auto transmission question

[cmills]

This maybe a dumb question, but I'll ask anyway. In a vehicle with an automatic (not just our trucks, but any vehicle) does it hurt to shift from neutral to drive while moving (forward) as long as you are not on the throttle, just idling? Like rolling down a hill at 5 mph and going from N to D or coasting down the highway at 55 and doing the same thing.

 

[Tractorat]

Im not a mechanic, and I sure someone who is can give a better answer here.



But, if you are coasting in neutral to get better mileage, I've heard that is very bad for your auto trans. I like to listen to a local car repair show (actually a few of them) on saturday mornings, and this question has come up several times. And each time they say to not coast in neutral, at least not for very far. Someone with a transmission background can hopefully explain why. Im pretty sure it has something to do the the trans not getting lubricated when in neutral



My 2 cents

 

[Hoefler]

At a slow crawl, less than 5 mph, not a big deal. At highway speeds, yes, it can cause more than damage to the transmission. It could put you in a spin especially if the road is wet. Check with your jurisdiction, it is illegal to coast out of gear and or with the clutch disengaged in most jurisdictions. If you are doing it to save gas, you are not. Whether you are at a stop or at highway speeds, you are not saving any fuel unless you shut the engine off. Today's electronically controlled engines, will shut the fuel off if you take your foot off the throttle and the throttle plates are closed and the rpms are higher than idle speed.

 

[cmills]

No, I don't do the coasting thing to save gas, but what got me thinking about this was that exact topic, that I came across the other day where some people said it works, some said it doesn't. It made me stop and think about when I sometimes coast down the driveway in N and when I get to the end I just slide it in drive and go, but I'm only talking speeds of 5-8 mph, so I just wanted to make sure I wasn't hurting anything.