No harm, no foul. I figured that a little show and tell might help to clarify things a little bit. This first picture is a standard 3rd gear assembly. It's the 3rd gear idler, a steel synchronizer ring and the slider and hub assembly.

The second picture is a 997 Cup Car sequential gearset and it's corresponding slider and hub assembly.


So, you can see there's a pretty significant physical difference. I am going to take this from ground zero so that anyone reading this that has no understanding of how the internals of a gearbox work will be able to understand. For those of you with a working knowledge of this already, please bear with me.

Something that a lot of people don't realize when they think about what goes on inside of a gearbox is that all of the gears (6 in this instance) are always spinning. That's why the inside of each of those gears is smooth. Those are what are known as the idler gears and they run on the shaft (in this case the mainshaft) on top of a bearing, which is not shown.

When you shift, what you are doing is sliding the "slider" over the teeth on the idler gear and locking it in place. See how the hub of the slider assembly is splined? It's always locked to the shaft. So when you select the gear with the slider, you have now engaged a gear and have power.

Because of changes in ratio from one gear to the next, as you make a change you will be going from having your shafts moving at one speed to another. The purpose of the synchronizer is to speed up or slow down the idler gear so that it's moving at the same speed as the slider and hub assembly. When you "crunch" a shift, what you've done is generally pulled it into gear too quickly before the synchronizer has managed to bite on the cone of the idler gear and get it to the same speed as the slider, which is moving over to capture it.

Now look at the sequential parts. In a real sequential gearbox, it's what we call a dog engagement. There's no synchro. The engagement teeth are much larger and there's a lot less of them. This is because you actually slam it into gear with no synchronization process. The gap has got to be big enough to get the slider teeth in there to capture the teeth on the gear while it's still spinning, and then in essence shockload it up or down to the same speed as the slider and hub.

You can have a dog box without it being sequential. Dog boxes have been used in standard H pattern shifting for decades and in fact, early gearboxes weren't synchronized at all. That's why they called them crash boxes. You can mitigate some of the "crash" with rev matching and double clutching, but you still aren't perfectly synchronized when you select the gear.

A sequential gearbox, by definition, means that the internal functionality of the shifting only allows that the gears be selected in order. On a sequential one cannot be in 5th gear, skip 4th and downshift straight to 3rd. You've got to go through and engage each gear. The sequential shifters that you can buy don't change the gearbox over to a dogbox. They really just remove the H pattern shift from your console and using a module on the outside of the gearbox manually force you to select the gears in order. Nothing inside of the gearbox has changed, and it's still synchronized. Overall, for a street driven car, this is going to be the better choice because synchronizers will be more durable. It still allows the synchros to do their job and doesn't shock load everything.

With a sequential gearbox, or any kind of dog box for that matter, one has to be commited. You can't shift slowly. It's all or nothing, which is why so many people moving up to a sequential Cup Car from something like a 964 or 996 club race car have a hard time. They are used to progessing into the gear as the synchronizer works. You don't do that on a sequential. You slam it hard with full commitment. If you don't, you miss knock the edges down on the teeth or worst case break something. Which is why I wouldn't recommend our coming sequential gearbox for street use for most people. It will require 100% mental commitment from you at all times. If one gets lazy and makes a half shift on a sequential stuff breaks. If you do the same thing on your synchronized gearbox with a sequential shifter attached, you might glaze your synchros a little bit, but you're probably not going to really fubar something.

Make sense?

 

^^Great explanation.

 

Best description I have read yet. Thanks Matt.