Vehicle slowing on steep descents - trailer brake drag?

[JArry]

I had a strange experience yesterday towing across the Rockies. The first 30-60 minutes of my drive west into the mountains on I-70 (from Denver) went fine. But then I noticed I was gaining little if any speed on descents, and even needing to accelerate in a lower gear to maintain speed. It was also clear I was not coasting, as my mpg readout was only in the low double digits, not 99.9 as usual on a steep downhill. And when I had to maintain speed uphill, it took more effort than usual to get out of "lugging" mode.

I have not done a lot of driving in the mountains, but I have done enough to know how this vehicle and transmission should behave. I habitually use the paddle shifters for engine braking downhill. When I had this experience yesterday, losing or merely maintaining speed on declines, it felt like when I have paddle-shifted into a lower gear. I felt "held back" the same way. But that was not the case, as I would have heard the revving, the RPMs (on tach) were generally in overdrive range, and gear selector displayed "D" the whole time, versus a number that displays when using paddle shifters.

My first thought was this could be an issue with the trailer brakes (which is why I posted here). But I exited the freeway three times to check things out, felt around the trailer hubs/drums, and they were not abnormally warm. Vehicle brakes were fine too - not unusually warm, no rubber smell or anything.

After my third stop, which took me off the freeway for probably about half an hour, things went back to normal. I noticed when pulling out of a parking lot to get back on the freeway, the trailer brakes were working, as they grabbed abruptly when I stopped (TOO abrupt, but more on that later). Back on the freeway, I stopped losing speed downhill (and there was a LOT of downhill, going from Vail to Grand Junction) or having to give more gas than usual uphill.

Other notes:

• Loss of speed on descents, followed by acceleration w/downshift, was happening in cruise control but required the same inputs from me manually when I turned CC off (yes, I know it is generally advised not to use CC in mountain driving and towing, but I usually have no issues with it when using occasionally on "uneventful" stretches; I sense when I need to cancel it)
• This Escape does not have tow/haul mode
• Other than this one experience, the Escape has done fine in the mountains, both up and down, with the trailer I am towing. I did this same drive a year ago and experienced nothing of this sort.
• Vehicle engine temp gauge never rose much (slightly moved over half once on a long climb, which is not unusual).
• I talked to a nearby Ford dealer on the phone while trying to troubleshoot, and he couldn't come up with any good explanation other than trailer brakes. But I guess it's possible the Escape's computer just had a really bad day...
• I checked the brake controller (Tekonsha Primus) output with a voltmeter and it was acceptable, corresponding to gain adjustment when I activated manual lever - about 12V at max gain but lower with gain decreased.

I have a theory I am not very comfortable with because it doesn't entirely make sense. Here it is: I had the trailer brake gain set too high to begin with (didn't sufficiently test before entering mountains), and when I started steep descents, the trailer brakes were being applied with too much force. I didn't notice this because I was slowing the vehicle primarily with the paddle shifters, so I didn't think of turning down the gain. Eventually the over-applied trailer brakes overheated and began to drag continuously. But after I rested the brakes for awhile and turned down the gain, they cooled off and went back to normal.

Why it doesn't make sense: 1) I wasn't using the brakes much to slow the vehicle on descents, so it seems trailer brakes shouldn't have been applied enough to overheat, 2) normally overheated brakes would have the opposite effect (fade and loss of effectiveness, rather than continuous drag on the vehicle), and 3) as I said, the hubs/drums were not hot. Is it possible that something got stuck in one or both of the trailer brake mechanisms and slowed the vehicle significantly but never got hot?

I would welcome any thoughts on my theory or any other theories or experiences that could be relevant. I am done with the worst day of mountain driving but will definitely see some more passes on this trip, and I am hoping the issue stays resolved!

[DougW]

How much of a headwind did you have? It would likely have taken a pretty stiff wind to cause what you describe. I have no other theories at the moment.

[Reverse_snowbird]

We have a 2006 Tundra with the tow package, but no 'tow mode'
Yet when we're towing, the computer decides if we're going too fast downhill and will shift into a lower gear when in Drive. It's pretty subtle and it's difficult to detect.
The computer is smarter than I am and will adjust to my driving style and the road conditions going up and down hill.

[JArry]

Thanks for the replies. There was no headwind and it wasn’t automatic downshift/deceleration to slow me. The escape was accelerating downhill at times to maintain speed. Very puzzling!

[avid108]

Could the e-brake have been partially engaged?

[Rhumblefish]

I'm wondering about the brake controller - description shows it adjusts for level (though this might have been thrown by the descent slope) and has a booster function for variable trailer weight.

[JArry]

Good thought on e-brake, but it’s electronic, on or off. Boost is normally off on controller but I’ll double check. It was mounted at same angle as always..

[mwdilday]

Two things come to mind. On my F350 the engine brake, when activated in automatic, will automatically slow to maintain the last speed when either the accelerator or the brake were released. Sort of like maintaining the last coasting speed. Second thing is that some brake controllers use an inertia detector to determine braking and a downhill will activate it. It does require brake sensing before it activates. If you brake controller is wired wrong it might be getting a power input on the brake sensing wire that could cause the brake controller to apply trailer brakes on a downhill.

[jbflag21ds]

Does your vehicle have "hill descent control"? I have two vehicles that do and once it senses you are going downhill and have been braking a bit, the ECM will enter hill descent control and automatically control transmission gearing and engine speed

[NXR]

Go to a Harbor Freight or similar and buy an infrared temperature gun with a laser pointer. Get in the habit of "shooting" all of the trailer wheel hubs as soon as you stop because they cool down fast. You don't need an expensive model, just one that you can aim with the pointer.

You'll soon learn what temps are normal for yours. If one or more start showing a lot hotter than normal then you may have a dragging brake or a failing wheel bearing.

If they're all cool at the end of a long descent it's not the brakes.

Ray

[Tom48]

Originally Posted by jbflag21ds

Does your vehicle have "hill descent control"? I have two vehicles that do and once it senses you are going downhill and have been braking a bit, the ECM will enter hill descent control and automatically control transmission gearing and engine speed

No matter who is in charge you or the ECM, if it's the engine slowing you down the mileage will be very high on the meter, if it's a brakes slowing you down they're going to heat up.

I go with the heat gun advice and every time I stop first thing I do is walk around the rig take all the temperatures and make mental note of where my truck and trailer are on a normal day where it is on a downhill day where it is on an uphill day and where it is on a hot day.

This could be a driver not familiar with the rig, but if the trailer brakes are doing this slowing they're going to get very hot. If the truck breaks or doing the slowing on their own they are going to get very hot. The only way to control downhill speed without warming the brakes up is with the engine and transmission and if you are running downhill with the gears the vacuum gauge calibrated for your mileage or the computer read out of your mileage should show as said above; the 9999 that I'm so fond of seeing on my Cummins to compensate for all the times that it says 4.2.

[moose074]

Any head winds that day was traveling alongside the Columbia river last year basically same thing. I was pressing down on accelerator to go down hill.

[JArry]

Well, I will take the advice on the infrared thermo as it seems to be the easiest thing to do and good insurance for the future.

In some "city" driving, unhitched, a couple days ago, my transmission seemed to be slipping a bit from second gear into first while coasting. I have not noticed that in the past. Will be paying attention to see whether this recurs as it could be connected with the towing issue.

[Red Roadrunner]

Originally Posted by JArry

I had a strange experience yesterday towing across the Rockies. The first 30-60 minutes of my drive west into the mountains on I-70 (from Denver) went fine. But then I noticed I was gaining little if any speed on descents, and even needing to accelerate in a lower gear to maintain speed. It was also clear I was not coasting, as my mpg readout was only in the low double digits, not 99.9 as usual on a steep downhill. And when I had to maintain speed uphill, it took more effort than usual to get out of "lugging" mode.

I have not done a lot of driving in the mountains, but I have done enough to know how this vehicle and transmission should behave. I habitually use the paddle shifters for engine braking downhill. When I had this experience yesterday, losing or merely maintaining speed on declines, it felt like when I have paddle-shifted into a lower gear. I felt "held back" the same way. But that was not the case, as I would have heard the revving, the RPMs (on tach) were generally in overdrive range, and gear selector displayed "D" the whole time, versus a number that displays when using paddle shifters.

My first thought was this could be an issue with the trailer brakes (which is why I posted here). But I exited the freeway three times to check things out, felt around the trailer hubs/drums, and they were not abnormally warm. Vehicle brakes were fine too - not unusually warm, no rubber smell or anything.

After my third stop, which took me off the freeway for probably about half an hour, things went back to normal. I noticed when pulling out of a parking lot to get back on the freeway, the trailer brakes were working, as they grabbed abruptly when I stopped (TOO abrupt, but more on that later). Back on the freeway, I stopped losing speed downhill (and there was a LOT of downhill, going from Vail to Grand Junction) or having to give more gas than usual uphill.

Other notes:

• Loss of speed on descents, followed by acceleration w/downshift, was happening in cruise control but required the same inputs from me manually when I turned CC off (yes, I know it is generally advised not to use CC in mountain driving and towing, but I usually have no issues with it when using occasionally on "uneventful" stretches; I sense when I need to cancel it)
• This Escape does not have tow/haul mode
• Other than this one experience, the Escape has done fine in the mountains, both up and down, with the trailer I am towing. I did this same drive a year ago and experienced nothing of this sort.
• Vehicle engine temp gauge never rose much (slightly moved over half once on a long climb, which is not unusual).
• I talked to a nearby Ford dealer on the phone while trying to troubleshoot, and he couldn't come up with any good explanation other than trailer brakes. But I guess it's possible the Escape's computer just had a really bad day...
• I checked the brake controller (Tekonsha Primus) output with a voltmeter and it was acceptable, corresponding to gain adjustment when I activated manual lever - about 12V at max gain but lower with gain decreased.

I have a theory I am not very comfortable with because it doesn't entirely make sense. Here it is: I had the trailer brake gain set too high to begin with (didn't sufficiently test before entering mountains), and when I started steep descents, the trailer brakes were being applied with too much force. I didn't notice this because I was slowing the vehicle primarily with the paddle shifters, so I didn't think of turning down the gain. Eventually the over-applied trailer brakes overheated and began to drag continuously. But after I rested the brakes for awhile and turned down the gain, they cooled off and went back to normal.

Why it doesn't make sense: 1) I wasn't using the brakes much to slow the vehicle on descents, so it seems trailer brakes shouldn't have been applied enough to overheat, 2) normally overheated brakes would have the opposite effect (fade and loss of effectiveness, rather than continuous drag on the vehicle), and 3) as I said, the hubs/drums were not hot. Is it possible that something got stuck in one or both of the trailer brake mechanisms and slowed the vehicle significantly but never got hot?

I would welcome any thoughts on my theory or any other theories or experiences that could be relevant. I am done with the worst day of mountain driving but will definitely see some more passes on this trip, and I am hoping the issue stays resolved!

Perhaps need to go to dealership have them run diagnostic check, you may need more oxygen for the altitude. Experience on same highway going up from Silverthorn just before the tunnel. had to be towed back to dealership due to loss of power.

[JArry]

I may need to write off this experience as a fluke. I never experienced the issue again after the day I posted.

Driving through Glenwood Canyon for the first time was an absolute pleasure, by the way - most beautiful and impressive stretch of freeway in the U.S. that I have experienced. Already thinking about next year's route! I'm hoping forum users come to visit my part of Michigan as I continue to explore the West.