Cruise Control

[marpel]

I travel to/from BC and Denver quite often (Sierra, 6.2L) sometimes towing a smallish (under 4000 ibs) trailer and sometimes, not. I travel the major highways and, depending on whether the trailer is attached or not, will do under 65 (with trailer, in manual 5th gear) or at the speed limit (without trailer, OD at 80 on some stretches). And, of course, some of the hills are quite steep and/or long. I use cruise control whenever I get a chance but do not use tow/haul.

In cruise, going uphill, the cruise will kick in and accelerate when the speed drops down only a couple KMH. makes sense. However, when going downhill, often the cruise will not slow the vehicle until it is about 8 or 9 km above the set speed - this is sort of dependent on the steepness of the hill.

So, two questions - Is it normal for cruise to kick in and slow the vehicle this much above the set speed? and - Sometimes it seems the cruise will use the transmission to slow the vehicle and other times, the brake (or maybe even a combo of both). And often, especially when it is slowing from the 8 or 9 above the set speed, the deceleration is quite severe. It has been like this since new. So, for these severe decelerations, do the vehicle brake lights come on? I expect they would if the brake is involved but do they activate when the cruise utilizes the transmission to rapidly slow down? There has been occasions when a following vehicle comes up on me rapidly when this slowing occurs and am wondering if they are lulled into a false sense of confidence because they don't see a brake light.

Sorry for the long post but wanted to include all the pertinent info.

Marv

[4x4ord]

The Ford with adaptive cruise control applies the wheel brakes when descending down hill and illuminates the brake lights. If the brakes get too hot It sounds a warning and shuts cruise off. Your Chevy might be the same.

[Grit_dog]

And tow haul doesn't cause higher rpms when cruising unless they're needed. And you said you're downshifting as needed, so virtually no difference.

[Grit_dog]

stickdog wrote:

RoyF wrote:
I don't like to use cruise control when towing because, when cruise control is on, the tranmission will downshift on every little grade, including overpasses. I might use cruise if the road is absolutely flat, but such roads are few and far between. I don't mind glancing at the speedometer. After all, I glance at side mirrors every few seconds while driving.

Sounds like your towing near or over your CGWR. I had the same problen with my 09 6.4 I was 500# over. No problem with my new rig in sig and I'm 5000# heavier but thousands lower than my GCWR. On open road I run cruise,tow haul, exhaust brake and just keep it between the lines.

Re read the orig post. 2 ton trailer isn't too big for any 1/2 ton much less a 6.2.

To the OP, cruise doesn't use brakes unless it's adaptive cruise then it only brakes when it sense a vehicle in the way.
The fact cruise kicks the trans down and holds speed is great and that's how it works. Not sure how much you want the truck to do for you. Holding within 5 mph downhill with a trailer is pretty good IMO. There is nothing wrong other than if you want to control speed better on freewheeling hills, drive the truck with the brakes instead of the cruise.

[marpel]

Thanks all for the replies.

Just to clarify/better explain,

I don't use tow/haul (may use very seldom in certain situations) for a couple reasons - the trailer is fairly light and both the manual and some GMC reps I spoke to state to use tow/haul when the trailer is at or above 75% of the vehicles tow capacity - On most of the route, I can tow at about 62-ish in manual 5th gear (so OD is locked out) at about 2100 rpm. With tow/haul, the rpm's are much higher. Occasionally, when I come up on a bit of an elevated overpass or similar. I will manually accelerate so cruise won't kick in a lower gear (and much higher rpm).

The driving time alone, along the noted route, is about 24 hours. Much of that is reasonably flat (of course with some areas of high hill climbs). So that would be hours and hours of higher rpm's that tow/haul would "inflict".

On most hills, especially the steep ones, I turn off cruise and can pull the trailer in 4th, occasionally 3rd, at around 55-60 (I just gently tap the brakes as approaching to turn CC off, then re-set it once at the crest). Not sure tow/haul would be of any benefit, even under those conditions. Having said that, there are a couple spots where I have used tow/haul, but de-activate it once at the crest.

The 80 mph speeds are only without trailer.

So, to re-ask one of the questions - Is it normal for CC, on a downhill, to allow the speed to exceed the set speed by 8-9 kmh before stepping in and slowing the vehicle down? I think the brake question was answered.

Marv

[stickdog]

RoyF wrote:
I don't like to use cruise control when towing because, when cruise control is on, the tranmission will downshift on every little grade, including overpasses. I might use cruise if the road is absolutely flat, but such roads are few and far between. I don't mind glancing at the speedometer. After all, I glance at side mirrors every few seconds while driving.

Sounds like your towing near or over your CGWR. I had the same problen with my 09 6.4 I was 500# over. No problem with my new rig in sig and I'm 5000# heavier but thousands lower than my GCWR. On open road I run cruise,tow haul, exhaust brake and just keep it between the lines.

[DutchmenSport]

Artum Snowbird wrote:
I have often wished for a three level cruise control. First level, it holds you within a narrow speed, uphill it downshifts, downhill it brakes. Third level, it's like you are cruising on the open highway, uphill it lets the vehicle slow down almost ten percent if it's gradual, downhill it lets you over the save ten percent if it's not sudden. In the middle zone, most of us would just be happy to be there.

Actually, there is. I use Cruise Control all the time when towing. I also active Tow-Haul mode, and I also activate my exhaust brake, and never have to touch the brake or the (gas) peddle, even up and down some of the mountains in West Virginia, Kentucky, Tennessee, and North Carolina.

Cruise hold the speed steady. Cruise only sets minimum speed. If going down hill, cruise by itself, will allow gravity to gain speed of the vehicle.

Thus comes exhaust brake. Exhaust brake keep the vehicle from gaining speed. It uses the engine and transmission from shifting into higher gears when gravity (down hill) is causing speed to increase. And if towing a trailer, this REALLY works well. With cruise control, the vehicle will never go below the selected speed.

Third comes tow-haul mode. This keeps the transmission shifting at a higher RPM and lower gears, causing more torque and pulling power (great for uphills), an cruise control will hold the speed, but the transmission will shift lower automatically to hold that speed.

At 80 mph, I don't recommend using the three settings zooming over mountains. That can get hairy real fast. But at 55-60 mph, it's a sweet ride! Of course, you also have to have the tow vehicle with big enough engine and the right transmission that can comfortably tow up steep inclines without puttering out too. An F150 towing a 20,000 pound 5er would never have a chance! 🙂

[RoyF]

I don't like to use cruise control when towing because, when cruise control is on, the tranmission will downshift on every little grade, including overpasses. I might use cruise if the road is absolutely flat, but such roads are few and far between. I don't mind glancing at the speedometer. After all, I glance at side mirrors every few seconds while driving.

[eHoefler]

Use tow/haul all the time, the cruise will do a better job in the hills.

[Halmfamily]

You need to be using tow/haul mode on hills while towing. This will change the shift points and keep it out of overdrive and should lock up the torque converter on down hills all g with downshifting to help keep you at speed.

[Artum_Snowbird]

I have often wished for a three level cruise control. First level, it holds you within a narrow speed, uphill it downshifts, downhill it brakes. Third level, it's like you are cruising on the open highway, uphill it lets the vehicle slow down almost ten percent if it's gradual, downhill it lets you over the save ten percent if it's not sudden. In the middle zone, most of us would just be happy to be there.

[Gonzo42]

Doubt the brakes are actually activated.

The transmission is controlled by your computer box new) or by your vacuum level (old), to make the transmission efficient and not over-stress it.

You could easily use the tow feature which locks out the highest gear, thereby keeping the RPM higher, but if you still try to cruise at high speed in this way, you will over-stress the trans.