Originally Posted by grey (Post 109278)

oh well, highly scientific research is hard to dispute...
ask a person who knows, such as a reputable transmission mechanic.

Originally Posted by theholycow (Post 109282)

What causes the failure? How does it fail?

Originally Posted by grey (Post 109326)

To be fair I did a search to see why this bit of information is not widely known. This took 14 seconds to find:

action.publicbroadcasting.net/cartalk/posts/list/669010.page

Originally Posted by theholycow (Post 109387)

So? It's just another forum. I can find loads of forum replies saying it's okay in the same 14 seconds, probably using exactly the same search terms.



My automatic has an idiot light that's known to come on in stages as the transmission gets warm. It comes on long before temperatures cause long-term damage, let alone immediate damage. It has never come on during neutral coasting, even at highway speeds on long down slopes.

Anyway, in D with the torque converter unlocked and your foot off the gas, the engine speed goes WAY down. Depending on your road speed, engine may get very close to idle.

Some people with automatics report that their engine does not go completely down to idle when in N. Perhaps their computer is keeping the speed up to keep the tranny cool, that was one proposed explanation (another being fluid resistance in the tranny transmitting small amounts of power).

Can someone with a tranny temp gauge or ScanGauge give us the straight dope on this? Does your tranny temp go up while neutral coasting, and if so, how much? My ELM327 ought to show up soon, so I'll be able to log some data too.



Blah blah blah, same old FUD there. I do dozens of sharp turns in neutral every day with my tires complaining so I don't have to waste any energy by braking before a turn. Handling is the same as being off the gas pedal in an automatic (don't forget that at the speeds we're talking about, the torque converter lets the engine down to ALMOST idle). If you're going so fast around the turn that not having the drive wheels* drag slightly is going to upset stability, you are going WAY too fast.

*: BTW, is your idea for front or rear wheel drive? Having the front wheels drag slightly from engine braking will upset the car differently from having the rear wheels do so...and then there's weight distribution, pavement changes, general differences in the car and the driver...

If you're not confident in your safety while coasting in neutral, then you definitely should not do it. Most people who do neutral coasting are fine, we manage to survive without being able to accelerate away from a deer crossing the road or whatever, and do not have handling problems.

Originally Posted by grey (Post 109326)

as with most transmission failures, HEAT

To be fair I did a search to see why this bit of information is not widely known. This took 14 seconds to find:

action.publicbroadcasting.net/cartalk/posts/list/669010.page
In short, don't do it.

The tranny hydraulic pump is driven by the input shaft from the torque convertor. Therefore if the output shaft is spinning at 50mph and the engine is idling it won't be delivering the required pressure to the tranny. It's the same as running your engine at 3000rpm with an oil pump delivering 1000rpm of oil pressure. The result is increased wear, burnt tranny fluid and a premature visit to the tranny shop.

Originally Posted by RoadWarrior (Post 109399)

Ummmm my transmission pump is driven by the OUTPUT shaft.

Originally Posted by grey (Post 109326)

The tranny hydraulic pump is driven by the input shaft from the torque convertor. Therefore if the output shaft is spinning at 50mph and the engine is idling it won't be delivering the required pressure to the tranny.

Originally Posted by theholycow (Post 109404)

AFAIK, that's not a common design, most automatics are pumped by the input shaft. That makes EOC bad for them but engine-on neutral coasting seems to be fine.