when and how to shift into first when towing up a mountain

[greggraves]

Just checking my methodology to see if "all" agrees. I am towing a 5000 lb TT with a 2006 Chevy Trailblazer with the 5.3 vortex v8. I tow in 3rd. When going up a steep hill, I wait until the computer decides to go into 2nd, then pull the lever down to 2nd so it stays there until I get to the top of the hill. My max speed in 2nd is 45 mph, ~3500 rpm. On a few occasions (like getting up onto Skyline Drive from Orange VA) I've had to go all the way down into 1st and crawl to the top, keeping an eye on tranny temps as I go. So what is the best way to go into 1st? I've got a Scanguage and can see the engine "load", and it worries me when the engine is pumping out 95% of available power, and then downshifting to first with that much torque might break something. I've had both my motor mounts replaced, though I don't know whether the guy that owned this vehicle previously did that, or whether it was me. I've towed this trailer some 40,000 miles. I am thinking that I should let the vehicle slow down to 30 mph, and then jam it into 1st, rather than let the computer make that decision. The risk is that if I let the rpm's get too low in first, then I could slowly slow down to a stop ... and that would suck, not only for me, but for everyone that is behind me!!! Do I trust the computer, or trust me brain?

I am heading to the Arches/Glen Canyon NP area next week.....

 

[CaptainXL]

The risk is that if I let the rpm's get too low in first, then I could slowly slow down to a stop ... and that would suck, not only for me, but for everyone that is behind me!!! Do I trust the computer, or trust me brain?

Mechanical advantage is best in lower gears. You get more torque (force that gets you going) albeit with a resultant loss in mpg and more heat.

Depending on what you are loaded down with you might be maxed out as far as tow weight limits. Its either 6300 or 6800 pounds depending on final drive ratio. And that's with the driver, passengers and cargo in the back plus add another 500lbs for stuff inside the trailer. So your probably right at the limit depending on gear ratio.

Do you have the 3.42 or 3.73 gear ratio?

Most 32 foot and longer trailers weighing 5000 lbs or more require a 3/4 ton pickup as the limits are very close with SUV,s and 1/2 ton pickips and its best to have extra in case your going up hill or in higher altitudes.

A 6.0 liter 3/4 ton pickup with a long wheel base and towing gears (4.10) is ideal up to about 10-12000 lbs.

 

[Trios]

Just checking my methodology to see if "all" agrees. I am towing a 5000 lb TT with a 2006 Chevy Trailblazer with the 5.3 vortex v8. I tow in 3rd. When going up a steep hill, I wait until the computer decides to go into 2nd, then pull the lever down to 2nd so it stays there until I get to the top of the hill. My max speed in 2nd is 45 mph, ~3500 rpm. On a few occasions (like getting up onto Skyline Drive from Orange VA) I've had to go all the way down into 1st and crawl to the top, keeping an eye on tranny temps as I go. So what is the best way to go into 1st? I've got a Scanguage and can see the engine "load", and it worries me when the engine is pumping out 95% of available power, and then downshifting to first with that much torque might break something. I've had both my motor mounts replaced, though I don't know whether the guy that owned this vehicle previously did that, or whether it was me. I've towed this trailer some 40,000 miles. I am thinking that I should let the vehicle slow down to 30 mph, and then jam it into 1st, rather than let the computer make that decision. The risk is that if I let the rpm's get too low in first, then I could slowly slow down to a stop ... and that would suck, not only for me, but for everyone that is behind me!!! Do I trust the computer, or trust me brain?

I am heading to the Arches/Glen Canyon NP area next week.....

I wouldn't be too awfully concerned with torque when shifting to first. The 4L60E that is in our trucks is the same that is in automatic 97-2004 Corvettes. In '04, the 'Vette made 350 HP and 360 lb/ft of torque, and folks have been known to hammer them into 1st gear coming out of slow curves. As long as you aren't shifting to first under full load 10 times a day for months on end, you should be fine.

That being said, towing that much weight on a regular basis definitely constitutes 'harsh service.' You should be performing maintenance on the trans fluid, filter, and the rear end at more regular intervals than those of us who do normal mostly-highway driving.

 

[greggraves]

As Yoda might say, "Oh service me does." I change the oil every 5000 with Mobil 1, change the tranny filter every 40K, and just put the grape juice in the differential last week at 95K. I figure I am in Ultra Severe Service mode. I forget which rear end I have but it is rated at 6200 lbs. The trailer weighs empty 4300 so I figure with all my crap, including my 120 lb wife and 6 lb dog, I am ~5000, in any case below the 6200 lbs this thing is rated for. I have to hand it to Chevy for designing the 2006 TB (that is why they don't make them anymore ... smart move GM corporate geniuses!!). I get 12 to 13 mpg, maybe 14 with a tail wind, when towing. When I unhook I am getting 21-22 mpg. That is the downside of getting a more capable tow vehicle ... everything is a tradeoff, more power, more torque, less mpg. Plus this thing is paid off!! I only use this vehicle to either tow this trailer or tow my boat, and it ain't broke ... yet ...

In another post I read earlier claimed that the computer drops the torque prior to downshifting. Certainly doesn't feel like it. Is that true? If so, I won't worry about it, and if the computer pops it into 1st when 2nd craps out, I'll just pull the stick down to keep it there until I figure I'm past the worst of it. So far I've only ran into two ridiculously steep hills where this happened. The worst of the hills I have to climb in my upcoming adventure is a 2 mile 8%.

 

[CaptainXL]

4300 lb trailer? This must be an ultra light. What year and model is your trailer. I'm curious what the dry weight and gross weights are.

 

[BRomanJr]

As Yoda might say, "Oh service me does." I change the oil every 5000 with Mobil 1, change the tranny filter every 40K, and just put the grape juice in the differential last week at 95K. I figure I am in Ultra Severe Service mode. I forget which rear end I have but it is rated at 6200 lbs. The trailer weighs empty 4300 so I figure with all my crap, including my 120 lb wife and 6 lb dog, I am ~5000, in any case below the 6200 lbs this thing is rated for. I have to hand it to Chevy for designing the 2006 TB (that is why they don't make them anymore ... smart move GM corporate geniuses!!). I get 12 to 13 mpg, maybe 14 with a tail wind, when towing. When I unhook I am getting 21-22 mpg. That is the downside of getting a more capable tow vehicle ... everything is a tradeoff, more power, more torque, less mpg. Plus this thing is paid off!! I only use this vehicle to either tow this trailer or tow my boat, and it ain't broke ... yet ...

In another post I read earlier claimed that the computer drops the torque prior to downshifting. Certainly doesn't feel like it. Is that true? If so, I won't worry about it, and if the computer pops it into 1st when 2nd craps out, I'll just pull the stick down to keep it there until I figure I'm past the worst of it. So far I've only ran into two ridiculously steep hills where this happened. The worst of the hills I have to climb in my upcoming adventure is a 2 mile 8%.

Is this what you meant to say?

 

[C-ya]

Looking at the fuel mileage, you must have 3.42 gears.

A quick check of the 2006 manual shows a 2WD V8 w/ 3.42 gears to have a 6300# max trailer weight, so I guessed right. :wootwoot:

 

[gmcman]

What Trios said....these tranny's are built pretty good with a few weak areas but downshifting is going to happen whether or not you do it or the computer does. I would suggest strongly to add a tranny cooler if you haven't already. Pretty much when you are losing speed pulling a grade then the next lower gear is ideal and likely inevitable. Trying to get around 5K RPM's or more with the VVT maxed instead of using a lower gear and taking it easy is where the tranny's start to get too hot, sounds like you have it under control though.

 

[Trios]

Is this what you meant to say?

I believe he means Royal Purple, but I hear Welch's concentrated grape juice is a reasonable substitute. Just don't water it down too much, it needs to be thick enough to provide lubrication.

 

[BRomanJr]

I believe he means Royal Purple, but I hear Welch's concentrated grape juice is a reasonable substitute. Just don't water it down too much, it needs to be thick enough to provide lubrication.

Sounds right, was just hoping he didn't put AutoTrac II (smurf juice) in the diff.

 

[Playsinsnow]

When I pulled fully loaded to the west coast and back I left it in 2nd.

When I was cruising up a several miles long mountain pass, I would ease off the gas when I felt it needed it. This made the shift feom 3-2 and 2-1 (if nec) much easier. Sometimes you top the grade only doing 20-25mph and the truck is still running great. Or try and break something trying to stay at highway speeds.


I only used first on second coming back down, adds time to tge drive but you won't use your brakes much.

 

[IllogicTC]

A note on engine load:

It's generally a normalized value between 0-95 (I6 reports up to 100, at least with Actron CP9575 scanner), which is a determination of how much air mass is being pulled in per intake stroke. It doesn't necessarily define the amount of output as compared to rated output is being pushed out, and is mainly used to schedule spark timing and EGR, and can be used as a figure for determining pumping efficiency. It's a value pushed out by the PCM, not factored by the scanner.

I can be at idle, push my throttle in half-way and hit 100. In fact, it seems like any time I'm doing anything beyond extremely light acceleration or at cruise speed, it's easy to peak the number out. While torque remains consistent over a wide band on the I6, I KNOW I'm not getting 100% of rated horsepower through the whole range. I'd say a better way of understanding how much your engine is putting out would require knowing where you have the throttle, what your current tachometer reading is, and a disturbingly-accurate knowledge of your engine's horse/torque charts.

Letting off the gas long enough to let the engine settle down if you're getting a decent slip in the torque converter before shifting to 1st is all I see as needed, assuming you're already at a proper speed to engage low gear.