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-   -   Newbie needs help knowing when to downshift in mountains (http://www.irv2.com/forums/f258/newbie-needs-help-knowing-when-to-downshift-in-mountains-205719.html)

snickers1 05-29-2014 08:13 PM

Newbie needs help knowing when to downshift in mountains
 
Know it might seem foolish but new to Rving and need to know when to shift out of OD to Drive and lower gears? is there a speed, RPM? Going to leave NM and will be driving first time in CO mountains and do not want to burn up engine or brakes. Thanks

Shadow0120 05-29-2014 08:24 PM

What engine, transmission side or rear radiator

ThorEvo1029 05-29-2014 08:29 PM

I to am new and unsure as to the correct way. I have a 2012 thor ace 29.1 with a ford v10. I've been using the tow haul feature which downshifts when I hit the brakes. However, when I speed up I don't feel the automatic transmission change gears so to prevent damaging the engine I just shut off the tow haul feature. I don't think anything I'm doing is right though!

Grandpere 05-29-2014 08:44 PM

Being born and raised in Montana, driving the mountain passes was a normal occurrence so ignore my current Arkansas location. :) For going up hill, you want to keep the engine at peak torque RPMs and the gas pedal as far away from the floor as possible. So manually downshift to lower gears to make this happen. You may be down to 40 MPH, but do not let this disturb you, getting over the pass and using the least amount of fuel is the main point for me and most others who are striving for the best fuel economy.

Going down hill is quite different, the steeper the grade the slower you want to be going as you start down; if following a semi, follow their lead, they probably have been over the pass many times and know what to do to maintain control. Shift into the lowest gear and let the compression of the engine hold you back, and only apply the brakes for short durations. If you get going too fast so the engine is revving too fast, then pump the breaks till you slow down again. Over heated brakes will develop what is called brake fade, which means they will not work as well and will eventually quit working all together.

If you have a diesel engine, use the exhaust brake to hold you back, this will help reduce the amount of braking you need to do.

IF you need further clarification on what I have said, please feel free to ask.

Gordon Dewald 05-29-2014 09:06 PM

Quote:

Originally Posted by George1285 (Post 2073479)
I to am new and unsure as to the correct way. I have a 2012 thor ace 29.1 with a ford v10. I've been using the tow haul feature which downshifts when I hit the brakes. However, when I speed up I don't feel the automatic transmission change gears so to prevent damaging the engine I just shut off the tow haul feature. I don't think anything I'm doing is right though!

I have a F450 and 5er that grosses around 30,000.

The tow haul transmission makes the shifting crisper. I generally drive without using it until I get to the hills, mostly downhill.

It does shift down in order to help you engine brake. On the upshift it will hold it longer depending upon how the engine is pulling and how you are feathering the throttle.

I use the tow haul going up the hill to hold the selected gear. I let the truck select the gear and run at an rpm I am comfortable with. The tow haul will keep it in that gear even when the going gets a bit lighter. This keeps the transmission from shifting up and down. Once I get to a grade I feel the engine can maintain I pull my foot out and let it shift up and then maintain the speed.

As I crest the hill I have slowed up, especially if there are steep grade signs ahead. Leaving the tow haul on will keep the engine in that gear until the engine is nearing red line when it will automatically shift up (I tried it once to see what would happen). Normally I watch the grade ahead and the rpm and brake crisply as required to keep my speed at a comfortable pace and the rpm near optimal. As I near the bottom of the grade I shut the tow haul off to let the momentum build up to the speed I like to travel and the add throttle as the grade flattens out.

Takes a bit of practice and experimentation but after a bit it will become second nature.

JFXG 05-30-2014 12:23 AM

Snickers......

General rule of thumb #1: what grandpere said. going upgrade, keep near your peak torque rpm, and don't floor the pedal. A diesel is just a fuel pump, and if you try to pump too much fuel through it will just jam things up. Torque is your friend.

General rule of thumb #2: downhill. The guy that teaches the Freightliner class states it simply: go down a hill at the same speed you went up the hill. Think about your downhill speed while you're on the way up. Watch the truckers, pay attention to the speed signs. As you crest and start downhill, turn on your exhaust brake and let it do the work. You may have to brake a bit occasionally. Be patient. If you're in a hurry, take a plane.

If no exhaust brake, another rule of thumb: let your transmission hold you back. Note how quickly you accelerate, and how quickly moderate braking slows you down. They should balance. Example: if gravity alone accelerates you from 40 to 50 in 5 seconds, then moderate braking should be able to slow you from 50 to 40 in 5 seconds. If gravity accelerates you faster than moderate braking will slow you, then you need to be in a lower gear to get more help from the engine. You should be braking less than 50% of the time. The brake pads need plenty of time to cool.

The fact that you're thinking about it in advance tells me you'll be cautious and you'll likely be fine. The most important part of problem solving is problem recognition.

Good Luck!

ga traveler 05-30-2014 08:06 AM

John: He said he had a V10 ford not a diesel.

89sandman 05-30-2014 08:23 AM

if you have a v10 2750 rpms is where it makes the greatest amount of torque, going up hill I'd shift the trans by hand to keep it close to that range.

Crasher 05-30-2014 08:23 AM

snickers did not say what he had, so it is hard to give him proper advise. He needs to clarify what he is driving or we are shooting in the dark.

JFXG 05-30-2014 09:57 AM

ga traveler, I was addressing snickers, the OP. george1285 with his V10 jumped in and piggybacked.

frankdamp 05-30-2014 10:54 AM

Modern transmission control computers know what's most appropriate - why bother messing about with the shift?

Shellback1 05-30-2014 11:07 AM

Good article here:

http://www.intermotive.net/Tech%20Ti...ugust%2006.pdf

89sandman 05-30-2014 11:56 AM

Quote:

Originally Posted by frankdamp (Post 2074114)
Modern transmission control computers know what's most appropriate - why bother messing about with the shift?

Lugging it in overdrive up a small hill and overheating the trans is the first reason of many. If you have a trans temp gauge it surprises you how little lugging it takes to make the trans temp start to rise.

koda59 05-30-2014 02:42 PM

When going up the mountain you need to shift down to keep your rpms up so the engine does not overheat. What ever gear you go up in, is the gear you need to come down in. If your start to go to fast apply your brakes firmly, do not pump your brakes, to get your speed 10 miles under what you feel safe at and release your brakes." DONOT" apply light pressure, you will overheat your brakes. When your speed increases again over your safe driving speed or rpms get to high apply your brakes firmly again to bring you back down to 10 mile under your safe speed and release. DO this until you get to the bottom. Retired otr driver. Drove down many mountains with just the transmission and brakes.


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