Main IndexAuto Repair Home Search Posts SEARCH
Who's Online WHO'S
Log in LOG

Search Auto Parts

Does input shaft/turbine turn when in Neutral?

  Email This Post

New User

Apr 16, 2019, 8:31 PM

Post #1 of 4 (129 views)
Does input shaft/turbine turn when in Neutral? Sign In

Does anyone out there know if an automatic transmission's input shaft/turbine is spun up by the TC impeller when the transmission is in Neutral? other words, is the input shaft/turbine free to be turned by the impeller, or is there some mechanism that I am not aware of that prevents the input shaft/turbine from turning while the transmission is in Neutral?

My online research about automatic transmissions in general would seem to indicate that input shaft/turbine IS spun up by the TC impeller when the transmission is in Neutral, but a professional experienced mechanic is telling me that the input shaft/turbine is to NOT supposed spin up when the transmission is in Neutral.

My symptom is that when I shift (at a standstill) from Reverse into Drive quickly and directly, the shift is very smooth, but if I pause in Neutral at all then the shift is comparatively violent (clunk/lurch). One explanation for this would be that if the input shaft/turbine is spinning up in Neutral, then that would allow the input shaft/turbine to build up rotational momentum, which would then cause a more violent shift into Drive.

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Apr 17, 2019, 1:57 AM

Post #2 of 4 (116 views)
Re: Does input shaft/turbine turn when in Neutral? Sign In

? Just from ancient hand on training and trust me you probably were not born yet. In neutral the trans isn't turning or you'd be moving if wheels were on the ground so the pro is right for most of the question.
The TC as we know them is a coupler that locks up such that you get one to one engine RPM and same to transmission vs loss of about 10% varies how much slip/loss.

This is calculated for each application. The engine will turn I'll call a front pump that allows fluid/hydraulic pressure to be available in most, at the ready to engage bands for transfer of torque available at the ration of which ones.
How much do you want to learn about "automatic transmissions" and what for? One you own now to work on or learn how they work so you can make it a trade of your own? It will totally matter as there are near endless ways they operate TMK most on the first concepts of "braking" a drum mechanically to vacuum actuated to electrical actuators most limited by governors at least once just centrifugal forces against weights on springs at a set RPM forced the next move.

It did not become my specialty part of a whole trade for one simple reason. I've never had the room to spread out all the components, clean area with the unique tools, parts cleaners and more. It has to be clean always important more imperative for this.

Concepts began with the Model T now well over 100 years ago, some totally different idea came and went that worked well lost due to size, weight, ease of control plus of course not wasting the power available however something turning is powered.

Not my trade obviously did learn enough to know I'd never have the room to work on many types AND other service items as well.
Good luck if you can grasp the concepts of how many work that alone is quite the course of study before you touch a thing totally understand what it's supposed to do when it's right as intended,


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Apr 17, 2019, 3:31 AM

Post #3 of 4 (110 views)
Re: Does input shaft/turbine turn when in Neutral? Sign In

To answer your question, yes the input shaft will be turning all the time when the engine is running in neutral. The output shaft will only turn when the wheels are moving. That is how the module interprets what is or isn't happening in the trans. If the input shaft was not turning, there would be no response when the trans is shifted into gear. I believe once you shift into gear, the clutches will hold it still against the torque converter until the vehicle moves.

I'm sure our resident trans expert (gsferraro) will be along to clarify.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.


Apr 19, 2019, 4:14 PM

Post #4 of 4 (78 views)
Re: Does input shaft/turbine turn when in Neutral? Sign In

Yes input shaft is turning. What type of car do you have? what is the year make and model? Gary

  Email This Post

Feed Button

Search for (options) Privacy Sitemap