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

[Cyberian]

wilber1 wrote:

Cyberian wrote:
Doesn't matter. ABS, 2wd, 4wd, duals, 10 wheeler, 18 wheeler, any vehicle with locked brakes is nearly uncontrollable. Putting your transmission in neutral removes a crucial element of control and increases the likelyhood of locking your brakes.

Yes any vehicle with locked brakes is almost uncontrollable and if the rear brakes need extra pressure to override the engine, the greater the likelihood you will lock the fronts in the attempt. Basically the same reason manufacturers emphasize not to use cruise control or the exhaust brake in slippery conditions, you wind up with the wrong end steering the vehicle.

Cruise powers your rear into slides, Jakes brake the rear axle too much and cause slides. Your drive axle is already trying to slow more than the steer axle when you release the throttle due to engine braking. Ever notice that on RWD vehicles, the front brakes always wear out sooner than the rears? It's because native engine braking is helping the rear brakes!

Override engine power in order to slow the vehicle...sure, if one's right foot were on the throttle and left foot on the brakes.

The only time any vehicle should be in neutral with the engine running is while parked on a level surface with the parking brake set and tires chocked.

[MitchF150]

You know what you should do when going downhill when it's icy out??? Drop the trans to a LOWER GEAR and let the engine braking maintain your speed and you don't need to touch the brakes at all. Go figure. 😉

I have no idea how this works with DIESEL engines, since I understand they don't do that without an exhaust brake, but for GAS engines, this is the way I've always done with no ABS at all.

If you have a 4wd vehicle, doing this will allow both axles to aid in the engine braking, so even less chance of skidding.

Of course, if you are going too fast you'll still skid, regardless of what gear your trans is in, but to just say putting it in neutral going downhill in the snow won't lock up your brakes is just nuts IMO...

I know this has nothing to do with the OP original question and he found his answer SOMEWHERE ELSE... 🙂 But, I just couldn't let the snow part go..

Do whatever works for you... I know what works for me and it ain't putting it in neutral going downhill in the freaking SNOW... 😉

Mitch

[davisenvy]

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.

[wilber1]

Cyberian wrote:
Doesn't matter. ABS, 2wd, 4wd, duals, 10 wheeler, 18 wheeler, any vehicle with locked brakes is nearly uncontrollable. Putting your transmission in neutral removes a crucial element of control and increases the likelyhood of locking your brakes.

Yes any vehicle with locked brakes is almost uncontrollable and if the rear brakes need extra pressure to override the engine, the greater the likelihood you will lock the fronts in the attempt. Basically the same reason manufacturers emphasize not to use cruise control or the exhaust brake in slippery conditions, you wind up with the wrong end steering the vehicle.

[Cyberian]

wilber1 wrote:

Cyberian wrote:
Come to MT and put it in neutral on Bozeman or Butte passes some time, snow or otherwise doesn't matter.

Congratulations on getting me to sign up just to point out how dumb an idea this is.

Can depend on how your ABS works. Back in the day when RWD cars were most common it wasn't unusual to see someone slowly going down a hill in snow with the front wheels locked and the rears still turning because the vehicle was still in gear.

Watched a guy in an older car do it on the Coquihalla just a couple of years ago. He couldn't figure out why he wasn't slowing down any more.

His brakes were locked because he screwed up and stood on the pedal. Had nothing to do with it being in gear. Going to fast for conditions, topped the hill going too fast, didn't see slower traffic ahead, didn't recognize changing road conditions...

Doesn't matter. ABS, 2wd, 4wd, duals, 10 wheeler, 18 wheeler, any vehicle with locked brakes is nearly uncontrollable. Putting your transmission in neutral removes a crucial element of control and increases the likelyhood of locking your brakes.

I take it none of ya'll espousing "neutral" have taken a driving test lately or better yet have CDLs?

[wilber1]

Cyberian wrote:
Come to MT and put it in neutral on Bozeman or Butte passes some time, snow or otherwise doesn't matter.

Congratulations on getting me to sign up just to point out how dumb an idea this is.

Can depend on how your ABS works. Back in the day when RWD cars were most common it wasn't unusual to see someone slowly going down a hill in snow with the front wheels locked and the rears still turning because the vehicle was still in gear.

Watched a guy in an older car do it on the Coquihalla just a couple of years ago. He couldn't figure out why he wasn't slowing down any more.

[Cyberian]

Come to MT and put it in neutral on Bozeman or Butte passes some time, snow or otherwise doesn't matter.

Congratulations on getting me to sign up just to point out how dumb an idea this is.

[Gdetrailer]

Winged One wrote:

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.

Yep.

Even now days with anti-lock brakes this trick actually not only still works but also works even better. A lot less brake pressure means the chances of the anti-lock brakes having to step in is reduced but yet the anti-lock system can step in to prevent total lockup, without it being over aggressive.

I used to argue this point with my inlaws, and to this day they have not learned what a valuable tool this can be in bad weather.

For my DW, it only took ONE preventable accident on snow covered roads and was a believer after that. :B

[mkriedel78]

Hi Everyone...

Thanks(?) for all the replies. I was kind of hoping someone with this actual truck who's done this before would chime in. I didn't realize quite the can of worms I was opening when I asked.

Regardless, I found this elsewhere:

Another neat trick is that if you're going down the road and you shift into neutral, the engine wont drop down to idle...the TCM has whats called "neutral tracking", meaning it will automatically raise the engine speed to the proper "rev-matched" speed, so when you move the shifter back into drive, the engagement from neutral to drive at X mph will be smooth and rev-matched so theres no huge clunk.

Source

So, it does in fact seem that it's supposed to do this.

Thanks for everyone's concern. I'll stop being public highway enemy number one now, and leave it in drive. 😉

[UsualSuspect]

I would guess it does that so when you put it back into gear everything is running close to the speed the truck is moving.

[Dave_H_M]

Whoah, that truck has to go into the shop immediately.

On the problem sheet, have the tech put down that the engine sped up some when you put it into Ja Ja overdrive.

[PaulJ2]

Grit dog 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

You should try it sometime! Lol. Seriously though. Guy said he wasn't towing and it was a slight hill.
You'd be surprised, can get some good fuel mileage doing that. Coming down a big grade running empty if you don't need much brake to keep speed I've coasted 8-10 miles like that at an idle. Just tap the brakes once in awhile. Uses virtually no fuel that way. Nothing wrong with it.
And I have yet to meet a transmission that grenaded from coasting!

That was true in the old days of carbed units. With todays fuel injected models most cut off the fuel when coasting at speed--both gas and diesel--so no savings there any more.

[Grit_dog]

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

You should try it sometime! Lol. Seriously though. Guy said he wasn't towing and it was a slight hill.
You'd be surprised, can get some good fuel mileage doing that. Coming down a big grade running empty if you don't need much brake to keep speed I've coasted 8-10 miles like that at an idle. Just tap the brakes once in awhile. Uses virtually no fuel that way. Nothing wrong with it.
And I have yet to meet a transmission that grenaded from coasting!

[wilber1]

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

Right, so engine RPM should be following vehicle speed not throttle position and there is no way it should be at 900 -1000 RPM at 65 MPH if the truck is in gear.

[bovellois]

2oldman wrote:
You just can't say things like that and not get a load of guff first.

🙂