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Old 04-05-2020, 03:18 PM   #1
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Brand: Thor Motor Coach
Model: Miramar 37.1
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THOR #16645
Hill Descent Control

have a brand new 2020 Thor Miramar 37.1 on Ford Chassis (F550) - issue is the hill descent control. Have NO documentation or ANY information on how to adjust or TURN OFF the hill decent control. Haven't seen any sort of button (like the Utube video shows) in our VERY basic ford dash (looks like a 1970's dash - or very basic commercial - no frills version) does any one have any information that might help us to control or turn off the hill descent control?
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Old 04-05-2020, 03:27 PM   #2
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Why would you want to turn it off?

FYI your chassis is an F-53.

Usually "hill descent" is simply: when going downhill tap the brake and it will downshift a gear to provide some engine braking. On older models it would only do that when tow/haul is engaged but I think newer models do that all the time. (Tow/haul is turned on/off with the switch on the end of the transmission shift arm.)

There really isn't any other bells & whistles with these basic Ford chassis (ABS is about the only other thing we get) so don't bother looking for any extra controls anywhere.
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Old 04-05-2020, 03:29 PM   #3
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THOR #1469
Quote:
Originally Posted by Kate1025 View Post
have a brand new 2020 Thor Miramar 37.1 on Ford Chassis (F550) - issue is the hill decent control. Have NO documentation or ANY information on how to adjust or TURN OFF the hill decent control. Haven't seen any sort of button (like the Utube video shows) in our VERY basic ford dash (looks like a 1970's dash - or very basic commercial - no frills version) does any one have any information that might help us to control or turn off the hill decent control?
Are you sure you’re not on an F53 chassis? Don’t think Thor makes anything on the F550 chassis. F53 does not have hill descent on the V10 that I am aware of and I have had 2 motor homes with the V10.
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Old 04-05-2020, 03:51 PM   #4
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THOR #16645
Assuming we have it as going down the Grapevine 6% grade for 5 miles (CA) had issues with engine torking way down as we descended. I understand it is supposed to help with braking but it may be a bigger issue when traveling at 45mph - engine went from 2800 rpm to 4000 rpm when it kicked in. Releasing the tow/haul switch at this point did NOTHING!
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Old 04-05-2020, 04:05 PM   #5
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I believe the engine computer won't let the engine go faster than redline.

At that point I think stepping on the brake and slowing down even further would have reduced RPM. (Or, ironically enough, accelerating--probably something you wouldn't want to do.)
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Old 04-05-2020, 04:18 PM   #6
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Quote:
Originally Posted by Kate1025 View Post
Assuming we have it as going down the Grapevine 6% grade for 5 miles (CA) had issues with engine torking way down as we descended. I understand it is supposed to help with braking but it may be a bigger issue when traveling at 45mph - engine went from 2800 rpm to 4000 rpm when it kicked in. Releasing the tow/haul switch at this point did NOTHING!
One of the drawbacks of having such a long coach on a gasser. Using the Tow/Haul going down hills of such grades will make the RPMs scream. It takes a bit of practice of switching between the Tow/Hall and light use of the brakes. I just don't like the very high RPMs whether going up or down hills.
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Old 04-05-2020, 04:22 PM   #7
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THOR #1469
Quote:
Originally Posted by Kate1025 View Post
Assuming we have it as going down the Grapevine 6% grade for 5 miles (CA) had issues with engine torking way down as we descended. I understand it is supposed to help with braking but it may be a bigger issue when traveling at 45mph - engine went from 2800 rpm to 4000 rpm when it kicked in. Releasing the tow/haul switch at this point did NOTHING!
So what't the problem with the engine running at 4000 RPM in a lower gear going downhill? The V10 is designed to do that and it handles the higher RPMs quite well. If you don't like it turn off tow/haul and cruise control before the ascent and take your life in your hands and hope the brakes don't overheat while you are riding them going down.
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Old 04-05-2020, 04:59 PM   #8
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Quote:
Originally Posted by Kate1025 View Post
Assuming we have it as going down the Grapevine 6% grade for 5 miles (CA) had issues with engine torking way down as we descended. I understand it is supposed to help with braking but it may be a bigger issue when traveling at 45mph - engine went from 2800 rpm to 4000 rpm when it kicked in. Releasing the tow/haul switch at this point did NOTHING!
Maximum engine rpm for the single overhead cam, Triton V-10 is 5,200 rpm. The engine's computer will not let the engine exceed that rpm. The normal operation rpm for the Triton used in the F-53 chassis with the 6R140 transmission is 800 to 4,500 rpm. The only engine ever used in the F-53 chassis (until 2020) has been the Triton, although it has been back with 4 different transmissions. The engines design life is 200,000 miles.
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Old 04-05-2020, 05:53 PM   #9
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THOR #16645
more so it just seamed extreme - if it is normal for this to occur we'll have to get used to it. This was our FIRST trip with a Class A!
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Old 04-06-2020, 01:04 PM   #10
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So what't the problem with the engine running at 4000 RPM in a lower gear going downhill? The V10 is designed to do that and it handles the higher RPMs quite well. If you don't like it turn off tow/haul and cruise control before the ascent and take your life in your hands and hope the brakes don't overheat while you are riding them going down.

Well said, Dave!
Our Georgetown was on the F53 chassis and the brakes always seemed iffy, to the point of us keeping the tow/haul on all the time.


No such issues with our Aria 4000 on the Freightliner chassis.
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Old 04-10-2020, 02:55 PM   #11
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IOE we use the tow/haul mode and depending on the length of the grade, I will actually downshift one gear to hold the speed I am attempting to maintain. Normally that is about 55 mph. As the speed moves towards 60, I will brake taking the speed down under 55. I don't have to wait on the shift, I already did it. I am not going to burnout our brakes because only jabbing them periodically. Done that across country 4 times, down the Grapevine, through Montana/Wyoming/Idaho twice, up and down the east coast from Maine to Florida, up and down Monteagle, and on I77 through Virginia. Total of 67k miles in 5 years. Still got brakes and never been close to runaway.
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Old 04-11-2020, 07:20 PM   #12
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THOR #15932
I do something a lot like BigBen's technique.

I downshift to a gear I like by pressing the brake pedal. (BTW in newer coaches, mine is a 2019, the trans operates almost the same in or out of tow/haul going down hill.)

It's difficult to get the right gear sometimes, but practice doing what BigBen says.

What I do is set a target speed and a max speed. When I reach the max speed, I very lightly press the brake with my big toe - pretending there's an egg between my toe and the brake pedal. Remarkably quickly, the speed will drop to my target range.

The trick I had to learn was to downshift BEFORE I really needed to.

I really disliked this feature at first. It's taken some considerable time to adjust my thinking.

At 4k rpm, our Honda CRV just purrs along. But 4k rpm with the V10.... well...You have to get used to the engine sounding like it's screaming bloody murder.
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Old 04-11-2020, 08:03 PM   #13
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THOR #17484
Occasional high revs that stay within the acceptable range are not unlike what we Back East used to call the Italian Tuneup ... a hot rodder's lazy way to displace engine deposits. This technique was used most often by teenagers who got a chance to drive Mom or Dad's big block Impala, Galaxy, or Belvedere.
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Old 04-11-2020, 08:16 PM   #14
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THOR #14439
Quote:
Originally Posted by Kate1025 View Post
have a brand new 2020 Thor Miramar 37.1 on Ford Chassis (F550) - issue is the hill descent control. Have NO documentation or ANY information on how to adjust or TURN OFF the hill decent control. Haven't seen any sort of button (like the Utube video shows) in our VERY basic ford dash (looks like a 1970's dash - or very basic commercial - no frills version) does any one have any information that might help us to control or turn off the hill descent control?
Is your Tow/Haul light on the dash lit up? The button to turn Tow/Haul mode on or off is in the end of your gear shifter. Thor only makes the Magnitude Super C on the F550 platform. Miramar 37.1 is on the F53 chassis as is all TMC’s large class A gas MH’s
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Old 04-11-2020, 09:09 PM   #15
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Kate, I have a 37’ Challenger with the F53. I’ve driven it, solo, 3 times cross-country OR-MD thru the Blue Mountains on I-84 and the long 6% grades in Western MD, and once from SoCal up I-5 back to Portland via the Siskiyou Pass. All while towing a relatively heavy MKX. Yes, the screaming engine is loud. Yes, it revs alarmingly high. But that engine braking gives great peace of mind on those long downhill grades where you only have to tap the brakes briefly a few times. I usually use Tow Haul but not always. The Ford manual has a good explanation of how and when engine braking kicks in. High revs are your friend in the mountains. In WY I didn’t use TH as much and just tapped brakes when needed to keep the speed down. Enjoy your travels!
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Old 04-11-2020, 09:56 PM   #16
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PS: We have a Brake Buddy in our Ford Explorer toad. I love to feel the Brake Buddy engage when I hit my coach brakes on the long descents.
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Old 04-12-2020, 12:54 AM   #17
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THOR #13025
I have a Thor on the 550 truck chassis and it doesn’t have Hill descent control just the tow hall mode that down shifts to a lower gear when you tap the brake. The switch is at the end of the gear selector.
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Old 04-13-2020, 04:03 PM   #18
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Love this Forum!

I just bought a Used, sort of... Only had 2100 miles on the Odo when I bought it, 2018 Thor Miramar 35.2. This Forum has been so helpful as I wade through the "issues" that we all have with RV ownership. So, until reading this Post, I didn't even know I had a Tow/Haul switch on the Shift Lever! I haven't pulled my 2019 Sonic Toad as yet, but it does have the Invisabrake System installed. Hopefully that will help as I ascend and descend hills in the future!
thx for you wonderful Posts... Keep'em comin'
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Old 04-14-2020, 07:55 PM   #19
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Originally Posted by Kate1025 View Post
more so it just seamed extreme - if it is normal for this to occur we'll have to get used to it. This was our FIRST trip with a Class A!
It is normal operations for the engine to do approximately 4500 RPMs when it is in tow-haul mode, going down a significant grade. You will just have to get used to it, or at least accept that your engine is designed to handle it with no long term negative effects. It is noisy...
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