Shifting into neutral

[mkriedel78]

Hi everyone,

I'm fairly certain this is "normal," but since diesel trucks are new to me, I figured I'd ask.

I have a 2008 Chevy Silverado 3500 Duramax w/ the 6-speed Allison transmission.

Last night, I was driving home at about 60-65 mph down a very slight grade, but downhill nonetheless. I was not towing or anything like that, just driving.

So, while in drive with my foot off the accelerator, my RPMS were in the 900-1000 RPM range. When I shifted into neutral, however, the RPMs went up to ~1200-1400.

This surprised me, as any other automatic I've ever owned, shifting into neutral brought the RPMs down to idle speed.

It didn't seem to hurt anything, and I just shifted back into Drive and carried on. I just want to know if that's, indeed, 'normal' behavior in a truck like this.

Thanks!
Matt

[Winged_One]

Gdetrailer wrote:

kaydeejay wrote:
I'm another one who is wondering why you would NOT want your engine to act as a brake when going downhill.:h

Umm.. Have you ever tried braking or stopping down hill on snow/slush/icy roads in the winter time?

I learned when I first started driving that on extremely bad winter roads the ONLY sure fire way to keep control and be able to stop safely was to simply slip the vehicle into neutral.

When you do that your brakes are no longer fighting the engine and transmission and you will not need as much pressure on the brake pedal to stop faster on slick roads.

Saved my bacon many times EVERY winter..

Funny you say that. Years ago my 1988 Ford F150 2wd had rear ONLY anti-lock brakes. In heavy road snow that meant, you step on the brakes, the front tires lock up preventing you from steering, while the rear tires kept driving you forward into oncoming traffic. Helluva design. Learned to put in neutral very quick.

[Turtle_n_Peeps]

Bmach wrote:
My guess is put it neutral on a long and maybe gradual down hill. Reason is an engine at ideal will probably use less fuel than one running higher than ideal.

I will say it again. The engine in question uses NO fuel when going down hill with your foot off of the accelerator. The injectors will go to 0 duty cycle.

[45Ricochet]

larry barnhart wrote:

if you owned an Allison you would know it does a great job grade braking.
chevman

Yeah. Let's just ask someone like NChauler who has owned both :w
No difference between the Ally grade braking and a exhaust brake :B

[Bmach]

My guess is put it neutral on a long and maybe gradual down hill. Reason is an engine at ideal will probably use less fuel than one running higher than ideal.

[john_bet]

larry barnhart wrote:

wilber1 wrote:
Exactly the opposite of what I thought would happen. Thought one of the features of the Allison is grade braking.

if you owned an Allison you would know it does a great job grade braking.

chevman

Not in the 2013 Navistar school bus I drive. In fact it is just like the '97 Chevy Express van I drove for 11 years. My Dodge is way better. JMHO.

[larry_barnhart]

wilber1 wrote:
Exactly the opposite of what I thought would happen. Thought one of the features of the Allison is grade braking.

if you owned an Allison you would know it does a great job grade braking.

chevman

[wilber1]

Exactly the opposite of what I thought would happen. Thought one of the features of the Allison is grade braking.

[Gdetrailer]

kaydeejay wrote:
I'm another one who is wondering why you would NOT want your engine to act as a brake when going downhill.:h

Umm.. Have you ever tried braking or stopping down hill on snow/slush/icy roads in the winter time?

I learned when I first started driving that on extremely bad winter roads the ONLY sure fire way to keep control and be able to stop safely was to simply slip the vehicle into neutral.

When you do that your brakes are no longer fighting the engine and transmission and you will not need as much pressure on the brake pedal to stop faster on slick roads.

Saved my bacon many times EVERY winter..

[Old-Biscuit]

Did it stay at the higher RPMs.....1200-1400?

OR did you see the increase in RPMs, panicked and shifted right back into drive?

You unloaded engine/tranny so RPMs increased. They should have dropped to idle (700 RPMs) shortly after shifting into neutral.

[darsben]

Okay so what is the idle speed on your truck when stopped in neutral and park?
Was a/c on? including defroster

[45Ricochet]

LOL
Purely a guess but maybe the puter knew there was a driver input error and just downshifted automatically.
Maybe drive the same spot one day and manually downshift one gear and see what your tack reads.

[2oldman]

You just can't say things like that and not get a load of guff first.

[kaydeejay]

I'm another one who is wondering why you would NOT want your engine to act as a brake when going downhill.:h

[rvten]

It is called Georgia Over Drive. Shifting to neutral going down hill.

[BenK]

Illegal in Calif V C Section 21710 Coasting Prohibited

Calif./DMV wrote:

Coasting Prohibited

21710. The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral.

Also, in automatics that do NOT have a rear pump...coasting in neutral will have
little to no lube pumped to the bearings inside the automatic and will ruin them in a hurry