Colorado mountains towing 5th wheel - Diesel Forum

JoeF350 · 07-10-2008, 03:04 PM

Okay, all you towing gurus, I have a questions about towing our 15,000 lb fifth wheel trailer in the Colorado mountains.

What is the rule for going down the mountain using tow/haul? We did this last summer and I started smelling brakes when I got to the bottom of Slumgullion pass going into Lake City. Should I shift to 1st gear with tow/haul enabled? I ask because I remember using tow/haul on the Slumgullion pass trip and the transmission was in D. Should I downshift to 3, 2, or 1? I'm confused and would like to have an answer before we start our trip next week.

Thanks,
JoeF350

Mark Kovalsky · 07-10-2008, 03:21 PM

Tow/haul will downshift automatically. It will downshift to a lower gear if you press the brake pedal enough to turn on the brake lights. It will downshift to an even lower gear if you press the brakes enough to active the brake pressure switch. That's around half pedal.

You can manually downshift, too, and at ANY speed. If you move the shifter to a gear that is too low for the speed of the vehicle the PCM will prevent the shift until the truck slows down. It's impossible to overspeed the engine by moving the shifter to 3, 2, or 1.

SoB · 07-10-2008, 09:47 PM

I can say go slow with out using the brakes if possable. I don't have a tow haul but, I do have a suncoast built tranny with a converter lock switch. I do that drive with the tranny down in first with the converter locked up and let the motor handle the braking. Going back up is fun also, NOT!

Steve

patchzx7r · 07-11-2008, 02:34 PM

Keep the tow/haul on and as stated above just take it slow. I frequently drive the passes with the 5'er. The tranny on our trucks is second to none and does just fine.

Take your time and enjoy the scenery..

BudMan5 · 07-11-2008, 03:25 PM

I pulled all sorts of trailersd all over the country and western Canada. The tow/haul does all the work for me. I pull three axle 15K toy haulers and 6K TTs and have never had a problem going up or down.

BudMan

JW350 · 07-11-2008, 04:01 PM

Quote:

Originally Posted by Mark Kovalsky

...You can manually downshift, too, and at ANY speed. If you move the shifter to a gear that is too low for the speed of the vehicle the PCM will prevent the shift until the truck slows down. It's impossible to overspeed the engine by moving the shifter to 3, 2, or 1.

That assumes the truck is calibrated for the given tire size, correct?

Mark Kovalsky · 07-13-2008, 10:02 AM

No, it doesn't matter. The limit is by output shaft speed. The output shaft speed sensor doesn't care if the truck has been calibrated for the right tires.

JoeF350 · 07-13-2008, 03:38 PM

Okay, so what is the correct procedure for using the tow/haul to slow me down? I know to start out slow. After I start picking up speed due to gravity, do I get on the brakes hard to slow down again? and keep repeating this process? I think that's why I was smelling brakes on Slumgullion Pass last time, I was having to use the brakes too much. It would seem that with tow/haul I shouldn't need to use brakes as much, but it didn't work that way last time.

I'm so confused.

Joe

BudMan5 · 07-13-2008, 09:07 PM

When starting down hill, let your speed to whatever you feel comfortable with and then as the truck goes past that point, step on the brake. Push it down enouigh that you feel the truck slow and you will feel the tranny kick in and gear down.

It will keep you at that speed all the way down. If the descent increases, step on the brake again and push down hard enough to feel the truck solow, the tranny will sense it also and gear down again.

I love the tow/haul. I was hauling a three axle Raptor toyhauler (which I hate) weighing somewhere around 13K on the west side of Elk Mountain on I-80 in Wyoming. Pretty impressive grade. The tow/haul kept me at a steady 50 mph all the way down and then geared up when i gave it some fuel as I nearted the bottom.

Neat stuff.

BudMan

JoeF350 · 07-13-2008, 11:12 PM

Thanks to all who responded. I shall try Budman5's suggestions on our trip and hopefully, you will not be reading about the black F350 dually that went over the cliff and all aboard were killed in a Colorado road accident. ha

I'll report back.

Joe

JW350 · 07-14-2008, 11:49 AM

Quote:

Originally Posted by Mark Kovalsky

No, it doesn't matter. The limit is by output shaft speed. The output shaft speed sensor doesn't care if the truck has been calibrated for the right tires.

OK, that's good to know. A couple of times mine downshifted sending the tach to 4K. Seems kind of high to me and thought it was my setup causing the PCM to think the truck is traveling slower than it really was.

Thanks for the info!

Mark Kovalsky · 07-14-2008, 01:39 PM

That's the maximum speed that is allowed on a downshift.