on thier needle bearings on the output shaft at a given ratio of engine speed but not engaged. The synchros aren't moving yet as they move with the wheels via the output shaft (for simplicity sake)
FUN FACT: Pressing the clutch disengages the input shaft from the engine. At that point the gears slow down on their needle bearings, depending on just momentum. If your car is moving, the synchros continue to rotate at road speed.
Simply put, when a gear is selected, the shift fork acts on the synchro sleeve, sliding it's beveled dog teeth over a set of beveled teeth on the selected gear, locking that gear to the output shaft and transferring the engine rotation at the selected gear ratio to the wheels. Remember, the gear is rotating at a reduced speed (clutching in disengaged engine input briefly) and the synchro is moving at full road speed. The thing to understand is that they move at different speeds until synchronized and fully engaged.
Let's get into more detail...ignore starting from a stop as we are discussing short shifter which are used while moving.
One of the jobs of a synchro assembly is to match the speed of the selected gear (moving at a some factor of engine speed) to the speed of the output shaft (wheels). It begins this process with a brass blocker ring. It has a conical inner surface that mates with the conical surface of the forward gear on the ouput shaft. Think of it as a male/female realtionship. The male being the gear. As the shift fork moves the synchro sleeve toward the selected gear, the ring is literally pressed onto the gear and via friction, begins to match the speed of the gear to the synchro assembly that is spinning at road speed.
Once the speed of the synchro assembly and the forward gear are beginng to sync, a series of beveled teeth on the ring and on the gear start to align. They don't have to align perfectly and frankly, at the RPMs they operate, odds are they will never perfectly align every shift. For that reason there's a bit of play designed into the movement of the ring. Also, the teeth are at an angle (beveled) allowing them to kind of bump and glide. This facilitates the many teeth of all of these surfaces to mesh smoothly even though they may not align perfectly.
At this point, the gear is still not engaged. The inner dog teeth on the synchro sleeve have to manuever the beveled teeth on the block ring and the gear itself. This is what ultimately locks the gear to the shaft, engaging it. The sleeve will only engage when the teeth on the gear and the blocker ring are in close enough alignment to allow the dog teeth inside the sleeve to bump and glide over BOTH the blocker ring and the selected gear.
It's hard to explain but picture it. You have teeth on one side spinning and a whole other set of teeth spinning on the other side. They have to somehow mate without the whole thing shattering into bits. Having bevels or angles in the teeth allows them to shift and move and grove however they need to so that the sleeve can lock the gear to the output shaft without grinding. An engineering marvel really.
FUN FACT: I'm a bit fuzzy on this detail but another job of the synchro is to block the gear change (blocker ring) if the delta between the input and output shafts is too great, usually due to ratio. For instance, try going into the 2nd at highway speeds and the synchro will prevent it.
HOW COULD A SHORT SHIFTER INCREASE SYNCHRO WEAR?
Parts of the synchros are brass and designed to wear. They are of a softer material than the gears themselves. It's a part of how they effectively smooth out gear changes. Remember, the different speeds are matched up via the friction applied on the gear by the blocker ring found on the synchro assembly. A synchro needs time to accomplish this miraculous feat. I would think that the chosen friction materials for a given tranny all work within a given set of design paramaters. For arguments sake, say a friction material is designed to sync a gear within 5-7ms or whatever. It's now being asked to do the same thing in 25% less time via a short shifter. This will increase the odds of a grind, at worst, and at best increase the wear on the brass beveled teeth and sleeve as we don't give the teeth time to come into their designed and expected alignment.
FUN FACT: You know those times when you are at a light and it won't go into 1st, so you clutch in and out then it goes in no prob....synchro is not aligning on the first attempt. Disengaging and re-engaging the input shaft quickly changes the rotation of the input shaft, changing the rotation of the gear, allowing a different alignment of the teeth and so the the gear goes in the second time. If you find yourself doing that ALL the time, you may have a worn synchro.
For those who note that an SS like Coolerworx works on the mechanical arm of the shifting mechanism, you are correct. But you are missing a critical point. The mechanical arm you speak of is directly acting on the shift rods whose sole purpose in life is to act on the shift forks...and as mentioned above, the shift forks move the synchros and lock the gear to the output shaft. Shorten that mechanical action by 25% and you reduce the time it takes to act on the rod, that acts on the fork, that wears down the synchro...Theoretical, but technically possible and imo a sound argument.
And that is why I do use an SS but only at it's lowest setting...
What are your thoughts FiST'rs?
The synchros move at road speed (or lack there of) because they are directly connected to the OUTPUT shaft. The gears (1-6) themselves are also on the output shaft but spinning independently from it on needle bearings. In other words, the forward gears are NOT directly connected to the output shaft, at all.
The gears are spun via engine power brought into the transmission on the INPUT shaft. It has its own set of directly connected gears that are meshed (in contact) with the gears on the output shaft. So the moment you turn on your car, the gears are freely spinning on thier needle bearings on the output shaft at a given ratio of engine speed but not engaged. The synchros aren't moving yet as they move with the wheels via the output shaft (for simplicity sake)
FUN FACT: Pressing the clutch disengages the input shaft from the engine. At that point the gears slow down on their needle bearings, depending on just momentum. If your car is moving, the synchros continue to rotate at road speed.
Simply put, when a gear is selected, the shift fork acts on the synchro sleeve, sliding it's beveled dog teeth over a set of beveled teeth on the selected gear, locking that gear to the output shaft and transferring the engine rotation at the selected gear ratio to the wheels. Remember, the gear is rotating at a reduced speed (clutching in disengaged engine input briefly) and the synchro is moving at full road speed. The thing to understand is that they move at different speeds until synchronized and fully engaged.
Let's get into more detail...ignore starting from a stop as we are discussing short shifter which are used while moving.
One of the jobs of a synchro assembly is to match the speed of the selected gear (moving at a some factor of engine speed) to the speed of the output shaft (wheels). It begins this process with a brass blocker ring. It has a conical inner surface that mates with the conical surface of the forward gear on the ouput shaft. Think of it as a male/female realtionship. The male being the gear. As the shift fork moves the synchro sleeve toward the selected gear, the ring is literally pressed onto the gear and via friction, begins to match the speed of the gear to the synchro assembly that is spinning at road speed.
Once the speed of the synchro assembly and the forward gear are beginng to sync, a series of beveled teeth on the ring and on the gear start to align. They don't have to align perfectly and frankly, at the RPMs they operate, odds are they will never perfectly align every shift. For that reason there's a bit of play designed into the movement of the ring. Also, the teeth are at an angle (beveled) allowing them to kind of bump and glide. This facilitates the many teeth of all of these surfaces to mesh smoothly even though they may not align perfectly.
At this point, the gear is still not engaged. The inner dog teeth on the synchro sleeve have to manuever the beveled teeth on the block ring and the gear itself. This is what ultimately locks the gear to the shaft, engaging it. The sleeve will only engage when the teeth on the gear and the blocker ring are in close enough alignment to allow the dog teeth inside the sleeve to bump and glide over BOTH the blocker ring and the selected gear.
It's hard to explain but picture it. You have teeth on one side spinning and a whole other set of teeth spinning on the other side. They have to somehow mate without the whole thing shattering into bits. Having bevels or angles in the teeth allows them to shift and move and grove however they need to so that the sleeve can lock the gear to the output shaft without grinding. An engineering marvel really.
FUN FACT: I'm a bit fuzzy on this detail but another job of the synchro is to block the gear change (blocker ring) if the delta between the input and output shafts is too great, usually due to ratio. For instance, try going into the 2nd at highway speeds and the synchro will prevent it.
HOW COULD A SHORT SHIFTER INCREASE SYNCHRO WEAR?
Parts of the synchros are brass and designed to wear. They are of a softer material than the gears themselves. It's a part of how they effectively smooth out gear changes. Remember, the different speeds are matched up via the friction applied on the gear by the blocker ring found on the synchro assembly. A synchro needs time to accomplish this miraculous feat. I would think that the chosen friction materials for a given tranny all work within a given set of design paramaters. For arguments sake, say a friction material is designed to sync a gear within 5-7ms or whatever. It's now being asked to do the same thing in 25% less time via a short shifter. This will increase the odds of a grind, at worst, and at best increase the wear on the brass beveled teeth and sleeve as we don't give the teeth time to come into their designed and expected alignment.
FUN FACT: You know those times when you are at a light and it won't go into 1st, so you clutch in and out then it goes in no prob....synchro is not aligning on the first attempt. Disengaging and re-engaging the input shaft quickly changes the rotation of the input shaft, changing the rotation of the gear, allowing a different alignment of the teeth and so the the gear goes in the second time. If you find yourself doing that ALL the time, you may have a worn synchro.
For those who note that an SS like Coolerworx works on the mechanical arm of the shifting mechanism, you are correct. But you are missing a critical point. The mechanical arm you speak of is directly acting on the shift rods whose sole purpose in life is to act on the shift forks...and as mentioned above, the shift forks move the synchros and lock the gear to the output shaft. Shorten that mechanical action by 25% and you reduce the time it takes to act on the rod, that acts on the fork, that wears down the synchro...Theoretical, but technically possible and imo a sound argument.
And that is why I do use an SS but only at it's lowest setting...
What are your thoughts FiST'rs?