TOW/HAUL MODE

[DMAXTODD]

Im back!! I used to be on here a lot but have been real busy with work lately. Anyway, I was wondering if anyone else has experienced this: I was Towing about 12,000 worth of Oak logs on my flat bed trailer in the mountains on I-68 in MD today with the truck in tow/haul mode, now usually as I brake the truck would downshift one gear, but lately as I hit the brake the truck drops two and sends the motor above redline on the tach. This has recently gotten worse and it seems like tow/haul is over reacting?? Any ideas? Todd

[More Power]

Good to see you back!

Have you had the ECM/TCM reprogrammed since the last towing session, or anytime in the recent past?

The grade-braking redline is 4800 rpm. This is the maximum engine rpm the ECM will allow it to run before upshifting. It would take an extraordinary situation to see that kind of rpm (i.e. extra heavy load, steep-steep grade, little or no service brake use).

I rode in a 3500 Duramax a few years ago down a long 6% grade at 27,000-lbs GCVW. The engine ran at about 3100-3500 rpm in grade braking. This was with little use of the truck/trailer service brakes.

Jim

[DMAXTODD]

Morepower, Thanks for the reply.The ECM/TCM has had no upgrades lately. I was not sure of the redline when grade braking,thanks for that info I was usually only seeing 3000 to 3200 rpm so maybe I was just a little too worried about it, I thought anywhere over 3000 rpm (red area of tach) was overrevving it. Those hills in western maryland are surprising!!

[Kennedy]

Grade braking is an AWESOME feature!

[Buck]

I don't mean to hijack your thread ;)

I just got back from Canada towing 12K. In the steep hills near the Canada border on HWY 61 (along Lake Superior) My LLY's grade braking would send RPM to 3554 (highest according to the Attitude.) It is the first time I ever witnessed "grade Braking". The normal downshifting in Tow/haul is seperate. It is a cool feature, My buddy was leading the way with his '04.5 Cummins 600 towing about 6K. I got on the CB and asked him why he was on the brakes so much :D :D

[markrinker]

So what is the difference between 'grade braking' and the normal tow/haul downshifting I have experienced?

[Paul Clancy]

I believe the allison gets info from a sensor about the trucks attitude and that combined with your brake use and speed make it decide what gear to grab. In practice it behaves much the same as when it traffic but will hold the load back more agressively. You need to accelerate more to get an upshift when grade braking is engaged. That's how I see it/use it and yes it's a great feature and has save me the cost of an exhaust brake.