What is happening to the engine and transmission when a car is stopped but in gear?

I have been learning how cars work for fun but have been unable to find an explanation for this on the web. When the engine is running the crankshaft is turning. If I am in first gear (or reverse) the transmission is engaged with the crankshaft, so it should be turning the wheels. However if my foot is on the brake the wheels aren’t turning… but this obviously doesn’t feed back to the engine, stopping it. So at what point is the motion of the engine disappearing??

The motion of the engine is “disappearing” inside the torque converter:

Ingenious! Very cool, thanks!

Automatic transmissions have what amounts to a fluid clutch that allows the engine to run but not transmit (much) power to the transmission…Stick shift cars have foot operated clutch to disengage the engine…

The engine is connected to the transmission input shaft by a torque converter, which is a “fluid coupling device”. Basically, it’s similar to a bagel sliced in half, hollowed out, and with vanes in each side, then filled with tranny fluid. When the engine is spinning slowly and your foot is on the brakes, the amount of energy transmitted from the front half of the converter is insufficient to overcome the brakes and the energy is converted to heat energy (via the fluid turbulence) and dissipated by the transmission cooling system. When you let off the brakes and begin to rev the engine to accelerate, the faster spinning front half of the converter creates sufficient energy in the fluid to drag the back half of the torque converter along with it, causing the car to move forward. At a predetermined speed, the TC is “locked up” via a special clutch to prevent slippage while driving and to prevent the loss of mileage and the associated heat buildup that would come with it.

My dad show me how a torque converter worked by using an old Mixmaster mixer. My mom had just made cake batter and before she put it in the baking pans…my dad called me over. He told me to hold the mixing bowl still while the beaters were beating the cake batter and said that was like putting on the brakes with the transmission in drive. When I let go of the bowl it started to spin while the beaters were running. The cake batter was the transmission fluid. I caught on to the idea and sometimes when I think about the workings of an automatic transmission…I smell cake. I love cake.

That’s more like what viscous coupling is doing rather than a torque converter, unless that bowl has vanes on the side to absorb the momentum of the spinning batter

The OP didn’t state but we all assumed the discussion centered on an automatic transmission.

@zakharov There are other types or transmissions; conventional manual, DSG and fully automatic clutch-type automatics that don’t have the fluid coupling of a torque converter. In these transmissions a friction plate clutch disk must lifted off the spinning flywheel to keep the engine from stalling either by a foot pedal applied by the driver or with a computer controlled hydraulic device.

Missileman, that is an outstanding analogy. Your dad is a smart man. With your permission, I think I’ll steal it for future use. Extend my thanks to your dad.

Now I’ve got a hankering for cake!!!


For some reason I got to thinking about waffles for dinner!

Now I’ll be damned to thinking about cake at every stoplight… there goes my diet!