Looking to get an 08 and it has 37" tires with stock gearing...I have a 37' toy hauler. Is it going to tow it? rather is it going to tow it well? Called around and getting quotes of 2800.00 for front and rear regear.

What type of lift is it using? That's going to be the key...as to how well the suspension was set up. Sway could be an issue if it's a poor lift setup, but it will easily tow the toy hauler...and I don't see why you'd need to re-gear it. I'm using a Banks 6-Gun and I run in SL and level 6 most of the time. Have pulled a 14' loaded to 7K lbs with my setup, with zero issue through mountains....it doesn't even have to downshift and never loses even 1 MPH through that type of pull. I suspect that a 3500 would pull it better with less sway though.

I would definately re-gear it with at least a 4:10 or 4:56. I tow a 31' 5th wheel and mine tows pretty awesome. Comparing your rig to a 14', 7,000 lb rig is like comparing apples to oranges. Granted it would probably tow it, but your mileage will suck and your EGT's and tranny temps will be through the roof. I spent $1,500.00 for just my rear differential (2WD), but that included the 4:10 gear, a better posi unit, and a Mag-Hytec cover. The differential shop that did mine said that a 4:10 with a 35" tire will put it back to how the truck ran stock with a 265 tire and 3:73 gear.

my 09 was a little sluggish with the stock gears and 37's pulling through the mountains and was always hunting for the better gear. I did the 4.56's and detroit truetrac and the tow power is way better as well as fuel economy. unloaded though i dont think the truck is any faster in a drag race though.

Moved to Drivetrain

2800.00 is unbelievable just for a re gear. 13-1400 with gears and install kit is PLENTY!!! we did mine in about 4 hours. front and rear. start to finish

Looking to get an 08 and it has 37" tires with stock gearing...I have a 37' toy hauler. Is it going to tow it? rather is it going to tow it well? Called around and getting quotes of 2800.00 for front and rear regear.


Even though your rig could pull the toy hauler, if you get up into the mountains your diffs and tranny are going to generate a lot of heat, which causes wear. I would regear to at least a 4.10 which is about a 10% increase over what you have now. If you spend a lot of time towing then you might even think about 4.56's unless you want a top speed in excess of the legal limit. You should be able to get a complete gear re & re for around $1700.00 including gears.

I do recommend moving up to 4.56s for your situation. I am running 4.10s in my dually and have been thoroughly pleased with the results from swapping from my 3.73s. The 4.56s will be great for your 37s and towing. 4.10s will work too. I can hook you up with the ring and pinion sets and install kits if needed. i can get you a good deal on them. Let me know if you have any questions or need any additional info.

I'd get 4.56's.

I have 4.56's with 35's and pull a 40ft toyhauler that weighs around 17000#.

It's a little lower gear than stock but it accelerates betters.

a 4.56 would be pretty close to the stock gear ratio for you with 37's.

Your truck will be lugging thru the mountains with 3.73s and 37's.

ok i have a question. didnt want to start a new thread though. so hope somone see's this again. even though its almost a year old...

say you have a truck that runs 12.00 at XX MPH on the 1/4 with stock 3.73 gears,
then you swapped out to 3.42 gears without changing ANYTHING in the truck...

would said truck go faster or slower than 12.00 in the 1/4???

slower.... you are setting yourself up better for topend, when you want low end....to get there quicker, you want the higher # gears, which are considered to be lower gears, like the 4:10's or 4:56's

the sad part is that it is so freekin expensive to swap them out

OOOOHHHH. i had it ass backwards. i was thinking 3.42 is lower than 3.73... hahah woops.

thanks cheese

also, wtf does FAI stand for. i see it all the time and always ask myself that.

I have no idea what FAI stands for. I had it backwards when I first started dealing with it too.....kinda like wheel backspacing n shit lol

I was thinking about regearing my truck as well. I am running 35's currently should I go to 4.10's or 4.56's. How many more rpm am I looking at on the highway? Better or worse mileage with the 4.56's?

Same question^^

Also does anyone have a gear ratio chart that works for our trucks cuz all i can find is charts for gas trucks and all the formulas to figure gear ratios dont come out correctly for my truck.

I have fabtech 8" lift with 37" tires
I was told 4:10 and 4:56
Which ones?

Same question^^

Also does anyone have a gear ratio chart that works for our trucks cuz all i can find is charts for gas trucks and all the formulas to figure gear ratios dont come out correctly for my truck.

What exactly are you trying to figure out? If you are looking to find out road speed based on Engine RPM there is no difference between gas and diesel. Engine revolutions are based on Gear Ratio, Tire Size and Transmission Ratio. Engine power at comparible RPM's is different between the two but if you have a gas and diesel truck side by side with the same tires, gears and transmission ratio, engine RPM 's will be almost if not exactly the same although the HP and Torque supplied by the motor will be different. Normally you don't need as tall (Numerically higher) a gear ratio with a Diesel because they make way more torque than a Gasser, especially at a lower RPM, plus they don't normally rev as high. It's kind of a trial and error thing depending on how you use or want to use your truck.

Well see I come across gear ratio charts that give the gear ratio on one axis and tire size on the other and it gives the engine rpm at the intersection point. there is also a diagonally color coded line that gives the economical gear, the power=economy gear, and the power gear. All of the charts I find do not give rpms anywhere close to my readings... for example at 80 mph my rpm is 2056 (3.73 gears w/ 35" tires) and the majority of charts I find are 65 mph at the same intersection read about 21-2300 rpm depending on the vehicle application. Perhaps it is simply I need to find the correct gearing for the final drive on the transmission and find a corresponding chart but have had no luck so far.

I do understand what you are saying in your post btw and so if all my rambling made no since just let me know and ill try to explain better

http://www.4lo.com/calc/geartable.htm

This is one example

....All of the charts I find do not give rpms anywhere close to my readings...
Read my post in this thread: http://www.dieselplace.com/forum/showthread.php?t=428065

http://www.4lo.com/calc/geartable.htm

This is one example

Sorry, didn't mean to give you a bad time. The chart that you showed is based on tire size, gears and a 1 to 1 transmission ratio. Since every trans made these days has an overdrive your RPM's will be a lot different(Lower) than what that chart shows you. IIRC, 6th gear in the Allison is .61 to 1 if you have the 6 speed and it's .71 to 1 if you have the 5 speed. Here's one you might want to try.

http://www.rearendparts.com/pages.php?pageid=16

Oh no worries aprilwine I knew i wasnt explainin myself the best so i tried to do better the second time around hahah but i think those are the numbers that i was missing and blackart I havent punched the numbers in the formula you made up yet but it looks like it should give me a good result... ill let ya know if it dont come out right lol