Grade brake?

[ammoaddict]

I bought a 2018 Sierra 1500 SLT last month. I was coming down Black Mountain in NC when the grade brake activated. I didn't even know the truck had this feature. It freaked me out a little when the rpm shot up and the truck started sounding like a semi. Does anyone know exactly how the grade brake works? Thanks.

 

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[Nasty]

I think it only works when tow mode is activated

[ammoaddict]

I think it only works when tow mode is activated

No, I have never used the tow mode.

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[BIGDOGx]

No grade braking is active at all times, hold in your tow haul button for 3 seconds or more then let off and you can toggle it on or off. It is also the main cause of the jerkiness and overall poor shifting habits at least with the 6 speed imo. Disabling this feature makes the trans a much smoother ride as your transmission is not trying to use it's gearing to help with braking. I have complain to GM that this feature should be disabled at the turn of the key and should only be activated when the user selects it, but gm would rather not it seems.

[swathdiver]

Look up Cruise Grade Braking Normal and Powertrain Grade Braking Normal.

[Grjfer]

2 minutes ago, BIGDOGx said:

No grade braking is active at all times, hold in your tow haul button for 3 seconds or more then let off and you can toggle it on or off. It is also the main cause of the jerkiness and overall poor shifting habits at least with the 6 speed imo. Disabling this feature makes the trans a much smoother ride as your transmission is not trying to use it's gearing to help with braking. I have complain to GM that this feature should be disabled at the turn of the key and should only be activated when the user selects it, but gm would rather not it seems.

Agree 100%. It is a nice feature when driving an area with a lot of down grades, or towing a trailer. However for daily in town driving I disable it. 

[ammoaddict]

I was wondering if it is just a matter of transmission gear selection or if it's actually a compression brake like a Jacob brake on a semi truck.

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[Jon A]

For these trucks, it's just the transmission shifting, the same as if you manually shift.

 

Jake brakes, or "exhaust brakes" are for diesels.  They typically have no throttle so even with the fuel cut off, the engine sucks air through it and provides very little resistance--basically "freewheeling," as the power used compressing the air is mostly returned when the air pushes the piston back down, providing little net effect.  A jake brake typically interrupts the cycle by releasing a portion of the air into the exhaust after compression creating a net effect--it takes energy to compress the air, but the air is not allowed to return that energy by pushing back down on the piston.  That's over-simplified but why diesels need the additional system to provide much engine braking.

 

Gas engines can provide a lot of engine braking without any such system.  Since they have a throttle, when that is closed the engine provides a lot of resistance to turning.  The engine is basically an air pump--think of a large vacuum cleaner that is blocked off and trying to suck large amounts of air through a pinhole.  It becomes much harder to turn that pump over.

 

Personally I love the grade braking on the 6-speed trucks (I believe it's programmed to be "less aggressive" on the 8-speeds), especially when towing.  When you've got 15K headed down a long 6% grade, not having to ride the brakes or even touch them at all is fantastic and much safer than having to rely on the brakes to maintain a safe speed.  Even when not towing, it's nice to not have the truck run away on you unless you hit the brakes going down hills.

 

That's my question for those who don't like it.  I can understand how some might like the added smoothness of fewer shifts and the hypermilers might like the slightly better mileage...but do you guys normally cruise at 10 MPH below the speed limit or something?  If you normally cruise 0-5 MPH above the limit and you let the truck coast another 10-15 MPH faster at the bottom of every hill that's just asking for a ticket--and can raise real safety concerns when the limit is 75 or 80 MPH even when empty.

 

 

 

Edited December 24, 2018 by Jon A

[ammoaddict]

For these trucks, it's just the transmission shifting, the same as if you manually shift.
 
Jake brakes, or "exhaust brakes" are for diesels.  They typically have no throttle so even with the fuel cut off, the engine sucks air through it and provides very little resistance--basically "freewheeling," as the power used compressing the air is mostly returned when the air pushes the piston back down, providing little net effect.  A jake brake typically interrupts the cycle by releasing a portion of the air into the exhaust after compression creating a net effect--it takes energy to compress the air, but the air is not allowed to return that energy by pushing back down on the piston.  That's over-simplified but why diesels need the additional system to provide much engine braking.
 
Gas engines can provide a lot of engine braking without any such system.  Since they have a throttle, when that is closed the engine provides a lot of resistance to turning.  The engine is basically an air pump--think of a large vacuum cleaner that is blocked off and trying to suck large amounts of air through a pinhole.  It becomes much harder to turn that pump over.
 
Personally I love the grade braking on the 6-speed trucks (I believe it's programmed to be "less aggressive" on the 8-speeds), especially when towing.  When you've got 15K headed down a long 6% grade, not having to ride the brakes or even touch them at all is fantastic and much safer than having to rely on the brakes to maintain a safe speed.  Even when not towing, it's nice to not have the truck run away on you unless you hit the brakes going down hills.
 
That's my question for those who don't like it.  I can understand how some might like the added smoothness of fewer shifts and the hypermilers might like the slightly better mileage...but do you guys normally cruise at 10 MPH below the speed limit or something?  If you normally cruise 0-5 MPH above the limit and you let the truck coast another 10-15 MPH faster at the bottom of every hill that's just asking for a ticket--and can raise real safety concerns when the limit is 75 or 80 MPH even when empty.
 
 
 

I like it. It just startled me when it came on because I had never heard of it before and I didn't know I had it on my truck. Mine is the 5.3 with the 8 speed.

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[Mozzer]

Would have been nice if the sales guy mentioned it & how to have it turned off following the 'make sure you don't drive hard or use high rpm for the first..... kms'

First time I went down a long hill applied light brakes for a couple of seconds it changed down two gears, hit 4k & I had visions of a warranty refusal if anything ever went wrong with the engine.

Before that same long hill I now usually change to manual which disables the grade brake & if I do feel I need to change down it is a quick tap on the stalk.

It is worthwhile for not cooking brakes for folks who only ever select Drive.



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[TRKLGND]

My truck shakes or jitters ever so slightly just before coming to a complete stop.  I tried turning off grade braking.  No change.