Changing rear end?

It is cheaper to go to a wrecker n trade in your diffs for a set. Why do you want 2.93 gearing? That is the worst gearing you can have unless you are hauling light on flat ground. Ask anyone who drove a swift truck back in the day, they had lots of trucks specced like that. If it were me, I'd want at least some flexibility n go with 2.79's, but thats me...

 

depends on what motor you have detroits are not made to run low rpms. they get best mpg between 1450 and 1650 rpms. lower than 1450 it loses all power lugs hard. same with cats but numbers alittle diff...bout the only motor setup for low rpm is a cummins and from what i have been hearding and seeing they are holding up to well on the low side either....also you need the tranny info. if its lower rpms your after you could change wheels size different tranny or rears. personal i want go for low rears. i run hills alot and still pull 6 to 7 mpg having the power to get up the hill quickly and get back off teh fuel is the biggest fuel saver.....

 

my boy 22 years old has a 379 pete with an N14 set at 460hp 9 speed overdrive and 390 rears on 24.5 low profile rubber. this is a set up that no one in thier wright mind would want. he runs 60 mph or less (yes at his age)he was at 7.86 mpg last week pulling a dropdeck with oversize (wide)that thing goes up hill like a raped ape.he is thinking he may be able to get 8 mpg out of it when he gets about 75 to 80000 miles on it. he has 40000 or so on it since the rebuild. the numbers and the pulling power he has are almost unbelieveable. We figured he might be able to get 6 mpg out of it ,I am sure glad we were wrong.my point is you may want to try a similar set up and go with 370 or 390 rear gears and a 9 or 10 speed overdrive transmission just the oppisite of what Kevin Rutherford recomends.

 

I dont get why you would recommend a 9 or 10 over a 13 or 18. What is the logic behind it? Just cause a tranny has all those gears doesnt mean you have to run in high gear all the time. What about a truck with 2.64's n an 18 spd? Run in 16th (direct gear 1:1) and if you need to move faster to make a last minute friday pickup then you got 2 more gears to go. Its pretty simple math to figure if you run in direct gear then you will get better fuel mileage. Why should anybody have to run in OD to compensate for poorly specced rear ends?

 

I was just stating what works for us.I never wanted a 10 speed but after getting one it worked best for me my second choice would be a 15 speed but don't see many of them these days. You guys listen to Kevin Rutherford too much I have run 18 speeds in direct like he talks about transmisson runs much hotter on the guage At 58 to 60 mph in direct than it does at 75 in high gear and fuel milage never seemed to get any better. Now we are talkin about 550 cats with18 speeds and 3.21 rears on 24.5 tall rubber. running between seattle and philoadelphia with 50 foot spread axle reefers. (did you notice that I spelled axle correctly?)

 

i dont understand why people want to spend thousands more on gears they wont use....why not just get a direct 10 and spec the rears the REAL RIGHT WAY.....

 

It depends on what you want to do. Your going to save the most mpg with the guy staying off his foot. Some engines like my C15 get very similar mpg no matter what speed i run. Granted 66 iere i e to keep it. 1500 rpm or so. For me the way the wind blowing makes the biggest difference.

I like where i am geared but going over 70 is pretty much out of the questions. The engine itself will make the most difference in mpg... gears wont help that much.

 

Well, my truck would sure be surprised to think you can't get mpg and good power from tall rear ratios. I am running 2.64 behind an 18 speed which is behind a 500 hp DDEC IV Series 60. My winter mpg average is just under 7 mpg average, my summer mpg average is almost 8 mpg. I recently yanked a 44,000 lb load around SE Ohio Amish country on skinny, hilly, roads with 20 mph corners and some interesting grades. I do that more frequently than I really care to, but it pays a premium.

carrkool, generally I would agree, why spend more for gears you do not use? But some of us actually made pretty good deals on trannies we have and those extra gears offer a lot of flexibility that is not available with a 10. It can be rather advantageous to have a selection of 18 gears to choose from, with tighter rpms between gears than is available with a 10. Now true, in my case, I never use the top gear. I did use 17th some today when a bed bugger was messing with me in traffic and I wanted to just plain get on ahead of him and his nonsense. He gave up when I went to 17th at 75 mph and left him in the dust. And I had 40K in the box. Every once in a while, we all have to let the dog out. Try that with a 10 speed. And at the same time, I have the same low end grunt as a direct 10, and my tranny can deal with torque that a 10 direct can only dream of. There are many reasons why some would go with a lot of gears combined with tall ratios. Just because you can't understand it, doesn't mean it isn't a viable option. There is not a 10 direct out there that is rated for anything above roughly 1600 lb torque, unless it is an old version that is no longer made. Sometimes is takes a 13 or 18 to get the torque rating you need and still be able to do a tall rear ratio. Now that is doing things right. As for paying for gears I never use, only 1 gear has never been used in my 18... 18th. Every other gear has been used at one time or another based on the situation at hand. Sure, not every gear is used each and every time, but that would be true even with a 10 speed direct. Ever hear of skip shifting? Sure you have. And under a light load, I would skip lower gears to get into the high range as quickly as possible with a 8, 9, 10, 13, 18 etc. So even buying a 10 speed, it can be argued that someone is buying more gears than they need all the time, every time. And my 18 was not "thousands more" than I could have gotten a 10 direct for. Sure it was more expensive, but there is no need on your part to make such a ludicrous comment. It shows a very myopic understanding of things.