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Is it worth the money to switch from 3.73's to 3.55/3.58's?

I have 1.6M on my truck. I have to rebuild the power divider and front drive axle. It will cost me about $3000 to do this. I have an opportunity to do a complete swap for 3.55/3.58 for the same money. The rears will come out of a 244K truck. . The axles are exactly the same except the gears. Will it be cost effective and will I have any fuel mileage gain?

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well, it depends on how fast you want to run- What engine? what year? which tire size?

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Its a 2000 freight liner classic, with a 550 cat , 13 speed double over and 24 low pro tires. usually run average of 65 mph. & Run moderate hilly areas. Was looking to find out the speed at 1350 Rpm. but moreso ..opinion on repairing existing front drive axle and power divider, or replacing both axles with slightly used , for the same cost.

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since it's up for discussion, wouldn't it also depend on if you're pulling a lot of hills too? 3.58/3.55 sounds like it'd only be a marginal difference anyway... tho, I hear guys running with low gears too, 2.70's - I also don't understand the dynamics that well

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The concept behind running tall ratios like 2.64 and such is so that you are running in direct drive at normal road speed. i.e. 16th with an 18 spd or 11th with a 13 spd. Similar to using a 10 spd direct tranny. Direct is more efficient than the overdrives, and transmission runs cooler. Not practical for every situation, but most could do it comfortably. My truck has 18 spd with 2.64 rears.

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i have a similar decision as we speak. i just dropped front differential today with 370 ratio because of pinion shaft bearing play. i had to decide if i wanted to pull rear diff too and go to 355's or 358's; or only repair/rebuild front diff. i decided to stay with a 370 ratio because at 60 mph and slower, the truck will get better fuel mileage. and besides the truck has 11.1 detroit 365 hp, so will do a little better pulling. i have a dedicated situation which i almost always stay at 60 mph and below, but sometimes i have to pick up the pace or sacrifice what little free time i have. i'm not sure exactly what the fuel mileage drop would have been had i went with 358's and drove 62-63 mph and rpm's slightly below running 60 mph with 370's; but if i am right, most of a truck's fuel mileage loss is from aerodynamics, not higher rpm's. however, if you know your going to run 65 mph, i would make the switch to the used diff's because the price is the same and not many miles on them. besides,if you doing the front diff now, i am guessing the rear diff has it's wear.

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i did way better with the 3:55 instead of 3:70's now i run 3:36 with 22.5 lp that gives me the same pull power 3:55 pulls great even better with the heavy haul pgm. winter 6.84 mpg summer 7.28 mpg @ 62mph and i run north central Canada 2 lanr black top will real hills.. lol you'll love the 3:55's with 24.5lp

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Go to www.analysis-inc.com there is a road speed calculator you can put in your ratios and rpms it will tell you what speed you'll be at.

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I would go ahead and switch the rears to the 3:55 since you want to run 65. If you wanted to run slower like 60 Id stay with the 3:73. Have you priced just rebuilding yours with 3:55 gears? Id rather have bran new than salavage if the price was close.

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No.

I can always tell a truck driver from a business owner. Only truck drivers talk about CHANGING gear ratios.

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could you elaborate on this? I'm not sure what your talking about. Sometimes changing the gear ratio is the right choice and can really improve your bottom line. In this case I don't think its going to make a huge change either way. So are you saying changing a gear ratio is a good or bad choice?

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sorry , I meant no to changing gear ratio will not improve your bottom line net profit. The sarcastic part of my answer was that owners of carriers dont think about changing gear ratios in there fleets. They will think about gearing when ordering new trucks but the idea of changing ratios of existing trucks in a fleet makes no financial sense. The trucks we are buying now are 2.50 10 speed direct drives , so yes we think about it but not to change existing trucks. Bottom line is if it doesnt change our bottom line , we are not interested.

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This guy needs to rebuild his axle anyways. So if he wants to change gears now is the time. If his front axle needs rebuilding then his rear axle is most likely not far behind. As for people changing their gear ratios, people are doing it all the time and saving money. In this case I think your right, it's not going to be a huge game changer either way. However in many cases it makes a lot of sense. My friend bought really nice truck, for a good price, with an 18 spd and 3:90 gears, he changed the rears to 2:79 so he could run mainly in 16 gear (direct) and have 17 gear for when he needed to really make time and it made a huge difference in his operation.

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With 22.5's the speed differential holds at about 2mph faster with the 3.55's over the 3.73's.

If your gears are good now, don't spend the money. No ROI there.

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I am going thru this as we type. If you are going to stay with 24.5 and run 65 or less stay with 3.70 and rebuild with a micro blue unit.I would do the extra step and convert to a single drive. I have a W900 475 cat with 3.70s I recently switched from 24.5 to 22.5 super singles and do real good when in the 55-58 speed range but when I have to run hard (run show loads occasionaly) 70mph is app1700 rpm and my milage drops to app 5.9-6.2 I am changing over as we type to a single drive setup and am changing to a3.55 micro blue unit (locker) $3200 that is without any labor as I am doing the work myself

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Do not convert to a single drive if your up to gross weight and running a lot of mountains cause you are not going to like the out come I did the single drive axle conversion 2 years ago and the tire wear so high I was going thru a set of super singles every 50,000 miles other words 6600 hundred dollars a year in just drive tires to save 2000 dollars in fuel just went back to a twin screw now and I am enjoying it

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not enough difference to justify cost.i have 3.58,and would prefer 3.70,but too close if you were 4.11 or lower or 3.36 or higher,then it would make a cost difference.i'm only talking about cost difference,not what a better ratio would be.my choice 3.70or 3.58 (don't change)

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I have 358 rear ends would like to switch a 10-speed direct for an 18-speed

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