9% hills, diesel braking, RPM jumps to 3500RPM

[letsgo]

Just got back from a towing vacation 17,000 gcvw, very relaxing, the Duramax was FANTASTIC whatever the grade GOING UP (posted 6% to 9%) I could always accelerate, on the flat lands I wanted to try passing a slow car doing 55mph on a 2 lane highway to see if the rig was up to the demand (out and in safely) very pleased with the performance. the gas milage towing was anywhere between 11 to 13mpg US. or 13 to 16mpg Can.

QUESTION: when driving over the top of the pass and down 2 different (mountains) with 3 mile grades at 9% with DMax and trailer, with the tranny in tow mode, the exhaust brake came on the tranny down shifted, RPM JUMPED TO 3500 RPM scared the living *@^& out of me, to correct this high RPM I immediatly touched the gas peddle tranny shifted back up, RPM dropped to 2000rpm, then I applied light braking to control the exhaust braking and the DMax RPM at about 2000rpm every thing worked fine for the rest of the grade.... Did I do somthing wrong or is this rpm jump acceptable??????????

Any input would be most welcome.

GMC 2002 DURAMAX SLT 2500HD 4X4 AUTO.

[Jackmchome]

The dotted red lines on your tach are for the grade breaking perameters. From 3300 to 4700. I have used mine often in the 4400 to 4500 range. That is how it works. Keep in mind, the Allison will simply not allow the engine to overrev itself.

[NutNbutGMC]

^...What Jack said. :cool: :cool:

[mark45678]

you gota just love these truck!!!!! 9% with 17K in tow and hammer down I am coming threw! there isnt any reason to worry as long as your not in the solid red on the tack. the doted red lines are ok as long as the motor is defueled, It will not pull any higher then like 3300~3400 foot on the floor to the revlimiter.

[MaxDMax]

letsgo,
We have a big 5ver and my GCVW is right at 20,500lbs. We live in the middle of the Appalachian Mountains in KY and have to deal with about 50 to 100 miles of 7%+ grades to go anywhere. I was concerned about this at first, but after reading other posts here and a few months of just keeping it out of the redline area, I have gotten used to it. I have found that if you just let her scream and only use the brake to keep it out of the red, you will find this is one awesome feature of your truck. One thing I have found is that I can control the trans braking points very easily by varying the amperage output a little on the Jordan brake controller. If I want to maximize the trans braking I just lower the amperage output of the brake controller a little. If I want to minimize the trans braking I just turn the amperage up a little. Once you do this for a while, you will find you can control the timing and the RPMs of your trans braking to fit whatever makes you comfortable. I just make sure I keep my standard setting marked so I can always just go back to the standard setting when I get off the bigger grades. Hope this helps.

[ 05-20-2002: Message edited by: MaxDMax ]</p>