Steep Grade.

[TaterColo]

Wow! That's why I respect the OTR drivers. A lot to do and think about for sure! In the coach we only have 6 gears to worry about. I've encountered many "unaware" drivers that I've had to slow down quickly - and I'm only roughly 30,000 pounds. Fun to say the least! I can only wonder what's it's like at 80,000 pounds.


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[I-RV]

Originally Posted by Phil57

This is what I'm looking at. I need to do some more research on it but this seems better than having Cummins reprogram the 340 to a 360. The Cummins reprogram gives the same HP and torque as the 360 but of course I'm still stuck with the 2500 Trans. Not much I can do about that. The Parley chip is adjustable and the best part is it leaves no foot print so the remaining Allison warranty is still in effect.

http://
www.parleysdieselperformance.com/products/diesel-power-digi-crtv-power-module-for-2007-5-2013-cummins-6-7l-isb-diesel-pusher-rvs

Phil: In looking at the Allison 2500MH specs., I see several torque maximums, such as..........

Max Input Torque: 575 lb-ft
Max Input Torque w/SEM or Torque Limiting: 700 lb-ft
Max Turbine Torque: 950 lb-ft

The 6.7l-isb is the same engine in the 340hp or the 360hp, but can the 2500MH handle the increased torque?
http://www.allisontransmission.com/d...df?sfvrsn=4%20

[boowho]

Originally Posted by Tonkatoy77

I'll add to this..... There are also 8, 9, and 15 speed transmissions. My favorite is by far the 18 speed. With an 18 speed you have your normal gears that you would shift like a 9 speed, plus there is an air shifter that splits all the gears in half. When I am empty I don't split the gears. When loaded I do. An 18 speed is 400 RPM's between whole gears, so if you are splitting, there is 200 RPM's between gears. The reason I like the 18 speed is because you can keep the engine in the power band at all times. When you start pulling a hill and your RPM's start to drop, you just down shift 1/2 of a gear. With a 10 speed you have to let the RPM's drop out of the power band to go to the next lower gear.

We have two identical trucks. One with a 9 speed, and the other with an 18 speed. The 18 speed can go up any hill at least 10 mph faster than the 9 speed only because of staying in the power band.



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Thanks Tonka for your additional info. I knew most of what you said, even though I've never driven a 13 or 18 (other than for a few road tests when I've hired onto a new company).

You've added good info to my already long-winded message.

Boowho??

[boowho]

Originally Posted by TaterColo

Wow! That's why I respect the OTR drivers. A lot to do and think about for sure!

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Well, for most folks not really. As I said it pretty much becomes second nature. There are some folks that just can't ever get the hang of it, though. As I recall, the washout rate in my school was about 20%

The biggest thing to keep focused in your mind is other vehicles. You don't want do do something stupid and kill one (or more) people; like moving into the other lane before even looking in the mirrors (to make sure it's empty).

This sounds really basic, but it DOES happen. That's why it's best when in a car and passing a semi on the interstate, don't dally along side. Punch the gas and get around him as quickly as possible.

If you knew the quality of SOME (hopefully only a few) drivers on the road, you'd be aghast. Either they're incompetent, or think they are macho because they drive a truck. I call 'em "concrete cowboys".

Boowho??

[Phil57]

Originally Posted by I-RV

Phil: In looking at the Allison 2500MH specs., I see several torque maximums, such as..........

Max Input Torque: 575 lb-ft
Max Input Torque w/SEM or Torque Limiting: 700 lb-ft
Max Turbine Torque: 950 lb-ft

The 6.7l-isb is the same engine in the 340hp or the 360hp, but can the 2500MH handle the increased torque?
http://www.allisontransmission.com/d...df?sfvrsn=4%20

And there in lays the problem. I have talked to a lot of folks some in the know some with just an opinion. The folks in the know say officially don't do it. The reason given is it will void your warranty. I already assumed that. As I said before they added later in the conversation that the Trams is pretty much bulletproof and adding HP and Torque within reason is not going to cause a transmission failure. I guess it's a gamble and an expensive one. I don't want to get crazy with HP or torque but I would like a little more. I don't want to increase my GCVW ( well I really do but I won't) I just want the assurance of making the hill without breaking something. I for on feel that if I can pull a hill in a higher gear that the transmission will run cooler and cooler is good. Having the transmission constantly downshift seems harder on it than a little more HP. Lots to think about. Any input is welcome.

[Jersey Guy]

When I ordered my coach at the Hershey show in 2012 the salesman said, "you don't need the higher HP, 340 is plenty". Well, we ordered it with the 340 hp. This bothered me for several weeks, so I called the salesman about 4 weeks after the initial order and said, I want the bigger trans and higher HP motor. Cost me 10 grand more, but I am glad I did it.

[I-RV]

Phil, I thought that I would have some fun and renew my math, by figuring out the maximum grade that would bring a 33,000 lb GCWR motor home to a standstill. I however ran into a problem, since the torque given by FR is the output torque of the engine. To figure out what I wanted, I would need the Allison's gear ratio (for 1st gear), torque converter ratio and Freightliner's rear ratio and discount losses for an ideal case.

I did however figure that say for a 15% grade, the torque on the rear tires would have to be 8,160 ft-lbs. Somewhat meaningless, but at least my old scientific calculator still works.

[foretm]

2500MH
1st = 3.51:1
2nd = 1.90:1
3rd = 1.44:1
4th = 1.00:1
5th = .74:1
6th = .64:1


TC Ratio
TC-210 = 2.05
TC-211 = 1.91
TC-221 = 1.73
TC-222 = 1.58


Rear ratio. All I could find was from a 2015 newmar brochure on an XCR chassis:
http://www.newmarcorp.com/wp-content...a_Brochure.pdf

4.78:1

[boowho]

Originally Posted by I-RV

Phil, I thought that I would have some fun and renew my math, by figuring out the maximum grade that would bring a 33,000 lb GCWR motor home to a standstill. I however ran into a problem, since the torque given by FR is the output torque of the engine. To figure out what I wanted, I would need the Allison's gear ratio (for 1st gear), torque converter ratio and Freightliner's rear ratio and discount losses for an ideal case.

I did however figure that say for a 15% grade, the torque on the rear tires would have to be 8,160 ft-lbs. Somewhat meaningless, but at least my old scientific calculator still works.

Wow, an educated man..... I AM impressed. I wouldn't have a clue on how to calculate that.

Boowho??

[boowho]

Originally Posted by TaterColo

Wow! That's why I respect the OTR drivers. A lot to do and think about for sure! In the coach we only have 6 gears to worry about. I've encountered many "unaware" drivers that I've had to slow down quickly - and I'm only roughly 30,000 pounds. Fun to say the least! I can only wonder what's it's like at 80,000 pounds.


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I forgot to mention...... I know what it's like to TRY and stop 80K lbs quickly. I've been involved in only ONE accident in my entire 60 years of driving. YES!!! I slid a fully loaded rig into the back of a city bus in Zanesville, OH. I can tell you I got out of the truck almost shaking, it was so traumatic.

Both vehicles had to be towed and the other driver was ticketed for improper merge (on to I70). And only one minor injury on the bus; some dude complained of whiplash (lawsuit.... ya think??)

Boowho??

Boowho??

[I-RV]

Originally Posted by foretm

2500MH
1st = 3.51:1
2nd = 1.90:1
3rd = 1.44:1
4th = 1.00:1
5th = .74:1
6th = .64:1


TC Ratio
TC-210 = 2.05
TC-211 = 1.91
TC-221 = 1.73
TC-222 = 1.58


Rear ratio. All I could find was from a 2015 newmar brochure on an XCR chassis:
http://www.newmarcorp.com/wp-content...a_Brochure.pdf

4.78:1

Wow, I found that math still works. With some assumptions and using the 4.78 axle ratio and a TC of two, I found that the grade that would halt a Berk with a GCWR of 33,000lbs and rated torque of 660 ft-lbs is very approximately:

15% grade with a 25% loss through the drive train.
17% grade with a 15% loss through the drive train.