Clutchless speed shifting is not something you want to do to a synchromesh transmission. The input shaft has to be free to turn into a position that lets the dog clutch splines engage. The ends of the splines are rounded or diamond shaped so that if they are not perfectly aligned, the shift fork moving the splined ring onto the gear hub will cam the gear into the right position to allow the splined ring to engage.
The splined ring I am talking about looks like this.
Motorcycles, Indy cars, F-1 cars use a different type of transmission that does not have synchronizers. Instead of dozens of very fine splines, they use just a few very coarse dogs that have so much space to fall into that they do not need to be perfectly aligned. These can be and in race cars usually are shifted clutchless. The driver puts pressure on the shifter but the engine torque locks the dog in gear, as soon as he lifts the throttle, the absence of torque allows the gear to disengage and slam into the next gear. They don’t even have to lift the throttle anymore, there is a kill switch wired into the transmission that cuts the spark for a millisecond to allow the transmission to shift. This type of transmission is often called a crashbox or a dogbox. Here is what the engagement dogs on these transmissions looks like.
Check. Got it. Thanks. But I’m not interested in putting into gear without using the clutch. I didn’t know if it causes damage taking it out of gear without using the clutch. I think the majority rules that so long as there’s no torque being delivered, there’s no harm.
As soon as I see a red light or stop sign, I take it out of gear and coast up cooly and casually, a light tap on the brake to stop the roll and relax a while. Or, more often, I slow my roll and the light turns green before I even get there and before I stop. And we all know it takes much less energy to accellerate an already moving object than it takes to get one moving from a complete stop. I prefer to spend as much time in motion as possible, thus reducing fuel consumption and wear and tear on the car.
I was pretty sure that banging it into gear without the clutch would wreck it. I just didn’t know if slipping it out of gear was harmful. The majority seems to rule that, so long as there’s no torque on the plate, then there’s no harm done.
I know you wrote your description of the technique earlier, and I know that coasting early can prevent you from having to stop. I fully understand those concepts. However, that isn’t what I am asking about.
What I don’t understand is how this technique, used without clutching, saves gas better than a modified technique where you coast in gear, letting the engine slow you down a little, and then take it out of gear while using the clutch.
By leaving it in the current gear a little bit longer (but not lugging the engine), you use less fuel. The sooner you take it out of gear, the more time the engine spends idling. It uses more fuel idling in neutral than it does coasting in gear.
We are past the question about whether or not this will damage the transmission or the clutch. Now I am asking about your claim that this technique, done without clutching, saves fuel. I contend that it doesn’t save fuel.
I would continue, but the holiday weekend is over and I have to quit goofing off and get back to work. Thanks for the input. I always enjoy a spirited exchange. Adios and happy driving.
If you have to use engine braking to not get to the intersection before the light turns green, then you didn’t start coasting soon enough. That’s where freewheeling with an idling engine wins.
I’m aware of deceleration fuel cut off in modern efi and I take advantage of it if I’m approaching the intersection so hot that I have to brake.
If you are going down a slight downgrade that is just steep enough to maintain your intended speed while freewheeling, then the choice is not freewheeling or coasting in gear, the choice is freewheeling with idling engine or freewheeling in gear while giving the engine just enough gas to match the rpm of the transmission input shaft with no load on the engine. Otherwise the engine is braking and you slow down which means you have to re-accelerate and use gas.
