What happens when I shift gears without pressing the clutch in a manual transmission while the car is running?

Question

Is it OK to change gear without pressing down the clutch when the car is running ?

Does it damage or wear anything? Just wanted to know what actually happen to the car.

Answer 1

It is not a good idea to change gear without using the clutch, you will cause unnecessary wear that will end up causing an expensive bill.

When you select a gear, there is a component in the gearbox called a synchromesh that synchronises the speed of the gears in the gearbox, with the speed of the vehicle. If the clutch is disengaged, there is very little load on the synchromesh, causing very little wear on each gear change.

However, if you don’t disengage the clutch, the synchromesh now needs to synchronise the engine speed with the vehicle speed. This causes a significant extra wear on the synchromesh and will eventually lead to early failure.

Before selecting gear, you could manually try to match the engine speed with the vehicle speed, which will reduce the load on the synchromesh, but you are never going to do this accurately, so there is always going to be unnecessary wear.

Failure of the synchromesh will lead to difficulty selecting gears and gears grinding, followed by a big bill.

Answer 2

If your vehicle is not moving, you will be unable to move the shift lever from neutral without causing excessive damage. Within the transmission, a portion of the mechanism is spinning with the force provided by the engine. Other portions of the mechanism (gears, bearings, levers) are not moving, as they are connected to the power train that ends at the wheels. Forcing a moving part into a non-moving part in the manner you describe is catastrophic.

When one uses a clutch, one disconnects the engine-moving portion and engages the wheel-moving portion. Gently releasing the clutch to begin moving prevents the aforementioned destruction.

Note that one can shift from one gear to another while moving, without using the clutch, but one must be well aware of the speed differences involved and carefully match engine speed, selected gear, and ground speed in order to prevent damage. I have had more than one clutch linkage failure in my youth and was able to accomplish this with a minimum of difficulty in order to arrive at my destination.

Answer 3

It's not a good idea to change gears without the clutch while moving, but it can be done when the situation requires it.

You cannot start the vehicle moving from stationary by pushing the gearstick from neutral to any gear. As soon as the tip of the first geartooth enters the triangular space where it should be, it will immediately hit the tip of the next geartooth, and that will either crack one or other or both teeth. It will probably be a tiny chip, or it might rip the whole tooth clean off the gear.

If the vehicle is rolling along in any gear at any normal speed, you can generally change to a higher gear without using the clutch. Its not ideal, and depends on your timing skill.

1. Be accelerating gently through a gear (say second)
2. At a reasonable engine RPM (say 3000 RPM, not redlining it) lift off the accelerator pedal. This reduces pressure between the driven and driving gear teeth
3. Move your gearstick from second to neutral, give it a beat-pause (hard to quantify) and then shift into third. There should be no force required to go into third. Fingertip pressure at most.
   Why the pause? That allows engine RPM to drop to the right speed for the next gear at this road-speed.
4. Gently reapply accelerator pedal. This whole process should be relaxed and calm.

Doing this in a new manual car is a lot harder. I have a 50 year old Series 3 landrover and lets just say the tolerances are wide.

Downshifting is similar but you have to tap the accelerator while in the beat-pause. Instead of letting the engine slow, you need to make it spin faster, to match the road speed. This is a lot harder.

If you want to practice this, do it driving on gravel. That gives a little more tolerance in the drive train if you miss the shift.

ASIDE You can engage a gear with the motor stopped and the clutch out, and then crank the engine on the starter. This uses the starter to push the whole vehicle and is very bad, so is for "moving a stalled vehicle off a railway crossing when a train is coming" kind of emergency.

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Relevant Story-Time I was working at a Scout Jamboree (18th, 2007, Christchurch NZ) and managed to tear my left calf muscle, using a power pole, extension ladder, and gravity. I could barely walk let alone drive a manual.

I was totally unable to press the clutch pedal, so to get home I used my right leg on the clutch pedal to get rolling in first gear. I also used the manual choke as a throttle to keep the motor from stalling.

Once rolling I was able to use the technique described above to shift up through second/third/fourth. Overdrive needs the clutch so I just went without.

If a light went red ahead I coasted down, and put the gearbox into neutral until stopped. Then I repeated the right-foot on clutch start.

Other than a bit of herky-jerkiness it worked surprisingly well. And yes I drove straight to the after-hours care to get the leg looked at.

Answer 4

If you want to learn how to do this,

• Put your hand on the stick and get ready to nudge it in to NEUTRAL

• Here's the process you have to perfect. There will be one exact "amount of power" where IT WILL EASILY POP down in to neutral. (Without using the clutch.)

• It's kind of hard to explain but put it this way: push the accelerator somewhat hard so you're rather accelerating and you have a good speed. Now more or less take your foot off the accelerator and obviously the engine will ease back more and more. During the couple of seconds that is happening, continue very gently pressing on the gear stick trying to get it into neutral. You'll find that at one exact moment it WILL click down into neutral easily and perfectly when the two "amounts of power on both sides of the gearbox". That's just a poetic explanation, it's more complex than that, but that's how it feels.

• Now you want to get it in the other gear! (Let's assume you were changing downwards.)

• Start easing the revs up and up and up with a gentle press of your foot

• Again, during the couple of seconds that is happening, continue very gently pressing on the gear stick trying to get it into the new gear

• Once again there will be an "exact" moment when this happens. (If you kinds of "miss it" you're screwed, revert to driving normally and try again next time.)

Once you start doing this you'll realize that everything else is lame.

Indeed if you're an incredibly good operator (like me of course!) you essentially do this every time you change gear as a matter of course, and you just kind of use the clutch a little to help you through that exact moment where you line up the changing momentum and changing engine power

Another practice is, if you kind of getting rolling really smoothly, in say third, you can bump it out of third in to neutral, back in to third, back to neutral and so on, in and out, as practice.

The good thing is if you do this badly it will screw up your gearbox and maybe clutch, but that's a good thing because we should all drive cars that are cheap enough to fool around with and have fun in!

Answer 5

There's already plenty of answers about shifting between gears without clutch, but starting is only really possible in a tractor. Without extreme physical force that actually deforms the gears, the only way is to shift into gear fast enough that the backlash in the series of gear trains leading to the wheels isn't "used up" between the time the gear begins engaging and when it is fully in place. With a tractor and a super low gear, there is a lot of backlash before the wheels would start moving. Even if you were fast enough in a regular car, though, the kinetic energy of the spinning engine is lower than the car even moving at idle which means it would have to have a huge rpm change in a tiny fraction of a second. As I'm sure you've learned in physics that makes a lot of things break.

Edit: I forgot to note that many modern cars have quite powerful starters and could theoretically start while in first gear with a little help from a hill. Many modern cars would also probably not let you even think about starting while in gear though