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-   -   Coasting in Neutral vs engine braking (http://www.peachparts.com/shopforum/showthread.php?t=342884)

thayer 08-26-2013 09:25 AM

Regenerative braking gave me a semi when I first read about it. Those electric guys are doing something right. Wonder If we could retrofit them onto a 126? Maybe charge a smaller secondary battery in the trunk to run the clock.

97 SL320 08-26-2013 06:06 PM

Quote:

Originally Posted by Hirnbeiss (Post 3197580)
if you have to go back up a hill, neutral may win if it saves you having to accelerate back up to speed.

Until the transmission planetaries blow apart. For all practical purposes, most auto trans when put in neutral and driven from the output shaft will spin the planetaries to very high speeds. Would you drive 65 MPH in first gear?

Hirnbeiss 08-26-2013 09:21 PM

Quote:

Originally Posted by 97 SL320 (Post 3197802)
Until the transmission planetaries blow apart. For all practical purposes, most auto trans when put in neutral and driven from the output shaft will spin the planetaries to very high speeds. Would you drive 65 MPH in first gear?

sounds scary, but I've never heard of any problems as long as there's enough oil and the pump is running (i.e. engine on).

97 SL320 08-27-2013 07:06 PM

The issues are more long term than short, it's kind of like running veg oil / waste oil in a diesel. Sure it will work but for how long and what overall cost?

Flat towing speed with a automatic is limited due to lack of oiling and planetary speed.

With the engine running you will still have oiling but won't be able to overcome planetary speed.

In a automatic trans, planetaries are locked and not spinning in top ( 1 to 1 ) gear relative to the sun and ring gear. Unlock everything and spin the drive shaft and they will now be spinning relative to the sun and ring gear.

What spins / how fast varies on the transmissions make up. The next time someone is rebuilding a trans, turn the output shaft and look at the gear train

Now, before someone says that Saturn cars are commonly towed behind a motor home, be aware that these transmissions are not of planetary design, they look more like a manual trans with clutch packs rather than sliders / syncros.

Other makes are towed, but they typically have a disconnect axle / drive shaft mod.

tjts1 08-27-2013 07:17 PM

If you're coming to a stop or trying to maintain your speed down a steep slope, keep it in gear. If you're trying to maximize the distance traveled without accelerating, pop it in neutral. Whether or not the engine is idling in neutral or in DFCO makes very little difference in your overall FE. The point is to always cover the maximum distance or anticipate your next move. I wouldn't put an automatic transmission in neutral while the car is still rolling to save fuel.

CamelotShadow 08-31-2013 10:18 PM

I have fun accelerating the beast leaving the cars in the dust & then lifting off to coast to next light. Gets to higher gears & uses most power more efficiencently then mosying down to another light.
Technically CA DMV does not like coasting to a light & alot of La'ers who like to gun it to the next light & brake hard.
Makes no sense to me but technically it 35 from start to finish...blaj blah blah.
I can't really do it when I got them road hogs breathing down my tailpipe.

:eek:


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