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

[Turtle_n_Peeps]

Beaker wrote:

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.

Would seem to me the engine would shut off with NO fuel.

The torque converter locks so the engine is driven through the wheels. The engine just turns over but no fuel is used.

[Beaker]

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.

Would seem to me the engine would shut off with NO fuel.

[Ric_Flair]

Cyberian wrote:

davisenvy wrote:
I can't believe all the ninny responses to this. I bet you guys don't remove the tag off your mattress either. You better not or else the flux capacitor will overload flipping world into reverse orbit. It is also against the law to whistle under water in Vermont.
Wilber1, I'm with you on this.

You know, Darwin had a point.

I can't believe any of you seriously advocate putting it in neutral.

Dumbest thing I've heard in years.

I'm guessing you've never driven a manual tranny.

[bucky]

Making friends quick aren't you Cyberian? 5 days in and busting on people already?

[Cyberian]

pitch wrote:
Cyberian,I delivered mail for twenty years in one of those death trap LLV's. The ONLY way you could keep them from being pushed through a slippery intersection was to place them in neutral and feather the e brake to control the rear axle. I never had an accident or mishap doing this. Several of my coworkers over the years were involved in accidents as a result of not using this technique!
Please go to General RVing issues above and read a thread called "Attitude"

Aren't you the guy that had to delete his own post crying about neighbors drinking beer and otherwise not conforming to your desired demographic? Seriously.

So now it's gone from coasting down hill, to pre-ABS coasting on snowy hills or otherwise, to just trying to slow or stop at an intersection with even more anecdotal "evidence" to justify it all primarily with equipment deficiencies. Huh.

To pass the CDL driving test, you have to keep the rig in gear until you are within one tractor length of the stop. It was the same when I got my passenger car class D when I was a kid. I had to keep my *motorcycle* in gear to within a length. This is nothing new. If you can't do it, you fail.

Knowing that your vehicle is traction challenged, would the correct answer not be to pay attention to conditions and slow down sooner if needed? Blame the equipment and weather all you like, insurance companies and law enforcement are going to call it "operator error" because it is.

Committing unsafe acts in unsafe equipment in potentially unsafe conditions and bragging about it.

Yeah, my bad attitude. Whatever man.

[tim_and_amy]

I want to clarify a few misnomers here.
For Ben this 1st one applies to your California Law.

1. All Ford Vehicles shift into neutral when they sense the vehicle speed versus throttle input while monitoring the BOO switch. If the PCM does not detect that you are applying the brake, and the TOW/HAUL mode is inactive, the PCM will shift the transmission and "coast" down hill all on it's own. This is designed as a way to save fuel. Anyone who drives a ford truck or car can tell you the feeling of the vehicle "speeding up on it's own" when their foot is off the gas.

2. The fact that the IPC and the Vehicle speed sensor on the truck is detecting movement in relation to the Fuel pressure, when shifting into neutral the PCM won't compensate right away. This is what one of the other posters were saying. The PCM is thinking it needs is off on the RPM input and increases fuel pressure. Odd and backwards of a "engine braking situation"

3. Any person who lives in a location that has snow, ice or black ice knows, to stop safely you need to shift into neutral and eliminate engine braking. The PCM's in most cars automatically do not engine brake any longer, unless you put your foot on the brake, at which point the transmission will automatically down shift at certain speeds. This can be dangerous in a RWD vehicle, it is best to shift into neutral and apply light brake pressure to slow the vehicle.

[pitch]

Cyberian,I delivered mail for twenty years in one of those death trap LLV's. The ONLY way you could keep them from being pushed through a slippery intersection was to place them in neutral and feather the e brake to control the rear axle. I never had an accident or mishap doing this. Several of my coworkers over the years were involved in accidents as a result of not using this technique!
Please go to General RVing issues above and read a thread called "Attitude"

[sparkydave]

BenK wrote:


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

Only if the engine is not running.

[PaulJ2]

I remember many having rear pumps back in the 50s and early 60s. I think the only reason they did then was so you could push start the car when you had a dead battery. A rear pump model would engage and turn the engine. When that was removed no more push starting. Thus today.

[Gdetrailer]

joshuajim wrote:

BenK wrote:
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

OMG... that means that if I'm sitting in my driveway and shift into neutral my transmission is going to blow up!

Well not really. Rear pumps haven't been used in most transmissions for more than 40 years.

As long as the engine is running, the front pump will lubricate the transmission.

Nice catch, I can't remember a Ford Automatic transmission ever having a "rear pump" from the 1950's on up (my Dad and I rebuilt a 1958 two speed Mercury transmission and we played with some Ford C4 and C6 transmissions too boot), they are ALL in the FRONT of the transmission and are ALWAYS PUMPING as long as the ENGINE is turning...

So I call BS on the burning up a transmission while coasting in neutral. Pretty much ALL automatics will have a pump driven by the engine at the front of said transmission. If it were at the back you wouldn't have any pressure to move a stopped vehicle :S

Lack of lubrication with automatics is more about TOWING a vehicle with all four down AND the engine OFF at highway speeds more than a few miles..

Older non computerized vehicles the speed of the engine was set by your FOOT so if you kept your foot on the gas and stabbed into neutral the engine would gain RPMs.

The idea of coasting in neutral on bad roads was to eliminate speed without locking the wheels. So therefore it was assumed that you WOULD take your foot OFF the gas and the engine WOULD return to normal idle and not shoot up..

Newer drive by wire vehicles with computerized throttle body the engine RPMs could go down to idle or as noted the engine may not idle down but go up which would most likely match the engine RPMs to the vehicle speed..

[joshuajim]

BenK wrote:
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

OMG... that means that if I'm sitting in my driveway and shift into neutral my transmission is going to blow up!

Well not really. Rear pumps haven't been used in most transmissions for more than 40 years.

As long as the engine is running, the front pump will lubricate the transmission.

[bucky]

I know one thing. If you bump a 79 Olds Cutlass with a console automatic into neutral while driving with the cruise engaged there was no safety switch to kick the cruise out. The tach was heading for outer space. I was proving a point to a factory rep at the time, so I was ready with the brake pedal. He couldn't believe it either. I don't remember if we were on a hill at the time. 🙂
Why in the hell would a legislature even be discussing a JaJa overdrive anyway? CA must be one weird place.

[Turtle_n_Peeps]

rupprider wrote:
Does a 2006 duramax have def injection? Maybe fast idle was from regen?

No on either.

[rupprider]

Does a 2006 duramax have def injection? Maybe fast idle was from regen?