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Discussion Starter #1
Help me understand how the grade-braking feature works. I was heading north on I5 on the grapevine down through the steepest section just before the San Joaquin Valley. I was doing about 75 MPH in the fast lane keeping up with traffic. One bone head several cars ahead thought this was too fast and instead of moving over a lane and slowing down, decides to start riding his brake in the fast lane
. So all I needed to do to stay safe was slow my speed 2 or 3 MPH. I gently applied the brakes and immediately the trans downshifted to 4<SUP>th</SUP> gear. The engine was at red line and dropped my speed more than was needed, so now there were two bone heads in the fast lane slowing up traffic
. With a little pedal I was back in 5<SUP>th</SUP> gear but to check it out I tried the brake again with the same results.


All I wanted was to check my speed by a couple MPH not hit redline in 4<SUP>th</SUP> and cause my family whiplash.


Plus I thought grade braking only worked in tow haul mode, which I was not in. I double checked.


Any thoughts or experience?
 

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I have had mine do it at a slower speed but I was in tow / haul mode. I was pulling a 6000# travel trailer down a slight 3 deg slope. I have pulled only about 1k miles so far and the rest of the time it has worked smooth as silk. I have heard that sometimes a truck gets shipped with with incorrect software and needs to be updated. If it does it again I would suggest you get it checked out. Were you towing anything at the time?
 

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Discussion Starter #3
No Cruz_Man, I was not towing. I was on my way back from So Cal doing the turkey day with family. Only had wife, one kid and we were traveling light.


75 MPH IMO was not the right time to go into grade braking mode.


Gave me the big pucker.
 

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I too have noticed the grade braking come in at some odd times, even out of T/H. The other day I was making the turn into our driveway off the highway, about a 25-30 mph turn, and right at the apex she grabbed a lower gear. Didn't cause any harm, but it definately catches you off guard. I can imagine it doing that at 75 in the left lane might be a little more startling.



Bob
 

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Go to: http://www.kennedydiesel.com/ . Click on "Tech Tips" at the top of the page. Then click on "Duramax", Then "Allison Grade Braking". I'm sure the Allison web site will also have this info, as this is probably where much if not all of this came from. Not sure though, but I know John has it here.


Steve
 

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Discussion Starter #6
Thanks for the link YZF1R, that was some good stuff. Sounds like my trany operated normaly.


Although I would have rather had control of the the brakes only. With the grade braking as an option.


But one thing I will say.


Over the Grapevine, I love that Diesel!
 

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It comes on if you hold the brake pedal down steady, if you just tap and release a few times mine doesn't come on. You will get used to it and it is a good feature towing or not. Saves brake pad wear and over heating the brakes if you have to ride the brake down long downgrades.


Best way to keep it from coming on is to get a "feel" for how long you can hold the pedal down steady (count seconds) before it downshifts, then in real situations you will know how long to lightly tap and release, tap and release to keep it from downshifting. OF course if you need to slow down and have to ride the brake the downshift will help you slow down without wearing or heating the brakes.


You will get used to it.
 

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Roscoe,

That sounds like the system is a bit sensitive. I've been in the same situation at about the same place and did not get the downshift. Though, as I recall consistent with what Chevyrus suggests, I didn't hold the brakes on very long as I slowed for the speed pirate ahead of me.

TC
 

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Discussion Starter #9
Hey Tsckey I have been thinking about what Chevysrus wrote and I tend to agree with you. I don't think I was on the brakes very long. But I guess I need to get into a simlar situation again and try to slow using just the brakes with short applications of pedal. IOW I will try Chevysrus suggestion.


Thanks all.


Roscoe
 

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It sounds like a nice thing to have, but SHOULD only be functional in tow/haul mode. What's going to happen when it does that on icy roads or compact snow?
 

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it took a while for me to get accustomed to my truck's Allison down shifting pattern ... must have gotten used to it because, until I read this thread, I haven't thought about it in a while ..... suspect some trucks are more sensitive to brake pedal pressures than others


Jim
 

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Don't worry about hitting redline either. Manual says redline during grade breaking is 4,700 RPM. I tow a fifth whell and have pulled it over the rockies a few times now as well as all the California mountains and I really like the grade breaking feature. I rarely ever have to use my breaks on downhills once it takes over and if I do it's just a tap and the Allison grabs the next gear down and all is well.
 

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Camstyn said:
It sounds like a nice thing to have, but SHOULD only be functional in tow/haul mode. What's going to happen when it does that on icy roads or compact snow?

Mine has done it A couple of times on an ice covered dirt road going down hill, it's A wild ride my friend, I popped mine into neutral to get the truck to straiten out again. I just figured it was cause the engine and trans was cold.
 
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