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Old 03-19-2017, 02:48 PM   #1
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I'm introducing myself to anyone who wants to read what I have to share. My back ground is as follows:
I've been a certified automotive; medium and heavy duty truck; marine and generator technician for over 35 years.
I worked for a Detroit Diesel and Allison transmission distributor ship for 23 years. We sold and serviced Detroit Diesel, Perkins, Hatz diesel engines along with Allison transmissions and Kohler Generators. We also serviced trucks, trailers, yachts, fishing vessels, fire apparatus and motorhomes. I was afield service technician for about 14 of my years there.
Prior to working there I worked for a trucking company and after working there I have been employed with a municipal fleet maintenance facility maintaining everything from the weed eaters to the Airport Heavy equipment with every public works department there is. We also do a lot of fabrication of vehicles for special needs.
In my "spare time" I build Wildland fire engines at my house.
I am also a volunteer firefighter and EMT in the rural area I live.
My goals are to help people whenever and wherever I can while learning from you all to assist me in picking the right vehicle for me for retirement. I'm liking DDC powered stuff since I know them inside and out. (Series 60 is a plus.)
Thanks for welcoming me.
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Old 03-19-2017, 08:22 PM   #2
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Great to have you here with the group! I am sure we will have a ton of questions for you and others. I for one have a Freightliner Columbia with the mbe 4000 435hp. Now if you can get me better mileage like BushPilot I would be a happy camper!

Sam
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2005 Renegade #1204 42 footer Columbia M3200CH-435,12 speed auto Cat 12 kw Genset, Roadtrip Mission in-mot Dish Network, Washer dryer combo, Jeep Liberty toad,1973 Cessna Skylane,1955 Chev 210 Belair survivor
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Old 03-19-2017, 08:49 PM   #3
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My pleasure. In all honesty mileage is effected by so many variables, my suggestion is always the same... If you want to play with big trucks then make sure you bring BIG BUCKS!...
Seriously though... What kind of mileage do you get and how heavy are you? I see you have a 2005 Columbia, is your engine maximum engine RPM 2100 or 1800 at no load speed? How many over drive gears in your transmission? What is your RPM at cruising speed? What is your cruising speed? How much idling do you do?
I know; I know; too many questions... I just like to help...
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Old 03-19-2017, 09:20 PM   #4
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not sure about no load but it get up to 2100 when it shifts, I have a 12 speed ZF/Meritor Smart Shift. I am 42, long tow a Jeep Liberty and we wt in at 34,500 to 800 depending on the water I haul. I cruise at 65 mph and turning 1500. 7.5 mpg, Not much on the idling and running the genset. Ask all you want I am ready.
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2005 Renegade #1204 42 footer Columbia M3200CH-435,12 speed auto Cat 12 kw Genset, Roadtrip Mission in-mot Dish Network, Washer dryer combo, Jeep Liberty toad,1973 Cessna Skylane,1955 Chev 210 Belair survivor
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Old 03-19-2017, 09:34 PM   #5
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The peak torque of the engine is down around 1200-1500 RPM. If you can feather foot the throttle see if it will up shift lower than 1600-1700. If not see if you can manually shift sooner to keep the RPM down between that 1200-1500 RPM. Slow and easy still gets you up to speed.
Torque is what pulls you up hills and down the road. RPM is just speed. With those weights I would be surprised if you couldn't get in the 9's pretty easy. Granted wind resistance plays in but Class A flat nosed push a lot more air and I had quite a few of those come through the shop in the 9's and 10's with Series 60.
I will say too for every 5 mph over 55 you are pushing 10 times more wind resistance, so at 65 you are pushing more than 100 times the amount of wind than 55.
Learned that from PACCAR Research in the 1990's. Just sayin...
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Old 03-19-2017, 10:01 PM   #6
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Bushpilot gets 9 at 70+ and lower rpms than I do. So I guess he has different rear end gear and he is 450 hp. I would think I should get 8+ when I set the cruise at 65 and go 500 to 600 miles down an interstate? And I use the cruise ALL the time.
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2005 Renegade #1204 42 footer Columbia M3200CH-435,12 speed auto Cat 12 kw Genset, Roadtrip Mission in-mot Dish Network, Washer dryer combo, Jeep Liberty toad,1973 Cessna Skylane,1955 Chev 210 Belair survivor
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Old 03-20-2017, 09:14 AM   #7
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You correct. I think you should get at least 8 mpg even with your gears. I think it still has to do with shift points. If you can get the transmission to shift sooner and utilize that torque I think you can get better mileage.
The other possibility is getting a recalibration for your engine for more horsepower which could change the ratio of horsepower to RPM. However this needs to be looked at closely. I can't remember the curves on the MBE4000 but I do know on a Series 60 that the torque curves and horsepower was identical between 1200-1500 on all the same size liters of engines. It was different when RPM exceeded 1500 that the bigger horsepower would cause a slower drop in the torque as RPM went up. This gave better hill climbing as well as increased mileage as the only fuel needed was to overcome the friction. So with more torque and RPM and when the load was not increased it was easier to pull it.
The rear end gears could be changed make them taller to help too get your RM of 1500 at 70 or 75 also.
The big question is return of dollars... Rear end change say $3000 per differential versus 1or 2 extra miles per $3.00 gallon of fuel. Is it worth it?
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Old 03-20-2017, 09:53 AM   #8
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Welcome Chief Mark!

Sam - Ill record the video but I don't recall our coach shifting that high (rpm), iirc I shift around 1300, maybe 1500 tops.

I'd love to be able to identify what ratios are in the trans.

Mark - I consistently see 9.9mpg at 70/72 mph...and I've never seen anything lower than low 8s. ONCE I achieved 13 running backroads (foggy night) between Atlanta & Destin...but I don't think I ever got over 55mph maybe 60 tops.

we are single rear axle similarly weighted to Sam - w/ the MBE4000 (DD13?) and the rear end is a 3.21





Am I correct in assuming all 12speeds have the same gearing?
Ours is an MO-16Z12A-A16...

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Old 03-20-2017, 10:04 AM   #9
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I think you are spot on with the rear end ratio of 3.21 keeping your RPM down. That engine is more than enough to pull those weights thus giving you good fuel mileage. (I like to agree with the statement "Go Big or Stay Home!")
I would be interested in seeing Sam's specs compared to yours...Apple to Apple.
Funny how one small change can make a huge difference...
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Old 03-20-2017, 10:10 AM   #10
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Quote:
Originally Posted by ChiefMechanicMark View Post
I think you are spot on with the rear end ratio of 3.21 keeping your RPM down. That engine is more than enough to pull those weights thus giving you good fuel mileage. (I like to agree with the statement "Go Big or Stay Home!")
I would be interested in seeing Sam's specs compared to yours...Apple to Apple.
Funny how one small change can make a huge difference...
I've added some more details (as I discovered / cross referenced the trans model number).

honestly id love to be able to cruise faster (need to have the cruise control reprogramed to something more than 72mph). I'm happy w/ the mpg but wouldn't mind getting my RPM's down a little lower (so I can cruise faster w/out giving up MPGs) -





I didn't do too well on this one - 8.03 mpg - but was running a little faster than usual.

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