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Old 11-11-2022, 08:24 AM   #43
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Originally Posted by PeterFTH View Post
Cummins 8.8 liter 400 hp 35,000 lb DP - I run the Allison in economy mode and in 9 years crossing the country a few times I have never manually shifted. The transmission knows what gear it needs to be in - you don't have to worry about it…
First, the Economy Mode does nothing if you are using cruise control.

Second, the “fatal flaw” in your driving procedure is that the computer cannot anticipate anything. It can only react to something that has already happened. By anticipating a grade and shifting down a gear BEFORE you get into the grade, several good things happen. Your engine is up on the horsepower peak, the cooling fan is running faster, and so is the water pump.

These big vehicles are not cars. You should not just put it in “D” and forget about actually driving them. Over time, driving like that will cause maintenance issues you otherwise would not have had.
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Old 11-11-2022, 02:19 PM   #44
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Down Shift my 04 Revolution 40 C (350 HP Cummins) on hills and it helps a lot on the RPM loss. That's what the up and down buttons are for. Catch it before the engine lugs to far.
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Old 11-11-2022, 02:35 PM   #45
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Originally Posted by RV Driver View Post
These big vehicles are not cars. You should not just put it in “D” and forget about actually driving them. Over time, driving like that will cause maintenance issues you otherwise would not have had.
If your Allison transmission is programmed correctly and it is interfacing correctly with the ECU, then in 99% of the possible situations having the transmission in D and having the cruise on will yield excellent results with zero damage to your drive train.

I drove 6,000 miles the last few months from TN, all around out west, and down to FL. My engine coolant temps stayed under 200 F and my transmission temps stayed under 205 F the entire time.

I agree that you should "drive" your RV. Keep your hands on the wheel and pay attention to what is going on around you - that does not include playing with the shift panel of your transmission.
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Old 11-11-2022, 05:04 PM   #46
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Another lively topic !
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Old 11-11-2022, 08:05 PM   #47
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You want to climb a hill at peak "torque" not horsepower.
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Old 11-11-2022, 08:40 PM   #48
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Originally Posted by RV Driver View Post
No, no, no!

You should not run your engine at max torque RPM on a grade! You should have the engine turning over at or near its maximum horsepower RPM. It is HORSEPOWER that gets you up a grade, not torque. Running at the lower max torque RPM (~1,300 to 1,500 RPM in the diesels) is a sure-fire recipe for an overheat condition.

That has never been my experience during mountain driving, see my reply for details.
2000 Winnebago Ultimate Freedom USQ40JD, ISC 8.3 Cummins 350, Spartan MM Chassis. USA IN 1SG 11B5MX,Infantry retired;Good Sam Life member,FMCA." My fellow Americans, ask not what your country can do for you, ask what you can do for your country. John F. Kennedy
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Old 11-12-2022, 05:06 AM   #49
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Originally Posted by wolfe10 View Post
I guess this would be OK, ASSUMING the grade you are going down is the same as the one you just went up (unknown, since you did not go up it).

Perhaps a better description is to choose a speed/gear/engine RPM/engine brake that KEEPS YOUR SPEED IN EQUILIBRIUM-- you are neither speeding up nor slowing down without using the service brakes. If you find you are speeding up, apply the service brakes long enough and firm enough to slow down enough to drop to a lower gear.

Personally, I can't imagine using cruise control on a serious descent in a heavy vehicle. This is exactly where maximum driver attention is needed!
I’m running a 40ft dp with 400 Cummins and a3000 gear.. my cruise will not apply Jake brake on a downhill.. I never use cruise on a serious downhill… pick a gear (generally the same as it would be for a similar uphill) and go.. If I find I need to change that up shift is easy and downshift I will select the lower gear first and if needed a good steady application of breaks until the speed is correct and the trans will shift itself.. the transmission will not shift if your speed is too much for the gear.. I have selected 3rd and been in 4th on several occasions and perhaps that is something we all failed to mention/consider… on a real grade with 36000+ lbs you do not want to use your brakes any more than what is absolutely necessary… thus if you find yourself needing to use them then select the lower gear first to prevent the need to brake again.. engines and gears are your best friend on a hill.. brakes can and will fail you.. that’s why we see runaway ramps..
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