OK let me establish one thing before anyone starts the flamewar. I am aware that neutral dropping is one of, if not THE worst thing you can do to ANY auto trans, no matter how much money or parts you hjave thrown at it. But since I am not 'that' familiar with the internal working of a trans, I'm curious.

Exactly what goes on when you do a neutral drop that makes it a bad idea vs doing a clutch dump with a manual?

 

when you neutral drop your going from neutral and slaming it in to gear so your taking a gear spinning and aligning it with another gear that isnt moving, and when you dump the clutch the car is already in gear so all your doing it applying power to the trans.

 

Dropping an auto into gear takes a spinning clutch pack and engauges it. Depending on what gear and what trans, either the frictions are spinning and not the steals, or the steals are spinning and not the frictions. Either way, you're dumping fluid to the apply piston and slamming the clutch pack. - Not good, but not the biggest issue. Automatic trans gears(known as planetaries) are not designed for shock loads. During normal gear changes they would already be spinning, the clutches just apply load either to the planetary or to the reaction carrier depending on the gear/ratio being engauged. The planetary gears are either bushed or needle bearing, neither of which is designed for side loading.

In the event of a neutral drop, the engine rpm and input shaft rpm is already up, but the planetary is not spinning. The instant shock of dropping it into gear, not only results in clutch pack slippage, but also impact loads the planatries, which thrust load that bushing or needle bearing. Be it they break due to the shock or just the exponential wear causing them to become loose and shift out of place and loose tooth contact. - I'm sure you can figure out what happens when the gears no longer contact properly.

Depending on the type of trans there are other factors at play, but that is the main issue for an auto trans.



For a manual trans, it all comes down to the over-all load rating. When doing a clutch drop, once again, you shock load a gear set which in turn tries to push apart. If you exceed the trans load handling abilities you will at some point have a failure due to the deflect between the gears/shafts/case.

 

Good info. Thanks *****.

I never knew exactly what went on when you did this, only knew it was extremely dumb and have never done it in my life.

 

Anyone who thinks neutral dropping an automatic is like a high rpm clutch dump can buy as many transmissions from me as they would like. As mentioned above, it's all how the clutch packs are designed inside an automatic. Everything is engaged by hydraulic pressure and because of how they're spinning inside the tranny, you can't safely put it into gear from neutral at high rpm.

It's like the episode of Mythbusters when they were testing a "Hit the ground with a running start". If you're running in mid air then suddenly touch the ground, you don't quickly move forward. They also tried using a bicycle by suspending the back wheel and pedaling up to speed. At speed, the back end was dropped and the amount if inertia required to keep the back wheel moving can't be done. Inside the transmission is the same way. Spinning it fast then engaging it causes parts to fail.

To properly launch at a higher rpm with an automatic, first you need a higher stall converter which stalls around the engines peak torque. To be able to launch at that high of an rpm, you need a transbrake. The transbrake locks the transmission in first and reverse. The shifter is in first gear and a solenoid engages reverse. When the transbrake is released, the reverse circuit oil is dumped and the car launches forward.

My converter stalls at 6000 rpm. I launch anywhere from 4500 right up to the full stall speed by using a 2-step to control the launch rpm.

 

in lay men's terms:

a neutral drop is like revving up a manual transmission and trying to jam it into gear. the clutch does the same thing that a torque converter does (to an extent).