I wasn't too sure if I should post this here or in the Tranny forum but anyway...

I am going to be renting a trailer this summer to go into the Rocky Mountains in BC. I have not towed much and really none in mountianous areas. My question is in regards to the grade braking feature on the Allison. I have a positive air shutoff valve on my truck for working in the oil patch to prevent a runaway engine scenario that automatically closes at 3400 Rpm. I have heard that the grade braking algorithm will allow the engine speed to go up to 4800 Rpm and now I'm concerned that when towing and this activates, my PAS valve will close and now I'm just a projectile with a dead engine.:eek2: The most my grade braking has ever revved to was about 3000 Rpm when hauling my service body. Does the high revving happen regularly or do you need to be at a heavy load. The trailers I'm looking at renting are about 6500 lbs dry.

Thanks.

on steep hills i have exceeded 3400 RPM with grade braking... can't you cimple disable the shutoff temporarily?

It has an electronic brain. I will need to put in a switch to interupt the 12v power source to the unit. What the installing shop originally wanted to do was just up the redline shutoff to 5000 Rpm to get out of the 4800 rpm range for the braking but I would say 5000 rpm under power in a runaway situation is not the same as 4800 rpm with grade braking. Correct me if I'm wrong but in the grade braking the engine is kindof just along for the ride as oppossed to being under power to that high of a rotational speed.

I have seen mine up around 4400rpm's! Wow, what a sound! This was accomplished by my buddy driving with a 5000-6000lbs trailer in tow.

Never had a problem with my Banks and this truck ... you can check the trailer in my signature ... I've had all tanks full of water and the unit packed about as tightly as you can imagine. To get it to jump into the red, you have to do a "kick down" ... pretty much never have to do that ... also driven some pretty steep grades (tried many of the big ones west of the Missouri).

... I don't think you'll have to worry (but it never hurts to be OVER prepared).

RJ

Well I'm leaning toward disabling the PAS because it will only need to happen once for a split second and boom - good night the engine is off and I'll be trying to herd this thing to the side of the road with no steering or brakes. I'll default to being a little anal in this case I believe.

Ally will up shift at around 4800 to the next gear. I have a 38 foot Toyhauler when loaded with 3 sportsman 500HO Quads, 100 gallons of water 30 gallons fuel, propane and the trimmings probably tops out at 15K or so. Descending 7% grades I have had mine go to 3400 or so as every time you step on the brake it will shift down until it hits the lowest gear. Never had the engine die but that would sure make you change your drawers. Trailer brakes would still work manually. I personally don't mind it redlining on the down grades but it rarely happens. Slow and easy on steep down hills....Jim


03 2500HD LB7 CC/SB LT 4x4, Juiced no/***, Isspro Guages, Stock everything else.

If you can really call these trucks stock.:ro)

Usually the "loud" noise of the engine is the fan engaged.

When mine downshifts, the dmax just purrrs at the higher rpm's.

"I have not towed much and really none in mountianous areas."

I don't totally understand the PAS system so nothing to add there. Just a quick spin-off on your towing experience and heading right into the mountains. IMHO you might spend some time in the ol' "towing saddle" before tackling mountains with a trailer behind you. 6500lbs dry weight on a trailer is a good sized trailer. What will be the final weight behind your truck? What will you be towing? :confused:

Towing heavy in mountainous areas has a multitude of differing dynamics. You push the truck hard to climb long steep grades, then it tries to push you to he?? and back on the way down. Sorry I didn't notice what kind of truck you have. Will this trailer be a hitch mount, gooseneck or 5ver hitch? :)

Not trying to kidnap your post, just get safety out front where it belongs. The PAS won't do anything for you if you get yourself in the wrong conditions at the wrong spot. PM me if need be. JJ :)