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We are spec'ing out a new CHU613 48-inch flattop with rawhide exterior package and grand touring interior package. Didn't really care for mdrive demo truck and really like our 13speed fuller mp485c. Question is what rear ratio would be recommended on a new one with 505c 13speed. Current truck has the 3.73 ratio and we seem to get decent fuel mileage(6.2-6.5) average on summer fuel running mix of side roads and interstate. Also whats everybodies opion on getting it with disc brakes, mack rears, and twin Y?

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Disc brakes are obviously superior to drum brakes but when I ordered my 16 in the fall of 15, they were a pain in the ass to get.   It sounds as though that has since been adressed.  I have the twin y with Mack S 38 rears and love the set up.   It's funny how Mack promotes the 400 lb weight savings on the twin Y set up, but fail to mention the Mack rears weigh a ton.   Anyhow it works well together.   I have a 13 sp Eaton with the 505 c+.   I can't reveal all of my secrets hahaha  but I will say this.....gear that truck to run and drive it reasonable and it will do well for you.   These motors do very well @ low rpm.   :thumb:

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salesman acts like he don't want to go with 3.73 but more like 3.40 something

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22 minutes ago, wiserfrombud said:

These motors do very well @ low rpm.

Says it! the longer the legs the better the mileage! 

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355 eaton rears 

Stay away from the twin Y suspension.

Lots of issues and little product support.

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2 hours ago, bbigrig said:

355 eaton rears 

Stay away from the twin Y suspension.

Lots of issues and little product support.

What have the issues been with the twin Y?  I have 200 000 miles on mine.  It rides decent and my tires are wearing perfectly.  

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5 hours ago, cxn613 said:

salesman acts like he don't want to go with 3.73 but more like 3.40 something

I would agree with the salesman.  3.7x will move freight up and down the road just fine but I would not want to be cruising @ 1400 rpm for fuel economy.  I think 3.3x is much more in line.  

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I would go 3.36 gears on this truck or maybe even 3.25. I am surprised you did not like the M-Drive - it is pretty much all I sell anymore - 445SE package with overdrive transmission, premium shifter, grade gripper and 2.64 gears. Plenty of power and torque to pull 80,000+. Disc brakes are becoming more accepted as the overall cost decreases. Staying below 460HP will save you significant $$$$ if you choose to be extended purchased engine and EATS coverage that I always recommend. Not a fan of the twin Y, there are other ways to save weight especially by reducing fuel capacity.

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I'd go with 2.79 gears with a 13 spd and drive in 11th for direct 12th up to 70 and 13th to get the hell out of dodge!

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Teamster Grrrl, I agree that the big fleets spec. The auto to appeal  to the clueless inexperienced drivers they love to hire! ( they're cheaper, and it's easier to blow smoke up their rear ends! And they will quit before it's time to give them a raise!) Another advantage the big fleets have is most have a buyback arrangement with their truck supplier so they can trade it while still under warranty! Who will then sell it to a first time owner operator who at some point will then probably lose it and they will have a parts truck!  The circle will be unbroken!

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My buddies 2016 CHU 505 Plus with a T310 trans and Meritor 3.21 rears , disc brakes all around and super single tires does a very good job even grossing 99,000 pounds when I rode with him a week or 2 ago. And gets regular 7MPG. Stay away from the twin Y ride, I've seen lots off handling issuses and pics of  mangled brackets during hard emergency braking. 

2017 common rail sweet spot RPM.pdf

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Teamster Grrrl, I agree that the big fleets spec. The auto to appeal  to the clueless inexperienced drivers they love to hire! ( they're cheaper, and it's easier to blow smoke up their rear ends! And they will quit before it's time to give them a raise!) Another advantage the big fleets have is most have a buyback arrangement with their truck supplier so they can trade it while still under warranty! Who will then sell it to a first time owner operator who at some point will then probably lose it and they will have a parts truck!  The circle will be unbroken!

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Mack pro,he gets 7 mpg grossing 99000?  Is he a coal hauler? My cousin bought a new GMC Astro in 1973, was hauling steel for a couple years,then we put a wet line on it and he started hauling coal,this was.In Pittsburgh Pa,he told me a funny story about the coal haulers in W va and Ky, when they were using two stick Mack compounds and the Dad was teaching his kid how to split the gears, he would sit next to him with a tire thumper,and every time the kid tried to use the clutch dad would crack him on the knee  with his tire thumper claimed it speeded up the training process!Lol

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22 minutes ago, BillyT said:

Mack pro,he gets 7 mpg grossing 99000?  Is he a coal hauler? My cousin bought a new GMC Astro in 1973, was hauling steel for a couple years,then we put a wet line on it and he started hauling coal,this was.In Pittsburgh Pa,he told me a funny story about the coal haulers in W va and Ky, when they were using two stick Mack compounds and the Dad was teaching his kid how to split the gears, he would sit next to him with a tire thumper,and every time the kid tried to use the clutch dad would crack him on the knee  with his tire thumper claimed it speeded up the training process!Lol

I didn't say he was legal! Lol . No , not coal. I'll try and pull his trip records next time he's in the shop and post it here. It always seemed to me that you were hurting the engine when running that low of RPM down the highway, but these MP8 engines seem to love it. 

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16 hours ago, Mackpro said:

I didn't say he was legal! Lol . No , not coal. I'll try and pull his trip records next time he's in the shop and post it here. It always seemed to me that you were hurting the engine when running that low of RPM down the highway, but these MP8 engines seem to love it.

Hey pro What was  old is new again maxidyne revisited ! Didnt hurt the V8 Didnt hurt the 285! ? Should be no problem for the MP 8 ! These seem to have a decent bottom end ;the heads are a little  in question at times! That tiny little window of rpm is why there pushing I shift / MDrive focus on milage! they take yet more control from the driver and let the computer do the thinking! Won't need the driver soon! Its coming!

Edited by fjh

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yup  e9 400 m had a huge working RPM 1100 to 1500

Edited by fjh

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On 23/03/2017 at 4:56 PM, wiserfrombud said:

What have the issues been with the twin Y?  I have 200 000 miles on mine.  It rides decent and my tires are wearing perfectly.  

Y arm issues. Cracking and breaking. The heavier the axle loading and doing lots of twists and turns the worse it gets. Good to hear yours are doing well.

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On 3/27/2017 at 10:34 AM, bbigrig said:

Y arm issues. Cracking and breaking. The heavier the axle loading and doing lots of twists and turns the worse it gets. Good to hear yours are doing well.

Hmph.  I'll have to keep an eye on mine.  What kind of operation is that in?  If I recall, the literature sold the twin Y as an over the road kind of haul 80,000 lbs type of suspension. I don't think it was intended for off road or heavy haul applications.  

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A large chicken producer  with a fleet here, tried the twin Y.    While not actually going off road, their feed haul trucks do get in some uneven conditions and some of their other locations had issuses with the trailing blades twisting and cracking. Also I have seen pictures of the trailing blades ( Y-arms) bent and twisted in panic stops. We did a campaign on replacing all the Y-arms with much heavier  ones. However , with the much heavier arms, your weight savings wasnt much over the standard proven air ride systems. The customers next two batches of truck orders had the standard air ride. I just test drove a 2015 CXU with the twin-Y after a engine repair. The customer has never complained but to me it feels squirrelly in the rear end. You change lanes and it feels like the rear axles are coming around to pass you. I inspected and everything seems tight. 

scan0437.pdf

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My cousin and his best friend (a former master freight driver) never pulled out with less than 96000 gross (in the 73280 days! They never got caught to my knowledge but they did "pay" the Astro had 34000# rears and a lot of drive line stuff wore out plus the aluminum cab structure cracked due to flexing of the frame! My cousin did all his own work so that helped!

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